Orthopedics

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Three-Dimensional Templating for Acetabular Component Alignment During Total Hip Arthroplasty

Ameer M. Elbuluk, BA; Paul Wojack, BA; Nima Eftekhary, MD; Jonathan M. Vigdorchik, MD

Abstract

Appropriate placement of the acetabular cup is an important determinant of implant stability and longevity. Malposition of acetabular cups negatively influences prosthesis survival and leads to an increased dislocation rate. The objective of the study was to determine the role of 3-dimensional templating in obtaining accurate acetabular component placement in total hip arthroplasty. In this computed tomography-based study, the authors identified 93 patients who underwent primary total hip arthroplasty with computer-assisted navigation. Using 3-dimensional planning, the authors templated the acetabular component at an inclination of 40° and anteversion of 20°. To classify acetabular cup coverage by bone, the acetabulum was used as a clock face with the center of the transverse acetabular ligament (TAL) as 6-o'clock. Analyses revealed that 72% of cups were uncovered between 9- to 1-o'clock for right hips. On the left side, 88% of cups were uncovered between 11- to 3-o'clock. Across all hips, 74% of cups had a 1-o'clock position at the most lateral aspect. Further analysis revealed that 46% of acetabular cups had a teardrop at the same level of the most inferior aspect of the cup, whereas only 37% of cups had a teardrop above the inferior aspect of the cup. Finally, the acetabular component was aligned with the TAL in 76% of hips, retroverted to the TAL in 16%, and anteverted to the TAL in 8%. The current study demonstrates a useful gross intraoperative reference tool to standardize cup position without the need for additional equipment and reliance on anatomical landmarks. [Orthopedics. 2017; 40(4):e708–e713.]

Abstract

Appropriate placement of the acetabular cup is an important determinant of implant stability and longevity. Malposition of acetabular cups negatively influences prosthesis survival and leads to an increased dislocation rate. The objective of the study was to determine the role of 3-dimensional templating in obtaining accurate acetabular component placement in total hip arthroplasty. In this computed tomography-based study, the authors identified 93 patients who underwent primary total hip arthroplasty with computer-assisted navigation. Using 3-dimensional planning, the authors templated the acetabular component at an inclination of 40° and anteversion of 20°. To classify acetabular cup coverage by bone, the acetabulum was used as a clock face with the center of the transverse acetabular ligament (TAL) as 6-o'clock. Analyses revealed that 72% of cups were uncovered between 9- to 1-o'clock for right hips. On the left side, 88% of cups were uncovered between 11- to 3-o'clock. Across all hips, 74% of cups had a 1-o'clock position at the most lateral aspect. Further analysis revealed that 46% of acetabular cups had a teardrop at the same level of the most inferior aspect of the cup, whereas only 37% of cups had a teardrop above the inferior aspect of the cup. Finally, the acetabular component was aligned with the TAL in 76% of hips, retroverted to the TAL in 16%, and anteverted to the TAL in 8%. The current study demonstrates a useful gross intraoperative reference tool to standardize cup position without the need for additional equipment and reliance on anatomical landmarks. [Orthopedics. 2017; 40(4):e708–e713.]

Hip instability remains one of the most common indications for revision total hip arthroplasty (THA). Approximately 22.5% of revision THAs and 33% of acetabular revisions are due to dislocations.1 Numerous risk factors, including implant design, surgical approach, and prior hip surgery, have been associated with dislocation. However, incorrect orientation of the acetabular component is the most important factor predisposing patients to hip instability.2 Acetabular component orientation significantly affects wear and osteolysis, acetabular migration, impingement, and the risk of dislocation in patients undergoing THA.3–6

In 1978, Lewinnek et al7 introduced a “safe zone” for the optimal orientation of the acetabular component in THA. A dislocation rate of 6.1% occurred for implants outside the safe range (5° to 25° anteversion and 30° to 50° inclination) as opposed to 1.5% for those within range. More recently, Callanan et al8 suggested a “modified safe zone” (5° to 25° version and 30° to 45° inclination) for cup placement to take into account the use of hard-on-hard bearing surfaces.9 High angles of inclination and highly anteverted cups have been shown to be correlated with higher rates of anterior and recurrent dislocations.10 Cup malposition is also linked to higher rates of wear debris and aseptic loosening of the prosthesis. In addition to dramatically reducing the risk of dislocation, proper component positioning optimizes forces on the implant and reduces accelerated implant wear.11–13

Placement of an acetabular component in accurate abduction and anteversion angles requires thorough preoperative planning and intraoperative execution. To assess cup position in conventional THA, surgeons use landmarks, including the transverse acetabular ligament (TAL), anterior wall of the native acetabulum, teardrop, and lateral most portion of the native acetabulum.14 However, the accuracy of conventional methods, which demonstrate approximately 59% to 68% ability to place the cup within the safe zone, have encouraged the development of several new modalities to improve the accuracy of cup position.8,15 Robotic- and computer-assisted navigation have been shown to successfully place the acetabular component in the desired position with up to 97% accuracy.16–19 However, these modalities are not readily available or financially feasible for all arthroplasty surgeons. Therefore, it is necessary to have conventions independent of these technologies to confirm precise cup placement.

The current study seeks to use the authors' experience with 3-dimensional (3D) templating and robotic hip replacement to provide objective data of the value of certain intraoperative anatomic landmarks in confirming accuracy of cup placement. These data may be useful in improving surgical accuracy, reproducibility, and correct positioning of the acetabular cup for non–computer-assisted, conventional surgeries. In the current analysis, the authors addressed the following questions:

  1. At 40° inclination and 20° anteversion:

    1. When looking at the anterior wall of the native acetabulum, where is the cup inside the bone (Figure 1)?

      Three-dimensional hip reconstruction showing clock face template and acetabular bone coverage measurements. Abbreviation: TAL, transverse acetabular ligament.

      Figure 1:

      Three-dimensional hip reconstruction showing clock face template and acetabular bone coverage measurements. Abbreviation: TAL, transverse acetabular ligament.

    2. When looking at the lateral and posterosuperior native acetabulum, where is the cup uncovered from bone (Figure 1)?

    3. Where on the clock face is the most lateral aspect of the native acetabulum, to correlate cup uncoverage seen on acetate or digital templating of an anteroposterior pelvis radiograph (Figure 2)?

      Digital 3-dimensional template measurements (A) and anteroposterior radiograph (B) showing abduction angles associated with position of the superior lateral acetabular rim.

      Figure 2:

      Digital 3-dimensional template measurements (A) and anteroposterior radiograph (B) showing abduction angles associated with position of the superior lateral acetabular rim.

    4. How often is the most inferior aspect of the hip joint above or below the teardrop?

    5. What is the position of the cup compared to the TAL?

    6. This analysis should complement other planning modalities in attaining optimal implantation of the cup and isolating a safe zone for THA. The purpose of this study is to provide an intraoperative reference for surgeons to increase accuracy of component positioning and ultimately to achieve hip joint stability.

      Materials and Methods

      This study was a retrospective investigation performed at a single academic center. All cases were performed by a fellowship-trained joint reconstruction surgeon (J.M.V.). The authors identified 93 patients who underwent primary THA from May 2014 to May 2015. All THA procedures were performed using a posterior approach and MAKOplasty Total Hip Application (Stryker, Mahwah, New Jersey). The software uses 3D modeling of the patient's hip, reconstructed from computed tomography (CT), which allows for preoperative planning, optimization of component position, and real-time adjustments intraoperatively. The use of this software in measuring parameters for THA has been validated in several studies.20

      Electronic medical records were used to obtain patients' baseline characteristics, including gender, laterality, preoperative diagnosis, and surgical procedure. Two cases with inadequate CT images were excluded from the study cohort. The main characteristics of the study cohort are presented in the Table.

      Patient Demographics

      Table:

      Patient Demographics

      Using 3D planning, the authors templated the acetabular component at an inclination of 40° and anteversion of 20°, which are almost at the center of the safe zone and are commonly referred to as the target angles for a THA. It should be emphasized that this study was a CT-based analysis and was not based on intraoperative measurements. The research questions examine previously reviewed criteria that are often used to guide acetabular component placement. Once the cup was positioned at the correct angles, the anterosuperior/anteroinferior and the posterosuperior coverage of the cup by the native acetabular bone was determined. To classify acetabular cup coverage by bone, the acetabulum was used as a clock face, with the center of the TAL as 6 o'clock. Studies suggest that the rate of dislocation can be reduced to 0.6% by using the TAL as a reference for acetabular cup alignment.21,22 The position of the cup was also determined to be anteverted, aligned, or retroverted to the native TAL.

      Using the software, 2 lines were created from the center of the cup to the acetabular edge to form a reference for assigning clock values to (1) where the cup was within bone, (2) where the cup was not inside the bone (Figure 2), and (3) where the lateral most aspect of the acetabulum was. These measurements were used as an alignment guide for 2 reviewers (A.M.E., N.E.) to independently assign clock values based on visual comparison. All data entries were confirmed by the surgeon to ensure reproducibility and repeatability.

      The final criterion examined was whether the most inferior part of the cup was above or below the teardrop. The acetabular teardrop is a radiographic projection of cortical bone of the medial wall of the acetabulum and the superior pubic ramus. It is commonly used as a landmark to guide acetabular component placement during templating for THA. By placing the acetabular component aspect at the same level as the inferior teardrop edge, it is assumed to restore the hip's center of rotation.23,24 When templating, the position of the acetabular component in a superior/inferior direction dictates the next steps in templating to restore leg length. Categorization (above, below, or same level) was determined based on whether a difference between the position of the most inferior aspect of the cup and the most inferior aspect of the teardrop was possible via the observer's judgment.

      Statistical analysis was performed using Excel software (Microsoft, Redmond, Washington). The number of hips with covered and uncovered cups was calculated at each clock value. Hips were also compared by laterality. For the combined analysis, the values of the left hip were mirrored and added to those of the right hip. A final chart was created to identify the cumulative percentage for each clock value where the acetabular cup was covered and uncovered by bone. These figures were used to make generalized predictors of bony coverage for acceptable cup positioning.

      Results

      Computed tomography scans for all 93 patients were identified and measured. Seven left and 11 right hips were excluded from this analysis because no portion of the cup was uncovered. In these 18 (19.4%) hips, no anatomic acetabular landmarks were available for component positioning. In the remaining 75 cups, each was examined for coverage at every position using the clock face convention. In right hips, the majority of cups revealed the acetabular component uncovered between 9- to 1-o'clock. In comparison, the majority of left hips were uncovered between 11- to 3-o'clock. After mirroring all left hips onto the right, the authors were able to calculate the percentage of cups with coverage at each clock value (Figures 34).

      Clock face results for cup uncoverage. Right (A), left (B), and right plus left (C) total hip arthroplasty cup uncoverage.

      Figure 3:

      Clock face results for cup uncoverage. Right (A), left (B), and right plus left (C) total hip arthroplasty cup uncoverage.

      Right and left total hip arthroplasty cup uncoverage (A) and coverage (B) mirrored onto a right hip as seen by the operative surgeon. Abbreviation: TAL, transverse acetabular ligament.

      Figure 4:

      Right and left total hip arthroplasty cup uncoverage (A) and coverage (B) mirrored onto a right hip as seen by the operative surgeon. Abbreviation: TAL, transverse acetabular ligament.

      The current analysis revealed that 72% of cups were uncovered between 9- to 1-o'clock for right hips. On the left side, 88% of cups were uncovered between 11-to 3-o'clock. Conversely, 85% of right cups were covered in the range of 2- to 8-o'clock, and 87% of left cups were covered in the range of 4- to 10-o'clock. After the values of left hips were added to right hip data, combined results showed that 80% of cups were uncovered between 9- to 1-o'clock. Finally, combined data showed 86% of cups were tucked inside the native acetabular anterior wall in the range of 2- to 8-o'clock.

      The authors then measured the clock position of the most lateral aspect of the acetabular cup. Figure 5 details results of these lateral measurements. Across all hips, 74% of cups had a 1-o'clock position at the most lateral aspect—with only 12% at 11-o'clock and 14% at the 12-o'clock position. Figure 6 demonstrates evaluation of the 3D cup template with respect to the teardrop. Analysis revealed that 46% of native acetabular sockets had a teardrop at the same level of the most inferior aspect of the socket, whereas only 37% of cups had a teardrop above the inferior aspect of the socket.

      Percentage of hips based on lateral position of cup.

      Figure 5:

      Percentage of hips based on lateral position of cup.

      Graph showing teardop results (A), and 3-dimensional template identifying teardrop landmarks (B).

      Figure 6:

      Graph showing teardop results (A), and 3-dimensional template identifying teardrop landmarks (B).

      Finally, the authors found that at an inclination of 40° and anteversion of 20°, the acetabular component was aligned with the TAL in 76% of hips, retroverted to the TAL in 16%, and anteverted to the TAL in 8% (Figure 7).

      Position of cups compared with transverse acetabular ligament.

      Figure 7:

      Position of cups compared with transverse acetabular ligament.

      Discussion

      Acetabular cup positioning is a critical component in THA that affects long-term THA survivorship.25,26 As the number of THAs continues to increase, the importance of improving accuracy of acetabular component positioning needs to be considered. New robotic and computer navigation technology have helped improve the accuracy and consistency for implantation of the acetabular component. However, these modalities are often associated with higher costs and longer surgical duration.27 Therefore, other reliable landmarks and tools must be investigated to help reproduce native cup orientation.

      The purpose of this study was to investigate a new method of assessing the hip implant intraoperatively to improve alignment of the acetabular component. There were 5 major findings from the study. First, when doing a THA at 40° inclination and 20° anteversion, the acetabular component should be uncovered between 9- and 1-o'clock in right hips and 11- and 3-o'clock in left hips. Similarly, the cup should be within the native anterior wall and acetabular bone covered between 2- and 8-o'clock in right hips and 4- and 10-o'clock in left hips. Second, the most lateral aspect of the cup corresponds with the 1-o'clock position in most cases. Third, the most inferior aspect of the cup should be at (46%) or below (37%) the most inferior aspect of the teardrop. Fourth, the TAL aligns to 20° anteversion 76% of the time. Finally, no anatomic acetabular landmarks were available for component positioning in 19.4% of hips, requiring alternative pelvic bony landmarks to be used to accurately position the acetabular component.

      It is important to remove any curtain osteophytes in these cases to ensure that the true medial wall is identified to adequately expose the acetabulum. To account for individual variations in hip and pelvic anatomy, one must rely on the sciatic notch angle or position of the body—both of which have inaccuracies.28 In these instances, computer navigation and robotics can be used to help obtain accurate anteversion and inclination angles. To the current authors' knowledge, this is the first study to utilize such techniques to confirm prior thinking and to provide guidance for intraoperative acetabular component alignment.

      Techniques for the alignment of the acetabular component remain controversial. Several studies have shown that freehand positioning of the acetabular cup increases misalignment.16 Although robotic- and navigation-assisted surgeries have proven to successfully improve cup accuracy, these systems are not readily available to all surgeons. Furthermore, anatomical landmarks are often obscured due to osteophytes or degenerative changes in local pelvic anatomy and differences in pelvic orientation. The need for consistent acetabular placement is an important factor in reducing dislocation rates and the likelihood of revision surgery.

      The current results suggest that surgeons can use the clock face values as an intraoperative reference to ensure correct acetabular placement without the need for additional equipment and reliance on anatomical landmarks. However, given the relationship of pelvic tilt and flexible versus rigid spinal deformities, it must also be understood that in these cases the safe zone may not be the appropriate orientation. The presence of hip flexion contracture and adduction deformities may also further complicate the position of the pelvis and subsequent placement of the cup. Furthermore, acetabular dysplasia, heavy osteophytes, or even post-traumatic deformity must be taken into account when anatomic reference points are not available.

      The current study has a few limitations. First, there was some interobserver variability in assigning clock values to the 3D templates. Interobserver agreement and validity were analyzed using weighted κ statistics. Mean κ value was 0.89 (0.83–0.94), which represents substantial agreement. Furthermore, any final radiographic disagreements were assessed by the senior author (J.M.V.).

      Second, the authors assessed acetabular orientation at 40° inclination and 20° anteversion based on a global coronal plane of the body in a CT scanner. This does not factor in the standing functional pelvic plane, the anterior pelvic plane, or pelvic tilt. Lewinnek et al7 created the safe zone using a supine position and a radiograph taken with the patient's anterior pelvic plane at 0° of pelvic tilt. It has been shown in prior studies that up to 50% of patients have between 5° and 10° of pelvic tilt, with 17% having greater than 10° of pelvic tilt.29

      Third, this does not factor in subtle changes in anteversion that the surgeon may opt for in anterior or anterolateral approaches to the hip in patients with underlying spinal pathology or pelvic tilt. Fourth, anatomic variations of the proximal femur must also be addressed in the development of hip pathology. Future studies should also aim to find intraoperative techniques to better define the axis of the femoral neck in relationship to the acetabular component.

      Finally, although this retrospective study suggests that certain anatomic landmarks can be used as an intraoperative check to cup positioning, a prospective, randomized control study with intraoperative use of the landmarks above would be of significant value in determining the clinical utility of this tool in reducing future dislocations and component wear. A similar study was performed using 3D templating for native anatomical landmarks to help guide acetabular position, helping to increase success of proper positioning of the planned component anteversion and inclination.16 However, further study is warranted.

      Conclusion

      It is important to consider new methods to ensure greater accuracy for cup positioning. Evidence has already shown that surgeons do not reliably position the cup intraoperatively based on mechanical guides alone. However, the precision of these angles is increased when combined with accurate preoperative planning, correct patient positioning based on pelvic tilt, and ultimately intraoperative execution. This study introduces a useful tool for arthroplasty surgeons to intraoperatively improve accuracy in placing the acetabular cup in the safe zone. However, these suggestions need to be further investigated to observe the clinical benefits for patients in the short- and long-term.

      References

      1. Bozic KJ, Kurtz SM, Lau E, Ong K, Vail TP, Berry DJ. The epidemiology of revision total hip arthroplasty in the United States. J Bone Joint Surg Am. 2009; 91 (1):128–133. doi:10.2106/JBJS.H.00155 [CrossRef]
      2. Goudie ST, Deakin AH, Deep K. Natural acetabular orientation in arthritic hips. Bone Joint Res. 2015; 4 (1):6–10. doi:10.1302/2046-3758.41.2000286 [CrossRef]
      3. Kennedy JG, Rogers WB, Soffe KE, Sullivan RJ, Griffen DG, Sheehan LJ. Effect of acetabular component orientation on recurrent dislocation, pelvic osteolysis, polyethylene wear, and component migration. J Arthroplasty. 1998; 13 (5):530–534. doi:10.1016/S0883-5403(98)90052-3 [CrossRef]
      4. Jolles BM, Zangger P, Leyvraz PF. Factors predisposing to dislocation after primary total hip arthroplasty: a multivariate analysis. J Arthroplasty. 2002; 17 (3):282–288. doi:10.1054/arth.2002.30286 [CrossRef]
      5. Barrack RL. Dislocation after total hip arthroplasty: implant design and orientation. J Am Acad Orthop Surg. 2003; 11 (2):89–99. doi:10.5435/00124635-200303000-00003 [CrossRef]
      6. Wan Z, Boutary M, Dorr LD. The influence of acetabular component position on wear in total hip arthroplasty. J Arthroplasty. 2008; 23 (1):51–56. doi:10.1016/j.arth.2007.06.008 [CrossRef]
      7. Lewinnek GE, Lewis JL, Tarr R, Compere CL, Zimmerman JR. Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am. 1978; 60 (2):217–220. doi:10.2106/00004623-197860020-00014 [CrossRef]
      8. Callanan MC, Jarrett B, Bragdon CR, et al. The John Charnley Award. Risk factors for cup malpositioning: quality improvement through a joint registry at a tertiary hospital. Clin Orthop Relat Res. 2011; 469 (2):319–329. doi:10.1007/s11999-010-1487-1 [CrossRef]
      9. De Haan R, Pattyn C, Gill HS, Murray DW, Campbell PA, De Smet K. Correlation between inclination of the acetabular component and metal ion levels in metal-on-metal hip resurfacing replacement. J Bone Joint Surg Br. 2008; 90 (10):1291–1297. doi:10.1302/0301-620X.90B10.20533 [CrossRef]
      10. Kelley SS, Lachiewicz PF, Hickman JM, Paterno SM. Relationship of femoral head and acetabular size to the prevalence of dislocation. Clin Orthop Relat Res. 1998; (355):163–170. doi:10.1097/00003086-199810000-00017 [CrossRef]
      11. Bradford L, Kurland R, Sankaran M, Kim H, Pruitt LA, Ries MD. Early failure due to osteolysis associated with contemporary highly cross-linked ultra-high molecular weight polyethylene: a case report. J Bone Joint Surg Am. 2004; 86 (5):1051–1056. doi:10.2106/00004623-200405000-00026 [CrossRef]
      12. Holt G, Murnaghan C, Reilly J, Meek RM. The biology of aseptic osteolysis. Clin Orthop Relat Res. 2007; (460):240–252.
      13. Little NJ, Busch CA, Gallagher JA, Rorabeck CH, Bourne RB. Acetabular polyethylene wear and acetabular inclination and femoral offset. Clin Orthop Relat Res. 2009; 467 (11):2895–2900. doi:10.1007/s11999-009-0845-3 [CrossRef]
      14. Della Valle AG, Padgett DE, Salvati EA. Preoperative planning for primary total hip arthroplasty. J Am Acad Orthop Surg. 2005; 13 (7):455–462. doi:10.5435/00124635-200511000-00005 [CrossRef]
      15. Domb BG, El Bitar YF, Sadik AY, Stake CE, Botser IB. Comparison of robotic-assisted and conventional acetabular cup placement in THA: a matched-pair controlled study. Clin Orthop Relat Res. 2014; 472 (1):329–336. doi:10.1007/s11999-013-3253-7 [CrossRef]
      16. Kalteis T, Handel M, Bäthis H, Perlick L, Tingart M, Grifka J. Imageless navigation for insertion of the acetabular component in total hip arthroplasty: is it as accurate as CT-based navigation?J Bone Joint Surg Br. 2006; 88 (2):163–167. doi:10.1302/0301-620X.88B2.17163 [CrossRef]
      17. Leenders T, Vandevelde D, Mahieu G, Nuyts R. Reduction in variability of acetabular cup abduction using computer assisted surgery: a prospective and randomized study. Comput Aided Surg. 2002; 7 (2):99–106. doi:10.3109/10929080209146021 [CrossRef]
      18. Parratte S, Argenson JN. Validation and usefulness of a computer-assisted cup-positioning system in total hip arthroplasty: a prospective, randomized, controlled study. J Bone Joint Surg Am. 2007; 89 (3):494–499.
      19. Ybinger T, Kumpan W, Hoffart HE, Muschalik B, Bullmann W, Zweymüller K. Accuracy of navigation-assisted acetabular component positioning studied by computed tomography measurements: methods and results. J Arthroplasty. 2007; 22 (6):812–817. doi:10.1016/j.arth.2006.10.001 [CrossRef]
      20. Domb BG, El Bitar YF, Sadik AY, Stake CE, Botser IB. Comparison of robotic-assisted and conventional acetabular cup placement in THA: a matched-pair controlled study. Clin Orthop Relat Res. 2014; 472 (1):329–336. doi:10.1007/s11999-013-3253-7 [CrossRef]
      21. Archbold HAP, Slomczykowski M, Cairns H, Eckman K, Jaramaz B, Beverland DE. Patient specific cup anteversion in total hip arthroplasty: a computed tomography study investigating the use of the transverse acetabular ligament to control cup placement. Curr Orthop Pract. 2009; 20 (1):73–76. doi:10.1097/BCO.0b013e3181944dd2 [CrossRef]
      22. Griffin AR, Perriman DM, Bolton CJ, Smith PN. An in vivo comparison of the orientation of the transverse acetabular ligament and the acetabulum. J Arthroplasty. 2014; 29 (3):574–579. doi:10.1016/j.arth.2013.08.002 [CrossRef]
      23. Lu Y, Cheng L, Guo W, et al. Ability of lower teardrop edge to restore anatomical hip center height in total hip arthroplasty. Chin Med J (Engl). 2014; 127 (22):3915–3920.
      24. Bowerman JW, Sena JM, Chang R. The teardrop shadow of the pelvis: anatomy and clinical significance. Radiology. 1982; 143 (3):659–662. doi:10.1148/radiology.143.3.7079492 [CrossRef]
      25. Moskal JT, Capps SG. Improving the accuracy of acetabular component orientation: avoiding malposition. J Am Acad Orthop Surg. 2010; 18 (5):286–296. doi:10.5435/00124635-201005000-00005 [CrossRef]
      26. Patil S, Bergula A, Chen PC, Colwell CW Jr, D'Lima DD. Polyethylene wear and acetabular component orientation. J Bone Joint Surg Am. 2003; 85 (suppl 4):56–63. doi:10.2106/00004623-200300004-00007 [CrossRef]
      27. Deep K, Picard F. Computer assisted navigation in primary total hip arthroplasty. Orthop Trauma. 2014; 28:309–314. doi:10.1016/j.mporth.2014.08.004 [CrossRef]
      28. McCollum DE, Gray WJ. Dislocation after total hip arthroplasty: causes and prevention. Clin Orthop Relat Res. 1990; (261):159–170
      29. Maratt JD, Esposito CI, McLawhorn AS, Jerabek SA, Padgett DE, Mayman DJ. Pelvic tilt in patients undergoing total hip arthroplasty: when does it matter?J Arthroplasty. 2015; 30 (3):387–391. doi:10.1016/j.arth.2014.10.014 [CrossRef]

      Patient Demographics

      VariableNo.
      Patients93
      Sex
        Male34
        Female59
      Laterality
        Left44
        Right49
      Preoperative diagnosis
        Osteoarthritis82
        Avascular necrosis10
        Rheumatoid arthritis1
    Authors

    The authors are from the Department of Orthopaedic Surgery, NYU Langone Medical Center, Hospital for Joint Diseases, New York, New York.

    The authors have no relevant financial relationships to disclose.

    Correspondence should be addressed to: Jonathan M. Vigdorchik, MD, Department of Orthopaedic Surgery, NYU Langone Medical Center, Hospital for Joint Diseases, 301 E 17th St, Ste 1402, New York, NY 10003 ( jonathan.vigdorchik@nyumc.org).

    Received: January 27, 2017
    Accepted: April 10, 2017
    Posted Online: May 31, 2017

    10.3928/01477447-20170522-05

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