Original article 237
Evaluation of the cartilaginous acetabulum by magnetic resonance imaging in developmental dysplasia of the hip Ryoko Takeuchia, Hiroshi Kamadab, Hajime Mishimab, Naoki Mukaic, Shumpei Miyakawac and Naoyuki Ochiaid MRI findings for 51 hips in 45 pediatric patients (mean age 2.3 years; range, 1.1–4.1 years) with suspected acetabular dysplasia or residual subluxations were analyzed retrospectively. We attempted to predict the growth of osseous acetabulum and future acetabular coverage on MRI performed at 2 years of age. The cut-off value of the cartilaginous angle was 188 for the cartilage acetabular index and 138 for the cartilage center edge angle. However, follow-up assessments to monitor the progress of changes in the congruity between femoral head and acetabular development are important. J Pediatr Orthop B 23:237–243
c 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins.
Introduction In a considerable number of patients, reduction of developmental dysplasia of the hip (DDH) is followed by residual subluxation or acetabular dysplasia. Residual subluxation and acetabular dysplasia represent major causes of early-onset degenerative osteoarthritis. Several reports have suggested that secondary surgery for the sequelae should be performed before 5 or 6 years of age, accompanied by radiographic evaluation [1–4]. However, it is difficult to predict the sufficiency of remodeling of the acetabulum, which is often evaluated only on plain radiographs. We surmised that apart from osseous acetabulum evaluation, evaluation of the cartilaginous acetabulum is important for predicting future acetabular development. We investigated acetabular cartilage of patients with DDH suspected residual subluxation and acetabular dysplasia in patients at B2 years of age using MRI scans. We propose that if the acetabular cartilage is sufficiently formed, osseous acetabulum is also sufficiently formed by the ossification of the cartilaginous acetabulum, and secondary surgery may be unnecessary. The aim of this report was to analyze the relevance of the cartilaginous acetabulum by MRI in patients at 2 years of age and predict future osseous acetabular development.
Patients and methods The present study was approved by the institutional review board at our institute. We included 119 patients with DDH who we treated in our institute, and were suspected to have residual subluxation or acetabular dysplasia after reduction at c 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins 1060-152X
Journal of Pediatric Orthopaedics B 2014, 23:237–243 Keywords: cartilaginous acetabulum, developmental dysplasia of the hip, magnetic resonance imaging a Department of Orthopaedic Surgery, Graduate School of Comprehensive Human Science, bDepartment of Orthopaedic Surgery, Faculty of Medicine, c Faculty of Health and Sport Science, University of Tsukuba, Ibaraki and d Department of Orthopaedic Surgery, Kikkoman General Hospital, Chiba, Japan
Correspondence to Ryoko Takeuchi, MD, Department of Orthopaedic Surgery, Graduate School of Comprehensive Human Science, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan Tel: + 81 29 853 3219; fax: + 81 29 853 3214; e-mail: [email protected]
our institute from 1988 to 2008. No cases of teratological or neurological dislocation were included. We excluded patients who had previously undergone surgery for residual subluxation or acetabular dysplasia to observe the natural maturation after the initial therapy. We regularly performed MRI scans on patients B2 years of age to examine cartilaginous acetabular coverage. Complete data sets, including MRI at B2 years of age and radiographs from 6 years of age and older, were available for 51 hips in 45 patients. Patient characteristics were as follows (Table 1): there were two boys and 43 girls; 11 were affected on the right side, 27 on the left side, and seven on both sides. We excluded one hip of one case showing bilateral incidence because the hip had been subjected to a femoral osteotomy. Twenty-six hips (n = 26) were diagnosed by radiography or ultrasound with dislocation; 13 hips (n = 12) with subluxation; and 12 hips (n = 7) with acetabular dysplasia at the first visit to our institute. The mean follow-up age was 11.7 years (range, 6–22 years) and the mean age at MRI scanning was 2.3 years (range, 1.1–4.1 years). Eighteen of 51 joints progressed to bone maturity. Twenty-eight hips (n = 22) were reduced by the Pavlik harness; 19 hips (n = 19) by closed reduction; and four hips (n = 4) by open reduction (Table 2). The mean age of reduction was 0.7 years (range, 0.1–2.5 years). Severin classification [5] at the time of the last investigation was as follows: group Ia, 17 hips; group Ib, nine hips; group IIb, two hips; group III, 22 hips; and group IV, one hip. MRI was performed using a 1.5-T Philips Achieva scanner (Philips, Eindhoven, the Netherlands). Patients were placed in a supine position with the hip in a neutral position. Spin-echo techniques were used, and section DOI: 10.1097/BPB.0000000000000032
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Journal of Pediatric Orthopaedics B 2014, Vol 23 No 3
Table 1
Characteristics of patient 1
Fig. 1 Affected side
Number of hip joints Male : female Right : left : bilateral The mean follow-up age The mean age of MRI scanning
Table 2
45 patients, 51 hips 2 : 43 11 : 27 : 7 11.7 years old (range, 6–22 years old) 2.3 years old (range, 1.1–4.1 years old)
B A
Characteristics of patient 2 Number of joints (hips)
Diagnosis Dislocation Subluxation Acetabular dysplasia Treatment Pavlik harness Closed method Open reduction
26 (n = 26) 13 (n = 12) 12 (n = 7) 28 (n = 22) 19 (n = 19) 4 (n = 4)
MRI measurements: magnetic resonance scan showing cartilaginous acetabular formation at 2 years; (A) cartilaginous acetabular index (CAI), (B) and cartilaginous center edge (CCE) angle.
thickness was adjusted at 4 mm. T1-weighted images (TE16/TR600 ms) and T2-weighted images (TE15/ TR1500 ms) were obtained. MRI examination was performed with the patient under sedation with chloral hydrate (80 mg/kg body weight).
Modified Severin classification of hips in developmental dysplasia of the hip
Table 3
We measured the cartilaginous acetabular index (CAI) and the cartilaginous center edge (CCE) angle from coronal images. The CAI was measured between the horizontal line connecting both triradiate cartilages (the Hilgenreiner line), extending along the lateral acetabular cartilaginous margin (A in Fig. 1). The CCE angle was measured by a line drawn from the center of the femoral head to the outer edge of the acetabular cartilage and a vertical line drawn through the center of the cartilaginous femoral head. We measured the coronal plane through the largest diameter of the femoral head (B in Fig. 1).
Positive-outcome group I. Normal a. CE angle > 191: age 6–13 years, CE angle > 251: age Z 14 years b. CE angle: 15–191: age 6–13 years, CE angle: 20–251: age Z 14 years II. Moderate deformity of the femoral head or neck or acetabulum, but otherwise as group Ia or Ib Poor-outcome group III. Dysplastic but without subluxation CE angle < 151: age 6–13 years, CE angle < 201: age Z 14 years IV. Subluxation a. Moderate, CE angle Z 01 b. Severe, CE angle < 01 V. Femoral head articulates with a secondary acetabulum in the upper part of the original acetabulum VI. Redislocation
At the beginning of this study, we evaluated the reproducibility of the measurement of CAI and CCE angle. The pediatric orthopedic surgeon R.T. measured the CAI and CCE angle of 20 hips of 10 randomly selected cases twice per month. For the same cases, the orthopedic surgeon Y.T. independently measured CAI and CCE angle. The findings of these two observers (R.T. and Y.T.) were compared to assess interobserver reliability.
CE, center edge
We also measured the acetabular index (AI) and the center edge (CE) angle on radiographs at 2 years of age and the last investigation. The triradiate cartilage ossifies with age; therefore, when the triradiate cartilage was found to be closed on radiography at the last investigation in older children, the AI was measured from radiographs at the maximal age at which the angle could be measured. Bony formation by radiography and cartilage formation by MRI were compared at 2 years of age. On the basis of the modified Severin classification, we defined the positive-outcome group as Severin groups I
and II, and the poor-outcome group as Severin groups III and IV on the basis of radiographic findings at the last investigation (Table 3). Furthermore, in addition to the assessment of cartilaginous acetabulum by the MRI, we investigated data from medical records and radiographs, including associations with sex (male and female), laterality (right and left, bilateral), diagnosis at first visit (dislocation, subluxation, and dysplasia), method of reduction (Pavlik harness, manual reduction, and open reduction), age at reduction, and presence of a vascular necrosis on the basis of Kalamchi and MacEwen’s classification [6]. Statistical analysis
The averages and 95% confidence intervals (95% CI) between the positive-outcome group and the pooroutcome group of CAI and CCE angles were calculated.
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Evaluation of the cartilaginous acetabulm Takeuchi et al.
The averages were also compared using Student’s t-test (P < 0.05). A receiver operating characteristic (ROC) curve was drawn for CAI and CCE angle to assess the cut-off value. The ROC curve plotted sensitivity against the falsepositive rate (1 – specificity) for different cut-off values. We judged the most effective cut-off value of CAI and CCE angles with greater sensitivity and specificity. Furthermore, we calculated the positive predictive value and likelihood ratio. Univariate analysis was carried out between the positiveoutcome group and the poor-outcome group to assess the differences with respect to sex, laterality, diagnosis, method of reduction, age at reduction, and presence of avascular necrosis by the Pearson test or the Fisher exact test. In terms of age at reduction, we classified age at reintegration into the following three age groups: less than 0.5 years (r 0.5), between 0.5 years and 1 year (0.5–1.0), and more than 1 year (>1.0). In addition, multivariate logistic regression was performed on variables with a P value of less than 0.2 from the univariate analysis. These analyses were carried out using JMP SAS software version 7 (SAS Institute, Cary, North Carolina, USA). The intraclass correlation coefficient (ICC) was used for the quantification of interobserver and intraobserver reliability using SPSS software version 20 (SPSS Inc., Chicago, Illinois, USA). A significance level of 5% was chosen for all tests (P < 0.05).
Results Bony formation by radiography and cartilage formation by MRI were compared. We plotted the correlations of osseous AI versus CAI and the osseous CE angle versus CCE angle in patients at 2 years of age (Fig. 2).
239
The decision coefficient of AI was 0.091 and CE angle was 0.103, indicating a lack of statistical correlation between the two angles. The mean CAIs were 15.2±4.11 (95% CI, 13.4–16.71) and 17.6±5.61 (95% CI, 15.2–20.01) for the positive-outcome and poor-outcome groups, respectively. Furthermore, the mean CCE angles were 16.2±7.51 (95% CI, 13.7–19.61) and 7.5±7.11 (95% CI, 3.0–12.01) for the positive-outcome and poor-outcome group, respectively. The mean CCE angle for the positive-outcome group was significantly larger than that for the poor-outcome group (P < 0.01); however, the mean CAI for the positive-outcome group was not significantly different from that of the poor-outcome group (P = 0.06; Fig. 3). An ROC curve was drawn for the CAI and CCE angles. The most effective cut-off value for CAI was 181, with a sensitivity of 79.3%, a specificity of 45.5%, a positive predictive value of 65.7%, and a likelihood ratio of 1.45. The most effective cut-off value for the CCE angle was 131, with a sensitivity of 72.4%, a specificity of 63.6%, a positive predictive value of 72.4%, and a likelihood ratio of 1.98 (Table 4). We next investigated whether the future osseous CE angle coincided with a prediction on the basis of a cutoff CCE angle value of 131 for every diagnosis (Table 5). For acetabular dysplasia, six of 12 hips were in accordance with the prediction, whereas the remaining six hips were not. Of the 13 hips with subluxation, 11 were in accordance with the prediction, and of the 26 hips with dislocation, 18 coincided with the prediction. No significant difference was observed between the positive-outcome group and the poor-outcome group with respect to sex, laterality, diagnosis at first visit, method of reduction, age at reduction, and CAI. Significant differences were observed between the positive-outcome
Fig. 2
(a)
(deg.) 40 CCE angle (MRI)
CAI (MRI)
(b)
AI at 2 years of age
(deg.) 30
20
10 R2 = 0.091 P < 0.05
0
15
20
25
30 AI (X-p)
35
40 45 (deg.)
CE angle at 2 years of age
30 20 10 0 −10 −20 −30 −30
R2 = 0.103 P < 0.05
−20
−10
0
10
20 30 (deg.)
CE angle (X-p)
Correlation between bony and cartilage formation at 2 years of age. (a) Correlation between acetabular index (AI) and cartilaginous acetabular index (CAI). (b) Correlation between center edge (CE) angle and cartilaginous center edge (CCE) angle. There was no correlation between bony formation by radiography and cartilage formation by MRI.
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Journal of Pediatric Orthopaedics B 2014, Vol 23 No 3
Fig. 3
(a)
(b)
(deg.) 30
30
(deg.) ∗
20
CAI
CCE angle
20
10
10
0
0 ∗t-test
Good outcome
Poor outcome
Good outcome
Poor outcome
Mean cartilaginous acetabular angle. (a) Mean cartilaginous acetabular index (CAI). Mean of the positive-outcome group was lower than that of the poor-outcome group. (b) Mean cartilaginous center edge (CCE) angle. Mean of the positive-outcome group was significantly greater than that of the poor-outcome group (P < 0.05).
Table 4 Cartilaginous acetabular index of MRI: the most useful cut-off value for predicting
Cut-off value (deg.) Sensitivity (%) Specificity (%) Positive predictive value (%) Likelihood ratio
CAI
CCE angle
18 79.3 45.4 65.7 1.45
13 72.4 63.6 72.4 1.98
CAI, cartilaginous acetabular index; CCE angle, cartilaginous center edge angle.
group and the poor-outcome group in CCE angle (P = 0.0004) and the presence of avascular necrosis (P = 0.0457) by univariate analysis (Table 6). Furthermore, multiple analysis showed CCE angle to be the most powerful predictor of a favorable outcome (P = 0.0128; Table 7). In this study, the intraobserver reliability values for measurement errors of CAI and the CCE angle were 2.9±3.5 and 4.9±4.81, respectively. The corresponding values for interobserver reliability were 4.2±3.61 for CAI and 4.3±3.21 for the CCE angle. The ICC for intraobserver reliability for CAI was 0.897 (95% CI, 0.785–0.954), and for the CCE angle, it was 0.892 (95% CI, 0.776–0.954). The ICC for interobserver reliability for CAI was 0.801 (95% CI, 0.394–0.927), and for the CCE angle, it was 0.888 (95% CI, 0.715–0.956; Table 8).
Discussion After reduction of DDH, some patients experience residual subluxation or acetabular dysplasia. A few reports on the potential of acetabular development are available
in the literature. Salter [7] reported that the potential for normal osseous development of the hip joint after reduction is maximal at birth and decreases gradually thereafter. This potential for normal development remains relatively adequate during the first year and a half of life. Harris [8] reported that when congruous reduction is achieved until the age of 3 or 4 years, the acetabulum has the capacity to develop, on an average, for an additional 6 years. However, when functional congruity is delayed beyond the age of 4 years, this potential is considerably reduced. Many reports have suggested that secondary surgery should be performed on the basis of a radiographical parameter [1–4]. Ohmori et al. [1] suggested the use of the OE angle (the angle between the perpendicular line running along the middle point O of the proximal metaphysis of the femur and the lateral edge point E of the acetabulum) [9] of less than or equal to 21 at 3 years of age. Albinana et al. [2] reported that early measurements of the AI were predictive of the Severin grade of patients with DDH treated by closed and open reduction. They reported that an AI of 351 or more at 2 years after reduction was associated with an 80% probability of progression to Severin grade III/IV and an AI of 301 or more at 4 years after reduction was associated with an 80% probability of progression to Severin grade III/IV. Nakamura et al. [3] suggested that AI of more than 301 at about 5 years of age is the most useful predictor of residual acetabular dysplasia and an indicator for the recommendation for additional surgery in patients treated with the Pavlik harness because AI is correlated with the
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Evaluation of the cartilaginous acetabulm Takeuchi et al. 241
Table 5
Consistency Inconsistent [number of joints (%)]
Diagnosis
Total [number of joints (%)]
Consistent [number of joints (%)]
Better than the prediction
Worse than the prediction
Acetabular dysplasia Subluxation Dislocation
12 13 26
6 (50.0) 11 (84.6) 18 (69.2)
1 (8.3) 1 (7.7) 6 (23.0)
5 (41.7) 1 (7.7) 2 (7.8)
Table 6
Univariate analysis Good outcome (number of the hip joint) Poor outcome (number of the hip joint) P-value
Sex (male : female) Laterality (right + left : bilateral) Diagnosis (dislocation : subluxation : dysplasia) Method of reduction (Pavlik harness : manual reduction + open reduction) Necrosis (+ : –) Age at reduction (r 0.5 : > 0.5–1.0 : > 1.0) CAI (average) CCE (average)
0/28 20/8 15/8/5 17/11 5/23 18/7/3 15.2±4.11 16.2±7.51
2/21 18/5 11/5/7 11/12 10/13 8/7/8 17.6±5.61 7.5±7.11
0.1984 0.5775 0.5593 0.3574 0.0457* 0.0583 0.0678 0.0007*
CAI, cartilaginous acetabular index; CCE angle, cartilaginous center edge angle. *P < 0.05.
Table 7
Multiple analysis P-value
Sex (male : female) Necrosis (+ : –) Age at reduction CAI CCE
0.5446 0.2452 0.9203 0.9329 0.0061*
CAI, cartilaginous acetabular index; CCE angle, cartilaginous center edge angle. *P < 0.05.
CE angle and center-head distance discrepancy (CHDD), and satisfactory outcomes (86%) were observed in the supplementary group. Kim et al. [4] evaluated annual radiographs of patients treated by closed reduction. They reported that remodeling of the acetabulum was possible when CHDD was less than 6% and the orientation of the sourcil was horizontal. Surgery is recommended to prevent residual acetabular dysplasia when the CHDD is at least 6% and the sourcil is oriented upwards between 4 and 5 years of age. Conversely, there is an opinion that it is difficult to predict the acetabular coverage from radiological findings when growth stops [10,11]. We surmised that in addition to osseous evaluation, cartilaginous acetabulum evaluation is also important in predicting future acetabulum growth. Figure 2 shows the difference between bony formation and cartilage formation in patients at 2 years of age. This result reflects the fact that clinicians cannot recognize acetabular formation by radiography alone at early stages of growth. We hypothesized that cartilage formation was quite important in acetabular formation and, if the coverage of cartilaginous acetabulum was sufficient, the osseous acetabulum would grow properly. In terms of the evaluation of cartilaginous acetabulum formation, Mohammed et al. [10] measured acetabular
cartilaginous angles (ACA) by arthrography during reductions and reported a cut-off value for ACA of 201 (below which 99.5% of all hips developed satisfactorily) and another cut-off value for ACA of 241 (above which 100% of hips needed acetabuloplasty). Arthrographic imaging is used to evaluate the condition of the acetabulum. Dynamic evaluation is possible using arthrographic evaluation, but this procedure is invasive and clinicians have difficulty in observing the real threedimensional structures. The condition of the articular cartilage, labrum, and ligamentum teres is deduced from a reflected image. By contrast, the advantages of MRI are its noninvasiveness, direct visualization capability, and safety on the basis of the lack of exposure to radiation [12]. We believe that MRI has many benefits that render it suitable as a method for the evaluation of the cartilaginous acetabulum. Wiem et al. [11] measured cartilaginous acetabular angle, cartilaginous coronal head index, and cartilaginous sagittal head index with MRI performed at a mean age of 5 years for patients with residual dysplasia. Investigators reported that 27 of 31 hips with residual acetabular dysplasia had MRI-identified thick cartilage of the acetabular roof (mean cartilaginous coronal head index, 85%; cartilaginous sagittal head index, 95%) and showed spontaneous progressive ossification. In this study, 65.7% of the patients with CAI of less than 181 showed positive acetabulum coverage during growth. Moreover, among patients with CCE angle of more than 131, 72.4% showed positive outcomes (Table 4). Furthermore, the mean CCE angle for the positive-outcome group was significantly larger than that for the pooroutcome group (Fig. 3). In other words, the AI values of the poor-outcome group varied widely. Therefore, we
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242 Journal of Pediatric Orthopaedics B 2014, Vol 23 No 3
Table 8
Intraobserver and interobserver reliability Intraobserver reliability
Mean±SD of measurement errors ICC 95% confidence interval
Interobserver reliability
CAI
CCE angle
CAI
CCE angle
2.9±3.51 0.897 P < 0.01 0.785–0.954
4.9±4.81 0.892 P < 0.01 0.776–0.956
4.2±3.61 0.801 P < 0.01 0.394–0.927
4.3±3.21 0.888 P < 0.01 0.715–0.956
CAI, cartilaginous acetabular index; CCE angle, cartilaginous center edge angle; ICC, intraclass correlation coefficient.
evaluated outcomes using the Severin classification on the basis of the CE angle as we surmised that the CCE angle has a higher reliability than the CAI in this study. However, some cases did not correspond with the prediction of the CCE angle. In this study, the osseous acetabulum of eight hips grew sufficiently at the time of the last investigation, although the CCE angle was poor at about 2 years of age. Of eight hips, six were diagnosed with a dislocation, one with subluxation, and one with acetabular dysplasia (Table 5). In the six dislocated hips, the congruity of the femoral head improved gradually after MRI examination. Therefore, a follow-up examination on the progress of the change of congruity of the femoral head and the growth of acetabulum coverage is important. Conversely, a few patients had poor growth of the osseous acetabulum, even when cartilaginous acetabulum coverage was sufficient. Among the eight hips, five were diagnosed with acetabular dysplasia (Table 5). Okano et al. [13] suggested that acetabular dysplasia in many patients occurred as a result of bone malformation. The investigators suggested that genetic research is required to elucidate the pathological mechanism of acetabular dysplasia. It is believed that even if cartilaginous acetabulum formation is sufficient, it is possible that ossification potential is poor owing to the genetic background (at least for the acetabulum dysplasia cases). We specifically focused on the shape of the acetabulum in this study. However, because cartilaginous quality is poor, it is possible that ossification is incomplete (even if the coverage of the cartilaginous acetabulum is sufficient). Therefore, it might be necessary to evaluate quality, as well as shape, of the cartilaginous acetabulum. Fisher et al. [14] suggested that if qualitative differences could be quantified such that potential acetabular development could be determined accurately, surgical intervention for patients with persistent dysplasia could be instituted early during the course of hip joint development to maximize cartilage remodeling. Wakabayashi et al. [15] reported that patients with residual subluxation showed high signal intensity areas within the weight-bearing acetabular cartilage (as measured on T2-weighted MRI) and had poor acetabular growth. The investigators proposed that extraordinary stress loaded onto acetabular cartilage may cause an edematous change or maldistribu-
tion of proteoglycan, resulting in disturbance of ossification in the acetabular cartilage. However, no reports to date have evaluated cartilaginous acetabulum quantitatively by MRI in patients at about 2 years of age. Here, we report the reference value for the cartilaginous acetabulum. The evaluation of cartilaginous acetabulum coverage by MRI enables the prediction of future osseous acetabulum formation earlier than the evaluation by radiography. If the cartilaginous acetabulum is sufficient early on, osseous acetabulum coverage may grow sufficiently afterwards to prevent premature secondary surgery. However, it is believed that the ossification potential of the cartilaginous acetabulum is high at 2 years of age; therefore, clinicians should be warned that sometimes the osseous acetabulum grows well, irrespective of the CCE angle, with congruity improving gradually afterwards. Therefore, we should further investigate the change in the congruity of the femoral head and the development of acetabulum coverage. In addition to the evaluation of femoral head position and obstructive factors to reduction, MRI is a useful method in the prediction of future acetabular formation. This study has several limitations. First, the CCE angle was a single, meaningful predictor, with an optimal cut-off value of 131, a sensitivity of 72.4%, a specificity of 63.6%, a positive predictive value of 72.4%, and a positive likelihood ratio of 1.98. However, the CCE angle is not a complete predictor. In this study, we measured the acetabular coverage in the anteroposterior view by radiography and in coronal images with MRI. In such assessments, it is insufficient to evaluate the coverage of the anterior acetabular formation and the anteroposterior congruity of the femoral head. It is believed that the significance of the CCE angle could have been improved if it was combined with other relevant indices measured on sagittal and transverse images. In future studies, in addition to studying other indicators, we will assess the three-dimensional cartilaginous acetabular angle and other similar measures. Second, the (C)CE angle can vary depending on the position of the hip and lower extremity. In this study, MRI was performed with patients placed in a supine position and the hip in the neutral position. As these conditions were confirmed by checking the patient’s posture on the table, they appeared to be slightly different in each
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Evaluation of the cartilaginous acetabulm Takeuchi et al. 243
patient. Therefore, it is considered that some variation occurs in the measured values of the (C)CE angle. In the future, we will consider the possibility of accurate positioning using a setting apparatus. Third, we were able to obtain follow-up data on bone maturity for only 18 of the 51 hips in this study. As the follow-up duration was insufficient, a longitudinal follow-up study will be necessary to estimate future hip development (acetabular angle, CE angle, CHDD) with a linear mixed model. Fourth, the ICC of intraobserver reliability for CAI and CCE angle was 0.897 and 0.892, respectively. The ICC of interobserver reliability for CAI and CCE angle was 0.801 and 0.888, respectively. We may consider that the ICCs for intraobserver and interobserver reliability were substantial; however, we expect that there will be variances in measurement. Therefore, on the basis of the border of the cut-off value that we calculated in this study, we expect that an analysis with more cases is necessary. Conclusion
(1) We report the cut-off value of the cartilaginous angle on MRI at 2 years of age to predict the future growth of osseous acetabulum on radiography. This cut-off value had a CAI of 181 and a CCE angle of 131 on MRI performed in patients at 2 years of age. (2) MRI may predict future acetabular coverage; however, it is important to follow up the progress of the change of congruity of the femoral head and the growth of acetabulum development.
Acknowledgements Conflicts of interest
There are no conflicts of interest.
References 1
2
3
4 5
6 7 8 9
10
11
12
13 14 15
Ohmori T, Endo H, Mitani S, Minagawa H, Tetsunaga T, Ozaki T. Radiographic prediction of the results of long-term treatment with the Pavlik harness for developmental dislocation of the hip. Acta Med Okayama 2009; 63:123–128. Albinana J, Dolan LA, Spatt KF, Morcuende J, Meyer MD, Weinstein SL. Acetabular dysplasia after treatment for developmental dysplasia of the hip. J Bone Joint Surg [Br] 2004; 86-B:876–886. Nakamura J, Kamegaya M, Saisu T, Someya M, Koizumi W, Moriya H. Treatment for developmental dysplasia of the hip using the Pavlik harness. J Bone Joint Surg [Br] 2007; 89-B:230–235. Kim HT, Kim JI, Yoo CI. Acetabular development after closed reduction of developmental dislocation of the hip. J Pediatr Orthop 2000; 20:701–708. Severin E. Contribution of the knowledge of congenital dislocation of the hip joint. Late results of closed reduction and arthrographic studies of recent cases. Acta Chir Scand 1941; 84 (Supp 63):1–142. Kalamchi A, MacEween GD. Avascular necrosis following treatment of congenital dislocation of the hip. J Bone Joint Surg 1980; 62-A:876–888. Salter RB. Innominate osteotomy in the treatment of congenital dislocation and subluxation of the hip. J Bone Joint Surg Br 1961; 43-B:518–538. Harris NH. Acetabular development in congenital dislocation of the hip. J Bone Joint Surg Br 1975; 57-B:46–52. Noguchi Y, Oishi T, Sugioka Y, Matsumoto N, Fujii T. Prediction of final radiological results in early childhood after closed reduction for congenital dislocation of the hip [in Japanese]. Orthop Traumatol 1990; 39:197–200. Mohammed MZ, Mamoun KK, Khalid IK, Alshahid AA, Khalid AB, Abdul MMA, Kholoud OA. Acetabular cartilaginous angle. A new method for predicting acetabular development in developmental dysplasia of the hip in children between 2 and 18 month of age. J Pediatr Orthop 2008; 28: 518–528. Wiem DK, Mahmoud S, Hela L, Lilia BH, Sami B, Walid S, et al. Magnetic resonance evaluation of acetabular residual dysplasia in developmental dysplasia of the hip: a preliminary study of 27 patients. J Pediatr Orthop 2010; 30:37–43. Guidera KJ, Einbecker ME, Berman CG, Ogden JA, Arrington JA, Murtagh R. Magnetic resonance imaging evaluation of congenital dislocation of the hips. Clin Orthop Relat Res 1990; 261:96–101. Okano K, Takaki M, Okazaki N, Shindo H. Bilateral incidence and severity of acetabular dysplasia of the hip. J Orthop Sci 2008; 13:401–404. Fisher R, O’Brien TS, Davis KM. Magnetic resonance imaging of congenital dislocation of the hip. J Pediatr Orthop 1991; 11:617–622. Wakabayashi K, Wada I, Hirouchi O, Otsuka T. MRI finding in residual hip dysplasia. J Pediatr Orthop 2011; 31:381–387.
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Evaluation of the cartilaginous acetabulum by magnetic resonance imaging in developmental dysplasia of the hip Ryoko Takeuchia, Hiroshi Kamadab, Hajime Mishimab, Naoki Mukaic, Shumpei Miyakawac and Naoyuki Ochiaid MRI findings for 51 hips in 45 pediatric patients (mean age 2.3 years; range, 1.1–4.1 years) with suspected acetabular dysplasia or residual subluxations were analyzed retrospectively. We attempted to predict the growth of osseous acetabulum and future acetabular coverage on MRI performed at 2 years of age. The cut-off value of the cartilaginous angle was 188 for the cartilage acetabular index and 138 for the cartilage center edge angle. However, follow-up assessments to monitor the progress of changes in the congruity between femoral head and acetabular development are important. J Pediatr Orthop B 23:237–243
c 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins.
Introduction In a considerable number of patients, reduction of developmental dysplasia of the hip (DDH) is followed by residual subluxation or acetabular dysplasia. Residual subluxation and acetabular dysplasia represent major causes of early-onset degenerative osteoarthritis. Several reports have suggested that secondary surgery for the sequelae should be performed before 5 or 6 years of age, accompanied by radiographic evaluation [1–4]. However, it is difficult to predict the sufficiency of remodeling of the acetabulum, which is often evaluated only on plain radiographs. We surmised that apart from osseous acetabulum evaluation, evaluation of the cartilaginous acetabulum is important for predicting future acetabular development. We investigated acetabular cartilage of patients with DDH suspected residual subluxation and acetabular dysplasia in patients at B2 years of age using MRI scans. We propose that if the acetabular cartilage is sufficiently formed, osseous acetabulum is also sufficiently formed by the ossification of the cartilaginous acetabulum, and secondary surgery may be unnecessary. The aim of this report was to analyze the relevance of the cartilaginous acetabulum by MRI in patients at 2 years of age and predict future osseous acetabular development.
Patients and methods The present study was approved by the institutional review board at our institute. We included 119 patients with DDH who we treated in our institute, and were suspected to have residual subluxation or acetabular dysplasia after reduction at c 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins 1060-152X
Journal of Pediatric Orthopaedics B 2014, 23:237–243 Keywords: cartilaginous acetabulum, developmental dysplasia of the hip, magnetic resonance imaging a Department of Orthopaedic Surgery, Graduate School of Comprehensive Human Science, bDepartment of Orthopaedic Surgery, Faculty of Medicine, c Faculty of Health and Sport Science, University of Tsukuba, Ibaraki and d Department of Orthopaedic Surgery, Kikkoman General Hospital, Chiba, Japan
Correspondence to Ryoko Takeuchi, MD, Department of Orthopaedic Surgery, Graduate School of Comprehensive Human Science, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan Tel: + 81 29 853 3219; fax: + 81 29 853 3214; e-mail: [email protected]
our institute from 1988 to 2008. No cases of teratological or neurological dislocation were included. We excluded patients who had previously undergone surgery for residual subluxation or acetabular dysplasia to observe the natural maturation after the initial therapy. We regularly performed MRI scans on patients B2 years of age to examine cartilaginous acetabular coverage. Complete data sets, including MRI at B2 years of age and radiographs from 6 years of age and older, were available for 51 hips in 45 patients. Patient characteristics were as follows (Table 1): there were two boys and 43 girls; 11 were affected on the right side, 27 on the left side, and seven on both sides. We excluded one hip of one case showing bilateral incidence because the hip had been subjected to a femoral osteotomy. Twenty-six hips (n = 26) were diagnosed by radiography or ultrasound with dislocation; 13 hips (n = 12) with subluxation; and 12 hips (n = 7) with acetabular dysplasia at the first visit to our institute. The mean follow-up age was 11.7 years (range, 6–22 years) and the mean age at MRI scanning was 2.3 years (range, 1.1–4.1 years). Eighteen of 51 joints progressed to bone maturity. Twenty-eight hips (n = 22) were reduced by the Pavlik harness; 19 hips (n = 19) by closed reduction; and four hips (n = 4) by open reduction (Table 2). The mean age of reduction was 0.7 years (range, 0.1–2.5 years). Severin classification [5] at the time of the last investigation was as follows: group Ia, 17 hips; group Ib, nine hips; group IIb, two hips; group III, 22 hips; and group IV, one hip. MRI was performed using a 1.5-T Philips Achieva scanner (Philips, Eindhoven, the Netherlands). Patients were placed in a supine position with the hip in a neutral position. Spin-echo techniques were used, and section DOI: 10.1097/BPB.0000000000000032
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Table 1
Characteristics of patient 1
Fig. 1 Affected side
Number of hip joints Male : female Right : left : bilateral The mean follow-up age The mean age of MRI scanning
Table 2
45 patients, 51 hips 2 : 43 11 : 27 : 7 11.7 years old (range, 6–22 years old) 2.3 years old (range, 1.1–4.1 years old)
B A
Characteristics of patient 2 Number of joints (hips)
Diagnosis Dislocation Subluxation Acetabular dysplasia Treatment Pavlik harness Closed method Open reduction
26 (n = 26) 13 (n = 12) 12 (n = 7) 28 (n = 22) 19 (n = 19) 4 (n = 4)
MRI measurements: magnetic resonance scan showing cartilaginous acetabular formation at 2 years; (A) cartilaginous acetabular index (CAI), (B) and cartilaginous center edge (CCE) angle.
thickness was adjusted at 4 mm. T1-weighted images (TE16/TR600 ms) and T2-weighted images (TE15/ TR1500 ms) were obtained. MRI examination was performed with the patient under sedation with chloral hydrate (80 mg/kg body weight).
Modified Severin classification of hips in developmental dysplasia of the hip
Table 3
We measured the cartilaginous acetabular index (CAI) and the cartilaginous center edge (CCE) angle from coronal images. The CAI was measured between the horizontal line connecting both triradiate cartilages (the Hilgenreiner line), extending along the lateral acetabular cartilaginous margin (A in Fig. 1). The CCE angle was measured by a line drawn from the center of the femoral head to the outer edge of the acetabular cartilage and a vertical line drawn through the center of the cartilaginous femoral head. We measured the coronal plane through the largest diameter of the femoral head (B in Fig. 1).
Positive-outcome group I. Normal a. CE angle > 191: age 6–13 years, CE angle > 251: age Z 14 years b. CE angle: 15–191: age 6–13 years, CE angle: 20–251: age Z 14 years II. Moderate deformity of the femoral head or neck or acetabulum, but otherwise as group Ia or Ib Poor-outcome group III. Dysplastic but without subluxation CE angle < 151: age 6–13 years, CE angle < 201: age Z 14 years IV. Subluxation a. Moderate, CE angle Z 01 b. Severe, CE angle < 01 V. Femoral head articulates with a secondary acetabulum in the upper part of the original acetabulum VI. Redislocation
At the beginning of this study, we evaluated the reproducibility of the measurement of CAI and CCE angle. The pediatric orthopedic surgeon R.T. measured the CAI and CCE angle of 20 hips of 10 randomly selected cases twice per month. For the same cases, the orthopedic surgeon Y.T. independently measured CAI and CCE angle. The findings of these two observers (R.T. and Y.T.) were compared to assess interobserver reliability.
CE, center edge
We also measured the acetabular index (AI) and the center edge (CE) angle on radiographs at 2 years of age and the last investigation. The triradiate cartilage ossifies with age; therefore, when the triradiate cartilage was found to be closed on radiography at the last investigation in older children, the AI was measured from radiographs at the maximal age at which the angle could be measured. Bony formation by radiography and cartilage formation by MRI were compared at 2 years of age. On the basis of the modified Severin classification, we defined the positive-outcome group as Severin groups I
and II, and the poor-outcome group as Severin groups III and IV on the basis of radiographic findings at the last investigation (Table 3). Furthermore, in addition to the assessment of cartilaginous acetabulum by the MRI, we investigated data from medical records and radiographs, including associations with sex (male and female), laterality (right and left, bilateral), diagnosis at first visit (dislocation, subluxation, and dysplasia), method of reduction (Pavlik harness, manual reduction, and open reduction), age at reduction, and presence of a vascular necrosis on the basis of Kalamchi and MacEwen’s classification [6]. Statistical analysis
The averages and 95% confidence intervals (95% CI) between the positive-outcome group and the pooroutcome group of CAI and CCE angles were calculated.
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Evaluation of the cartilaginous acetabulm Takeuchi et al.
The averages were also compared using Student’s t-test (P < 0.05). A receiver operating characteristic (ROC) curve was drawn for CAI and CCE angle to assess the cut-off value. The ROC curve plotted sensitivity against the falsepositive rate (1 – specificity) for different cut-off values. We judged the most effective cut-off value of CAI and CCE angles with greater sensitivity and specificity. Furthermore, we calculated the positive predictive value and likelihood ratio. Univariate analysis was carried out between the positiveoutcome group and the poor-outcome group to assess the differences with respect to sex, laterality, diagnosis, method of reduction, age at reduction, and presence of avascular necrosis by the Pearson test or the Fisher exact test. In terms of age at reduction, we classified age at reintegration into the following three age groups: less than 0.5 years (r 0.5), between 0.5 years and 1 year (0.5–1.0), and more than 1 year (>1.0). In addition, multivariate logistic regression was performed on variables with a P value of less than 0.2 from the univariate analysis. These analyses were carried out using JMP SAS software version 7 (SAS Institute, Cary, North Carolina, USA). The intraclass correlation coefficient (ICC) was used for the quantification of interobserver and intraobserver reliability using SPSS software version 20 (SPSS Inc., Chicago, Illinois, USA). A significance level of 5% was chosen for all tests (P < 0.05).
Results Bony formation by radiography and cartilage formation by MRI were compared. We plotted the correlations of osseous AI versus CAI and the osseous CE angle versus CCE angle in patients at 2 years of age (Fig. 2).
239
The decision coefficient of AI was 0.091 and CE angle was 0.103, indicating a lack of statistical correlation between the two angles. The mean CAIs were 15.2±4.11 (95% CI, 13.4–16.71) and 17.6±5.61 (95% CI, 15.2–20.01) for the positive-outcome and poor-outcome groups, respectively. Furthermore, the mean CCE angles were 16.2±7.51 (95% CI, 13.7–19.61) and 7.5±7.11 (95% CI, 3.0–12.01) for the positive-outcome and poor-outcome group, respectively. The mean CCE angle for the positive-outcome group was significantly larger than that for the poor-outcome group (P < 0.01); however, the mean CAI for the positive-outcome group was not significantly different from that of the poor-outcome group (P = 0.06; Fig. 3). An ROC curve was drawn for the CAI and CCE angles. The most effective cut-off value for CAI was 181, with a sensitivity of 79.3%, a specificity of 45.5%, a positive predictive value of 65.7%, and a likelihood ratio of 1.45. The most effective cut-off value for the CCE angle was 131, with a sensitivity of 72.4%, a specificity of 63.6%, a positive predictive value of 72.4%, and a likelihood ratio of 1.98 (Table 4). We next investigated whether the future osseous CE angle coincided with a prediction on the basis of a cutoff CCE angle value of 131 for every diagnosis (Table 5). For acetabular dysplasia, six of 12 hips were in accordance with the prediction, whereas the remaining six hips were not. Of the 13 hips with subluxation, 11 were in accordance with the prediction, and of the 26 hips with dislocation, 18 coincided with the prediction. No significant difference was observed between the positive-outcome group and the poor-outcome group with respect to sex, laterality, diagnosis at first visit, method of reduction, age at reduction, and CAI. Significant differences were observed between the positive-outcome
Fig. 2
(a)
(deg.) 40 CCE angle (MRI)
CAI (MRI)
(b)
AI at 2 years of age
(deg.) 30
20
10 R2 = 0.091 P < 0.05
0
15
20
25
30 AI (X-p)
35
40 45 (deg.)
CE angle at 2 years of age
30 20 10 0 −10 −20 −30 −30
R2 = 0.103 P < 0.05
−20
−10
0
10
20 30 (deg.)
CE angle (X-p)
Correlation between bony and cartilage formation at 2 years of age. (a) Correlation between acetabular index (AI) and cartilaginous acetabular index (CAI). (b) Correlation between center edge (CE) angle and cartilaginous center edge (CCE) angle. There was no correlation between bony formation by radiography and cartilage formation by MRI.
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Journal of Pediatric Orthopaedics B 2014, Vol 23 No 3
Fig. 3
(a)
(b)
(deg.) 30
30
(deg.) ∗
20
CAI
CCE angle
20
10
10
0
0 ∗t-test
Good outcome
Poor outcome
Good outcome
Poor outcome
Mean cartilaginous acetabular angle. (a) Mean cartilaginous acetabular index (CAI). Mean of the positive-outcome group was lower than that of the poor-outcome group. (b) Mean cartilaginous center edge (CCE) angle. Mean of the positive-outcome group was significantly greater than that of the poor-outcome group (P < 0.05).
Table 4 Cartilaginous acetabular index of MRI: the most useful cut-off value for predicting
Cut-off value (deg.) Sensitivity (%) Specificity (%) Positive predictive value (%) Likelihood ratio
CAI
CCE angle
18 79.3 45.4 65.7 1.45
13 72.4 63.6 72.4 1.98
CAI, cartilaginous acetabular index; CCE angle, cartilaginous center edge angle.
group and the poor-outcome group in CCE angle (P = 0.0004) and the presence of avascular necrosis (P = 0.0457) by univariate analysis (Table 6). Furthermore, multiple analysis showed CCE angle to be the most powerful predictor of a favorable outcome (P = 0.0128; Table 7). In this study, the intraobserver reliability values for measurement errors of CAI and the CCE angle were 2.9±3.5 and 4.9±4.81, respectively. The corresponding values for interobserver reliability were 4.2±3.61 for CAI and 4.3±3.21 for the CCE angle. The ICC for intraobserver reliability for CAI was 0.897 (95% CI, 0.785–0.954), and for the CCE angle, it was 0.892 (95% CI, 0.776–0.954). The ICC for interobserver reliability for CAI was 0.801 (95% CI, 0.394–0.927), and for the CCE angle, it was 0.888 (95% CI, 0.715–0.956; Table 8).
Discussion After reduction of DDH, some patients experience residual subluxation or acetabular dysplasia. A few reports on the potential of acetabular development are available
in the literature. Salter [7] reported that the potential for normal osseous development of the hip joint after reduction is maximal at birth and decreases gradually thereafter. This potential for normal development remains relatively adequate during the first year and a half of life. Harris [8] reported that when congruous reduction is achieved until the age of 3 or 4 years, the acetabulum has the capacity to develop, on an average, for an additional 6 years. However, when functional congruity is delayed beyond the age of 4 years, this potential is considerably reduced. Many reports have suggested that secondary surgery should be performed on the basis of a radiographical parameter [1–4]. Ohmori et al. [1] suggested the use of the OE angle (the angle between the perpendicular line running along the middle point O of the proximal metaphysis of the femur and the lateral edge point E of the acetabulum) [9] of less than or equal to 21 at 3 years of age. Albinana et al. [2] reported that early measurements of the AI were predictive of the Severin grade of patients with DDH treated by closed and open reduction. They reported that an AI of 351 or more at 2 years after reduction was associated with an 80% probability of progression to Severin grade III/IV and an AI of 301 or more at 4 years after reduction was associated with an 80% probability of progression to Severin grade III/IV. Nakamura et al. [3] suggested that AI of more than 301 at about 5 years of age is the most useful predictor of residual acetabular dysplasia and an indicator for the recommendation for additional surgery in patients treated with the Pavlik harness because AI is correlated with the
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Evaluation of the cartilaginous acetabulm Takeuchi et al. 241
Table 5
Consistency Inconsistent [number of joints (%)]
Diagnosis
Total [number of joints (%)]
Consistent [number of joints (%)]
Better than the prediction
Worse than the prediction
Acetabular dysplasia Subluxation Dislocation
12 13 26
6 (50.0) 11 (84.6) 18 (69.2)
1 (8.3) 1 (7.7) 6 (23.0)
5 (41.7) 1 (7.7) 2 (7.8)
Table 6
Univariate analysis Good outcome (number of the hip joint) Poor outcome (number of the hip joint) P-value
Sex (male : female) Laterality (right + left : bilateral) Diagnosis (dislocation : subluxation : dysplasia) Method of reduction (Pavlik harness : manual reduction + open reduction) Necrosis (+ : –) Age at reduction (r 0.5 : > 0.5–1.0 : > 1.0) CAI (average) CCE (average)
0/28 20/8 15/8/5 17/11 5/23 18/7/3 15.2±4.11 16.2±7.51
2/21 18/5 11/5/7 11/12 10/13 8/7/8 17.6±5.61 7.5±7.11
0.1984 0.5775 0.5593 0.3574 0.0457* 0.0583 0.0678 0.0007*
CAI, cartilaginous acetabular index; CCE angle, cartilaginous center edge angle. *P < 0.05.
Table 7
Multiple analysis P-value
Sex (male : female) Necrosis (+ : –) Age at reduction CAI CCE
0.5446 0.2452 0.9203 0.9329 0.0061*
CAI, cartilaginous acetabular index; CCE angle, cartilaginous center edge angle. *P < 0.05.
CE angle and center-head distance discrepancy (CHDD), and satisfactory outcomes (86%) were observed in the supplementary group. Kim et al. [4] evaluated annual radiographs of patients treated by closed reduction. They reported that remodeling of the acetabulum was possible when CHDD was less than 6% and the orientation of the sourcil was horizontal. Surgery is recommended to prevent residual acetabular dysplasia when the CHDD is at least 6% and the sourcil is oriented upwards between 4 and 5 years of age. Conversely, there is an opinion that it is difficult to predict the acetabular coverage from radiological findings when growth stops [10,11]. We surmised that in addition to osseous evaluation, cartilaginous acetabulum evaluation is also important in predicting future acetabulum growth. Figure 2 shows the difference between bony formation and cartilage formation in patients at 2 years of age. This result reflects the fact that clinicians cannot recognize acetabular formation by radiography alone at early stages of growth. We hypothesized that cartilage formation was quite important in acetabular formation and, if the coverage of cartilaginous acetabulum was sufficient, the osseous acetabulum would grow properly. In terms of the evaluation of cartilaginous acetabulum formation, Mohammed et al. [10] measured acetabular
cartilaginous angles (ACA) by arthrography during reductions and reported a cut-off value for ACA of 201 (below which 99.5% of all hips developed satisfactorily) and another cut-off value for ACA of 241 (above which 100% of hips needed acetabuloplasty). Arthrographic imaging is used to evaluate the condition of the acetabulum. Dynamic evaluation is possible using arthrographic evaluation, but this procedure is invasive and clinicians have difficulty in observing the real threedimensional structures. The condition of the articular cartilage, labrum, and ligamentum teres is deduced from a reflected image. By contrast, the advantages of MRI are its noninvasiveness, direct visualization capability, and safety on the basis of the lack of exposure to radiation [12]. We believe that MRI has many benefits that render it suitable as a method for the evaluation of the cartilaginous acetabulum. Wiem et al. [11] measured cartilaginous acetabular angle, cartilaginous coronal head index, and cartilaginous sagittal head index with MRI performed at a mean age of 5 years for patients with residual dysplasia. Investigators reported that 27 of 31 hips with residual acetabular dysplasia had MRI-identified thick cartilage of the acetabular roof (mean cartilaginous coronal head index, 85%; cartilaginous sagittal head index, 95%) and showed spontaneous progressive ossification. In this study, 65.7% of the patients with CAI of less than 181 showed positive acetabulum coverage during growth. Moreover, among patients with CCE angle of more than 131, 72.4% showed positive outcomes (Table 4). Furthermore, the mean CCE angle for the positive-outcome group was significantly larger than that for the pooroutcome group (Fig. 3). In other words, the AI values of the poor-outcome group varied widely. Therefore, we
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242 Journal of Pediatric Orthopaedics B 2014, Vol 23 No 3
Table 8
Intraobserver and interobserver reliability Intraobserver reliability
Mean±SD of measurement errors ICC 95% confidence interval
Interobserver reliability
CAI
CCE angle
CAI
CCE angle
2.9±3.51 0.897 P < 0.01 0.785–0.954
4.9±4.81 0.892 P < 0.01 0.776–0.956
4.2±3.61 0.801 P < 0.01 0.394–0.927
4.3±3.21 0.888 P < 0.01 0.715–0.956
CAI, cartilaginous acetabular index; CCE angle, cartilaginous center edge angle; ICC, intraclass correlation coefficient.
evaluated outcomes using the Severin classification on the basis of the CE angle as we surmised that the CCE angle has a higher reliability than the CAI in this study. However, some cases did not correspond with the prediction of the CCE angle. In this study, the osseous acetabulum of eight hips grew sufficiently at the time of the last investigation, although the CCE angle was poor at about 2 years of age. Of eight hips, six were diagnosed with a dislocation, one with subluxation, and one with acetabular dysplasia (Table 5). In the six dislocated hips, the congruity of the femoral head improved gradually after MRI examination. Therefore, a follow-up examination on the progress of the change of congruity of the femoral head and the growth of acetabulum coverage is important. Conversely, a few patients had poor growth of the osseous acetabulum, even when cartilaginous acetabulum coverage was sufficient. Among the eight hips, five were diagnosed with acetabular dysplasia (Table 5). Okano et al. [13] suggested that acetabular dysplasia in many patients occurred as a result of bone malformation. The investigators suggested that genetic research is required to elucidate the pathological mechanism of acetabular dysplasia. It is believed that even if cartilaginous acetabulum formation is sufficient, it is possible that ossification potential is poor owing to the genetic background (at least for the acetabulum dysplasia cases). We specifically focused on the shape of the acetabulum in this study. However, because cartilaginous quality is poor, it is possible that ossification is incomplete (even if the coverage of the cartilaginous acetabulum is sufficient). Therefore, it might be necessary to evaluate quality, as well as shape, of the cartilaginous acetabulum. Fisher et al. [14] suggested that if qualitative differences could be quantified such that potential acetabular development could be determined accurately, surgical intervention for patients with persistent dysplasia could be instituted early during the course of hip joint development to maximize cartilage remodeling. Wakabayashi et al. [15] reported that patients with residual subluxation showed high signal intensity areas within the weight-bearing acetabular cartilage (as measured on T2-weighted MRI) and had poor acetabular growth. The investigators proposed that extraordinary stress loaded onto acetabular cartilage may cause an edematous change or maldistribu-
tion of proteoglycan, resulting in disturbance of ossification in the acetabular cartilage. However, no reports to date have evaluated cartilaginous acetabulum quantitatively by MRI in patients at about 2 years of age. Here, we report the reference value for the cartilaginous acetabulum. The evaluation of cartilaginous acetabulum coverage by MRI enables the prediction of future osseous acetabulum formation earlier than the evaluation by radiography. If the cartilaginous acetabulum is sufficient early on, osseous acetabulum coverage may grow sufficiently afterwards to prevent premature secondary surgery. However, it is believed that the ossification potential of the cartilaginous acetabulum is high at 2 years of age; therefore, clinicians should be warned that sometimes the osseous acetabulum grows well, irrespective of the CCE angle, with congruity improving gradually afterwards. Therefore, we should further investigate the change in the congruity of the femoral head and the development of acetabulum coverage. In addition to the evaluation of femoral head position and obstructive factors to reduction, MRI is a useful method in the prediction of future acetabular formation. This study has several limitations. First, the CCE angle was a single, meaningful predictor, with an optimal cut-off value of 131, a sensitivity of 72.4%, a specificity of 63.6%, a positive predictive value of 72.4%, and a positive likelihood ratio of 1.98. However, the CCE angle is not a complete predictor. In this study, we measured the acetabular coverage in the anteroposterior view by radiography and in coronal images with MRI. In such assessments, it is insufficient to evaluate the coverage of the anterior acetabular formation and the anteroposterior congruity of the femoral head. It is believed that the significance of the CCE angle could have been improved if it was combined with other relevant indices measured on sagittal and transverse images. In future studies, in addition to studying other indicators, we will assess the three-dimensional cartilaginous acetabular angle and other similar measures. Second, the (C)CE angle can vary depending on the position of the hip and lower extremity. In this study, MRI was performed with patients placed in a supine position and the hip in the neutral position. As these conditions were confirmed by checking the patient’s posture on the table, they appeared to be slightly different in each
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Evaluation of the cartilaginous acetabulm Takeuchi et al. 243
patient. Therefore, it is considered that some variation occurs in the measured values of the (C)CE angle. In the future, we will consider the possibility of accurate positioning using a setting apparatus. Third, we were able to obtain follow-up data on bone maturity for only 18 of the 51 hips in this study. As the follow-up duration was insufficient, a longitudinal follow-up study will be necessary to estimate future hip development (acetabular angle, CE angle, CHDD) with a linear mixed model. Fourth, the ICC of intraobserver reliability for CAI and CCE angle was 0.897 and 0.892, respectively. The ICC of interobserver reliability for CAI and CCE angle was 0.801 and 0.888, respectively. We may consider that the ICCs for intraobserver and interobserver reliability were substantial; however, we expect that there will be variances in measurement. Therefore, on the basis of the border of the cut-off value that we calculated in this study, we expect that an analysis with more cases is necessary. Conclusion
(1) We report the cut-off value of the cartilaginous angle on MRI at 2 years of age to predict the future growth of osseous acetabulum on radiography. This cut-off value had a CAI of 181 and a CCE angle of 131 on MRI performed in patients at 2 years of age. (2) MRI may predict future acetabular coverage; however, it is important to follow up the progress of the change of congruity of the femoral head and the growth of acetabulum development.
Acknowledgements Conflicts of interest
There are no conflicts of interest.
References 1
2
3
4 5
6 7 8 9
10
11
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Ohmori T, Endo H, Mitani S, Minagawa H, Tetsunaga T, Ozaki T. Radiographic prediction of the results of long-term treatment with the Pavlik harness for developmental dislocation of the hip. Acta Med Okayama 2009; 63:123–128. Albinana J, Dolan LA, Spatt KF, Morcuende J, Meyer MD, Weinstein SL. Acetabular dysplasia after treatment for developmental dysplasia of the hip. J Bone Joint Surg [Br] 2004; 86-B:876–886. Nakamura J, Kamegaya M, Saisu T, Someya M, Koizumi W, Moriya H. Treatment for developmental dysplasia of the hip using the Pavlik harness. J Bone Joint Surg [Br] 2007; 89-B:230–235. Kim HT, Kim JI, Yoo CI. Acetabular development after closed reduction of developmental dislocation of the hip. J Pediatr Orthop 2000; 20:701–708. Severin E. Contribution of the knowledge of congenital dislocation of the hip joint. Late results of closed reduction and arthrographic studies of recent cases. Acta Chir Scand 1941; 84 (Supp 63):1–142. Kalamchi A, MacEween GD. Avascular necrosis following treatment of congenital dislocation of the hip. J Bone Joint Surg 1980; 62-A:876–888. Salter RB. Innominate osteotomy in the treatment of congenital dislocation and subluxation of the hip. J Bone Joint Surg Br 1961; 43-B:518–538. Harris NH. Acetabular development in congenital dislocation of the hip. J Bone Joint Surg Br 1975; 57-B:46–52. Noguchi Y, Oishi T, Sugioka Y, Matsumoto N, Fujii T. Prediction of final radiological results in early childhood after closed reduction for congenital dislocation of the hip [in Japanese]. Orthop Traumatol 1990; 39:197–200. Mohammed MZ, Mamoun KK, Khalid IK, Alshahid AA, Khalid AB, Abdul MMA, Kholoud OA. Acetabular cartilaginous angle. A new method for predicting acetabular development in developmental dysplasia of the hip in children between 2 and 18 month of age. J Pediatr Orthop 2008; 28: 518–528. Wiem DK, Mahmoud S, Hela L, Lilia BH, Sami B, Walid S, et al. Magnetic resonance evaluation of acetabular residual dysplasia in developmental dysplasia of the hip: a preliminary study of 27 patients. J Pediatr Orthop 2010; 30:37–43. Guidera KJ, Einbecker ME, Berman CG, Ogden JA, Arrington JA, Murtagh R. Magnetic resonance imaging evaluation of congenital dislocation of the hips. Clin Orthop Relat Res 1990; 261:96–101. Okano K, Takaki M, Okazaki N, Shindo H. Bilateral incidence and severity of acetabular dysplasia of the hip. J Orthop Sci 2008; 13:401–404. Fisher R, O’Brien TS, Davis KM. Magnetic resonance imaging of congenital dislocation of the hip. J Pediatr Orthop 1991; 11:617–622. Wakabayashi K, Wada I, Hirouchi O, Otsuka T. MRI finding in residual hip dysplasia. J Pediatr Orthop 2011; 31:381–387.
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