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Effect of Changes in Pelvic Tilt on Range of Motion to Impingement and Radiographic Parameters of Acetabular Morphologic Characteristics James R. Ross, Jeffrey J. Nepple, Marc J. Philippon, Bryan T. Kelly, Christopher M. Larson and Asheesh Bedi Am J Sports Med 2014 42: 2402 originally published online July 24, 2014 DOI: 10.1177/0363546514541229 The online version of this article can be found at: http://ajs.sagepub.com/content/42/10/2402
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Effect of Changes in Pelvic Tilt on Range of Motion to Impingement and Radiographic Parameters of Acetabular Morphologic Characteristics James R. Ross,*yz MD, Jeffrey J. Nepple,§ MD, Marc J. Philippon,§ MD, Bryan T. Kelly,k MD, Christopher M. Larson,{ MD, and Asheesh Bedi,yk MD Investigation performed at University of Michigan, Ann Arbor, Michigan, USA Background: The current understanding of the effect of dynamic changes in pelvic tilt on the functional acetabular orientation and occurrence of femoroacetabular impingement (FAI) is limited. Purpose: To determine the effect of changes in pelvic tilt on (1) terminal hip range of motion and (2) measurements of acetabular version as assessed on 2- and 3-dimensional imaging. Study Design: Controlled laboratory study. Methods: Preoperative pelvic computed tomographic scans of 48 patients (50 hips) who underwent arthroscopic surgery for the treatment of FAI were analyzed. The mean age of the study population was 25.7 years (range, 14-56 years), and 56% were male. Three-dimensional models of the hips were created, allowing manipulation of the pelvic tilt and simulation of hip range of motion to osseous contact. Acetabular version was measured and the presence of the crossover sign, prominent ischial spine sign, and posterior wall sign was recorded on simulated plain radiographs. Measurements of range of motion to bony impingement during (1) hip flexion, (2) internal rotation in 90° of flexion, and (3) internal rotation in 90° of flexion and 15° adduction were performed, and the location of bony contact between the proximal femur and acetabular rim was defined. These measurements were calculated for –10° (posterior), 0° (native), and 110° (anterior) pelvic orientations. Results: In native tilt, mean cranial acetabular version was 3.3°, while central version averaged 16.2°. Anterior pelvic tilt (10° change) resulted in significant retroversion, with mean decreases in cranial and central version of 5.9° and 5.8°, respectively (P \ .0001 for both). Additionally, this resulted in a significantly increased proportion of positive crossover, posterior wall, and prominent ischial spine signs (P \ .001 for all). Anterior pelvic tilt (10° change) resulted in a decrease in internal rotation in 90° of flexion of 5.9° (P \ .0001) and internal rotation in 90° of flexion and 15° adduction of 8.5° (P \ .0001), with a shift in the location of osseous impingement more anteriorly. Posterior pelvic tilt (10° change) resulted in an increase in internal rotation in 90° of flexion of 5.1° (P \ .0001) and internal rotation in 90° of flexion and 15° adduction of 7.4° (P \ .0001), with a superolateral shift in the location of osseous impingement. Conclusion/Clinical Relevance: Dynamic changes in pelvic tilt significantly influence the functional orientation of the acetabulum and must be considered. Dynamic anterior pelvic tilt is predicted to result in earlier occurrence of FAI in the arc of motion, whereas dynamic posterior pelvic tilt results in later occurrence of FAI, which may have implications regarding nonsurgical treatments for FAI. Keywords: femoroacetabular impingement; pelvic tilt; computed tomography; acetabular version; computer modeling
Femoroacetabular impingement (FAI) has recently been recognized as one of the most common causes of hip pain and osteoarthritis in young active adults.12 FAI results from abnormal bony contact between the proximal femur and acetabulum during range of motion and is generally the result of developmental osseous pathomorphologic abnormalities. Pelvic tilt, defined as the angle between
the line connecting the midpoint of the sacral plate to the femoral heads axis and the vertical axis,20 may play a role in the occurrence of bony impingement and the development of symptoms in patients with bony deformities of FAI. Alterations in pelvic tilt may allow patients to compensate for secondary restrictions in terminal hip range of motion but are currently poorly understood. Pelvic tilt is a natural component of the patient’s posture and may vary significantly among patients, between genders, during different activities of daily living and sport-specific activities, and even between standing and supine radiographic studies.10,26
The American Journal of Sports Medicine, Vol. 42, No. 10 DOI: 10.1177/0363546514541229 Ó 2014 The Author(s)
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Radiographic evaluation is a critical component of the diagnostic evaluation and treatment decision-making process in patients with prearthritic hip disease. An understanding of the effect of pelvic tilt on the appearance of the hip on pelvic radiographs is important, especially when assessing young adults with hip pain.5,7,8,10,26,28,29 Previous studies have demonstrated a relationship between pelvic tilt and the distance between the superior border of the symphysis pubis and the position of the sacrococcygeal joint or tip of the coccyx.26,28 In patients with alterations of pelvic tilt on baseline radiography, current standards of radiographic evaluation attempt to reposition the radiograph to an ‘‘appropriate’’ pelvic tilt.28 However, this standardization is simplistic and fails to account for inherent differences in pelvic tilt among patients and the ability for dynamic muscular control to adjust tilt and thereby improve the functional range of motion. Failure to understand the influence of alterations in pelvic tilt may lead to inaccurate characterization of acetabular deformities and could result in over- or underresection of the acetabulum due to an inaccurate assessment of acetabular retroversion. In this regard, our current understanding of the varying relationship between the acetabulum and the femoral head on the basis of a patient’s native pelvic tilt is poor. The purpose of this study was to determine the effect of changes in pelvic tilt on terminal hip range of motion to impingement via computer-based software analysis, as well as to identify any change in the anatomic location of the impingement. Second, we aimed to determine the effect of changes in pelvic tilt on acetabular version parameters on two-dimensional and three-dimensional (3D) imaging studies. We believe that changes in pelvic tilt will significantly change the acetabular appearance as well as terminal hip range of motion.
MATERIALS AND METHODS We retrospectively identified a consecutive series of 50 hips in 48 patients with symptomatic FAI who underwent preoperative computed tomographic (CT) scans and were treated with arthroscopic hip surgery for FAI between June and August 2012 at a single institution. FAI was diagnosed via symptoms and physical examination findings in all patients and confirmed with corresponding radiographic pathomorphologic findings on plain films and 3D imaging (24 hips [48%] with isolated cam, 1 hip [2%] with isolated pincer, and 25 hips [50%] with both). No other hip conditions were noted (Perthes, slipped capital femoral epiphysis, etc). This study was performed under an institutional
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review board–approved protocol. The average age of patients in this series was 25.7 years (range, 14-54 years). Fifty-six percent of the patients (n = 28) were male, and 54% (n = 27) of the surgical procedures involved the right hip. In addition to a standardized plain radiographic series, the patients underwent high-resolution CT scans of the pelvis (and distal femur for assessment of femoral version) as part of their clinical care and preoperative surgical planning. A modified CT protocol using decreased radiation exposure of 2.85 mSv was used to maximize patient safety, as described by Milone et al.23 Positioning of the patient in the scanner was standardized, with the legs in native abduction or adduction and the patellae pointing directly anterior. The patient was positioned supine with a natural resting pelvic tilt. This resting, supine pelvic position was considered the patient’s ‘‘native’’ pelvic tilt. Static radiographic parameters (2-dimensional and 3D) and dynamic range of motion measurements to impingement were calculated for 3 pelvic positions: 110° (anterior tilt), 0° (native), and -10° (posterior tilt) (Figure 1). The preoperative CT scans were uploaded into a computed tomography–based computer software program (DYONICS PLAN Software; Smith & Nephew) to generate patient-specific 3D models of the hip joint. This software program also allowed manipulation of the pelvic tilt and subsequent generation of virtual plain radiographs. These virtual radiographs, which simulated an anteroposterior (AP) pelvic radiograph, were analyzed for parameters of acetabular and pelvic orientation. Two-dimensional radiographic parameters, including the presence or absence of the crossover,25 prominent ischial spine,16,17 and posterior wall signs,25 were determined. When a crossover sign was present, the retroversion index was also calculated.26 Additionally, the sacrococcygeal distance,26,28 lateral center-edge angle (LCEA),33 and acetabular inclination (AI)30 were measured. The sacrococcygeal distance was defined as ‘‘appropriate’’ if 20 to 40 mm in male patients and 20 to 55 mm in female patients, as described according to Tannast et al.28 Three-dimensional radiographic parameters measured included acetabular version measurements at the 1:30 (cranial) position and 3:00 (central) position.22 Additionally, the software system measured the femoral neck version relative to the posterior condylar axis of the knees as well as the alpha angles of the various clock-face positions in 15-minute increments circumferentially around the entire femoral head on radial sequences. Simulated hip range of motion was performed with the 3D-generated model as previously described.2,3 The pelvis was fixed in the predefined position, and the femur was free to move in all directions but constrained to rotate
*Address correspondence to James R. Ross, MD, Broward Orthopedic Specialists, 5301 N Dixie Highway, Suite 203, Fort Lauderdale, FL 33334, USA (e-mail: [email protected]). y Sports Medicine and Shoulder Service, Department of Orthopaedic Surgery, University of Michigan, Ann Arbor, Michigan, USA. z Broward Orthopedic Specialists, Fort Lauderdale, Florida, USA. § Steadman Clinic and Steadman Philippon Research Institute, Vail, Colorado, USA. k Hospital for Special Surgery, New York, New York, USA. { Minnesota Orthopedic Sports Medicine Institute at Twin Cities Orthopedics, Edina, Minnesota, USA. The authors declared that they have no conflicts of interest in the authorship and publication of this contribution.
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proximal femur and the acetabular rim was determined using standardized clockface nomenclature. The clockface was standardized between hips so that 12:00 was lateral and 3:00 was always anterior in both right and left hips.4,21,24 To assess interrater reliability of the various CT measurements, 10 patients’ CT scans were reuploaded and measurements made by a second observer. A 2-way analysis of variance using SPSS (IBM Corp) was performed to determine the absolute interobserver reliability (intraclass correlation coefficient for numerical and kappa for categorical variables). Femoral measurements demonstrated excellent interobserver reliability (version, 0.98; maximum alpha angle, 0.88; alpha angle range for 12:00 to 3:00 vector, 0.84-0.95) All CT acetabular measurements also demonstrated excellent interobserver reliability (1:30 version, 0.99; 3:00 version, 0.99; LCEA, 0.98; AI, 0.97; crossover sign, 1.00; posterior wall sign, 0.80; prominent ischial spine sign, 0.62). Finally range of motion also demonstrated excellent interobserver reliability (flexion, 0.96; IRF, 0.96; FADIR, 0.96).
Statistical Analysis Statistical analysis was performed with Excel software (Microsoft Corp) to compare the changes in radiographic parameters and range of motion to impingement between the different pelvic tilt conditions. A paired Student t test was used for comparison of continuous variables, while x2 testing was used for categorical variables. P values \ .05 were considered significant.
RESULTS Native Pelvic Tilt
Figure 1. Patient example demonstrating the virtual radiograph and three-dimensional model of the hip in (A) posterior, (B) native, and (C) anterior pelvic tilt positions.
about the proscribed rotation axis, against the congruous acetabular surface. A posteriorly and superiorly directed force was applied to the femur to maintain reduction of the femur during simulation.3 The femur was positioned with the posterior femoral condylar axis parallel to the horizontal axis of the pelvis (native femoral version). During the simulated range of motion maneuvers, the femur was moved in a specific motion until contact between the femur and acetabulum occurred (detected by the resultant translation of the femoral head). This point of collision was defined as the occurrence of mechanical impingement, which was recorded in degrees of motion. Three range of motion simulations were performed: (1) internal rotation in 90° of hip flexion (IRF), (2) internal rotation in 90° of hip flexion with 15° of adduction (FADIR), and (3) maximum hip flexion. The location of contact on both the
The mean maximum alpha angle for all hips was 71.2° 6 11.1° (range, 50° to 94°) and was located on average at the 1:15 clockface position. The mean alpha angles at 12:00, 1:30, and 3:00 were 50.0°, 65.5°, and 50.9°, respectively. The mean femoral version was 17.1° 6 9.0° (range, –4° to 35°) among this patient population. In native pelvic tilt, the mean cranial acetabular version (1:30) was 3.3° 6 8.4° (range, –12° to 24°), while central acetabular version (3:00) was 16.2° 6 6.7° (range, 3° to 30°). The mean sacrococcygeal distance in the supine position was 33.8 6 14.3 mm (range, 0 to 65 mm). Eighty percent of patients (40/50) were noted to have appropriate sacrococcygeal distance in native pelvic tilt, as defined by Tannast et al.28 Forty-eight percent of the patients (24/ 50) had positive crossover signs. The mean retroversion index was 24.3% (range, 11.3% to 38.5%) among the patients with positive crossover signs. The mean LCEA was 32.2° 6 5.3° (range, 21° to 44°), and the mean AI was 5.0° 6 4.1° (range, –5.3° to 14.2°). The posterior wall sign and prominent ischial spine signs were present in 38% and 28% of hips, respectively. Male patients had a significantly lower mean sacrococcygeal distance compared with female patients (25.4 vs 44.5 mm, P \ .0001). Among
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TABLE 1 Two- and 3-Dimensional Measurements in the Native, Anterior, and Posterior Pelvic Tilt Positions Radiographic Measurement Cranial acetabular version (1:30), deg Central acetabular version (3:00), deg Sacrococcygeal distance, mm Lateral center-edge angle, deg Acetabular inclination, deg Positive crossover sign Positive posterior wall sign Positive ischial spine sign Retroversion indexa
Native, Mean
Anterior (110°) Tilt, Mean
P
Posterior (–10°) Tilt, Mean
P
3.3 16.2 33.8 32.2 5.0 48% 38% 28% 24.3%
–2.6 10.4 54.9 32.4 3.6 86% 74% 68% 45.1%
\.0001 \.0001 \.0001 .58 \.0001 \.0001 .0003 \.0001 \.0001
12.3 22.2 11.7 33.1 5.8 14% 14% 0% 15.4%
\.0001 \.0001 \.0001 \.0001 \.0001 .0002 .006 \.0001 .007
Interobserver Reliability 0.995 0.995 0.949 0.981 0.966 1.0 0.800 0.615
a
This measurement was performed only in those patients in whom crossover signs were present in native pelvic tilt.
patients with sacrococcygeal distances between 20 and 45 mm, female patients had a significantly greater mean acetabular anteversion at 3:00 (19.4° vs 13.3°, P = .008). There was no significant difference in cranial version, although male patients had a trend toward greater retroversion.
Anterior Pelvic Tilt A simulated 10° increase in anterior pelvic tilt resulted in a significant relative retroversion of the acetabulum, with mean decreases in cranial acetabular version of 5.9° (P \ .0001) and central acetabular version of 5.8° (P \ .0001) (Table 1). Additionally, the sacrococcygeal distance increased by an average of 21.1 mm (P \ .0001). This also resulted in an increased percentage of positive radiographic signs of acetabular retroversion, namely, crossover (48% in native vs 86% in anterior tilt, P \ .0001), posterior wall (38% in native vs 74% in anterior tilt, P \ .0001), and prominent ischial spine signs (28% in native vs 68% in anterior tilt, P = .003). Seventy-three percent of patients (19/26) without crossover signs in their native tilt developed crossover signs with 10° of anterior pelvic tilt. There was also a significant increase in the mean retroversion index in those patients with a crossover sign in their native position (24.3% in native vs 45.1% in anterior tilt, P \ .0001). Although anterior pelvic tilt led to a small but significant decrease in the mean AI by 1.4° (P \ .0001), there was no significant change in the LCEA (32.2° vs 32.4°) (P = .58).
Posterior Pelvic Tilt Conversely, a 10° increase in posterior pelvis tilt resulted in a significant increase in relative anteversion of the acetabulum, with increases in the mean cranial (9.0°, P \ .0001) and central (6.0°, P \ .0001) acetabular version (Table 1). The sacrococcygeal distance decreased by an average of 22.1 mm (P \ .0001). There was also a significant decrease in the percentage of hips with positive crossover (48% in native vs 14% in posterior tilt, P = .0002), posterior wall (38% in native vs 14% in posterior tilt, P = .006), or prominent ischial spine (28% in native vs 0% in posterior tilt, P \ .0001) signs. In addition, there was
a significant decrease in the mean retroversion index in patients with crossover signs in their native positions (24.3% in native vs 15.4% in posterior tilt, P = .007). Only 29% of the patients (7/24) with crossover signs in their native tilt continued to have crossover signs with 10° of posterior pelvic tilt. Posterior pelvic tilt resulted in significant but small increases in both the mean AI by 0.8° (P \ .0001) and the mean LCEA by 0.8° (P \ .0001).
Range of Motion to Impingement A 10° increase in anterior pelvic tilt resulted in a significant decrease in IRF of 5.9° (P \ .0001), with an anterior shift in the location of the femoral impingement (2:45 vs 3:15; P \ .001) (Figure 2, Table 2). Similarly, the increase in anterior pelvic tilt also resulted in an 8.5° decrease in FADIR (P \ .0001), with a significant anterior shift in the femoral (3:00 vs 3:45, P \ .0001) and acetabular (1:30 vs 1:45, P = .0002) impingement locations, respectively. A 10° increase in posterior pelvic tilt, on the other hand, resulted in a 5.1° increase in IRF (32.0° vs 37.1°, P \ .0001) and a 7.4° increase in FADIR (24.0° vs 31.4°, P \ .0001). There was a superolateral shift in the femoral (2:45 vs 2:30, P \ .0001) and an anterior shift in the acetabular (1:00 vs 1:15, P = .03) impingement locations with IRF testing. Similar shifts were noted on the femoral (3:00 vs 2:45, P \ .0001) and acetabular (1:30 vs 1:45, P = .01) rims with FADIR testing. A 10° increase in anterior or posterior pelvic tilt also resulted in a 10° respective loss or gain in flexion, with no significant change in the contact positions.
DISCUSSION The role of dynamic and static alterations in pelvic tilt in FAI is poorly understood. Our present study demonstrates significant changes in functional acetabular version and secondary terminal hip range of motion to impingement with relatively small changes in pelvic tilt. Ten-degree increases in anterior pelvic tilt reduced the impingementfree range of motion arc of internal rotation by 5° to 9° on average, which may have implications regarding nonsurgical treatment of hip disorders. On the other hand,
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Figure 2. Clockface positions of femoral and acetabular impingement in (A) flexion, (B) internal rotation in 90° of flexion (IRF), and (C) internal rotation in 90° of flexion and 15° adduction (FADIR) maneuvers. posterior pelvic tilt improved the impingement-free range of motion arc of internal rotation, which may compensate for anterior impingement in patients with FAI. Additionally, changes in pelvic tilt resulted in significant changes in measurements of cranial and central acetabular version, as well as multiple plain radiographic parameters conventionally used to diagnosis pathologic acetabular retroversion in symptomatic patients with FAI. This is a critical finding with regard to defining pathomorphologic characteristics on imaging studies in patients with hip disorders,
and clinicians must understand this relationship when evaluating these patients, as changes in pelvic tilt can influence the acetabular orientation. Analysis and identification of acetabular deformity is critical in the decision-making process when evaluating patients with hip pain and defining the most appropriate joint preservation treatment options.11,18,27 Previous studies have demonstrated the effect of alterations in pelvic tilt on plain radiographic parameters of acetabular morphologic characteristics.7,8,10,26,28,29 Interpretation of plain
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TABLE 2 Range of Motion to Impingement and the Corresponding Femoral and Acetabular Impingement Locations in Native, Anterior, and Posterior Pelvic Tilt Positionsa Radiographic Measurement
Native, Mean
110° Tilt, Mean
P
–10° Tilt, Mean
P
IRF, deg Femoral impingement Acetabular impingement FADIR, deg Femoral impingement Acetabular impingement Flexion, deg Femoral impingement Acetabular impingement
32.0 6 12.6 2:45 1:00 24.0 6 12.9 3:00 1:30 119.3 6 10.8 5:15 1:30
26.1 6 13.5 3:15 1:15 15.5 6 12.7 3:45 1:45 109.3 6 10.9 5:15 1:30
\.0001 \.0001 .11 \.0001 \.0001 .0002 \.0001 .74 .57
37.1 6 12.4 2:30 1:15 31.4 6 13.8 2:45 1:45 129.3 6 10.8 5:15 1:30
\.0001 \.0001 .034 \.0001 \.0001 .01 \.0001 .29 .99
a
FADIR, internal rotation in 90° of flexion and 15° adduction; IRF, internal rotation in 90° of flexion.
radiographs in patients with current definitions of ‘‘appropriate’’ pelvic tilt via the sacrococcygeal distance28 at presentation is fairly straightforward. The interpretation of radiographs with a sacrococcygeal distance that is outside of the currently defined normal range, however, is more difficult. This is most commonly encountered in female patients with increased anterior pelvic tilt on radiographs. Repeat radiographs with altered projections or computer software manipulation of the projection have been proposed.29 However, these strategies ignore any role that static or dynamic muscular alterations in pelvic tilt may have on the underlying hip kinematics and ability to compensate for proximal femur or acetabular deformities. Additionally, changes in pelvic tilt between supine and standing radiographic studies have also been demonstrated.10 The present study demonstrates significant alterations in hip kinematics with relatively small alterations in pelvic tilt. Assessment of pelvic tilt may be important to understand the functional restriction of motion in the setting of FAI. In addition, rehabilitation for patients with FAI should include attempts to improve dynamic muscular control of the pelvis with resultant changes in pelvic tilt, which might compensate for impingement in some instances. The changes in contact with changes in pelvic tilt give some justification for nonsurgical treatment of hip-related disorders. This might be most appropriate for milder deformities and might explain the improvements seen after nonsurgical treatment of FAI in milder deformities.9,13 The concept of increased anterior tilt increasing anterior impingement and increased posterior tilt decreasing impingement, along with imaging studies defining the pathomorphologic characteristics present might better direct nonsurgical and postsurgical rehabilitation protocols. Pelvic tilt has historically been measured when evaluating spinal deformity, but recent literature has also documented the importance of pelvic tilt when evaluating acetabular deformity. Janssen et al15 demonstrated a mean standing posterior pelvic tilt of 11.5° 6 6.2° among asymptomatic volunteers. This was confirmed by Lee et al,19 who also reported a mean posterior standing pelvic tilt of 11.5° 6 5.3° (range, –6° to 24°). Babisch et al1 demonstrated variability in pelvic tilt when comparing supine
and standing pelvic radiographic studies among patients with osteoarthritis of the hip. They demonstrated a mean increase in posterior pelvic tilt of 6.7° 6 3.8° (range, 1° anterior to 14° posterior) from supine to standing. Thus, standing plain radiographs would allow the most accurate assessment of native pelvic tilt. One must keep in mind, however, that ‘‘appropriate tilt’’ on an AP pelvic study is evaluated using a surrogate measurement, such as sacrococcygeal distance, and that true measurement of pelvic tilt is done on a lateral radiographic assessment. Physicians who perform hip preservation surgery commonly do not obtain true lateral pelvic radiographs to determine the pelvic tilt and have thus relied on surrogate measurements from the AP pelvic radiographs. Siebenrock et al26 noted a correlation between pelvic inclination with sacrococcygeal distance on AP pelvic radiography. The sacrococcygeal distance was later confirmed to be the most accurate indicator of pelvic tilt on AP pelvic radiography.28 Our study confirms that changes in pelvic tilt have a corresponding change in the sacrococcygeal distance. We demonstrated that 10° of anterior pelvic tilt increases the sacrococcygeal distance by an average of 21.1 mm, while 10° of posterior pelvic tilt decreases this distance by an average of 22.1 mm. Our study confirms previous studies6,14,26,31 that demonstrated the radiographic appearance of the anterior and posterior acetabular rims is significantly affected by the amount of pelvic tilt and thus must be considered to avoid misinterpretation and subsequent inappropriate treatment. Siebenrock et al26 demonstrated that a 9° increase in pelvic tilt led to a change in the rate of positive crossover signs from 50% to 100% of acetabula. In our study population, 86% of patients had crossover signs after 10° of anterior pelvic tilt (compared with 48% in native position). Previous studies have also shown that conventional radiographic evaluation of acetabular retroversion using the crossover sign has limited sensitivity (57%-92%) and specificity (55%-61%) for identifying true acetabular retroversion via CT scan.6,31 The authors of both studies argued that pelvic tilt is responsible for a large component of this discrepancy,6,31 which we also noted in our study. Our study also demonstrated very small changes in LCEA and AI with 10° increments of pelvic tilt. The
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minimal changes in LCEA and AI that we demonstrated are important, in that evaluation of acetabular dysplasia and pincer deformity relies on these measurements. Therefore, a pelvic radiograph that is not positioned properly with respect to pelvic tilt may still be evaluated with these radiographic measures to determine acetabular deformity. Additionally, alterations in pelvic tilt would appear to play a lesser role in altering lateral acetabular coverage in dysplasia. It is important, however, to measure the LCEA to the most lateral aspect of the sclerotic sourcil, rather than the most lateral projection of bone. The most lateral extent of the sourcil, we have demonstrated, does not change significantly with tilt, but the most lateral projection of bone can be variable with changes in tilt and can represent changes in orientation of the anterior or posterior acetabular wall. Our understanding of the pathomechanics of FAI continues to improve. Yet the role of pelvic tilt in FAI has largely been ignored. Our study demonstrates a significant relationship between changes in pelvic tilt and the occurrence of bony impingement. Changes in pelvic tilt reorient the acetabulum and result in significant changes in acetabular version as measured by 2-dimenssional and 3D parameters. Pelvic tilt is clearly variable among individuals and is often assessed radiographically with surrogate measures such as the sacrococcygeal distance. We noted this variability within our study population, of whom 20% had sacrococcygeal distances outside of currently accepted standards of the normal range (20-40 mm in male patients and 20-55 mm in female patients).28 Our study demonstrates that in a population of patients with FAI, increases in anterior pelvic tilt result in earlier anterolateral bony impingement with flexion, internal rotation, or adduction for any given underlying proximal femoral pathomorphologic deformities. Dynamic changes in pelvic tilt during functional activities and the ability to alter a patient’s pelvic tilt through rehabilitation and dynamic muscular control are poorly understood. However, the present study suggests that relatively small increases in posterior pelvic tilt could decrease the occurrence of the more traditional anteriorly based FAI. Given the results of this study, dynamic pelvic tilt and muscular control of the pelvis may be an area for further clinical investigation regarding nonoperative and postoperative rehabilitation protocols. Dynamic posterior pelvic tilt may allow athletes with large, anteriorly based FAI deformities to lessen the occurrence of FAI, but the process of increasing pelvic tilt may lead to compensatory increases in motion in the surrounding joints (sacroiliac, lumbar spine). Ultimately, an understanding of both the underlying hip pathomorphologic characteristics and effect of changes in pelvic tilt on impingement might allow the most effective nonsurgical and postsurgical treatment strategies. Further research into these aspects of pelvic tilt is needed. The present study was not without limitations. Range of motion simulations in the study included only bony structure, ignoring contributions of labrum, cartilage, capsule, and periarticular soft tissue structures. This is reflected in the high level of IRF (mean, 32°; range, 3°-60°) present in this FAI population in the native position. Current
technology does not allow the inclusion of soft tissue structures. However, we believe that the trends demonstrated with alterations in pelvic tilt would likely be similar to those seen with soft tissue present, even if the absolute magnitudes were reduced. Additionally, the pelvic position was fixed in the simulations during range of motion, and in this regard, we have used a quasi-dynamic model in 3 fixed positions of pelvic tilt for each patient. Although changes in dynamic pelvic tilt do likely occur during range of motion, these changes are currently poorly understood and are an appropriate target for future research. Additionally, no true measurement of pelvic tilt was possible in our population, because the CT scans did not include the entire sacrum. However, rotational alterations in pelvic tilt could be corrected from the native position. Finally, femoral orientation is likely to influence range of motion and was standardized with the posterior femoral condylar axis parallel to the horizontal axis of the pelvis. Although this orientation may not represent physiologic orientation, it was uniform between tilt orientations, and by using a matched-pair study design, this is minimized. The present study included only patients with underlying FAI, and the findings may not be applicable to those without such deformities. However, the vast majority of patients with symptomatic labral tears have evidence of underlying FAI deformity.32
CONCLUSION Dynamic changes in pelvic tilt significantly influence the functional orientation of the acetabulum and must be considered when diagnosing and treating patients with symptomatic FAI. Dynamic anterior pelvic tilt is predicted to result in earlier occurrence of anteriorly based FAI in the arc of motion, whereas dynamic posterior pelvic tilt is predicted to result in later occurrence of anteriorly based FAI. In the present study, small changes in pelvic tilt were predicted to have a significant effect on terminal hip range of motion, and this may have significant implications for future nonsurgical and postsurgical treatment strategies.
REFERENCES 1. Babisch JW, Layher F, Amiot LP. The rationale for tilt-adjusted acetabular cup navigation. J Bone Joint Surg Am. 2008;90(2):357-365. 2. Bedi A, Dolan M, Hetsroni I, et al. Surgical treatment of femoroacetabular impingement improves hip kinematics: a computer-assisted model. Am J Sports Med. 2011;39(suppl):43S-49S. 3. Bedi A, Dolan M, Magennis E, Lipman J, Buly R, Kelly BT. Computerassisted modeling of osseous impingement and resection in femoroacetabular impingement. Arthroscopy. 2012;28(2):204-210. 4. Blankenbaker DG, De Smet AA, Keene JS, Fine JP. Classification and localization of acetabular labral tears. Skeletal Radiol. 2007; 36(5):391-397. 5. Clohisy JC, Carlisle JC, Beaule PE, et al. A systematic approach to the plain radiographic evaluation of the young adult hip. J Bone Joint Surg Am. 2008;90(suppl 4):47-66. 6. Dandachli W, Islam SU, Liu M, Richards R, Hall-Craggs M, Witt J. Three-dimensional CT analysis to determine acetabular retroversion and the implications for the management of femoro-acetabular impingement. J Bone Joint Surg Br. 2009;91(8):1031-1036.
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7. Dandachli W, Ul Islam S, Richards R, Hall-Craggs M, Witt J. The influence of pelvic tilt on acetabular orientation and cover: a three-dimensional computerised tomography analysis. Hip Int. 2013;23(1):87-92. 8. Dandachli W, Ul Islam S, Tippett R, Hall-Craggs MA, Witt JD. Analysis of acetabular version in the native hip: comparison between 2D axial CT and 3D CT measurements. Skeletal Radiol. 2011;40(7): 877-883. 9. Emara K, Samir W, Motasem el H, Ghafar KA. Conservative treatment for mild femoroacetabular impingement. J Orthop Surg (Hong Kong). 2011;19(1):41-45. 10. Fuchs-Winkelmann S, Peterlein CD, Tibesku CO, Weinstein SL. Comparison of pelvic radiographs in weightbearing and supine positions. Clin Orthop Relat Res. 2008;466(4):809-812. 11. Ganz R, Gill TJ, Gautier E, Ganz K, Krugel N, Berlemann U. Surgical dislocation of the adult hip a technique with full access to the femoral head and acetabulum without the risk of avascular necrosis. J Bone Joint Surg Br. 2001;83(8):1119-1124. 12. Ganz R, Parvizi J, Beck M, Leunig M, Notzli H, Siebenrock KA. Femoroacetabular impingement: a cause for osteoarthritis of the hip. Clin Orthop Relat Res. 2003;417:112-120. 13. Hunt D, Prather H, Harris Hayes M, Clohisy JC. Clinical outcomes analysis of conservative and surgical treatment of patients with clinical indications of prearthritic, intra-articular hip disorders. PM R. 2012;4(7):479-487. 14. Jamali AA, Mladenov K, Meyer DC, et al. Anteroposterior pelvic radiographs to assess acetabular retroversion: high validity of the ‘‘cross-over-sign.’’ J Orthop Res. 2007;25(6):758-765. 15. Janssen MM, Drevelle X, Humbert L, Skalli W, Castelein RM. Differences in male and female spino-pelvic alignment in asymptomatic young adults: a three-dimensional analysis using upright low-dose digital biplanar X-rays. Spine (Phila Pa 1976). 2009;34(23):E826E832. 16. Kakaty DK, Fischer AF, Hosalkar HS, Siebenrock KA, Tannast M. The ischial spine sign: does pelvic tilt and rotation matter? Clin Orthop Relat Res. 2010;468(3):769-774. 17. Kalberer F, Sierra RJ, Madan SS, Ganz R, Leunig M. Ischial spine projection into the pelvis: a new sign for acetabular retroversion. Clin Orthop Relat Res. 2008;466(3):677-683. 18. Kim WY, Hutchinson CE, Andrew JG, Allen PD. The relationship between acetabular retroversion and osteoarthritis of the hip. J Bone Joint Surg Br. 2006;88(6):727-729. 19. Lee CS, Chung SS, Kang KC, Park SJ, Shin SK. Normal patterns of sagittal alignment of the spine in young adults radiological analysis in
20.
21.
22.
23.
24.
25. 26.
27.
28.
29.
30. 31.
32. 33.
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a Korean population. Spine (Phila Pa 1976). 2011;36(25):E1648E1654. Legaye J, Duval-Beaupere G, Hecquet J, Marty C. Pelvic incidence: a fundamental pelvic parameter for three-dimensional regulation of spinal sagittal curves. Eur Spine J. 1998;7(2):99-103. Leunig M, Podeszwa D, Beck M, Werlen S, Ganz R. Magnetic resonance arthrography of labral disorders in hips with dysplasia and impingement. Clin Orthop Relat Res. 2004;418:74-80. Mast JW, Brunner RL, Zebrack J. Recognizing acetabular version in the radiographic presentation of hip dysplasia. Clin Orthop Relat Res. 2004;418:48-53. Milone MT, Bedi A, Poultsides L, et al. Novel CT-based three-dimensional software improves the characterization of cam morphology. Clin Orthop Relat Res. 2013;471(8):2484-2491. Philippon MJ, Stubbs AJ, Schenker ML, Maxwell RB, Ganz R, Leunig M. Arthroscopic management of femoroacetabular impingement: osteoplasty technique and literature review. Am J Sports Med. 2007;35(9):1571-1580. Reynolds D, Lucas J, Klaue K. Retroversion of the acetabulum. A cause of hip pain. J Bone Joint Surg Br. 1999;81(2):281-288. Siebenrock KA, Kalbermatten DF, Ganz R. Effect of pelvic tilt on acetabular retroversion: a study of pelves from cadavers. Clin Orthop Relat Res. 2003;407:241-248. Siebenrock KA, Schoeniger R, Ganz R. Anterior femoro-acetabular impingement due to acetabular retroversion. Treatment with periacetabular osteotomy. J Bone Joint Surg Am. 2003;85(2):278-286. Tannast M, Murphy SB, Langlotz F, Anderson SE, Siebenrock KA. Estimation of pelvic tilt on anteroposterior X-rays—a comparison of six parameters. Skeletal Radiol. 2006;35(3):149-155. Tannast M, Zheng G, Anderegg C, et al. Tilt and rotation correction of acetabular version on pelvic radiographs. Clin Orthop Relat Res. 2005;438:182-190. To¨nnis D, Legal H, Graf R. Congenital Dysplasia and Dislocation of the Hip in Children and Adults. New York: Springer-Verlag, 1987. Wassilew GI, Heller MO, Diederichs G, Janz V, Wenzl M, Perka C. Standardized AP radiographs do not provide reliable diagnostic measures for the assessment of acetabular retroversion. J Orthop Res. 2012;30(9):1369-1376. Wenger DR, Kishan S, Pring ME. Impingement and childhood hip disease. J Pediatr Orthop B. 2006;15(4):233-243. Wiberg G. Studies on dysplastic acetabula and congenital subluxation of the hip: with special reference to the complication of osteoarthritis. Acta Chir Scand. 1939;58:7-38.
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Effect of Changes in Pelvic Tilt on Range of Motion to Impingement and Radiographic Parameters of Acetabular Morphologic Characteristics James R. Ross, Jeffrey J. Nepple, Marc J. Philippon, Bryan T. Kelly, Christopher M. Larson and Asheesh Bedi Am J Sports Med 2014 42: 2402 originally published online July 24, 2014 DOI: 10.1177/0363546514541229 The online version of this article can be found at: http://ajs.sagepub.com/content/42/10/2402
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Effect of Changes in Pelvic Tilt on Range of Motion to Impingement and Radiographic Parameters of Acetabular Morphologic Characteristics James R. Ross,*yz MD, Jeffrey J. Nepple,§ MD, Marc J. Philippon,§ MD, Bryan T. Kelly,k MD, Christopher M. Larson,{ MD, and Asheesh Bedi,yk MD Investigation performed at University of Michigan, Ann Arbor, Michigan, USA Background: The current understanding of the effect of dynamic changes in pelvic tilt on the functional acetabular orientation and occurrence of femoroacetabular impingement (FAI) is limited. Purpose: To determine the effect of changes in pelvic tilt on (1) terminal hip range of motion and (2) measurements of acetabular version as assessed on 2- and 3-dimensional imaging. Study Design: Controlled laboratory study. Methods: Preoperative pelvic computed tomographic scans of 48 patients (50 hips) who underwent arthroscopic surgery for the treatment of FAI were analyzed. The mean age of the study population was 25.7 years (range, 14-56 years), and 56% were male. Three-dimensional models of the hips were created, allowing manipulation of the pelvic tilt and simulation of hip range of motion to osseous contact. Acetabular version was measured and the presence of the crossover sign, prominent ischial spine sign, and posterior wall sign was recorded on simulated plain radiographs. Measurements of range of motion to bony impingement during (1) hip flexion, (2) internal rotation in 90° of flexion, and (3) internal rotation in 90° of flexion and 15° adduction were performed, and the location of bony contact between the proximal femur and acetabular rim was defined. These measurements were calculated for –10° (posterior), 0° (native), and 110° (anterior) pelvic orientations. Results: In native tilt, mean cranial acetabular version was 3.3°, while central version averaged 16.2°. Anterior pelvic tilt (10° change) resulted in significant retroversion, with mean decreases in cranial and central version of 5.9° and 5.8°, respectively (P \ .0001 for both). Additionally, this resulted in a significantly increased proportion of positive crossover, posterior wall, and prominent ischial spine signs (P \ .001 for all). Anterior pelvic tilt (10° change) resulted in a decrease in internal rotation in 90° of flexion of 5.9° (P \ .0001) and internal rotation in 90° of flexion and 15° adduction of 8.5° (P \ .0001), with a shift in the location of osseous impingement more anteriorly. Posterior pelvic tilt (10° change) resulted in an increase in internal rotation in 90° of flexion of 5.1° (P \ .0001) and internal rotation in 90° of flexion and 15° adduction of 7.4° (P \ .0001), with a superolateral shift in the location of osseous impingement. Conclusion/Clinical Relevance: Dynamic changes in pelvic tilt significantly influence the functional orientation of the acetabulum and must be considered. Dynamic anterior pelvic tilt is predicted to result in earlier occurrence of FAI in the arc of motion, whereas dynamic posterior pelvic tilt results in later occurrence of FAI, which may have implications regarding nonsurgical treatments for FAI. Keywords: femoroacetabular impingement; pelvic tilt; computed tomography; acetabular version; computer modeling
Femoroacetabular impingement (FAI) has recently been recognized as one of the most common causes of hip pain and osteoarthritis in young active adults.12 FAI results from abnormal bony contact between the proximal femur and acetabulum during range of motion and is generally the result of developmental osseous pathomorphologic abnormalities. Pelvic tilt, defined as the angle between
the line connecting the midpoint of the sacral plate to the femoral heads axis and the vertical axis,20 may play a role in the occurrence of bony impingement and the development of symptoms in patients with bony deformities of FAI. Alterations in pelvic tilt may allow patients to compensate for secondary restrictions in terminal hip range of motion but are currently poorly understood. Pelvic tilt is a natural component of the patient’s posture and may vary significantly among patients, between genders, during different activities of daily living and sport-specific activities, and even between standing and supine radiographic studies.10,26
The American Journal of Sports Medicine, Vol. 42, No. 10 DOI: 10.1177/0363546514541229 Ó 2014 The Author(s)
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Radiographic evaluation is a critical component of the diagnostic evaluation and treatment decision-making process in patients with prearthritic hip disease. An understanding of the effect of pelvic tilt on the appearance of the hip on pelvic radiographs is important, especially when assessing young adults with hip pain.5,7,8,10,26,28,29 Previous studies have demonstrated a relationship between pelvic tilt and the distance between the superior border of the symphysis pubis and the position of the sacrococcygeal joint or tip of the coccyx.26,28 In patients with alterations of pelvic tilt on baseline radiography, current standards of radiographic evaluation attempt to reposition the radiograph to an ‘‘appropriate’’ pelvic tilt.28 However, this standardization is simplistic and fails to account for inherent differences in pelvic tilt among patients and the ability for dynamic muscular control to adjust tilt and thereby improve the functional range of motion. Failure to understand the influence of alterations in pelvic tilt may lead to inaccurate characterization of acetabular deformities and could result in over- or underresection of the acetabulum due to an inaccurate assessment of acetabular retroversion. In this regard, our current understanding of the varying relationship between the acetabulum and the femoral head on the basis of a patient’s native pelvic tilt is poor. The purpose of this study was to determine the effect of changes in pelvic tilt on terminal hip range of motion to impingement via computer-based software analysis, as well as to identify any change in the anatomic location of the impingement. Second, we aimed to determine the effect of changes in pelvic tilt on acetabular version parameters on two-dimensional and three-dimensional (3D) imaging studies. We believe that changes in pelvic tilt will significantly change the acetabular appearance as well as terminal hip range of motion.
MATERIALS AND METHODS We retrospectively identified a consecutive series of 50 hips in 48 patients with symptomatic FAI who underwent preoperative computed tomographic (CT) scans and were treated with arthroscopic hip surgery for FAI between June and August 2012 at a single institution. FAI was diagnosed via symptoms and physical examination findings in all patients and confirmed with corresponding radiographic pathomorphologic findings on plain films and 3D imaging (24 hips [48%] with isolated cam, 1 hip [2%] with isolated pincer, and 25 hips [50%] with both). No other hip conditions were noted (Perthes, slipped capital femoral epiphysis, etc). This study was performed under an institutional
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review board–approved protocol. The average age of patients in this series was 25.7 years (range, 14-54 years). Fifty-six percent of the patients (n = 28) were male, and 54% (n = 27) of the surgical procedures involved the right hip. In addition to a standardized plain radiographic series, the patients underwent high-resolution CT scans of the pelvis (and distal femur for assessment of femoral version) as part of their clinical care and preoperative surgical planning. A modified CT protocol using decreased radiation exposure of 2.85 mSv was used to maximize patient safety, as described by Milone et al.23 Positioning of the patient in the scanner was standardized, with the legs in native abduction or adduction and the patellae pointing directly anterior. The patient was positioned supine with a natural resting pelvic tilt. This resting, supine pelvic position was considered the patient’s ‘‘native’’ pelvic tilt. Static radiographic parameters (2-dimensional and 3D) and dynamic range of motion measurements to impingement were calculated for 3 pelvic positions: 110° (anterior tilt), 0° (native), and -10° (posterior tilt) (Figure 1). The preoperative CT scans were uploaded into a computed tomography–based computer software program (DYONICS PLAN Software; Smith & Nephew) to generate patient-specific 3D models of the hip joint. This software program also allowed manipulation of the pelvic tilt and subsequent generation of virtual plain radiographs. These virtual radiographs, which simulated an anteroposterior (AP) pelvic radiograph, were analyzed for parameters of acetabular and pelvic orientation. Two-dimensional radiographic parameters, including the presence or absence of the crossover,25 prominent ischial spine,16,17 and posterior wall signs,25 were determined. When a crossover sign was present, the retroversion index was also calculated.26 Additionally, the sacrococcygeal distance,26,28 lateral center-edge angle (LCEA),33 and acetabular inclination (AI)30 were measured. The sacrococcygeal distance was defined as ‘‘appropriate’’ if 20 to 40 mm in male patients and 20 to 55 mm in female patients, as described according to Tannast et al.28 Three-dimensional radiographic parameters measured included acetabular version measurements at the 1:30 (cranial) position and 3:00 (central) position.22 Additionally, the software system measured the femoral neck version relative to the posterior condylar axis of the knees as well as the alpha angles of the various clock-face positions in 15-minute increments circumferentially around the entire femoral head on radial sequences. Simulated hip range of motion was performed with the 3D-generated model as previously described.2,3 The pelvis was fixed in the predefined position, and the femur was free to move in all directions but constrained to rotate
*Address correspondence to James R. Ross, MD, Broward Orthopedic Specialists, 5301 N Dixie Highway, Suite 203, Fort Lauderdale, FL 33334, USA (e-mail: [email protected]). y Sports Medicine and Shoulder Service, Department of Orthopaedic Surgery, University of Michigan, Ann Arbor, Michigan, USA. z Broward Orthopedic Specialists, Fort Lauderdale, Florida, USA. § Steadman Clinic and Steadman Philippon Research Institute, Vail, Colorado, USA. k Hospital for Special Surgery, New York, New York, USA. { Minnesota Orthopedic Sports Medicine Institute at Twin Cities Orthopedics, Edina, Minnesota, USA. The authors declared that they have no conflicts of interest in the authorship and publication of this contribution.
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proximal femur and the acetabular rim was determined using standardized clockface nomenclature. The clockface was standardized between hips so that 12:00 was lateral and 3:00 was always anterior in both right and left hips.4,21,24 To assess interrater reliability of the various CT measurements, 10 patients’ CT scans were reuploaded and measurements made by a second observer. A 2-way analysis of variance using SPSS (IBM Corp) was performed to determine the absolute interobserver reliability (intraclass correlation coefficient for numerical and kappa for categorical variables). Femoral measurements demonstrated excellent interobserver reliability (version, 0.98; maximum alpha angle, 0.88; alpha angle range for 12:00 to 3:00 vector, 0.84-0.95) All CT acetabular measurements also demonstrated excellent interobserver reliability (1:30 version, 0.99; 3:00 version, 0.99; LCEA, 0.98; AI, 0.97; crossover sign, 1.00; posterior wall sign, 0.80; prominent ischial spine sign, 0.62). Finally range of motion also demonstrated excellent interobserver reliability (flexion, 0.96; IRF, 0.96; FADIR, 0.96).
Statistical Analysis Statistical analysis was performed with Excel software (Microsoft Corp) to compare the changes in radiographic parameters and range of motion to impingement between the different pelvic tilt conditions. A paired Student t test was used for comparison of continuous variables, while x2 testing was used for categorical variables. P values \ .05 were considered significant.
RESULTS Native Pelvic Tilt
Figure 1. Patient example demonstrating the virtual radiograph and three-dimensional model of the hip in (A) posterior, (B) native, and (C) anterior pelvic tilt positions.
about the proscribed rotation axis, against the congruous acetabular surface. A posteriorly and superiorly directed force was applied to the femur to maintain reduction of the femur during simulation.3 The femur was positioned with the posterior femoral condylar axis parallel to the horizontal axis of the pelvis (native femoral version). During the simulated range of motion maneuvers, the femur was moved in a specific motion until contact between the femur and acetabulum occurred (detected by the resultant translation of the femoral head). This point of collision was defined as the occurrence of mechanical impingement, which was recorded in degrees of motion. Three range of motion simulations were performed: (1) internal rotation in 90° of hip flexion (IRF), (2) internal rotation in 90° of hip flexion with 15° of adduction (FADIR), and (3) maximum hip flexion. The location of contact on both the
The mean maximum alpha angle for all hips was 71.2° 6 11.1° (range, 50° to 94°) and was located on average at the 1:15 clockface position. The mean alpha angles at 12:00, 1:30, and 3:00 were 50.0°, 65.5°, and 50.9°, respectively. The mean femoral version was 17.1° 6 9.0° (range, –4° to 35°) among this patient population. In native pelvic tilt, the mean cranial acetabular version (1:30) was 3.3° 6 8.4° (range, –12° to 24°), while central acetabular version (3:00) was 16.2° 6 6.7° (range, 3° to 30°). The mean sacrococcygeal distance in the supine position was 33.8 6 14.3 mm (range, 0 to 65 mm). Eighty percent of patients (40/50) were noted to have appropriate sacrococcygeal distance in native pelvic tilt, as defined by Tannast et al.28 Forty-eight percent of the patients (24/ 50) had positive crossover signs. The mean retroversion index was 24.3% (range, 11.3% to 38.5%) among the patients with positive crossover signs. The mean LCEA was 32.2° 6 5.3° (range, 21° to 44°), and the mean AI was 5.0° 6 4.1° (range, –5.3° to 14.2°). The posterior wall sign and prominent ischial spine signs were present in 38% and 28% of hips, respectively. Male patients had a significantly lower mean sacrococcygeal distance compared with female patients (25.4 vs 44.5 mm, P \ .0001). Among
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TABLE 1 Two- and 3-Dimensional Measurements in the Native, Anterior, and Posterior Pelvic Tilt Positions Radiographic Measurement Cranial acetabular version (1:30), deg Central acetabular version (3:00), deg Sacrococcygeal distance, mm Lateral center-edge angle, deg Acetabular inclination, deg Positive crossover sign Positive posterior wall sign Positive ischial spine sign Retroversion indexa
Native, Mean
Anterior (110°) Tilt, Mean
P
Posterior (–10°) Tilt, Mean
P
3.3 16.2 33.8 32.2 5.0 48% 38% 28% 24.3%
–2.6 10.4 54.9 32.4 3.6 86% 74% 68% 45.1%
\.0001 \.0001 \.0001 .58 \.0001 \.0001 .0003 \.0001 \.0001
12.3 22.2 11.7 33.1 5.8 14% 14% 0% 15.4%
\.0001 \.0001 \.0001 \.0001 \.0001 .0002 .006 \.0001 .007
Interobserver Reliability 0.995 0.995 0.949 0.981 0.966 1.0 0.800 0.615
a
This measurement was performed only in those patients in whom crossover signs were present in native pelvic tilt.
patients with sacrococcygeal distances between 20 and 45 mm, female patients had a significantly greater mean acetabular anteversion at 3:00 (19.4° vs 13.3°, P = .008). There was no significant difference in cranial version, although male patients had a trend toward greater retroversion.
Anterior Pelvic Tilt A simulated 10° increase in anterior pelvic tilt resulted in a significant relative retroversion of the acetabulum, with mean decreases in cranial acetabular version of 5.9° (P \ .0001) and central acetabular version of 5.8° (P \ .0001) (Table 1). Additionally, the sacrococcygeal distance increased by an average of 21.1 mm (P \ .0001). This also resulted in an increased percentage of positive radiographic signs of acetabular retroversion, namely, crossover (48% in native vs 86% in anterior tilt, P \ .0001), posterior wall (38% in native vs 74% in anterior tilt, P \ .0001), and prominent ischial spine signs (28% in native vs 68% in anterior tilt, P = .003). Seventy-three percent of patients (19/26) without crossover signs in their native tilt developed crossover signs with 10° of anterior pelvic tilt. There was also a significant increase in the mean retroversion index in those patients with a crossover sign in their native position (24.3% in native vs 45.1% in anterior tilt, P \ .0001). Although anterior pelvic tilt led to a small but significant decrease in the mean AI by 1.4° (P \ .0001), there was no significant change in the LCEA (32.2° vs 32.4°) (P = .58).
Posterior Pelvic Tilt Conversely, a 10° increase in posterior pelvis tilt resulted in a significant increase in relative anteversion of the acetabulum, with increases in the mean cranial (9.0°, P \ .0001) and central (6.0°, P \ .0001) acetabular version (Table 1). The sacrococcygeal distance decreased by an average of 22.1 mm (P \ .0001). There was also a significant decrease in the percentage of hips with positive crossover (48% in native vs 14% in posterior tilt, P = .0002), posterior wall (38% in native vs 14% in posterior tilt, P = .006), or prominent ischial spine (28% in native vs 0% in posterior tilt, P \ .0001) signs. In addition, there was
a significant decrease in the mean retroversion index in patients with crossover signs in their native positions (24.3% in native vs 15.4% in posterior tilt, P = .007). Only 29% of the patients (7/24) with crossover signs in their native tilt continued to have crossover signs with 10° of posterior pelvic tilt. Posterior pelvic tilt resulted in significant but small increases in both the mean AI by 0.8° (P \ .0001) and the mean LCEA by 0.8° (P \ .0001).
Range of Motion to Impingement A 10° increase in anterior pelvic tilt resulted in a significant decrease in IRF of 5.9° (P \ .0001), with an anterior shift in the location of the femoral impingement (2:45 vs 3:15; P \ .001) (Figure 2, Table 2). Similarly, the increase in anterior pelvic tilt also resulted in an 8.5° decrease in FADIR (P \ .0001), with a significant anterior shift in the femoral (3:00 vs 3:45, P \ .0001) and acetabular (1:30 vs 1:45, P = .0002) impingement locations, respectively. A 10° increase in posterior pelvic tilt, on the other hand, resulted in a 5.1° increase in IRF (32.0° vs 37.1°, P \ .0001) and a 7.4° increase in FADIR (24.0° vs 31.4°, P \ .0001). There was a superolateral shift in the femoral (2:45 vs 2:30, P \ .0001) and an anterior shift in the acetabular (1:00 vs 1:15, P = .03) impingement locations with IRF testing. Similar shifts were noted on the femoral (3:00 vs 2:45, P \ .0001) and acetabular (1:30 vs 1:45, P = .01) rims with FADIR testing. A 10° increase in anterior or posterior pelvic tilt also resulted in a 10° respective loss or gain in flexion, with no significant change in the contact positions.
DISCUSSION The role of dynamic and static alterations in pelvic tilt in FAI is poorly understood. Our present study demonstrates significant changes in functional acetabular version and secondary terminal hip range of motion to impingement with relatively small changes in pelvic tilt. Ten-degree increases in anterior pelvic tilt reduced the impingementfree range of motion arc of internal rotation by 5° to 9° on average, which may have implications regarding nonsurgical treatment of hip disorders. On the other hand,
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Figure 2. Clockface positions of femoral and acetabular impingement in (A) flexion, (B) internal rotation in 90° of flexion (IRF), and (C) internal rotation in 90° of flexion and 15° adduction (FADIR) maneuvers. posterior pelvic tilt improved the impingement-free range of motion arc of internal rotation, which may compensate for anterior impingement in patients with FAI. Additionally, changes in pelvic tilt resulted in significant changes in measurements of cranial and central acetabular version, as well as multiple plain radiographic parameters conventionally used to diagnosis pathologic acetabular retroversion in symptomatic patients with FAI. This is a critical finding with regard to defining pathomorphologic characteristics on imaging studies in patients with hip disorders,
and clinicians must understand this relationship when evaluating these patients, as changes in pelvic tilt can influence the acetabular orientation. Analysis and identification of acetabular deformity is critical in the decision-making process when evaluating patients with hip pain and defining the most appropriate joint preservation treatment options.11,18,27 Previous studies have demonstrated the effect of alterations in pelvic tilt on plain radiographic parameters of acetabular morphologic characteristics.7,8,10,26,28,29 Interpretation of plain
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TABLE 2 Range of Motion to Impingement and the Corresponding Femoral and Acetabular Impingement Locations in Native, Anterior, and Posterior Pelvic Tilt Positionsa Radiographic Measurement
Native, Mean
110° Tilt, Mean
P
–10° Tilt, Mean
P
IRF, deg Femoral impingement Acetabular impingement FADIR, deg Femoral impingement Acetabular impingement Flexion, deg Femoral impingement Acetabular impingement
32.0 6 12.6 2:45 1:00 24.0 6 12.9 3:00 1:30 119.3 6 10.8 5:15 1:30
26.1 6 13.5 3:15 1:15 15.5 6 12.7 3:45 1:45 109.3 6 10.9 5:15 1:30
\.0001 \.0001 .11 \.0001 \.0001 .0002 \.0001 .74 .57
37.1 6 12.4 2:30 1:15 31.4 6 13.8 2:45 1:45 129.3 6 10.8 5:15 1:30
\.0001 \.0001 .034 \.0001 \.0001 .01 \.0001 .29 .99
a
FADIR, internal rotation in 90° of flexion and 15° adduction; IRF, internal rotation in 90° of flexion.
radiographs in patients with current definitions of ‘‘appropriate’’ pelvic tilt via the sacrococcygeal distance28 at presentation is fairly straightforward. The interpretation of radiographs with a sacrococcygeal distance that is outside of the currently defined normal range, however, is more difficult. This is most commonly encountered in female patients with increased anterior pelvic tilt on radiographs. Repeat radiographs with altered projections or computer software manipulation of the projection have been proposed.29 However, these strategies ignore any role that static or dynamic muscular alterations in pelvic tilt may have on the underlying hip kinematics and ability to compensate for proximal femur or acetabular deformities. Additionally, changes in pelvic tilt between supine and standing radiographic studies have also been demonstrated.10 The present study demonstrates significant alterations in hip kinematics with relatively small alterations in pelvic tilt. Assessment of pelvic tilt may be important to understand the functional restriction of motion in the setting of FAI. In addition, rehabilitation for patients with FAI should include attempts to improve dynamic muscular control of the pelvis with resultant changes in pelvic tilt, which might compensate for impingement in some instances. The changes in contact with changes in pelvic tilt give some justification for nonsurgical treatment of hip-related disorders. This might be most appropriate for milder deformities and might explain the improvements seen after nonsurgical treatment of FAI in milder deformities.9,13 The concept of increased anterior tilt increasing anterior impingement and increased posterior tilt decreasing impingement, along with imaging studies defining the pathomorphologic characteristics present might better direct nonsurgical and postsurgical rehabilitation protocols. Pelvic tilt has historically been measured when evaluating spinal deformity, but recent literature has also documented the importance of pelvic tilt when evaluating acetabular deformity. Janssen et al15 demonstrated a mean standing posterior pelvic tilt of 11.5° 6 6.2° among asymptomatic volunteers. This was confirmed by Lee et al,19 who also reported a mean posterior standing pelvic tilt of 11.5° 6 5.3° (range, –6° to 24°). Babisch et al1 demonstrated variability in pelvic tilt when comparing supine
and standing pelvic radiographic studies among patients with osteoarthritis of the hip. They demonstrated a mean increase in posterior pelvic tilt of 6.7° 6 3.8° (range, 1° anterior to 14° posterior) from supine to standing. Thus, standing plain radiographs would allow the most accurate assessment of native pelvic tilt. One must keep in mind, however, that ‘‘appropriate tilt’’ on an AP pelvic study is evaluated using a surrogate measurement, such as sacrococcygeal distance, and that true measurement of pelvic tilt is done on a lateral radiographic assessment. Physicians who perform hip preservation surgery commonly do not obtain true lateral pelvic radiographs to determine the pelvic tilt and have thus relied on surrogate measurements from the AP pelvic radiographs. Siebenrock et al26 noted a correlation between pelvic inclination with sacrococcygeal distance on AP pelvic radiography. The sacrococcygeal distance was later confirmed to be the most accurate indicator of pelvic tilt on AP pelvic radiography.28 Our study confirms that changes in pelvic tilt have a corresponding change in the sacrococcygeal distance. We demonstrated that 10° of anterior pelvic tilt increases the sacrococcygeal distance by an average of 21.1 mm, while 10° of posterior pelvic tilt decreases this distance by an average of 22.1 mm. Our study confirms previous studies6,14,26,31 that demonstrated the radiographic appearance of the anterior and posterior acetabular rims is significantly affected by the amount of pelvic tilt and thus must be considered to avoid misinterpretation and subsequent inappropriate treatment. Siebenrock et al26 demonstrated that a 9° increase in pelvic tilt led to a change in the rate of positive crossover signs from 50% to 100% of acetabula. In our study population, 86% of patients had crossover signs after 10° of anterior pelvic tilt (compared with 48% in native position). Previous studies have also shown that conventional radiographic evaluation of acetabular retroversion using the crossover sign has limited sensitivity (57%-92%) and specificity (55%-61%) for identifying true acetabular retroversion via CT scan.6,31 The authors of both studies argued that pelvic tilt is responsible for a large component of this discrepancy,6,31 which we also noted in our study. Our study also demonstrated very small changes in LCEA and AI with 10° increments of pelvic tilt. The
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2408 Ross et al
The American Journal of Sports Medicine
minimal changes in LCEA and AI that we demonstrated are important, in that evaluation of acetabular dysplasia and pincer deformity relies on these measurements. Therefore, a pelvic radiograph that is not positioned properly with respect to pelvic tilt may still be evaluated with these radiographic measures to determine acetabular deformity. Additionally, alterations in pelvic tilt would appear to play a lesser role in altering lateral acetabular coverage in dysplasia. It is important, however, to measure the LCEA to the most lateral aspect of the sclerotic sourcil, rather than the most lateral projection of bone. The most lateral extent of the sourcil, we have demonstrated, does not change significantly with tilt, but the most lateral projection of bone can be variable with changes in tilt and can represent changes in orientation of the anterior or posterior acetabular wall. Our understanding of the pathomechanics of FAI continues to improve. Yet the role of pelvic tilt in FAI has largely been ignored. Our study demonstrates a significant relationship between changes in pelvic tilt and the occurrence of bony impingement. Changes in pelvic tilt reorient the acetabulum and result in significant changes in acetabular version as measured by 2-dimenssional and 3D parameters. Pelvic tilt is clearly variable among individuals and is often assessed radiographically with surrogate measures such as the sacrococcygeal distance. We noted this variability within our study population, of whom 20% had sacrococcygeal distances outside of currently accepted standards of the normal range (20-40 mm in male patients and 20-55 mm in female patients).28 Our study demonstrates that in a population of patients with FAI, increases in anterior pelvic tilt result in earlier anterolateral bony impingement with flexion, internal rotation, or adduction for any given underlying proximal femoral pathomorphologic deformities. Dynamic changes in pelvic tilt during functional activities and the ability to alter a patient’s pelvic tilt through rehabilitation and dynamic muscular control are poorly understood. However, the present study suggests that relatively small increases in posterior pelvic tilt could decrease the occurrence of the more traditional anteriorly based FAI. Given the results of this study, dynamic pelvic tilt and muscular control of the pelvis may be an area for further clinical investigation regarding nonoperative and postoperative rehabilitation protocols. Dynamic posterior pelvic tilt may allow athletes with large, anteriorly based FAI deformities to lessen the occurrence of FAI, but the process of increasing pelvic tilt may lead to compensatory increases in motion in the surrounding joints (sacroiliac, lumbar spine). Ultimately, an understanding of both the underlying hip pathomorphologic characteristics and effect of changes in pelvic tilt on impingement might allow the most effective nonsurgical and postsurgical treatment strategies. Further research into these aspects of pelvic tilt is needed. The present study was not without limitations. Range of motion simulations in the study included only bony structure, ignoring contributions of labrum, cartilage, capsule, and periarticular soft tissue structures. This is reflected in the high level of IRF (mean, 32°; range, 3°-60°) present in this FAI population in the native position. Current
technology does not allow the inclusion of soft tissue structures. However, we believe that the trends demonstrated with alterations in pelvic tilt would likely be similar to those seen with soft tissue present, even if the absolute magnitudes were reduced. Additionally, the pelvic position was fixed in the simulations during range of motion, and in this regard, we have used a quasi-dynamic model in 3 fixed positions of pelvic tilt for each patient. Although changes in dynamic pelvic tilt do likely occur during range of motion, these changes are currently poorly understood and are an appropriate target for future research. Additionally, no true measurement of pelvic tilt was possible in our population, because the CT scans did not include the entire sacrum. However, rotational alterations in pelvic tilt could be corrected from the native position. Finally, femoral orientation is likely to influence range of motion and was standardized with the posterior femoral condylar axis parallel to the horizontal axis of the pelvis. Although this orientation may not represent physiologic orientation, it was uniform between tilt orientations, and by using a matched-pair study design, this is minimized. The present study included only patients with underlying FAI, and the findings may not be applicable to those without such deformities. However, the vast majority of patients with symptomatic labral tears have evidence of underlying FAI deformity.32
CONCLUSION Dynamic changes in pelvic tilt significantly influence the functional orientation of the acetabulum and must be considered when diagnosing and treating patients with symptomatic FAI. Dynamic anterior pelvic tilt is predicted to result in earlier occurrence of anteriorly based FAI in the arc of motion, whereas dynamic posterior pelvic tilt is predicted to result in later occurrence of anteriorly based FAI. In the present study, small changes in pelvic tilt were predicted to have a significant effect on terminal hip range of motion, and this may have significant implications for future nonsurgical and postsurgical treatment strategies.
REFERENCES 1. Babisch JW, Layher F, Amiot LP. The rationale for tilt-adjusted acetabular cup navigation. J Bone Joint Surg Am. 2008;90(2):357-365. 2. Bedi A, Dolan M, Hetsroni I, et al. Surgical treatment of femoroacetabular impingement improves hip kinematics: a computer-assisted model. Am J Sports Med. 2011;39(suppl):43S-49S. 3. Bedi A, Dolan M, Magennis E, Lipman J, Buly R, Kelly BT. Computerassisted modeling of osseous impingement and resection in femoroacetabular impingement. Arthroscopy. 2012;28(2):204-210. 4. Blankenbaker DG, De Smet AA, Keene JS, Fine JP. Classification and localization of acetabular labral tears. Skeletal Radiol. 2007; 36(5):391-397. 5. Clohisy JC, Carlisle JC, Beaule PE, et al. A systematic approach to the plain radiographic evaluation of the young adult hip. J Bone Joint Surg Am. 2008;90(suppl 4):47-66. 6. Dandachli W, Islam SU, Liu M, Richards R, Hall-Craggs M, Witt J. Three-dimensional CT analysis to determine acetabular retroversion and the implications for the management of femoro-acetabular impingement. J Bone Joint Surg Br. 2009;91(8):1031-1036.
Downloaded from ajs.sagepub.com at ULB - Bibliotheque on January 19, 2015
Vol. 42, No. 10, 2014
Effect of Changes in Pelvic Tilt on ROM
7. Dandachli W, Ul Islam S, Richards R, Hall-Craggs M, Witt J. The influence of pelvic tilt on acetabular orientation and cover: a three-dimensional computerised tomography analysis. Hip Int. 2013;23(1):87-92. 8. Dandachli W, Ul Islam S, Tippett R, Hall-Craggs MA, Witt JD. Analysis of acetabular version in the native hip: comparison between 2D axial CT and 3D CT measurements. Skeletal Radiol. 2011;40(7): 877-883. 9. Emara K, Samir W, Motasem el H, Ghafar KA. Conservative treatment for mild femoroacetabular impingement. J Orthop Surg (Hong Kong). 2011;19(1):41-45. 10. Fuchs-Winkelmann S, Peterlein CD, Tibesku CO, Weinstein SL. Comparison of pelvic radiographs in weightbearing and supine positions. Clin Orthop Relat Res. 2008;466(4):809-812. 11. Ganz R, Gill TJ, Gautier E, Ganz K, Krugel N, Berlemann U. Surgical dislocation of the adult hip a technique with full access to the femoral head and acetabulum without the risk of avascular necrosis. J Bone Joint Surg Br. 2001;83(8):1119-1124. 12. Ganz R, Parvizi J, Beck M, Leunig M, Notzli H, Siebenrock KA. Femoroacetabular impingement: a cause for osteoarthritis of the hip. Clin Orthop Relat Res. 2003;417:112-120. 13. Hunt D, Prather H, Harris Hayes M, Clohisy JC. Clinical outcomes analysis of conservative and surgical treatment of patients with clinical indications of prearthritic, intra-articular hip disorders. PM R. 2012;4(7):479-487. 14. Jamali AA, Mladenov K, Meyer DC, et al. Anteroposterior pelvic radiographs to assess acetabular retroversion: high validity of the ‘‘cross-over-sign.’’ J Orthop Res. 2007;25(6):758-765. 15. Janssen MM, Drevelle X, Humbert L, Skalli W, Castelein RM. Differences in male and female spino-pelvic alignment in asymptomatic young adults: a three-dimensional analysis using upright low-dose digital biplanar X-rays. Spine (Phila Pa 1976). 2009;34(23):E826E832. 16. Kakaty DK, Fischer AF, Hosalkar HS, Siebenrock KA, Tannast M. The ischial spine sign: does pelvic tilt and rotation matter? Clin Orthop Relat Res. 2010;468(3):769-774. 17. Kalberer F, Sierra RJ, Madan SS, Ganz R, Leunig M. Ischial spine projection into the pelvis: a new sign for acetabular retroversion. Clin Orthop Relat Res. 2008;466(3):677-683. 18. Kim WY, Hutchinson CE, Andrew JG, Allen PD. The relationship between acetabular retroversion and osteoarthritis of the hip. J Bone Joint Surg Br. 2006;88(6):727-729. 19. Lee CS, Chung SS, Kang KC, Park SJ, Shin SK. Normal patterns of sagittal alignment of the spine in young adults radiological analysis in
20.
21.
22.
23.
24.
25. 26.
27.
28.
29.
30. 31.
32. 33.
2409
a Korean population. Spine (Phila Pa 1976). 2011;36(25):E1648E1654. Legaye J, Duval-Beaupere G, Hecquet J, Marty C. Pelvic incidence: a fundamental pelvic parameter for three-dimensional regulation of spinal sagittal curves. Eur Spine J. 1998;7(2):99-103. Leunig M, Podeszwa D, Beck M, Werlen S, Ganz R. Magnetic resonance arthrography of labral disorders in hips with dysplasia and impingement. Clin Orthop Relat Res. 2004;418:74-80. Mast JW, Brunner RL, Zebrack J. Recognizing acetabular version in the radiographic presentation of hip dysplasia. Clin Orthop Relat Res. 2004;418:48-53. Milone MT, Bedi A, Poultsides L, et al. Novel CT-based three-dimensional software improves the characterization of cam morphology. Clin Orthop Relat Res. 2013;471(8):2484-2491. Philippon MJ, Stubbs AJ, Schenker ML, Maxwell RB, Ganz R, Leunig M. Arthroscopic management of femoroacetabular impingement: osteoplasty technique and literature review. Am J Sports Med. 2007;35(9):1571-1580. Reynolds D, Lucas J, Klaue K. Retroversion of the acetabulum. A cause of hip pain. J Bone Joint Surg Br. 1999;81(2):281-288. Siebenrock KA, Kalbermatten DF, Ganz R. Effect of pelvic tilt on acetabular retroversion: a study of pelves from cadavers. Clin Orthop Relat Res. 2003;407:241-248. Siebenrock KA, Schoeniger R, Ganz R. Anterior femoro-acetabular impingement due to acetabular retroversion. Treatment with periacetabular osteotomy. J Bone Joint Surg Am. 2003;85(2):278-286. Tannast M, Murphy SB, Langlotz F, Anderson SE, Siebenrock KA. Estimation of pelvic tilt on anteroposterior X-rays—a comparison of six parameters. Skeletal Radiol. 2006;35(3):149-155. Tannast M, Zheng G, Anderegg C, et al. Tilt and rotation correction of acetabular version on pelvic radiographs. Clin Orthop Relat Res. 2005;438:182-190. To¨nnis D, Legal H, Graf R. Congenital Dysplasia and Dislocation of the Hip in Children and Adults. New York: Springer-Verlag, 1987. Wassilew GI, Heller MO, Diederichs G, Janz V, Wenzl M, Perka C. Standardized AP radiographs do not provide reliable diagnostic measures for the assessment of acetabular retroversion. J Orthop Res. 2012;30(9):1369-1376. Wenger DR, Kishan S, Pring ME. Impingement and childhood hip disease. J Pediatr Orthop B. 2006;15(4):233-243. Wiberg G. Studies on dysplastic acetabula and congenital subluxation of the hip: with special reference to the complication of osteoarthritis. Acta Chir Scand. 1939;58:7-38.
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