- Email: [email protected]
Even the Intraoperative Knowledge of Femoral Stem Anteversion Cannot Prevent Impingement in Total Hip Arthroplasty
The Journal of Arthroplasty xxx (2016) 1e6
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Original Article
Even the Intraoperative Knowledge of Femoral Stem Anteversion Cannot Prevent Impingement in Total Hip Arthroplasty Markus Weber, MD a, *, Michael L. Woerner, MD a, Ernst Sendtner, MD b, € llner, MD a, Joachim Grifka, MD a, Tobias F. Renkawitz, MD a Florian Vo a b
Department of Orthopedic Surgery, Regensburg University, Medical Center, Bad Abbach, Germany Department of Orthopedic and Trauma Surgery, Vilsbiburg Hospital, Vilsbiburg, Germany
a r t i c l e i n f o
a b s t r a c t
Article history: Received 23 January 2016 Received in revised form 16 April 2016 Accepted 21 April 2016 Available online xxx
Background: In this prospective study of 66 patients undergoing cementless total hip arthroplasty through a minimally invasive anterolateral approach, we evaluated the impact of an intraoperative hybrid combined anteversion technique on postoperative range of motion (ROM). Methods: After navigation of femoral stem anteversion, trial acetabular components were positioned manually, and their position recorded with navigation. Then, final components were implanted with navigation at the goals prescribed by the femur-first impingement detection algorithm. Postoperatively, three-dimensional computed tomographies were performed to determine achieved component position and model impingement-free ROM by virtual hip movement, which was compared with published values necessary for activities of daily living. This model was run a second time with the implants in the position selected by the surgeon rather than the navigation program. In addition, we researched into risk factors for ROM differences between the freehand and navigated cup position. Results: We found a lower flexion of 8.3 (8.8 , P < .001) and lower internal rotation of 9.2 (9.5 , P < .001) for the freehand implanted cups in contrast to a higher extension of 9.8 (11.8 , P < .001) compared with the navigation-guided technique. For activities of daily living, 58.9% (33/56) in the freehand group compared with 85.7% (48/56) in the navigation group showed free flexion (P < .001) and similarly 50.0% (28/56) compared with 76.8% (43/56) free internal rotation (P < .001). Body mass index, incision length, and cup size were identified as independent risk factors for reduced flexion and internal rotation in the freehand group. Conclusion: For implementation of a combined anteversion algorithm, intraoperative alignment guides for accurate cup positioning are required using a minimally invasive anterolateral approach. Obese patients are especially at risk of cup malpositioning. © 2016 Elsevier Inc. All rights reserved.
Keywords: combined anteversion femur first impingement range of motion total hip arthroplasty
Dislocation is a major patient-related and economic burden after total hip arthroplasty (THA) [1-3]. Recent studies have toppled the long-term tenet of Lewinnek's “safe zone” [4] because they found most postoperative dislocations within 40 ± 10 inclination and 15 ± 10 anteversion [5]. Therefore, novel concepts postulate
One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2016.04.024. The project on which this publication is based was funded by the German Federal Ministry of Education and Research (BMBF) under the grant number 01EZ0915. * Reprint requests: Markus Weber, MD, Department of Orthopedic Surgery, Regensburg University Medical Center, Asklepios Klinikum Bad Abbach, Kaiser-Karl V.-Allee 3, Bad Abbach 93077, Germany. http://dx.doi.org/10.1016/j.arth.2016.04.024 0883-5403/© 2016 Elsevier Inc. All rights reserved.
combined anteversion of cup and stem [6,7]. To realize combined anteversion in an intraoperative setting, different authors have recommended preparing the femur before the acetabulum and, consequently, orientating the cup in relation to the torsion of the femoral component [7,8]. However, the visual estimation of stem anteversion intraoperatively is susceptible to error even for experienced surgeons and, thus, cannot be regarded as reliable [9,10]. In contrast, the use of technical devices such as imageless navigation harbors the possibility to intraoperatively assess stem anteversion with high accuracy [11]. It remains unclear, though, if the orthopedic surgeon even with knowledge of femoral component anteversion is able to orientate the cup to prevent impingement. Hence, we developed a hybrid technique for THA and intraoperatively measured the torsion of the final broach using imageless navigation. We hypothesized, if the femoral anteversion is known, the cup can be positioned free hand by an experienced orthopedic surgeon
2
M. Weber et al. / The Journal of Arthroplasty xxx (2016) 1e6
Fig. 1. Flow chart of the study group. MIS, minimally invasive; THA, total hip arthroplasty.
in a position guaranteeing similar free postoperative range of motion (ROM) than a recently described fully navigation-guided implantation including an intraoperative impingement detection algorithm for ideal cup placement [11]. Furthermore, we researched into risk factors for differences in ROM between the freehand and navigation-guided cup implantation. Patients and Methods In the course of a registered, prospective controlled trial (DRKS00000739, German Clinical Trials Register), three-
dimensional computed tomographic scans (3D-CT) were obtained after minimally invasive cementless THA. The present study is an independent subgroup analysis of the navigated cohort. A sovereign power calculation was performed for investigation of postoperative ROM in this analysis on a two-sided 5% significance level. We set the difference of ROM at 5 including a standard deviation of 10 . Based on these considerations, a total sample size of 44 achieved a power of 90% using a two-tailed t test for dependent variables (GPower 3.1, Düsseldorf, Germany). The investigation was approved by the local medical ethics committee (no.: 10-1210263).
M. Weber et al. / The Journal of Arthroplasty xxx (2016) 1e6
3
Fig. 2. Intraoperative anteversion measurement of final broach using imageless navigation. The green arrow shows the anteversion of the final broach.
According to the study protocol, eligible participants were patients between the ages of 50 and 75 years with an American Society of Anesthesiologists (ASA) score 3 who were admitted for primary cementless unilateral THA due to primary or secondary osteoarthritis at our Department of Orthopedic Surgery at Regensburg University Medical Center, Germany. Figure 1 summarizes the data on the participants in the study. In all patients, THA was performed in the lateral decubitus position using a minimally invasive single-incision anterolateral approach by 4 orthopedic surgeons [12]. Two surgeons (M.Wo., T.R.) had experience of over 10 years of THA and 2 surgeons (E.S., J.G.) of over 20 years of THA. Femoral stem anteversion was intraoperatively measured using an imageless navigation system (Hip 6.0 prototype; Brainlab, Feldkirchen, Germany) with a newly developed “femur-first” prototype software as recently described [7,13]. In brief, for the registration process, the medial and lateral aspects of the epicondyles and ankle malleoli were registered. The midpoints of both epicondyles and ankle malleoli combined with the piriformis fossa point formed the ankle epicondyle piriformis plane. The normal to the ankle epicondyle piriformis plane is coincident with the condylar axis [13] and, thus, was used to define the anteversion of the final broach demonstrated on a screen intraoperatively (Fig. 2). Afterward, the navigation screen was covered, the final broach was removed, and the acetabulum was reamed. Then, the orthopedic surgeon inserted a trial cup free hand taking into account the measured femoral anteversion along with the patient individual anatomic situation of the acetabulum according to his experience. This position of the trial cup was registered, and then, the cup was removed. Meanwhile, the navigation system calculated an impingement-free coverage-optimized acetabular component position based on the information gathered during registration and preparation. On the femoral side, this included the resection plane along with the position and version of the final broach. On the acetabular side, rim points were registered, and the anterior pelvic plane used as reference. The accuracy of the navigation software modeling ROM without osseous and prosthetic impingement has been described in a previous study with differences below 5
compared to 3D-CT [11]. Guided by the three-dimensional projections on the uncovered navigation screen, the acetabular component was inserted, followed by insertion of the femoral component. In all patients, press-fit acetabular components with neutral liners and cement-free hydroxyapatite-coated stems (Pinnacle cup, Corail stem; DePuy, Warsaw, IN) with metal heads of 32 mm were used. Six weeks postoperatively, a pelvic/femoral 3DCT was performed (Somatom Sensation 16; Siemens, Erlangen, Germany). In total, 56 data sets were included for final analysis. Anthropometric characteristics of the study group as well as preoperative clinical ROM values are shown in Table 1 [12]. Independent manual CT segmentation was performed on the pelvic bone and on the metal acetabular and femoral components by an independent external institute (Fraunhofer MEVIS, Bremen, Germany), blinded to individual patient data. In addition, reference landmarks for providing the pelvic and femoral coordinate system were defined.
Table 1 Anthropometric Characteristics of the Study Group (n ¼ 56). Gender (female) Age (y) BMI (kg/m2) Treatment side (right) ASA 1 ASA 2 ASA 3 Kellgren-Lawrence score Preoperative ROM ( ) Flexion Internal rotation External rotation Abduction Adduction
33 62.4 27.0 27 9 32 15 8
(58.9%) (SD, 7.5) (SD, 4.1) (48.2%) (16.1%) (57.1%) (26.8%) (6-10)
90.6 2.8 15.4 20.7 7.4
(SD, (SD, (SD, (SD, (SD,
9.6) 5.3) 10.1) 8.7) 5.6)
For categorical data values are given as relative and absolute frequencies; for quantitative data, values are given as mean (standard deviation) or median (range). SD, standard deviation; BMI, body mass index; ASA, American Society of Anesthesiologists score; ROM, range of motion.
4
M. Weber et al. / The Journal of Arthroplasty xxx (2016) 1e6
This included both anterior superior iliac spine and pubic tubercle points to define the pelvic coordinate system and femoral head center, mechanical axis, and condyle axis to define the femoral coordinate system. Based on the manually segmented bone models, the postoperative ROM was calculated by a previously described algorithm which automatically determines osseous and prosthetic impingement by virtually moving the leg until a collision between the three-dimensional objects occurs [7,11]. For reproducibility, ROM calculations were performed twice, and the mean of the 2 measurements was used for further analysis. The high accuracy of this 3D-CT method was demonstrated in a previous study [14]. For every single patient, ROM analysis was performed twice, first using the freehand cup position and second using the final navigationoptimized cup position. We then comparatively assessed the proportion of patients reaching the hip joint ROM configurations without impingement for activities of daily living (ADLs) as given by Davis et al, Miki et al, and Turley et al with at least 110 of flexion, 30 of extension, 50 of abduction, 30 of adduction, 45 of external rotation during extension, and 30 of internal rotation during 90 of hip flexion, respectively [15-17]. For statistical analysis, normally and nonnormally distributed continuous data are presented as mean (standard deviation) or median (range), respectively. Group comparisons were performed by Wilcoxon tests on a 5% significance level. Absolute and relative frequencies were given for categorical data and compared between groups by McNemar tests on a 5% significance level. Multivariate logistic regression including surgical experience, gender, treatment side, body mass index (BMI), cup size, Kellgren score, and length of skin incision was performed to search for risk factors influencing a deviation in ROM between the freehand and navigation-guided group. IBM SPSS Statistics 23 (SPSS Inc, Chicago, IL) was used for analysis.
Table 2 Intraoperative Characteristics of the Study Group (n ¼ 56). Femoral component size Femoral anteversion ( ) Cup size Cup inclination ( ) nav Cup anteversion ( ) nav Cup inclination ( ) fh Cup anteversion ( ) fh Leg length differencesa (mm) Offset differencesa (mm)
12 9.0 54 42.4 18.6 41.7 10.8 0.7 0.4
(10-16) (SD, 10.3) (48-62) (SD, 5.1) (SD, 6.7) (6.5) (8.3) (2.5) (2.2)
Quantitative data values are given as mean (standard deviation) or median (range). SD, standard deviation; nav, navigation-guided cup implantation; fh, freehand implanted cups. a Differences between the operated and nonoperated side.
Regarding clinical hip stability, we observed in 1 patient a posterior hip dislocation 2 weeks after surgery. A CT analysis was undertaken which showed an acetabular component position of 41 inclination and 18 acetabular anteversion and a stem anteversion of 7. The postoperative leg length discrepancy was 1 mm longer compared to the contralateral side. Offset was restored to equal length in relation to the contralateral side. Closed reduction and revision surgery on the following day were performed, following the hospital’s standard treatment protocol for early nontraumatic dislocations. Intraoperatively, impingement between the unusually prominent inferior iliac spine and the greater trochanter in 90 of flexion and 20 of internal rotation was detected. Offset was improved by changing the standard acetabular component liner to an offset liner (4 mm) and by changing the head-neck length.
Results
Discussion
Intraoperative characteristics of the implant position and anatomic reconstruction of the study group are demonstrated in Table 2. Mean cup inclination was 41.7 (6.5 ) in the freehand group and 42.4 (5.1 ) in the navigation group, respectively. Mean cup anteversion was measured with 10.8 (8.3 ) for freehand implanted and 18.6 (6.7 ) for navigated cups. ROM without prosthetic and osseous impingement was 8.3 (8.8 , P < .001) less for flexion and 9.2 (9.5 , P < .001) less for internal rotation at 90 flexion in the freehand implanted cups than in navigation-guided technique. In contrast, the freehand group showed a 9.8 (11.8 , P < .001) higher extension compared with the navigated cup group. ROM differences below 5 were found for higher adduction 3.2 (6.2 , P < .001) and higher external rotation 1.0 (3.3 , P ¼ .006) if the cup implantation was performed free hand by the orthopedic surgeon with knowledge of the stem anteversion compared with the fully navigation-guided algorithm (Fig. 3). Regarding ADL, 58.9% (33/56) in the freehand group and 85.7% (48/56) in the navigation group reached the ROM boundaries for ADL in flexion (P < .001). Similarly, 50.0% (28/56) in the freehand group and 76.8% (43/56) in the navigation group showed impingement-free ROM for ADL in internal rotation at 90 flexion (P < .001, Fig. 4). Researching into risk factors for lower ROM in the freehand implanted cups, we found in a multivariate analysis, BMI (P ¼ .03) to be associated with reduced flexion. In terms of internal rotation at 90 flexion, BMI (P ¼ .004), cup size (P ¼ .04), and length of skin incision (P ¼ .04) were identified as risk factors for differences above 5 between the freehand and navigation-guided group (Table 3).
The purpose of this study was to determine whether the orthopedic surgeon knowing the torsion of femoral component is able to adjust the cup position free hand in an intraoperative femurfirst setting to provide a postoperative free ROM without osseous and prosthetic impingement. In a virtual 3D-ROM analysis, we
Fig. 3. Absolute range of motion for the navigation-guided and freehand implanted cups. nav, navigation group; free hand, freehand group; Int Rot, internal rotation at 90 flexion; Ext Rot, external rotation.
M. Weber et al. / The Journal of Arthroplasty xxx (2016) 1e6
Fig. 4. Impingement-free range of motion for activities of daily living.
found a 8.3 lower flexion and 9.2 lower internal rotation at 90 flexion in the freehand implanted group compared with a fully navigation-guided setting with an impingement detection algorithm. There are several limitations of this study. First, our 3DCTebased ROM analysis was able to detect prosthetic and/or osseous impingement. However, we did not account for soft-tissue impingement. In more obese patients, soft-tissue restrictions may limit ROM boundaries postoperatively. Second, we did not include the influence of femoral tilt (anterior bow of the femur) in our study. Although previous studies describe an impact of femoral tilt on postoperative ROM [18], the authors feel intraoperative assessment of femoral tilt has not been resolved yet. Therefore, we focused on intraoperative measurement of femoral stem version. Third, in our femur-first hybrid technique, we used navigation to determine the anteversion of the cementless femoral component and, then, implanted the cup free hand. This setting is not intended for clinical practice. Why should the orthopedic surgeon quit navigation after measurement of the femoral stem version? Therefore, easier and more practicable technical tools such as trial heads have to be developed for a freehand technique with intraoperative stem version estimation. However, this study did not intend to present a novel algorithm in femur-first THA but focused to assess the visual accuracy in preventing impingement, if the anteversion of the stem is a known parameter. Fourth, we used a minimally invasive anterolateral approach in the present study. The choice of approach may influence the accuracy of visual freehand cup implantation. Thus, Table 3 Multivariate Analysis of Risk Factors Associated With a Reduced ROM of at Least 5 in the Freehand Group Compared With the Navigated Group for Flexion and Internal Rotation at 90 Flexion. Risk Factors
Surgical experience >20 y BMI Treatment side (right) Gender (male) Cup size Kellgren score Length of skin incision
Flexion
Internal Rotation
Multivariate Analysis (HR, 95% CI)
P
Multivariate Analysis (HR, 95% CI)
P
0.83 1.22 1.79 2.02 1.29 0.52 0.60
.79 .03 .39 .54 .24 .16 .07
1.53 1.43 0.72 0.40 1.82 0.51 0.51
.58 .004 .67 .50 .04 .19 .04
(0.22-3.20) (1.02-1.46) (0.48-6.67) (0.22-18.88) (0.85-1.94) (0.21-1.29) (0.34-1.05)
(0.34-6.83) (1.12-1.81) (0.16-3.22) (0.03-5.56) (1.03-3.20) (0.18-1.40) (0.27-0.98)
HR, hazard ratio; CI, confidence interval; BMI, body mass index.
5
the results might be different in a posterior or straight lateral approach. In the present study, mean cup anteversion was 7.8 higher in the fully navigation-guided group. If the surgeons had aimed for higher anteversion, the difference between both techniques might have varied. Fifth, analysis were performed by virtual ROM analysis using 3D-CT. Owing to the methodology in this study, it was not possible to obtain comparative clinical data [19] on outcome enabling a comparison between the freehand and fully navigated technique. Therefore, the results do not allow correlation to important clinical parameter or outcome, such as dislocation, wear, or revision. A strength of the study is the fact that we used a single manufacturer's THA design manufacturer (CCD 135 , cone 12/14, head 32-mm diameter, head neck ratio 3.50 for extension/flexion, and 2.66 for abduction/adduction) thereby minimizing confounding factors. Furthermore, we analyzed biomechanical reconstruction accuracy such as leg length and offset discrepancies also possibly affecting postoperative ROM. Any difference with regard to individual hip joint ROM outcome in our analysis is due purely to the operative technique, rather than the prosthetic design of the component. Theoretically, femoral stems with a modular neck could allow control of femoral version and varus/valgus angulation of the neck [6,20]. However, such modularity has been the source of serious concern because of the potential release of metal ions [21]. Our hypothesis was not supported by the results of the study. Flexion and internal rotation at 90 flexion were 8.3 and 9.2 , respectively, lower in the freehand group than in the navigationguided group. The clinical relevance of these ROM differences was emphasized by a lower rate of patients with free ROM for ADL in the freehand group with 58.9% compared with navigation group 85.7% for flexion and similarly with 50,0% compared with 76.8% for internal rotation at 90 flexion. This means that anterior impingement and consecutively posterior dislocation might be increased in our hybrid technique, with freehand cup implantation in relation to the measured intraoperative stem anteversion, compared with the totally navigation-guided cup implantation. In contrast, we found a 9.8 higher extension in patients with freehand implanted cups than in the totally navigated patients. However, this difference was not clinically relevant because the intended ROM of 30 extension for ADL was reached in over 90% in both groups. Compared with previous studies, the ROM values and impingement rates of our hybrid technique were similar to conventional techniques in THA without knowledge of the femoral stem version using the same minimally invasive anterolateral approach [7]. Nevertheless, mean cup anteversion was 7.8 higher in the fully navigation-guided technique compared with the hybrid method. Therefore, the observed differences in ROM might be due to insufficient cup anteversion in relation to a mean stem anteversion of 9.0 . The difficulty in estimating the version of the femoral component intraoperatively has been described in literature [9]. Therefore, we sought to minimize the effect of inaccuracies in visual stem version assessment and concentrated on the accuracy of cup position in relation to the known femoral anteversion in a femur-first setting. Regarding the posterior dislocation in the study group, the anterior inferior iliac spine was not registered and thus not part of the intraoperative impingement detection algorithm. Therefore, the navigation system was not able to detect and prevent this form of impingement in this particular case. Even with navigation, it is not possible to prevent dislocation in all circumstances. Considering the fact that dislocation remains one of the main reasons for early revision surgery [22], it seems that the surgeon needs to control component position intraoperatively. Because restoration of biomechanics also plays a crucial role in preventing impingement in THA, we also aimed to investigate leg length and offset discrepancies in relation to the unaffected
6
M. Weber et al. / The Journal of Arthroplasty xxx (2016) 1e6
contralateral side. Both leg length and offset were restored within a mean difference under 1 mm and standard deviation below 3 mm. Researching into risk factors for the clinically relevant lower flexion and internal rotation in our freehand group, we identified high BMI to be associated with decreased flexion above 5 compared with the navigation-guided cup positioning. Similarly, high BMI, small skin incisions, and higher cup sizes correlated independently with lower internal rotation above 5 . Summarizing, especially obese patients are at risk of cup malpositioning by visual estimation, and a clear surgical exposition of the situs is essential for correct component alignment in THA. To the best of our knowledge, this is the first study evaluating intraoperative implementation of a hybrid femur-first algorithm with freehand cup positioning after measuring femoral stem anteversion regarding their impact on postoperative ROM after THA based on 3D-CT analysis. In summary, visual cup alignment in a combined anteversion setting failed to enable free flexion and internal rotation because of insufficient cup anteversion. High BMI was identified as a risk factor for cup malpositioning. Future models within the concept of combined anteversion for THA will, therefore, need to use an intraoperative cup alignment guide to ensure impingement-free ROM. Acknowledgments The authors thank Dipl-Ing Mario Schubert for his support in range of motion calculations. References 1. Abdel MP, Cross MB, Yasen AT, et al. The functional and financial impact of isolated and recurrent dislocation after total hip arthroplasty. Bone Jt J 2015;97B(8):1046. 2. Preininger B, Haschke F, Perka C. [Diagnostics and therapy of luxation after total hip arthroplasty]. Orthopade 2014;43(1):54. 3. Hube R, Dienst M, von Roth P. [Complications after minimally invasive total hip arthroplasty]. Orthopade 2014;43(1):47. 4. Lewinnek GE, Lewis JL, Tarr R, et al. Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am 1978;60(2):217.
5. Abdel MP, von Roth P, Jennings MT, et al. What safe zone? the vast majority of dislocated THAs are within the Lewinnek safe zone for acetabular component position. Clin Orthop Relat Res 2016;474:386. 6. Widmer KH, Zurfluh B. Compliant positioning of total hip components for optimal range of motion. J Orthop Res 2004;22(4):815. 7. Renkawitz T, Weber M, Springorum HR, et al. Impingement-free range of movement, acetabular component cover and early clinical results comparing ‘femur-first’ navigation and ‘conventional’ minimally invasive total hip arthroplasty: a randomised controlled trial. Bone Jt J 2015;97B(7):890. 8. Sendtner E, Muller M, Winkler R, et al. [Femur first in hip arthroplastydthe concept of combined anteversion]. Z Orthop Unfall 2010;148(2):185. 9. Dorr LD, Wan Z, Malik A, et al. A comparison of surgeon estimation and computed tomographic measurement of femoral component anteversion in cementless total hip arthroplasty. J Bone Joint Surg Am 2009;91(11):2598. 10. Woerner M, Sendtner E, Springorum R, et al. Visual intraoperative estimation of cup and stem position is not reliable in minimally invasive hip arthroplasty. Acta Orthop 2016 [Epub ahead of print]. 11. Renkawitz T, Haimerl M, Dohmen L, et al. Development and evaluation of an image-free computer-assisted impingement detection technique for total hip arthroplasty. Proc Inst Mech Eng H 2012;226(12):911. 12. Michel MC, Witschger P. MicroHip: a minimally invasive procedure for total hip replacement surgery using a modified Smith-Peterson approach. Ortop Traumatol Rehabil 2007;9(1):46. 13. Turley GA, Ahmed SM, Williams MA, et al. Validation of the femoral anteversion measurement method used in imageless navigation. Comput Aided Surg 2012;17(4):187. 14. Weber M, Weber T, Woerner M, et al. The impact of standard combined anteversion definitions on gait and clinical outcome within one year after total hip arthroplasty. Int Orthop 2015;39:2323. 15. Davis KE, Ritter MA, Berend ME, et al. The importance of range of motion after total hip arthroplasty. Clin Orthop Relat Res 2007;465:180. 16. Miki H, Yamanashi W, Nishii T, et al. Anatomic hip range of motion after implantation during total hip arthroplasty as measured by a navigation system. J Arthroplasty 2007;22(7):946. 17. Turley GA, Ahmed SM, Williams MA, et al. Establishing a range of motion boundary for total hip arthroplasty. Proc Inst Mech Eng H 2011;225(8):769. 18. Renkawitz T, Haimerl M, Dohmen L, et al. The association between femoral tilt and impingement-free range-of-motion in total hip arthroplasty. BMC Musculoskelet Disord 2012;13:65. 19. Grifka J, Keshmiri A, Maderbacher G, et al. [Clinical examination of the hip joint in adults]. Orthopade 2014;43(12):1115. 20. Dorr LD, Malik A, Dastane M, et al. Combined anteversion technique for total hip arthroplasty. Clin Orthop Relat Res 2009;467(1):119. 21. Krishnan H, Krishnan SP, Blunn G, et al. Modular neck femoral stems. Bone Jt J 2013;95-B(8):1011. 22. Bozic KJ, Kurtz SM, Lau E, et al. The epidemiology of revision total hip arthroplasty in the United States. J Bone Joint Surg Am 2009;91(1):128.
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Original Article
Even the Intraoperative Knowledge of Femoral Stem Anteversion Cannot Prevent Impingement in Total Hip Arthroplasty Markus Weber, MD a, *, Michael L. Woerner, MD a, Ernst Sendtner, MD b, € llner, MD a, Joachim Grifka, MD a, Tobias F. Renkawitz, MD a Florian Vo a b
Department of Orthopedic Surgery, Regensburg University, Medical Center, Bad Abbach, Germany Department of Orthopedic and Trauma Surgery, Vilsbiburg Hospital, Vilsbiburg, Germany
a r t i c l e i n f o
a b s t r a c t
Article history: Received 23 January 2016 Received in revised form 16 April 2016 Accepted 21 April 2016 Available online xxx
Background: In this prospective study of 66 patients undergoing cementless total hip arthroplasty through a minimally invasive anterolateral approach, we evaluated the impact of an intraoperative hybrid combined anteversion technique on postoperative range of motion (ROM). Methods: After navigation of femoral stem anteversion, trial acetabular components were positioned manually, and their position recorded with navigation. Then, final components were implanted with navigation at the goals prescribed by the femur-first impingement detection algorithm. Postoperatively, three-dimensional computed tomographies were performed to determine achieved component position and model impingement-free ROM by virtual hip movement, which was compared with published values necessary for activities of daily living. This model was run a second time with the implants in the position selected by the surgeon rather than the navigation program. In addition, we researched into risk factors for ROM differences between the freehand and navigated cup position. Results: We found a lower flexion of 8.3 (8.8 , P < .001) and lower internal rotation of 9.2 (9.5 , P < .001) for the freehand implanted cups in contrast to a higher extension of 9.8 (11.8 , P < .001) compared with the navigation-guided technique. For activities of daily living, 58.9% (33/56) in the freehand group compared with 85.7% (48/56) in the navigation group showed free flexion (P < .001) and similarly 50.0% (28/56) compared with 76.8% (43/56) free internal rotation (P < .001). Body mass index, incision length, and cup size were identified as independent risk factors for reduced flexion and internal rotation in the freehand group. Conclusion: For implementation of a combined anteversion algorithm, intraoperative alignment guides for accurate cup positioning are required using a minimally invasive anterolateral approach. Obese patients are especially at risk of cup malpositioning. © 2016 Elsevier Inc. All rights reserved.
Keywords: combined anteversion femur first impingement range of motion total hip arthroplasty
Dislocation is a major patient-related and economic burden after total hip arthroplasty (THA) [1-3]. Recent studies have toppled the long-term tenet of Lewinnek's “safe zone” [4] because they found most postoperative dislocations within 40 ± 10 inclination and 15 ± 10 anteversion [5]. Therefore, novel concepts postulate
One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2016.04.024. The project on which this publication is based was funded by the German Federal Ministry of Education and Research (BMBF) under the grant number 01EZ0915. * Reprint requests: Markus Weber, MD, Department of Orthopedic Surgery, Regensburg University Medical Center, Asklepios Klinikum Bad Abbach, Kaiser-Karl V.-Allee 3, Bad Abbach 93077, Germany. http://dx.doi.org/10.1016/j.arth.2016.04.024 0883-5403/© 2016 Elsevier Inc. All rights reserved.
combined anteversion of cup and stem [6,7]. To realize combined anteversion in an intraoperative setting, different authors have recommended preparing the femur before the acetabulum and, consequently, orientating the cup in relation to the torsion of the femoral component [7,8]. However, the visual estimation of stem anteversion intraoperatively is susceptible to error even for experienced surgeons and, thus, cannot be regarded as reliable [9,10]. In contrast, the use of technical devices such as imageless navigation harbors the possibility to intraoperatively assess stem anteversion with high accuracy [11]. It remains unclear, though, if the orthopedic surgeon even with knowledge of femoral component anteversion is able to orientate the cup to prevent impingement. Hence, we developed a hybrid technique for THA and intraoperatively measured the torsion of the final broach using imageless navigation. We hypothesized, if the femoral anteversion is known, the cup can be positioned free hand by an experienced orthopedic surgeon
2
M. Weber et al. / The Journal of Arthroplasty xxx (2016) 1e6
Fig. 1. Flow chart of the study group. MIS, minimally invasive; THA, total hip arthroplasty.
in a position guaranteeing similar free postoperative range of motion (ROM) than a recently described fully navigation-guided implantation including an intraoperative impingement detection algorithm for ideal cup placement [11]. Furthermore, we researched into risk factors for differences in ROM between the freehand and navigation-guided cup implantation. Patients and Methods In the course of a registered, prospective controlled trial (DRKS00000739, German Clinical Trials Register), three-
dimensional computed tomographic scans (3D-CT) were obtained after minimally invasive cementless THA. The present study is an independent subgroup analysis of the navigated cohort. A sovereign power calculation was performed for investigation of postoperative ROM in this analysis on a two-sided 5% significance level. We set the difference of ROM at 5 including a standard deviation of 10 . Based on these considerations, a total sample size of 44 achieved a power of 90% using a two-tailed t test for dependent variables (GPower 3.1, Düsseldorf, Germany). The investigation was approved by the local medical ethics committee (no.: 10-1210263).
M. Weber et al. / The Journal of Arthroplasty xxx (2016) 1e6
3
Fig. 2. Intraoperative anteversion measurement of final broach using imageless navigation. The green arrow shows the anteversion of the final broach.
According to the study protocol, eligible participants were patients between the ages of 50 and 75 years with an American Society of Anesthesiologists (ASA) score 3 who were admitted for primary cementless unilateral THA due to primary or secondary osteoarthritis at our Department of Orthopedic Surgery at Regensburg University Medical Center, Germany. Figure 1 summarizes the data on the participants in the study. In all patients, THA was performed in the lateral decubitus position using a minimally invasive single-incision anterolateral approach by 4 orthopedic surgeons [12]. Two surgeons (M.Wo., T.R.) had experience of over 10 years of THA and 2 surgeons (E.S., J.G.) of over 20 years of THA. Femoral stem anteversion was intraoperatively measured using an imageless navigation system (Hip 6.0 prototype; Brainlab, Feldkirchen, Germany) with a newly developed “femur-first” prototype software as recently described [7,13]. In brief, for the registration process, the medial and lateral aspects of the epicondyles and ankle malleoli were registered. The midpoints of both epicondyles and ankle malleoli combined with the piriformis fossa point formed the ankle epicondyle piriformis plane. The normal to the ankle epicondyle piriformis plane is coincident with the condylar axis [13] and, thus, was used to define the anteversion of the final broach demonstrated on a screen intraoperatively (Fig. 2). Afterward, the navigation screen was covered, the final broach was removed, and the acetabulum was reamed. Then, the orthopedic surgeon inserted a trial cup free hand taking into account the measured femoral anteversion along with the patient individual anatomic situation of the acetabulum according to his experience. This position of the trial cup was registered, and then, the cup was removed. Meanwhile, the navigation system calculated an impingement-free coverage-optimized acetabular component position based on the information gathered during registration and preparation. On the femoral side, this included the resection plane along with the position and version of the final broach. On the acetabular side, rim points were registered, and the anterior pelvic plane used as reference. The accuracy of the navigation software modeling ROM without osseous and prosthetic impingement has been described in a previous study with differences below 5
compared to 3D-CT [11]. Guided by the three-dimensional projections on the uncovered navigation screen, the acetabular component was inserted, followed by insertion of the femoral component. In all patients, press-fit acetabular components with neutral liners and cement-free hydroxyapatite-coated stems (Pinnacle cup, Corail stem; DePuy, Warsaw, IN) with metal heads of 32 mm were used. Six weeks postoperatively, a pelvic/femoral 3DCT was performed (Somatom Sensation 16; Siemens, Erlangen, Germany). In total, 56 data sets were included for final analysis. Anthropometric characteristics of the study group as well as preoperative clinical ROM values are shown in Table 1 [12]. Independent manual CT segmentation was performed on the pelvic bone and on the metal acetabular and femoral components by an independent external institute (Fraunhofer MEVIS, Bremen, Germany), blinded to individual patient data. In addition, reference landmarks for providing the pelvic and femoral coordinate system were defined.
Table 1 Anthropometric Characteristics of the Study Group (n ¼ 56). Gender (female) Age (y) BMI (kg/m2) Treatment side (right) ASA 1 ASA 2 ASA 3 Kellgren-Lawrence score Preoperative ROM ( ) Flexion Internal rotation External rotation Abduction Adduction
33 62.4 27.0 27 9 32 15 8
(58.9%) (SD, 7.5) (SD, 4.1) (48.2%) (16.1%) (57.1%) (26.8%) (6-10)
90.6 2.8 15.4 20.7 7.4
(SD, (SD, (SD, (SD, (SD,
9.6) 5.3) 10.1) 8.7) 5.6)
For categorical data values are given as relative and absolute frequencies; for quantitative data, values are given as mean (standard deviation) or median (range). SD, standard deviation; BMI, body mass index; ASA, American Society of Anesthesiologists score; ROM, range of motion.
4
M. Weber et al. / The Journal of Arthroplasty xxx (2016) 1e6
This included both anterior superior iliac spine and pubic tubercle points to define the pelvic coordinate system and femoral head center, mechanical axis, and condyle axis to define the femoral coordinate system. Based on the manually segmented bone models, the postoperative ROM was calculated by a previously described algorithm which automatically determines osseous and prosthetic impingement by virtually moving the leg until a collision between the three-dimensional objects occurs [7,11]. For reproducibility, ROM calculations were performed twice, and the mean of the 2 measurements was used for further analysis. The high accuracy of this 3D-CT method was demonstrated in a previous study [14]. For every single patient, ROM analysis was performed twice, first using the freehand cup position and second using the final navigationoptimized cup position. We then comparatively assessed the proportion of patients reaching the hip joint ROM configurations without impingement for activities of daily living (ADLs) as given by Davis et al, Miki et al, and Turley et al with at least 110 of flexion, 30 of extension, 50 of abduction, 30 of adduction, 45 of external rotation during extension, and 30 of internal rotation during 90 of hip flexion, respectively [15-17]. For statistical analysis, normally and nonnormally distributed continuous data are presented as mean (standard deviation) or median (range), respectively. Group comparisons were performed by Wilcoxon tests on a 5% significance level. Absolute and relative frequencies were given for categorical data and compared between groups by McNemar tests on a 5% significance level. Multivariate logistic regression including surgical experience, gender, treatment side, body mass index (BMI), cup size, Kellgren score, and length of skin incision was performed to search for risk factors influencing a deviation in ROM between the freehand and navigation-guided group. IBM SPSS Statistics 23 (SPSS Inc, Chicago, IL) was used for analysis.
Table 2 Intraoperative Characteristics of the Study Group (n ¼ 56). Femoral component size Femoral anteversion ( ) Cup size Cup inclination ( ) nav Cup anteversion ( ) nav Cup inclination ( ) fh Cup anteversion ( ) fh Leg length differencesa (mm) Offset differencesa (mm)
12 9.0 54 42.4 18.6 41.7 10.8 0.7 0.4
(10-16) (SD, 10.3) (48-62) (SD, 5.1) (SD, 6.7) (6.5) (8.3) (2.5) (2.2)
Quantitative data values are given as mean (standard deviation) or median (range). SD, standard deviation; nav, navigation-guided cup implantation; fh, freehand implanted cups. a Differences between the operated and nonoperated side.
Regarding clinical hip stability, we observed in 1 patient a posterior hip dislocation 2 weeks after surgery. A CT analysis was undertaken which showed an acetabular component position of 41 inclination and 18 acetabular anteversion and a stem anteversion of 7. The postoperative leg length discrepancy was 1 mm longer compared to the contralateral side. Offset was restored to equal length in relation to the contralateral side. Closed reduction and revision surgery on the following day were performed, following the hospital’s standard treatment protocol for early nontraumatic dislocations. Intraoperatively, impingement between the unusually prominent inferior iliac spine and the greater trochanter in 90 of flexion and 20 of internal rotation was detected. Offset was improved by changing the standard acetabular component liner to an offset liner (4 mm) and by changing the head-neck length.
Results
Discussion
Intraoperative characteristics of the implant position and anatomic reconstruction of the study group are demonstrated in Table 2. Mean cup inclination was 41.7 (6.5 ) in the freehand group and 42.4 (5.1 ) in the navigation group, respectively. Mean cup anteversion was measured with 10.8 (8.3 ) for freehand implanted and 18.6 (6.7 ) for navigated cups. ROM without prosthetic and osseous impingement was 8.3 (8.8 , P < .001) less for flexion and 9.2 (9.5 , P < .001) less for internal rotation at 90 flexion in the freehand implanted cups than in navigation-guided technique. In contrast, the freehand group showed a 9.8 (11.8 , P < .001) higher extension compared with the navigated cup group. ROM differences below 5 were found for higher adduction 3.2 (6.2 , P < .001) and higher external rotation 1.0 (3.3 , P ¼ .006) if the cup implantation was performed free hand by the orthopedic surgeon with knowledge of the stem anteversion compared with the fully navigation-guided algorithm (Fig. 3). Regarding ADL, 58.9% (33/56) in the freehand group and 85.7% (48/56) in the navigation group reached the ROM boundaries for ADL in flexion (P < .001). Similarly, 50.0% (28/56) in the freehand group and 76.8% (43/56) in the navigation group showed impingement-free ROM for ADL in internal rotation at 90 flexion (P < .001, Fig. 4). Researching into risk factors for lower ROM in the freehand implanted cups, we found in a multivariate analysis, BMI (P ¼ .03) to be associated with reduced flexion. In terms of internal rotation at 90 flexion, BMI (P ¼ .004), cup size (P ¼ .04), and length of skin incision (P ¼ .04) were identified as risk factors for differences above 5 between the freehand and navigation-guided group (Table 3).
The purpose of this study was to determine whether the orthopedic surgeon knowing the torsion of femoral component is able to adjust the cup position free hand in an intraoperative femurfirst setting to provide a postoperative free ROM without osseous and prosthetic impingement. In a virtual 3D-ROM analysis, we
Fig. 3. Absolute range of motion for the navigation-guided and freehand implanted cups. nav, navigation group; free hand, freehand group; Int Rot, internal rotation at 90 flexion; Ext Rot, external rotation.
M. Weber et al. / The Journal of Arthroplasty xxx (2016) 1e6
Fig. 4. Impingement-free range of motion for activities of daily living.
found a 8.3 lower flexion and 9.2 lower internal rotation at 90 flexion in the freehand implanted group compared with a fully navigation-guided setting with an impingement detection algorithm. There are several limitations of this study. First, our 3DCTebased ROM analysis was able to detect prosthetic and/or osseous impingement. However, we did not account for soft-tissue impingement. In more obese patients, soft-tissue restrictions may limit ROM boundaries postoperatively. Second, we did not include the influence of femoral tilt (anterior bow of the femur) in our study. Although previous studies describe an impact of femoral tilt on postoperative ROM [18], the authors feel intraoperative assessment of femoral tilt has not been resolved yet. Therefore, we focused on intraoperative measurement of femoral stem version. Third, in our femur-first hybrid technique, we used navigation to determine the anteversion of the cementless femoral component and, then, implanted the cup free hand. This setting is not intended for clinical practice. Why should the orthopedic surgeon quit navigation after measurement of the femoral stem version? Therefore, easier and more practicable technical tools such as trial heads have to be developed for a freehand technique with intraoperative stem version estimation. However, this study did not intend to present a novel algorithm in femur-first THA but focused to assess the visual accuracy in preventing impingement, if the anteversion of the stem is a known parameter. Fourth, we used a minimally invasive anterolateral approach in the present study. The choice of approach may influence the accuracy of visual freehand cup implantation. Thus, Table 3 Multivariate Analysis of Risk Factors Associated With a Reduced ROM of at Least 5 in the Freehand Group Compared With the Navigated Group for Flexion and Internal Rotation at 90 Flexion. Risk Factors
Surgical experience >20 y BMI Treatment side (right) Gender (male) Cup size Kellgren score Length of skin incision
Flexion
Internal Rotation
Multivariate Analysis (HR, 95% CI)
P
Multivariate Analysis (HR, 95% CI)
P
0.83 1.22 1.79 2.02 1.29 0.52 0.60
.79 .03 .39 .54 .24 .16 .07
1.53 1.43 0.72 0.40 1.82 0.51 0.51
.58 .004 .67 .50 .04 .19 .04
(0.22-3.20) (1.02-1.46) (0.48-6.67) (0.22-18.88) (0.85-1.94) (0.21-1.29) (0.34-1.05)
(0.34-6.83) (1.12-1.81) (0.16-3.22) (0.03-5.56) (1.03-3.20) (0.18-1.40) (0.27-0.98)
HR, hazard ratio; CI, confidence interval; BMI, body mass index.
5
the results might be different in a posterior or straight lateral approach. In the present study, mean cup anteversion was 7.8 higher in the fully navigation-guided group. If the surgeons had aimed for higher anteversion, the difference between both techniques might have varied. Fifth, analysis were performed by virtual ROM analysis using 3D-CT. Owing to the methodology in this study, it was not possible to obtain comparative clinical data [19] on outcome enabling a comparison between the freehand and fully navigated technique. Therefore, the results do not allow correlation to important clinical parameter or outcome, such as dislocation, wear, or revision. A strength of the study is the fact that we used a single manufacturer's THA design manufacturer (CCD 135 , cone 12/14, head 32-mm diameter, head neck ratio 3.50 for extension/flexion, and 2.66 for abduction/adduction) thereby minimizing confounding factors. Furthermore, we analyzed biomechanical reconstruction accuracy such as leg length and offset discrepancies also possibly affecting postoperative ROM. Any difference with regard to individual hip joint ROM outcome in our analysis is due purely to the operative technique, rather than the prosthetic design of the component. Theoretically, femoral stems with a modular neck could allow control of femoral version and varus/valgus angulation of the neck [6,20]. However, such modularity has been the source of serious concern because of the potential release of metal ions [21]. Our hypothesis was not supported by the results of the study. Flexion and internal rotation at 90 flexion were 8.3 and 9.2 , respectively, lower in the freehand group than in the navigationguided group. The clinical relevance of these ROM differences was emphasized by a lower rate of patients with free ROM for ADL in the freehand group with 58.9% compared with navigation group 85.7% for flexion and similarly with 50,0% compared with 76.8% for internal rotation at 90 flexion. This means that anterior impingement and consecutively posterior dislocation might be increased in our hybrid technique, with freehand cup implantation in relation to the measured intraoperative stem anteversion, compared with the totally navigation-guided cup implantation. In contrast, we found a 9.8 higher extension in patients with freehand implanted cups than in the totally navigated patients. However, this difference was not clinically relevant because the intended ROM of 30 extension for ADL was reached in over 90% in both groups. Compared with previous studies, the ROM values and impingement rates of our hybrid technique were similar to conventional techniques in THA without knowledge of the femoral stem version using the same minimally invasive anterolateral approach [7]. Nevertheless, mean cup anteversion was 7.8 higher in the fully navigation-guided technique compared with the hybrid method. Therefore, the observed differences in ROM might be due to insufficient cup anteversion in relation to a mean stem anteversion of 9.0 . The difficulty in estimating the version of the femoral component intraoperatively has been described in literature [9]. Therefore, we sought to minimize the effect of inaccuracies in visual stem version assessment and concentrated on the accuracy of cup position in relation to the known femoral anteversion in a femur-first setting. Regarding the posterior dislocation in the study group, the anterior inferior iliac spine was not registered and thus not part of the intraoperative impingement detection algorithm. Therefore, the navigation system was not able to detect and prevent this form of impingement in this particular case. Even with navigation, it is not possible to prevent dislocation in all circumstances. Considering the fact that dislocation remains one of the main reasons for early revision surgery [22], it seems that the surgeon needs to control component position intraoperatively. Because restoration of biomechanics also plays a crucial role in preventing impingement in THA, we also aimed to investigate leg length and offset discrepancies in relation to the unaffected
6
M. Weber et al. / The Journal of Arthroplasty xxx (2016) 1e6
contralateral side. Both leg length and offset were restored within a mean difference under 1 mm and standard deviation below 3 mm. Researching into risk factors for the clinically relevant lower flexion and internal rotation in our freehand group, we identified high BMI to be associated with decreased flexion above 5 compared with the navigation-guided cup positioning. Similarly, high BMI, small skin incisions, and higher cup sizes correlated independently with lower internal rotation above 5 . Summarizing, especially obese patients are at risk of cup malpositioning by visual estimation, and a clear surgical exposition of the situs is essential for correct component alignment in THA. To the best of our knowledge, this is the first study evaluating intraoperative implementation of a hybrid femur-first algorithm with freehand cup positioning after measuring femoral stem anteversion regarding their impact on postoperative ROM after THA based on 3D-CT analysis. In summary, visual cup alignment in a combined anteversion setting failed to enable free flexion and internal rotation because of insufficient cup anteversion. High BMI was identified as a risk factor for cup malpositioning. Future models within the concept of combined anteversion for THA will, therefore, need to use an intraoperative cup alignment guide to ensure impingement-free ROM. Acknowledgments The authors thank Dipl-Ing Mario Schubert for his support in range of motion calculations. References 1. Abdel MP, Cross MB, Yasen AT, et al. The functional and financial impact of isolated and recurrent dislocation after total hip arthroplasty. Bone Jt J 2015;97B(8):1046. 2. Preininger B, Haschke F, Perka C. [Diagnostics and therapy of luxation after total hip arthroplasty]. Orthopade 2014;43(1):54. 3. Hube R, Dienst M, von Roth P. [Complications after minimally invasive total hip arthroplasty]. Orthopade 2014;43(1):47. 4. Lewinnek GE, Lewis JL, Tarr R, et al. Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am 1978;60(2):217.
5. Abdel MP, von Roth P, Jennings MT, et al. What safe zone? the vast majority of dislocated THAs are within the Lewinnek safe zone for acetabular component position. Clin Orthop Relat Res 2016;474:386. 6. Widmer KH, Zurfluh B. Compliant positioning of total hip components for optimal range of motion. J Orthop Res 2004;22(4):815. 7. Renkawitz T, Weber M, Springorum HR, et al. Impingement-free range of movement, acetabular component cover and early clinical results comparing ‘femur-first’ navigation and ‘conventional’ minimally invasive total hip arthroplasty: a randomised controlled trial. Bone Jt J 2015;97B(7):890. 8. Sendtner E, Muller M, Winkler R, et al. [Femur first in hip arthroplastydthe concept of combined anteversion]. Z Orthop Unfall 2010;148(2):185. 9. Dorr LD, Wan Z, Malik A, et al. A comparison of surgeon estimation and computed tomographic measurement of femoral component anteversion in cementless total hip arthroplasty. J Bone Joint Surg Am 2009;91(11):2598. 10. Woerner M, Sendtner E, Springorum R, et al. Visual intraoperative estimation of cup and stem position is not reliable in minimally invasive hip arthroplasty. Acta Orthop 2016 [Epub ahead of print]. 11. Renkawitz T, Haimerl M, Dohmen L, et al. Development and evaluation of an image-free computer-assisted impingement detection technique for total hip arthroplasty. Proc Inst Mech Eng H 2012;226(12):911. 12. Michel MC, Witschger P. MicroHip: a minimally invasive procedure for total hip replacement surgery using a modified Smith-Peterson approach. Ortop Traumatol Rehabil 2007;9(1):46. 13. Turley GA, Ahmed SM, Williams MA, et al. Validation of the femoral anteversion measurement method used in imageless navigation. Comput Aided Surg 2012;17(4):187. 14. Weber M, Weber T, Woerner M, et al. The impact of standard combined anteversion definitions on gait and clinical outcome within one year after total hip arthroplasty. Int Orthop 2015;39:2323. 15. Davis KE, Ritter MA, Berend ME, et al. The importance of range of motion after total hip arthroplasty. Clin Orthop Relat Res 2007;465:180. 16. Miki H, Yamanashi W, Nishii T, et al. Anatomic hip range of motion after implantation during total hip arthroplasty as measured by a navigation system. J Arthroplasty 2007;22(7):946. 17. Turley GA, Ahmed SM, Williams MA, et al. Establishing a range of motion boundary for total hip arthroplasty. Proc Inst Mech Eng H 2011;225(8):769. 18. Renkawitz T, Haimerl M, Dohmen L, et al. The association between femoral tilt and impingement-free range-of-motion in total hip arthroplasty. BMC Musculoskelet Disord 2012;13:65. 19. Grifka J, Keshmiri A, Maderbacher G, et al. [Clinical examination of the hip joint in adults]. Orthopade 2014;43(12):1115. 20. Dorr LD, Malik A, Dastane M, et al. Combined anteversion technique for total hip arthroplasty. Clin Orthop Relat Res 2009;467(1):119. 21. Krishnan H, Krishnan SP, Blunn G, et al. Modular neck femoral stems. Bone Jt J 2013;95-B(8):1011. 22. Bozic KJ, Kurtz SM, Lau E, et al. The epidemiology of revision total hip arthroplasty in the United States. J Bone Joint Surg Am 2009;91(1):128.