Clinical Orthopaedics and Related Research®
Clin Orthop Relat Res DOI 10.1007/s11999-013-3361-4
A Publication of The Association of Bone and Joint Surgeons®
CLINICAL RESEARCH
Modular versus Nonmodular Neck Femoral Implants in Primary Total Hip Arthroplasty: Which is Better? Paul J. Duwelius MD, Bob Burkhart PA, Clay Carnahan PA, Grant Branam BSc, Laura Matsen Ko MD, YingXing Wu MD, Cecily Froemke MS, Lian Wang MS, Gary Grunkemeier PhD
Received: 25 June 2013 / Accepted: 22 October 2013 Ó The Association of Bone and Joint Surgeons1 2013
Abstract Background Restoration of the hip center is considered important for a successful THA and requires achieving the right combination of offset, anteversion, and limb length. Modular femoral neck designs were introduced to make achieving this combination easier. No previous studies have compared these designs in primary THA, and there is increasing concern that modular designs may have a higher complication rate than their nonmodular counterparts.
One of the authors (PJD) is a consultant for Zimmer (Warsaw, IN, USA), receives royalties from Zimmer for fracture and joint implants, is chairman of the adult hip reconstruction committee, medical legal defense expert, and a board member of an orthopedic surgical center. All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research editors and board members are on file with the publication and can be viewed on request. Clinical Orthopaedics and Related Research neither advocates nor endorses the use of any treatment, drug, or device. Readers are encouraged to always seek additional information, including FDAapproval status, of any drug or device prior to clinical use. Each author certifies that his or her institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained. This work was performed at Providence St Vincent Medical Center, Portland, OR, USA. P. J. Duwelius (&), B. Burkhart, C. Carnahan, L. M. Ko Orthopedic + Fracture Specialists, 11782 SW Barnes Road #300, Portland, OR 97225, USA e-mail: [email protected] G. Branam, C. Froemke Orthopedic Institute, Providence Health & Services, Portland, OR, USA Y. Wu, L. Wang, G. Grunkemeier Medical Data Research Center, Providence Health & Services, Portland, OR, USA
Questions/purposes We therefore asked (1) whether use of a stem with a modular neck would restore limb length and offset more accurately than a stem with a nonmodular neck, and (2) whether patients who received modular neck systems had better hip scores or a lower frequency of complications and reoperations than those receiving a comparable nonmodular stem. Methods Two cohorts of patients undergoing primary THAs, 284 patients with a nonmodular neck and 594 patients with a modular neck, were treated by one surgeon through a posterior approach. These were two nearly sequential series with little overlap. Harris hip scores and SF-12 outcomes surveys were administered at followup with a mean of 2.4 years (maximum, 5.9 years). Results In the modular neck cohort, a greater proportion of patients had equal (within 5 mm) radiographic limb lengths (89%, compared with 77% in nonmodular cohort p = 0.036), and a smaller offset difference (6.1 versus 7.5 mm, p = 0.047) was observed. Whether these statistical differences are clinically important is unclear. A smaller proportion of patients in the modular neck cohort achieved equal apparent or clinical limb length at 1 year (85% versus 95%, p \ 0.001) and at 2 years (81% versus 94%, p \ 0.001). In addition, these differences did not appear to result in better Harris hip or SF-12 scores, fewer complications, or reduced likelihood of revision surgery. Conclusions Use of modular neck stems did not improve hip scores nor reduce the likelihood of complications or reoperations. Because of their reported higher risks, there is no clear indication for modularity with a primary THA, unless the hip center cannot be achieved with a nonmodular stem, which is rare. Level of Evidence Level III, therapeutic study. See the Instructions to Authors for a complete description of levels of evidence.
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Clinical Orthopaedics and Related Research1
Introduction
Patient Demographics
Restoration of the hip center is considered important for a successful THA and involves achieving the correct limb length, anteversion, and offset. Limb-length inequality is a particular problem in THA [8, 11, 16, 17]. Proper cup position and total anteversion are important for ROM and to decrease impingement and wear [3, 6, 12, 14, 19, 20]. Appropriate offset is crucial for soft tissue balance, restoration of the center of rotation of the hip, and decreasing impingement [4, 10, 14]. Anatomic gender differences may further confound the surgeons’ ability to recreate the head center in certain cases [15]. Preoperative planning is essential for restoration of the femoral head center and correct hip biomechanics [21, 23]. Modular femoral neck designs can make a complex operation easier by supplying more options and offering more flexibility. Systems offering this added modularity allow the surgeon to adjust offset, version, and limb length and to make adjustments to these parameters independently of one another during preoperative planning and in the operating room. However, some studies report risks associated with added modularity, including implant fractures, fretting, and third-body wear for modular necks [1, 24–27]. In light of these issues, the use of a modular neck stem in THA remains controversial. We therefore asked (1) whether use of a stem with a modular neck would restore limb length and offset more accurately than a stem with a nonmodular neck, and (2) whether patients who received modular neck systems had better hip scores or a lower frequency of complications and reoperations than those receiving nonmodular stems.
From August 1, 2005 to December 31, 2009, 883 patients underwent THA by one surgeon (PJD) and consented to be included in a prospective followup database. Five patients who had bilateral THAs were excluded. Of the 878 patients who had a single arthroplasty, 284 received a hip stem with a nonmodular neck and 594 received a hip stem with a modular neck. Initially, we used nonmodular neck Zimmer1 M/L Taper stems exclusively. On introduction of the otherwise identical modular neck stem (May 9, 2007) and up to December 31, 2009, we switched to the modular neck almost exclusively, with only 10 nonmodular neck cases performed during this period. Of these 10 cases, which were included in the analysis for this study, seven were the result of increased offset issues (this is a drawback of the modular neck stem in that it offers less offset than the nonmodular neck), and the other three were because of poor bone density with a Dorr Type C pattern, for which a fit-and-fill stem was used. These decisions were made during preoperative radiographic templating or planning. Patient demographics and clinical profiles are similar between the two cohorts, except for diabetes and diagnosis (Table 1). Complete followup at a minimum of 2 years (mean, 2.4 years) was available for 197 patients in the nonmodular group (69%) and 459 patients in the modular stem group (77%). Outcomes at 1 and 2 years were similar for matched patients. This finding allowed us to merge the completed outcomes surveys from 1- and 2-year followups into a new group where followup was completed at either 1 or 2 years. This combination resulted in 90% completion of followup. For unexplained reasons, there was differential loss to followup between the modular (93%) and nonmodular (84%) groups (p \ 0.001).
Study Outcome End Points Materials and Methods This was a retrospective observational study using a prospectively maintained database to evaluate two cohorts of patients. One cohort received a nonmodular neck (Zimmer1 M/L Taper; Warsaw, IN, USA) and the other cohort received a modular neck (Zimmer1 M/L Taper Kinectiv). Both stems are identical except the modular neck stem has a separate neck piece that allows for 60 different options for head center versus 10 options with the nonmodular neck. In all cases, the same acetabular components were used, which consisted of a Trilogy1 fiber metal-backed cup and metal-on-polyethylene bearing surface with highly cross-linked polyethylene (Zimmer) [9, 22]. No elevated liners were used. The study was approved by the institutional review board.
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End points for this study include clinical and radiographic measurements and revisions and complications. Clinical end points include apparent or clinical limblength evaluation and Harris hip and SF-12 scores. Before the operation, all patients had an evaluation of apparent limb length. With the patient in the lateral decubitus position, an osteotome was placed at the level of the patellar tendon and the operative leg was compared with the nonoperative leg. Preoperatively patients whose apparent limb length was short were asked to stand on blocks of varying sizes to determine the desired correction. This became the target limb length to reproduce postoperatively, as described subsequently in the surgical technique. Clinical reevaluation of limb length was repeated postoperatively and at 1-year and
Modular Neck Femoral Implants Table 1. Clinical profile Item
Nonmodular
Modular
Number of patients
284
594
Surgery date
August 1, 2005, to September 8, 2009
May 9, 2007, to December 22, 2009
p value
Age (years)
62 ± 11
62 ± 10
0.65
Male sex
52% (148)
53% (312)
0.91
Diabetes
9% (25)
14% (81)
0.04
Side (left/right)
46%/54% (131/153)
49%/51% (291/303)
0.43
Preoperative diagnosis
0.01
Osteoarthritis
90% (212)
95% (558)
Avascular necrosis
6% (14)
2% (11)
Other
4% (9)
3% (20)
32 mm
59% (169)
9% (56)
36 mm
39% (110)
51% (302)
40 mm
2% (5)
40% (236)
\ 0.01
Head size
2-year followups, and Harris hip and SF-12 scores were assessed preoperatively and at 1- and 2-year followups. Radiographic end points include leg length and offset, evaluated before and after surgery, in a subset of patients who had no contralateral deformity or prior THA and whose radiographs were available electronically. Offset was based on the contralateral hip. Being within 5 mm of offset difference is considered a good result and tends to improve stability and hip biomechanics. For the purposes of this study, we compared the mean offset difference and the percentage of hips with an offset difference of 5 mm or less between the two study cohorts. We also calculated the percentage of hips in each stem group that was of equal radiographic leg length (within 5 mm).
was used in all cases in this series. In both cohorts, the femur was prepared first to best determine the optimal femoral anteversion. The acetabular cup then was placed based on the femoral anteversion so that a combined version of a 30° to 50° target zone could be attained based on the Ranawat sign [18]. If a cup size of 50 to 56 mm was achieved, then a 36-mm femoral head was used. A 32-mm femoral head was used in cups up to 50 mm. A 40-mm femoral head was used for cup sizes of 58 mm or larger. Components found to impinge or dislocate during a trial were changed or the cause of impingement (such as osteophytes or soft tissue) were removed. Anteverted or retroverted necks were not used to correct component malpositioning. Reduced or extended offset necks were used when outlier offset, based on preoperative radiographic templating, was encountered. The goal was to recreate the anatomic head center and provide for a clinically stable THA. For patients with a long leg resulting from pelvic obliquity such as scoliosis, the limb length was not changed. For patients with an apparent short leg, the limb length was corrected to the target length determined by the block test in the clinic. The active critical hip pathway was used for post operative care in this series [2, 7, 13].
Statistical Methods Continuous variables are presented as mean ±SD and comparisons between the two groups were done by unpaired t-tests. Categorical variables are presented as percentages and the comparisons were done by chi-square or Fisher’s exact tests. Hip function and quality-of-life measures are summarized as mean ± SD and compared by a linear mixed effect model for repeated measures. Freedom from revision was computed by the Kaplan-Meier method and compared by the log-rank test. Statistical analysis was performed using PASW 17 (SPSS Inc, Chicago, IL, USA) and R 2.15 (http://www.R-project.org).
Surgical Technique
Results
The desired head center was determined preoperatively by templating the head center on the acetabular radiograph. The films were either templates from acetate templates (early cases) or digital radiographs (later cases). The acetabular head center was templated first and then the femoral stem size was matched to the acetabular head center. The distance above the trochanter was measured to achieve the correct cut to recreate this offset and leg length. A radiographic marker was used in all cases to adjust for magnification and all radiographs were obtained from a standard distance. Version was determined intraoperatively. A mini-posterior approach
In the modular neck cohort, a greater proportion of patients had equal (within 5 mm) radiographic limb length (89%, compared with 77% in the nonmodular cohort, p = 0.036), and a smaller offset difference was observed (6.1 versus 7.5 mm, p = 0.047) (Table 2). However, the proportions of patients having an offset difference within 5 mm were similar. The slightly enhanced accuracy of the modular neck in restoring the head center did not translate into better shortterm (1–2 years) outcome scores, revisions, or complications. A smaller proportion of patients in the modular neck
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cohort achieved equal apparent or clinical limb length at 1 year (85% versus 95%, p \ 0.001) and at 2 years (81% versus 94%, p \ 0.001). Harris hip and SF-12 scores were not different between the groups (Table 3), and modularity did not affect these measures, even after adjusting for age, sex, diabetes, diagnosis, and head size (Table 4). There were no differences in revision rates at 2 years. Freedom from revision at 2 years was similar between the two groups, at 99% (97%–100%) and 99% (98%–100%) for the nonmodular and modular neck groups, respectively (p = 0.94). There were 10 revisions, three in the nonmodular neck group (two for dislocations and one for fracture of the femur) and seven in the modular neck group (two for dislocations, one for fracture of the femur, two for deep infections, one for fracture of the greater trochanter, and one for other). Finally, there were no differences in complication rates between the two groups (Table 5). No other safety issues (such as trunnion fractures or neck dissociations) were encountered with the modular neck during the period of this study.
Discussion The purpose of using a modular implant is to improve the head center by allowing for independent leg length, offset and version, thus improving hip biomechanics. We evaluated clinical and radiographic differences between modular
Table 2. Radiographic subset of offset and limb length
Age
0.01
0.00
0.12
Male sex
0.01
0.88
0.38
0.37
0.12 0.37
0.036
Head size 36 mm
0.26
0.61
0.02
0.047
Head size 40 mm Modular
0.06 0.17
1.00 0.40
0.19 0.65
77% (75/97)
89% (82/97)
47% (46/97)
SF-12 mental
0.71
Leg length equality (within 5 mm)
38% (31/82)
SF-12 physical
0.21
p value
Offset difference B 5 mm
Harris hip score
0.48
Modular
6.1
Source
Diagnosis of osteoarthritis
Nonmodular
7.5
Table 4. Linear regression for change in scores (combined 1-year or 2-year score minus preoperative score)
Diabetes
Measurement
Offset difference (mm)
and nonmodular hip stems. Although modularity is widely used, its superiority in outcome scores, hip biomechanics, and complications have not been shown over those of conventional implants. We found that use of modular neck stems did not improve hip scores or reduce the likelihood of complications or reoperation. Because of their reported higher risks [1, 5, 24–27], there is no clear indication for modularity with a primary THA, unless the hip center cannot be achieved with a nonmodular stem, which is extremely rare. One weakness of this study is that patient allocation was not randomized between the two treatment groups. Essentially, we had two consecutive cohorts spanning 5 years with nonmodular neck cases from the earlier years and modular neck cases from the later years. Possible differences in technology, improvements to surgical technique, and other changes that are hard to characterize in the context of a retrospective study potentially could confound the results of this study. These differences would tend to favor the later group, making the small observed differences that favored the modular stems even less likely to be clinically important. This retrospective observational study was not powered to detect differences in uncommon
0.197
Numbers are p values.
Table 3. Hip function and quality-of-life measures (preoperative and postoperative matched samples) Outcome tool
Nonmodular (mean ± SD) Number of patients
Preoperative
Modular (mean ± SD) 1-year
2-year
Number of patients
Preoperative
1-year
2-year
Harris hip score
110
50 ± 13
90 ± 13
90 ± 15
356
52 ± 13
92 ± 11
92 ± 10
SF-2 physical health
115
30 ± 7
49 ± 9
49 ± 8
376
33 ± 8
50 ± 8
50 ± 9
SF-12 Mental health
133
53 ± 11
55 ± 8
55 ± 8
387
54 ±10
56 ± 6
56 ± 6
1- or 2- year
1- or 2- year
Harris hip score
199
50 ± 14
90 ± 14
523
52 ± 13
91 ± 12
SF-12 physical health
202
30 ±8
48 ±10
530
33 ± 8
50 ± 9
SF-12 mental health
216
53 ± 11
55 ± 8
531
54 ± 10
55 ± 7
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Modular Neck Femoral Implants Table 5. Summary of complications Complication type
Nonmodular* Number of complications
Modular* Complication rate (95% CI)
Number of complications
Complication rate (95% CI)
Seroma
0
0% (0%–1.3%)
1
0.2% (0%–1.0%)
Dislocation
5
1.8% (0.8%–4.1%)
5
0.8% (0.4%–2.0%)
Deep infection Superficial infection
4 0
1.4% (0.6%–3.6%) 0% (0%–1.3%)
4 2
0.7% (0.3%–1.7%) 0.3% (0.1%–1.2%)
Fracture
4
1.4% (0.6%–3.6%)
8
1.3% (0.7%–2.6%)
Wound drainage
1
0.4% (0.1%–2.0%)
0
0% (0%–0.6%)
General medical
5
1.8% (0.8%–4.1%)
5
0.8% (0.4%–2.0%)
* None of the complication rates were significantly different between the groups (p[ 0.20 for all comparisons); general medical complications were: one gastrointestinal bleeding, three neurologic, and one hematoma in the nonmodular neck cohort, and one urinary retention, one hematoma, and three deep vein thrombosis/pulmonary embolism in the modular neck cohort. All medical complications resolved.
complications, although the point estimates suggest that the likelihood of important differences is low, and if a difference cannot be detected in a study of nearly 900 THAs, it seems unlikely to be clinically important. In addition, accurate parameter assessment is difficult. For instance, limb-length estimation can be different between the clinical (apparent) and radiographic (true) assessments. This was a difficult aspect of this study and a shortcoming in that limb length can vary between the two measurement methods and with time in the same patient owing to multiple factors such as abduction contractures, pelvic obliquity, and scoliosis. Furthermore, patients’ perceptions of limb length usually come from the apparent limb length, which also can change with time. Using the latest scanograms or CT technology to improve the true limb-length measurement is not justified in this setting and probably would not eliminate all of the discrepancies between the two assessment methods in any case. The intangible variables of offset and version are even harder to accurately reproduce clinically over radiographic parameters. Such intangibles include stability, soft tissue laxity, presence of osteophytes, congenital deformity, impingement issues, and surgeon preference. Because radiographs were available for only a subset of patients, the radiographic results could be confounded by selection bias. In our short-term study, we showed that use of a modular neck improved the surgeon’s ability to achieve correct offset based on radiographic parameters. However, the slight improvement in offset difference with a modular neck was small and the clinical significance questionable. Most patients in either the modular or nonmodular cohorts were outside the 5 mm offset difference target. One could argue that the addition of more modular options does not necessarily make a procedure easier, since the criteria for using these options may not be as clearly documented. One of the learning curves we overcame was to evaluate limb
length first, which seemed to be easiest intraoperatively, and then determine offset and version. Although there are some situations that seem to call for unusual stem designs, perhaps including modularity, we find these situations rare and the majority of patients can be treated with nonmodular neck stems. In terms of limb-length equality, we found disparate results. The radiographic limb length was closer in the modular neck group, but the clinical (apparent) limb length, which we believe to be the more important parameter, favored the nonmodular neck group. In addition, none of the observed differences in terms of radiographic leg length or offset were associated with improvements in outcomes scores, with a reduction in the frequency of important complications, or with a reduction in the frequency of revision surgery. Although we saw no complications associated with modularity, our followup was short term. In addition, there have been studies showing that corrosion is the main concern with these taper junctions [1, 5, 24–27]. The soft tissue reactions and destruction seen with the abductor mechanisms in some of these reported cases of trunionosis is compelling. We have identified five cases of corrosion which either happened outside our study period or did not occur in patients who consented to inclusion in our registry. We felt these complications were significant and should be reported. All these cases occurred at the head-neck junction in 36-mm femoral heads. Three involved the modular stem and two involved the nonmodular stem. Among the three modular cases, one used a standard offset neck and the other two used extended necks (one straight and one anteverted). The nonmodular cases used extended necks. The modular stems were revised to a new head-neck junction and ceramic head. The nonmodular stems were revised to a ceramic head with a titanium sleeve. There were significant soft tissue reactions in two of these cases and de´bridement was performed to remove the metallic stained tissue and to stop the inflammatory response. Fretting
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corrosion is known to be a time-dependent process. Therefore, in this short-term series, this type of complication might not have had a chance to reveal itself, particularly in the modular neck group, which is the more recent of the two nearly sequential cohorts. Even though this modular design has a cobalt-chromium-titanium head-neck junction, the titanium-titanium neck-stem junction still could pose risk for corrosion. For these reasons the senior author (PJD) now almost exclusively uses nonmodular stems and ceramic femoral heads to decrease the possibility of corrosion. Of our 450 recent consecutive THAs, the modular stem was used only once in a slender female. The patient in this case had a modular stem inserted on the opposite side in an extremely varus hip to avoid excessively lengthening the leg. Although there were no fractures or stem failures in this large and relatively unselected series, modular neck stems did not lead to improved clinical hip scores, reduction in complications, or decreased likelihood of revision hip surgery, and there are known risks of modularity (pseudotumors, implant fractures, fretting, third-body wear, and trunnion corrosion) [1, 5, 24–27]. Therefore we currently would consider only modularity if the clinical hip center is anticipated to be an extreme outlier (ie, the clinical hip center is anticipated to be greater than 5 mm away from the desired target, resulting in a significant leg-length discrepancy or offset issue). Long-term followup is needed to assess the ultimate durability of modular implants and to determine the frequency of complications associated with modular devices. References 1. Atwood SA, Patten EW, Bozic KJ, Pruitt LA, Ries MD. Corrosion-induced fracture of a double-modular hip prosthesis: a case report. J Bone Joint Surg Am. 2010;92:1522–1525. 2. Berger RA, Jacobs JJ, Meneghini RM, Della Valle C, Paprosky W, Rosenberg AG. Rapid rehabilitation and recovery with minimally invasive total hip arthroplasty. Clin Orthop Relat Res. 2004;429:239–247. 3. Biedermann R, Tonin A, Krismer M, Rachbauer F, Eibl G, Stockl B. Reducing the risk of dislocation after total hip arthroplasty: the effect of orientation of the acetabular component. J Bone Joint Surg Br. 2005;87:762–769. 4. Bourne RB, Rorabeck CH. Soft tissue balancing: the hip. J Arthroplasty. 2002;17(4 suppl 1):17–22. 5. Cooper HJ, Della Valle CJ, Berger RA, Tetreault M, Paprosky WG, Sporer SM, Jacobs JJ. Corrosion at the head-neck taper as a cause for adverse local tissue reactions after total hip arthroplasty. J Bone Joint Surg Am. 2012;94:1655–1661. 6. D’Lima DD, Urquhart AG, Buehler KO, Walker RH, Colwell CW Jr. The effect of the orientation of the acetabular and femoral components on the range of motion of the hip at different headneck ratios. J Bone Joint Surg Am. 2000;82:315–321. 7. Duwelius PJ, Moller HS, Burkhart RL, Waller F, Wu Y, Grunkemeier GL. The economic impact of minimally invasive total hip arthroplasty. J Arthroplasty. 2011;26:883–885.
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Clinical Orthopaedics and Related Research1 8. Hofmann AA, Skrzynski MC. Leg-length inequality and nerve palsy in total hip arthroplasty: a lawyer awaits! Orthopedics. 2000;23:943–944. 9. Howard JL, Kremers HM, Loechler YA, Schleck CD, Harmsen WS, Berry DJ, Cabanela ME, Hanssen AD, Pagnano MW, Trousdale RT, Lewallen DG. Comparative survival of uncemented acetabular components following primary total hip arthroplasty. J Bone Joint Surg Am. 2011;93:1597–1604. 10. Iorio R, Healy WL, Warren PD, Appleby D. Lateral trochanteric pain following primary total hip arthroplasty. J Arthroplasty. 2006;21:233–236. 11. Konyves A, Bannister GC. The importance of leg length discrepancy after total hip arthroplasty. J Bone Joint Surg Br. 2005;87:155–157. 12. Lewinnek GE, Lewis JL, Tarr R, Compere CL, Zimmerman JR. Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am. 1978;60:217–220. 13. Maheshwari AV, Boutary M, Yun AG, Sirianni LE, Dorr LD. Multimodal analgesia without routine parenteral narcotics for total hip arthroplasty. Clin Orthop Relat Res. 2006;453:231–238. 14. Malik A, Maheshwari A, Dorr LD. Impingement with total hip replacement. J Bone Joint Surg Am. 2007;89:1832–1842. 15. Maruyama M, Feinberg JR, Capello WN, D’Antonio JA. The Frank Stinchfield Award: Morphologic features of the acetabulum and femur: anteversion angle and implant positioning. Clin Orthop Relat Res. 2001;393:52–65. 16. Morrey BF. Instability after total hip arthroplasty. Orthop Clin North Am. Apr 1992;23:237–248. 17. Parvizi J, Sharkey PF, Bissett GA, Rothman RH, Hozack WJ. Surgical treatment of limb-length discrepancy following total hip arthroplasty. J Bone Joint Surg Am. 2003;85:2310–2317. 18. Ryan JA, Jamali AA, Bargar WL. Accuracy of computer navigation for acetabular component placement in THA. Clin Orthop Relat Res. 2010;468:169–177. 19. Sanchez-Sotelo J, Haidukewych GJ, Boberg CJ. Hospital cost of dislocation after primary total hip arthroplasty. J Bone Joint Surg Am. 2006;88:290–294. 20. Shon WY, Baldini T, Peterson MG, Wright TM, Salvati EA. Impingement in total hip arthroplasty: a study of retrieved acetabular components. J Arthroplasty. 2005;20:427–435. 21. Sugano N, Noble PC, Kamaric E. Predicting the position of the femoral head center. J Arthroplasty. 1999;14:102–107. 22. Thomas GE, Simpson DJ, Mehmood S, Taylor A, McLardySmith P, Gill HS, Murray DW, Glyn-Jones S. The seven-year wear of highly cross-linked polyethylene in total hip arthroplasty: a double-blind, randomized controlled trial using radiostereometric analysis. J Bone Joint Surg Am. 2011;93:716–722. 23. Tripuraneni KR, Archibeck MJ, Junick DW, Carothers JT, White RE. Common errors in the execution of preoperative templating for primary total hip arthroplasty. J Arthroplasty. 2010;25:1235– 1239. 24. Viceconti M, Baleani M, Squarzoni S, Toni A. Fretting wear in a modular neck hip prosthesis. J Biomed Mater Res. 1997;35:207– 216. 25. Viceconti M, Ruggeri O, Toni A, Giunti A. Design-related fretting wear in modular neck hip prosthesis. J Biomed Mater Res. 1996;30:181–186. 26. Wilson DA, Dunbar MJ, Amirault JD, Farhat Z. Early failure of a modular femoral neck total hip arthroplasty component: a case report. J Bone Joint Surg Am. 2010;92:1514–1517. 27. Wright G, Sporer S, Urban R, Jacobs J. Fracture of a modular femoral neck after total hip arthroplasty: a case report. J Bone Joint Surg Am. 2010;92:1518–1521.
Clin Orthop Relat Res DOI 10.1007/s11999-013-3361-4
A Publication of The Association of Bone and Joint Surgeons®
CLINICAL RESEARCH
Modular versus Nonmodular Neck Femoral Implants in Primary Total Hip Arthroplasty: Which is Better? Paul J. Duwelius MD, Bob Burkhart PA, Clay Carnahan PA, Grant Branam BSc, Laura Matsen Ko MD, YingXing Wu MD, Cecily Froemke MS, Lian Wang MS, Gary Grunkemeier PhD
Received: 25 June 2013 / Accepted: 22 October 2013 Ó The Association of Bone and Joint Surgeons1 2013
Abstract Background Restoration of the hip center is considered important for a successful THA and requires achieving the right combination of offset, anteversion, and limb length. Modular femoral neck designs were introduced to make achieving this combination easier. No previous studies have compared these designs in primary THA, and there is increasing concern that modular designs may have a higher complication rate than their nonmodular counterparts.
One of the authors (PJD) is a consultant for Zimmer (Warsaw, IN, USA), receives royalties from Zimmer for fracture and joint implants, is chairman of the adult hip reconstruction committee, medical legal defense expert, and a board member of an orthopedic surgical center. All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research editors and board members are on file with the publication and can be viewed on request. Clinical Orthopaedics and Related Research neither advocates nor endorses the use of any treatment, drug, or device. Readers are encouraged to always seek additional information, including FDAapproval status, of any drug or device prior to clinical use. Each author certifies that his or her institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained. This work was performed at Providence St Vincent Medical Center, Portland, OR, USA. P. J. Duwelius (&), B. Burkhart, C. Carnahan, L. M. Ko Orthopedic + Fracture Specialists, 11782 SW Barnes Road #300, Portland, OR 97225, USA e-mail: [email protected] G. Branam, C. Froemke Orthopedic Institute, Providence Health & Services, Portland, OR, USA Y. Wu, L. Wang, G. Grunkemeier Medical Data Research Center, Providence Health & Services, Portland, OR, USA
Questions/purposes We therefore asked (1) whether use of a stem with a modular neck would restore limb length and offset more accurately than a stem with a nonmodular neck, and (2) whether patients who received modular neck systems had better hip scores or a lower frequency of complications and reoperations than those receiving a comparable nonmodular stem. Methods Two cohorts of patients undergoing primary THAs, 284 patients with a nonmodular neck and 594 patients with a modular neck, were treated by one surgeon through a posterior approach. These were two nearly sequential series with little overlap. Harris hip scores and SF-12 outcomes surveys were administered at followup with a mean of 2.4 years (maximum, 5.9 years). Results In the modular neck cohort, a greater proportion of patients had equal (within 5 mm) radiographic limb lengths (89%, compared with 77% in nonmodular cohort p = 0.036), and a smaller offset difference (6.1 versus 7.5 mm, p = 0.047) was observed. Whether these statistical differences are clinically important is unclear. A smaller proportion of patients in the modular neck cohort achieved equal apparent or clinical limb length at 1 year (85% versus 95%, p \ 0.001) and at 2 years (81% versus 94%, p \ 0.001). In addition, these differences did not appear to result in better Harris hip or SF-12 scores, fewer complications, or reduced likelihood of revision surgery. Conclusions Use of modular neck stems did not improve hip scores nor reduce the likelihood of complications or reoperations. Because of their reported higher risks, there is no clear indication for modularity with a primary THA, unless the hip center cannot be achieved with a nonmodular stem, which is rare. Level of Evidence Level III, therapeutic study. See the Instructions to Authors for a complete description of levels of evidence.
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Introduction
Patient Demographics
Restoration of the hip center is considered important for a successful THA and involves achieving the correct limb length, anteversion, and offset. Limb-length inequality is a particular problem in THA [8, 11, 16, 17]. Proper cup position and total anteversion are important for ROM and to decrease impingement and wear [3, 6, 12, 14, 19, 20]. Appropriate offset is crucial for soft tissue balance, restoration of the center of rotation of the hip, and decreasing impingement [4, 10, 14]. Anatomic gender differences may further confound the surgeons’ ability to recreate the head center in certain cases [15]. Preoperative planning is essential for restoration of the femoral head center and correct hip biomechanics [21, 23]. Modular femoral neck designs can make a complex operation easier by supplying more options and offering more flexibility. Systems offering this added modularity allow the surgeon to adjust offset, version, and limb length and to make adjustments to these parameters independently of one another during preoperative planning and in the operating room. However, some studies report risks associated with added modularity, including implant fractures, fretting, and third-body wear for modular necks [1, 24–27]. In light of these issues, the use of a modular neck stem in THA remains controversial. We therefore asked (1) whether use of a stem with a modular neck would restore limb length and offset more accurately than a stem with a nonmodular neck, and (2) whether patients who received modular neck systems had better hip scores or a lower frequency of complications and reoperations than those receiving nonmodular stems.
From August 1, 2005 to December 31, 2009, 883 patients underwent THA by one surgeon (PJD) and consented to be included in a prospective followup database. Five patients who had bilateral THAs were excluded. Of the 878 patients who had a single arthroplasty, 284 received a hip stem with a nonmodular neck and 594 received a hip stem with a modular neck. Initially, we used nonmodular neck Zimmer1 M/L Taper stems exclusively. On introduction of the otherwise identical modular neck stem (May 9, 2007) and up to December 31, 2009, we switched to the modular neck almost exclusively, with only 10 nonmodular neck cases performed during this period. Of these 10 cases, which were included in the analysis for this study, seven were the result of increased offset issues (this is a drawback of the modular neck stem in that it offers less offset than the nonmodular neck), and the other three were because of poor bone density with a Dorr Type C pattern, for which a fit-and-fill stem was used. These decisions were made during preoperative radiographic templating or planning. Patient demographics and clinical profiles are similar between the two cohorts, except for diabetes and diagnosis (Table 1). Complete followup at a minimum of 2 years (mean, 2.4 years) was available for 197 patients in the nonmodular group (69%) and 459 patients in the modular stem group (77%). Outcomes at 1 and 2 years were similar for matched patients. This finding allowed us to merge the completed outcomes surveys from 1- and 2-year followups into a new group where followup was completed at either 1 or 2 years. This combination resulted in 90% completion of followup. For unexplained reasons, there was differential loss to followup between the modular (93%) and nonmodular (84%) groups (p \ 0.001).
Study Outcome End Points Materials and Methods This was a retrospective observational study using a prospectively maintained database to evaluate two cohorts of patients. One cohort received a nonmodular neck (Zimmer1 M/L Taper; Warsaw, IN, USA) and the other cohort received a modular neck (Zimmer1 M/L Taper Kinectiv). Both stems are identical except the modular neck stem has a separate neck piece that allows for 60 different options for head center versus 10 options with the nonmodular neck. In all cases, the same acetabular components were used, which consisted of a Trilogy1 fiber metal-backed cup and metal-on-polyethylene bearing surface with highly cross-linked polyethylene (Zimmer) [9, 22]. No elevated liners were used. The study was approved by the institutional review board.
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End points for this study include clinical and radiographic measurements and revisions and complications. Clinical end points include apparent or clinical limblength evaluation and Harris hip and SF-12 scores. Before the operation, all patients had an evaluation of apparent limb length. With the patient in the lateral decubitus position, an osteotome was placed at the level of the patellar tendon and the operative leg was compared with the nonoperative leg. Preoperatively patients whose apparent limb length was short were asked to stand on blocks of varying sizes to determine the desired correction. This became the target limb length to reproduce postoperatively, as described subsequently in the surgical technique. Clinical reevaluation of limb length was repeated postoperatively and at 1-year and
Modular Neck Femoral Implants Table 1. Clinical profile Item
Nonmodular
Modular
Number of patients
284
594
Surgery date
August 1, 2005, to September 8, 2009
May 9, 2007, to December 22, 2009
p value
Age (years)
62 ± 11
62 ± 10
0.65
Male sex
52% (148)
53% (312)
0.91
Diabetes
9% (25)
14% (81)
0.04
Side (left/right)
46%/54% (131/153)
49%/51% (291/303)
0.43
Preoperative diagnosis
0.01
Osteoarthritis
90% (212)
95% (558)
Avascular necrosis
6% (14)
2% (11)
Other
4% (9)
3% (20)
32 mm
59% (169)
9% (56)
36 mm
39% (110)
51% (302)
40 mm
2% (5)
40% (236)
\ 0.01
Head size
2-year followups, and Harris hip and SF-12 scores were assessed preoperatively and at 1- and 2-year followups. Radiographic end points include leg length and offset, evaluated before and after surgery, in a subset of patients who had no contralateral deformity or prior THA and whose radiographs were available electronically. Offset was based on the contralateral hip. Being within 5 mm of offset difference is considered a good result and tends to improve stability and hip biomechanics. For the purposes of this study, we compared the mean offset difference and the percentage of hips with an offset difference of 5 mm or less between the two study cohorts. We also calculated the percentage of hips in each stem group that was of equal radiographic leg length (within 5 mm).
was used in all cases in this series. In both cohorts, the femur was prepared first to best determine the optimal femoral anteversion. The acetabular cup then was placed based on the femoral anteversion so that a combined version of a 30° to 50° target zone could be attained based on the Ranawat sign [18]. If a cup size of 50 to 56 mm was achieved, then a 36-mm femoral head was used. A 32-mm femoral head was used in cups up to 50 mm. A 40-mm femoral head was used for cup sizes of 58 mm or larger. Components found to impinge or dislocate during a trial were changed or the cause of impingement (such as osteophytes or soft tissue) were removed. Anteverted or retroverted necks were not used to correct component malpositioning. Reduced or extended offset necks were used when outlier offset, based on preoperative radiographic templating, was encountered. The goal was to recreate the anatomic head center and provide for a clinically stable THA. For patients with a long leg resulting from pelvic obliquity such as scoliosis, the limb length was not changed. For patients with an apparent short leg, the limb length was corrected to the target length determined by the block test in the clinic. The active critical hip pathway was used for post operative care in this series [2, 7, 13].
Statistical Methods Continuous variables are presented as mean ±SD and comparisons between the two groups were done by unpaired t-tests. Categorical variables are presented as percentages and the comparisons were done by chi-square or Fisher’s exact tests. Hip function and quality-of-life measures are summarized as mean ± SD and compared by a linear mixed effect model for repeated measures. Freedom from revision was computed by the Kaplan-Meier method and compared by the log-rank test. Statistical analysis was performed using PASW 17 (SPSS Inc, Chicago, IL, USA) and R 2.15 (http://www.R-project.org).
Surgical Technique
Results
The desired head center was determined preoperatively by templating the head center on the acetabular radiograph. The films were either templates from acetate templates (early cases) or digital radiographs (later cases). The acetabular head center was templated first and then the femoral stem size was matched to the acetabular head center. The distance above the trochanter was measured to achieve the correct cut to recreate this offset and leg length. A radiographic marker was used in all cases to adjust for magnification and all radiographs were obtained from a standard distance. Version was determined intraoperatively. A mini-posterior approach
In the modular neck cohort, a greater proportion of patients had equal (within 5 mm) radiographic limb length (89%, compared with 77% in the nonmodular cohort, p = 0.036), and a smaller offset difference was observed (6.1 versus 7.5 mm, p = 0.047) (Table 2). However, the proportions of patients having an offset difference within 5 mm were similar. The slightly enhanced accuracy of the modular neck in restoring the head center did not translate into better shortterm (1–2 years) outcome scores, revisions, or complications. A smaller proportion of patients in the modular neck
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cohort achieved equal apparent or clinical limb length at 1 year (85% versus 95%, p \ 0.001) and at 2 years (81% versus 94%, p \ 0.001). Harris hip and SF-12 scores were not different between the groups (Table 3), and modularity did not affect these measures, even after adjusting for age, sex, diabetes, diagnosis, and head size (Table 4). There were no differences in revision rates at 2 years. Freedom from revision at 2 years was similar between the two groups, at 99% (97%–100%) and 99% (98%–100%) for the nonmodular and modular neck groups, respectively (p = 0.94). There were 10 revisions, three in the nonmodular neck group (two for dislocations and one for fracture of the femur) and seven in the modular neck group (two for dislocations, one for fracture of the femur, two for deep infections, one for fracture of the greater trochanter, and one for other). Finally, there were no differences in complication rates between the two groups (Table 5). No other safety issues (such as trunnion fractures or neck dissociations) were encountered with the modular neck during the period of this study.
Discussion The purpose of using a modular implant is to improve the head center by allowing for independent leg length, offset and version, thus improving hip biomechanics. We evaluated clinical and radiographic differences between modular
Table 2. Radiographic subset of offset and limb length
Age
0.01
0.00
0.12
Male sex
0.01
0.88
0.38
0.37
0.12 0.37
0.036
Head size 36 mm
0.26
0.61
0.02
0.047
Head size 40 mm Modular
0.06 0.17
1.00 0.40
0.19 0.65
77% (75/97)
89% (82/97)
47% (46/97)
SF-12 mental
0.71
Leg length equality (within 5 mm)
38% (31/82)
SF-12 physical
0.21
p value
Offset difference B 5 mm
Harris hip score
0.48
Modular
6.1
Source
Diagnosis of osteoarthritis
Nonmodular
7.5
Table 4. Linear regression for change in scores (combined 1-year or 2-year score minus preoperative score)
Diabetes
Measurement
Offset difference (mm)
and nonmodular hip stems. Although modularity is widely used, its superiority in outcome scores, hip biomechanics, and complications have not been shown over those of conventional implants. We found that use of modular neck stems did not improve hip scores or reduce the likelihood of complications or reoperation. Because of their reported higher risks [1, 5, 24–27], there is no clear indication for modularity with a primary THA, unless the hip center cannot be achieved with a nonmodular stem, which is extremely rare. One weakness of this study is that patient allocation was not randomized between the two treatment groups. Essentially, we had two consecutive cohorts spanning 5 years with nonmodular neck cases from the earlier years and modular neck cases from the later years. Possible differences in technology, improvements to surgical technique, and other changes that are hard to characterize in the context of a retrospective study potentially could confound the results of this study. These differences would tend to favor the later group, making the small observed differences that favored the modular stems even less likely to be clinically important. This retrospective observational study was not powered to detect differences in uncommon
0.197
Numbers are p values.
Table 3. Hip function and quality-of-life measures (preoperative and postoperative matched samples) Outcome tool
Nonmodular (mean ± SD) Number of patients
Preoperative
Modular (mean ± SD) 1-year
2-year
Number of patients
Preoperative
1-year
2-year
Harris hip score
110
50 ± 13
90 ± 13
90 ± 15
356
52 ± 13
92 ± 11
92 ± 10
SF-2 physical health
115
30 ± 7
49 ± 9
49 ± 8
376
33 ± 8
50 ± 8
50 ± 9
SF-12 Mental health
133
53 ± 11
55 ± 8
55 ± 8
387
54 ±10
56 ± 6
56 ± 6
1- or 2- year
1- or 2- year
Harris hip score
199
50 ± 14
90 ± 14
523
52 ± 13
91 ± 12
SF-12 physical health
202
30 ±8
48 ±10
530
33 ± 8
50 ± 9
SF-12 mental health
216
53 ± 11
55 ± 8
531
54 ± 10
55 ± 7
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Modular Neck Femoral Implants Table 5. Summary of complications Complication type
Nonmodular* Number of complications
Modular* Complication rate (95% CI)
Number of complications
Complication rate (95% CI)
Seroma
0
0% (0%–1.3%)
1
0.2% (0%–1.0%)
Dislocation
5
1.8% (0.8%–4.1%)
5
0.8% (0.4%–2.0%)
Deep infection Superficial infection
4 0
1.4% (0.6%–3.6%) 0% (0%–1.3%)
4 2
0.7% (0.3%–1.7%) 0.3% (0.1%–1.2%)
Fracture
4
1.4% (0.6%–3.6%)
8
1.3% (0.7%–2.6%)
Wound drainage
1
0.4% (0.1%–2.0%)
0
0% (0%–0.6%)
General medical
5
1.8% (0.8%–4.1%)
5
0.8% (0.4%–2.0%)
* None of the complication rates were significantly different between the groups (p[ 0.20 for all comparisons); general medical complications were: one gastrointestinal bleeding, three neurologic, and one hematoma in the nonmodular neck cohort, and one urinary retention, one hematoma, and three deep vein thrombosis/pulmonary embolism in the modular neck cohort. All medical complications resolved.
complications, although the point estimates suggest that the likelihood of important differences is low, and if a difference cannot be detected in a study of nearly 900 THAs, it seems unlikely to be clinically important. In addition, accurate parameter assessment is difficult. For instance, limb-length estimation can be different between the clinical (apparent) and radiographic (true) assessments. This was a difficult aspect of this study and a shortcoming in that limb length can vary between the two measurement methods and with time in the same patient owing to multiple factors such as abduction contractures, pelvic obliquity, and scoliosis. Furthermore, patients’ perceptions of limb length usually come from the apparent limb length, which also can change with time. Using the latest scanograms or CT technology to improve the true limb-length measurement is not justified in this setting and probably would not eliminate all of the discrepancies between the two assessment methods in any case. The intangible variables of offset and version are even harder to accurately reproduce clinically over radiographic parameters. Such intangibles include stability, soft tissue laxity, presence of osteophytes, congenital deformity, impingement issues, and surgeon preference. Because radiographs were available for only a subset of patients, the radiographic results could be confounded by selection bias. In our short-term study, we showed that use of a modular neck improved the surgeon’s ability to achieve correct offset based on radiographic parameters. However, the slight improvement in offset difference with a modular neck was small and the clinical significance questionable. Most patients in either the modular or nonmodular cohorts were outside the 5 mm offset difference target. One could argue that the addition of more modular options does not necessarily make a procedure easier, since the criteria for using these options may not be as clearly documented. One of the learning curves we overcame was to evaluate limb
length first, which seemed to be easiest intraoperatively, and then determine offset and version. Although there are some situations that seem to call for unusual stem designs, perhaps including modularity, we find these situations rare and the majority of patients can be treated with nonmodular neck stems. In terms of limb-length equality, we found disparate results. The radiographic limb length was closer in the modular neck group, but the clinical (apparent) limb length, which we believe to be the more important parameter, favored the nonmodular neck group. In addition, none of the observed differences in terms of radiographic leg length or offset were associated with improvements in outcomes scores, with a reduction in the frequency of important complications, or with a reduction in the frequency of revision surgery. Although we saw no complications associated with modularity, our followup was short term. In addition, there have been studies showing that corrosion is the main concern with these taper junctions [1, 5, 24–27]. The soft tissue reactions and destruction seen with the abductor mechanisms in some of these reported cases of trunionosis is compelling. We have identified five cases of corrosion which either happened outside our study period or did not occur in patients who consented to inclusion in our registry. We felt these complications were significant and should be reported. All these cases occurred at the head-neck junction in 36-mm femoral heads. Three involved the modular stem and two involved the nonmodular stem. Among the three modular cases, one used a standard offset neck and the other two used extended necks (one straight and one anteverted). The nonmodular cases used extended necks. The modular stems were revised to a new head-neck junction and ceramic head. The nonmodular stems were revised to a ceramic head with a titanium sleeve. There were significant soft tissue reactions in two of these cases and de´bridement was performed to remove the metallic stained tissue and to stop the inflammatory response. Fretting
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corrosion is known to be a time-dependent process. Therefore, in this short-term series, this type of complication might not have had a chance to reveal itself, particularly in the modular neck group, which is the more recent of the two nearly sequential cohorts. Even though this modular design has a cobalt-chromium-titanium head-neck junction, the titanium-titanium neck-stem junction still could pose risk for corrosion. For these reasons the senior author (PJD) now almost exclusively uses nonmodular stems and ceramic femoral heads to decrease the possibility of corrosion. Of our 450 recent consecutive THAs, the modular stem was used only once in a slender female. The patient in this case had a modular stem inserted on the opposite side in an extremely varus hip to avoid excessively lengthening the leg. Although there were no fractures or stem failures in this large and relatively unselected series, modular neck stems did not lead to improved clinical hip scores, reduction in complications, or decreased likelihood of revision hip surgery, and there are known risks of modularity (pseudotumors, implant fractures, fretting, third-body wear, and trunnion corrosion) [1, 5, 24–27]. Therefore we currently would consider only modularity if the clinical hip center is anticipated to be an extreme outlier (ie, the clinical hip center is anticipated to be greater than 5 mm away from the desired target, resulting in a significant leg-length discrepancy or offset issue). Long-term followup is needed to assess the ultimate durability of modular implants and to determine the frequency of complications associated with modular devices. References 1. Atwood SA, Patten EW, Bozic KJ, Pruitt LA, Ries MD. Corrosion-induced fracture of a double-modular hip prosthesis: a case report. J Bone Joint Surg Am. 2010;92:1522–1525. 2. Berger RA, Jacobs JJ, Meneghini RM, Della Valle C, Paprosky W, Rosenberg AG. Rapid rehabilitation and recovery with minimally invasive total hip arthroplasty. Clin Orthop Relat Res. 2004;429:239–247. 3. Biedermann R, Tonin A, Krismer M, Rachbauer F, Eibl G, Stockl B. Reducing the risk of dislocation after total hip arthroplasty: the effect of orientation of the acetabular component. J Bone Joint Surg Br. 2005;87:762–769. 4. Bourne RB, Rorabeck CH. Soft tissue balancing: the hip. J Arthroplasty. 2002;17(4 suppl 1):17–22. 5. Cooper HJ, Della Valle CJ, Berger RA, Tetreault M, Paprosky WG, Sporer SM, Jacobs JJ. Corrosion at the head-neck taper as a cause for adverse local tissue reactions after total hip arthroplasty. J Bone Joint Surg Am. 2012;94:1655–1661. 6. D’Lima DD, Urquhart AG, Buehler KO, Walker RH, Colwell CW Jr. The effect of the orientation of the acetabular and femoral components on the range of motion of the hip at different headneck ratios. J Bone Joint Surg Am. 2000;82:315–321. 7. Duwelius PJ, Moller HS, Burkhart RL, Waller F, Wu Y, Grunkemeier GL. The economic impact of minimally invasive total hip arthroplasty. J Arthroplasty. 2011;26:883–885.
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