Early acetabular cup migration may be a source of error in the assessment of intra-operative placement accuracy

Shahnaz Taleb; Jennifer S. Polus; Brent Lanting; Matthew G. Teeter

doi:10.1016/j.jorep.2025.100620

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Research Article

2025

:4;

100620

doi:

10.1016/j.jorep.2025.100620

Early acetabular cup migration may be a source of error in the assessment of intra-operative placement accuracy

Shahnaz Taleb^a,b,, Jennifer S. Polus^a,b, Brent Lanting^c, Matthew G. Teeter^a,b

a School of Biomedical Engineering, Western University, London, Ontario, Canada

b Imaging Group, Robarts Research Institute, Schulich School of Medicine & Dentistry, Western University, London, ON, Canada

c Division of Orthopaedic Surgery, Department of Surgery, London Health Sciences Centre, London, ON, Canada

⁎Corresponding author: Shahnaz Taleb. staleb3@uwo.ca

Received: 2024-12-10, Accepted: 2025-2-28, Published: 2025-3-7

The Authors

Disclaimer:
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.

Abstract

Proper alignment of the acetabular cup is essential for long-term success total hip arthroplasty (THA) success. Computer navigation and robotic techniques have been of interest to improve cup alignment, with their accuracy often reported by comparing the intraoperative alignment to six-week postoperative alignment; however, early component migration is known to occur within the first six weeks. This study aimed to assess the potential error in cup position measurements caused by early acetabular cup migration within the first six weeks following THA.

Acetabular cup inclination and anteversion angles were measured by two raters from radiographs taken intra-operatively and at six weeks post-operation. An RSA examination was performed on the day of surgery as well as 6-weeks post-operation. Thirty-three patients were included in our analysis. Mean inclination angles were 31.2° intra-operatively and 32.8° at six weeks post-operation (maximum difference = 11.1°). Mean anteversion angles were 23.5° and 29.3° intra-operatively and at six weeks post-operation (maximum difference = 15.3°). Mean anterior tilt, internal rotation, and valgus rotation between the day of surgery and six weeks post-operation were 1.33°, 0.98°, and 0.80°, respectively.

This study demonstrated that early migration of acetabular cups may introduce an error in studies reporting computer navigation accuracy in acetabular cup placement based on post-operative imaging follow-ups.

Keywords

Primary arthroplasty

Radiostereometric analysis

Acetabular cup

Computer navigation

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1 Introduction

Proper alignment of the acetabular cup is essential for the biomechanical reconstruction of the hip joint, and the overall long-term success of total hip arthroplasty (THA). The Lewinnek safe zone is widely used as the standard for assessing acceptable cup alignment, with optimal ranges defined as an inclination of 40° ± 10° and an anteversion of 15° ± 10°.¹ Failure to achieve adequate cup alignment can lead to several postoperative complications, including intra-component impingement, dislocation, pelvic osteolysis, component loosening, and the need for revision surgery.^2–7 Conventional freehand and mechanically guided techniques can often exhibit a steep learning curve; however, suboptimal cup alignment occurs even in the hands of experienced surgeons with high surgical volumes.⁴^,^8–11 As a result, there has been increasing interest in computer navigation and robotic techniques for optimal acetabular cup alignment in an effort to minimize post-operative complications.

Computer navigation provides surgeons with intra-operative information on component alignment and has been reported to improve the predictability and reproducibility of acetabular cup position and reduce positional outliers.⁸^,¹² For surgeons, the goal is to utilize the real-time feedback from the computer navigation system to accurately execute the predetermined cup position of interest. The precision and accuracy of such systems is often reported by comparing the intraoperative measures of cup position to postoperative measures of cup position, often at six weeks post-operation.³^,⁸^,¹²^,¹³ However, it is known that early migration of implant components occurs after THA, which may impact measures of cup position postoperatively and introduce a potential error in the analysis of computer navigation accuracy.⁸^,^12–18

Radiostereometric analysis (RSA) is the gold standard for in vivo implant tracking, with an accuracy of 0.2 mm for translations and 0.5° for rotations.¹⁹^,²⁰ RSA has played an important role in evaluating the early migration of implant components and provides measures of implant movement over time. The objective of this study is to assess whether early implant migration may cause potential error in cup position measurements within the first six-weeks following THA.

2 Materials and methods

2.1

2.1 Study design & participants

Patients were enrolled and informed consent was collected pre-operatively between January 2018 and July 2019 as part of a larger prospective randomized clinical trial (NCT03558217) approved by our institutional research ethics board.¹⁶ Included were patients with end-stage unilateral hip osteoarthritis, necessitating primary THA. Excluded were patients with a body mass index greater than 40 kg/m², symptomatic contralateral osteoarthritis, revision procedures, cognitive defects, or lived more than 100 km from our institution.

A single fellowship trained arthroplasty surgeon performed all surgeries using the direct anterior approach on a specialized fracture table with adjuvant fluoroscopy. Patients received a Pinnacle cup with AltrX highly crosslinked acetabular liner (DePuy Synthes, Warsaw, IN) with either no (n = 7), one (n = 16), or two (n = 10) screws, a Corail cementless femoral stem (standard or high-offset, as required), and a 28 mm, 32 mm, or 36 mm cobalt-chromium femoral head. No significant differences were found in placement change between groups; therefore, all patients were combined for the analysis. A minimum of four 1 mm tantalum beads were inserted into the acetabulum surrounding the cup implant for subsequent radiostereometric analysis (RSA).

2.2

2.2 Radiographic analysis

Intra-operative fluoroscopy images were taken for all participants. A subsequent standard anteroposterior radiograph was taken six weeks post-operation. Acetabular cup inclination and anteversion angles were measured by two raters from radiographs taken intra-operatively and at the six-week follow-up. Inclination was measured as the angle between the bi-ischial line and a line tangent to the opening of the acetabular cup. Anteversion was measured using the technique described by Lewinnek et al. as: version = arcsin(D1/D2)

where D1 denotes the short axis of the acetabular cup while D2 is the long axis of the acetabular ellipse (Fig. 1).¹

(A) Inclination and (B) anteversion measurements on standard AP radiographs. Inclination was measured as the angle between the bi-ischial line and a line tangent to the opening of the acetabular cup. Anteversion was measured as described by Lewinnek et al.1.

An RSA exam was performed on the day of surgery, within the first 24 h post-operatively, before the patient was discharged from the hospital. A subsequent follow-up exam was performed six weeks post-operation. RSA exams were performed with patients in a supine position using an uni-planar calibration cage (RSA Biomedical, Umea, Sweden). RSA radiographs were analyzed using model-based RSA software (RSAcore, Leiden, The Netherlands). Positive rotation directions were defined as anterior tilt about the x-axis, internal rotation about the y-axis, and valgus rotation about the z-axis.

2.3

2.3 Statistical method

Intra-operative and six-week post-operative acetabular cup angles were averaged between both raters, and reported as mean, ranges, and standard deviation. Reliability between- and within-subject interclass correlation (ICC) analysis was done using the Hopkins (2009) method.²¹ RSA rotation data was reported as mean and range for rotations about the x-, y-, and z-axes. Total rotation was calculated using the following equation:TR=Rx2+Ry2+Rz2and reported as mean and standard deviation. Pearson correlation coefficient was used to correlate RSA rotational movement about each axis to the change in anteversion and inclination angles. All statistical tests were completed using Prism version 8.2.1 (GraphPad Software, La Jolla, CA).

3 Results

Eligible patients were recruited and provided written consent prior to participation. Forty-nine patients were recruited and participated in the study. Three patients were excluded due to missing anatomical landmarks on their radiographs rendering angle measurements unattainable. Patient demographics for the remaining 46 patients are presented in Table 1.

Table 1 Patient demographics of participants. Values are reported as mean ± standard deviation (SD) or actual numbers.

Characteristic	Mean ± SD
Age at surgery (years)	64.5 ± 8.0 (44–89)
Height	1.75 ± 0.1 (1.42–1.89)
Weight	88.7 ± 19.3 (49–130)
Body mass index (kg/m²)	29.7 ± 4.9 (22.0–38.9)
	Number
Sex (M: F)	16:17
Surgical side (L: R)	15:18

Inclination and anteversion angles were measured intraoperatively and at six-week post-operation. Thirteen patients were subsequently excluded from the implant rotation analysis due to a missed RSA exam or inability to measure RSA movement due to inadequate bead position.

Inter-reviewer reliability of radiographic measurements confirmed excellent reliability for inclination measurements and good reliability for anteversion measurements (Table 2). Thus, the average measurement between reviewers was calculated and used for intra-operative and post-operative comparison. Mean inclination angles were 31.2° ± 4.7° (20.3°–40.9°) intra-operatively, and 32.8° ± 4.5° (25.0°–43.3°) at six-weeks post-operation (mean difference = 1.6°). Intra-operative to post-operative inclination changes ranged from 0.05° to 11.1°. Mean anteversion angles were 23.5° ± 3.9° (17.8°–37.4°) intra-operatively and 29.3° ± 4.2° (18.0°–39.5°) at six-weeks post-operation (mean difference = 4.2°). Patients with change greater than 10° in inclination (n = 1) and anteversion (n = 5) had one screw and no screws, respectively. Intra-operative to post-operative anteversion changes ranged from 0.13° to 15.3°.

Table 2 Inter-reviewer reliability of radiographic measurements, intraclass correlation coefficient (ICC) and confidence limits and Radiological analysis of inclination and anteversion of acetabular cups intra-operatively and at six-weeks post-operative.

	ICC (95 % CI)	Mean ± SD
Inclination
Intra-operation	0.96 (0.93–0.98)	31.23° ± 4.7° (20.3–40.9)
6-weeks post-operation	0.93 (0.88–0.96)	32.8° ± 4.5° (25.0–43.3)
Anteversion
Intra-operation	0.79 (0.6–0.88)	23.5° ± 3.9° (17.8–37.4)
6-weeks post-operation	0.85 (0.74–0.91)	29.3° ± 4.2° (18.0–39.5)

Mean anterior tilt, internal rotation, and valgus rotation between day of surgery and six-weeks post-operation were 1.33° (0.01°–3.84°), 0.98° (0.12–2.79°), and 0.80° (0.02°–2.20°) respectively. Mean total rotation was 1.95° (0.33°–4.98°). No correlations were observed between change in inclination or anteversion and the individual planar rotations (Fig. 2) or total rotation (Fig. 3).

Pearson correlation of change in inclination (A) and anteversion (B) and anterior tilt, internal rotation, and valgus rotation between day of surgery and 6-weeks post-operation (p = 0.053–0.730). No correlations were found.

Pearson correlation of total cup rotation and change in (A) inclination (p = 0.122) and (B) anteversion (p = 0.768) and total rotation (°) between day of surgery and 6-weeks post-operation. No correlations were found.

4 Discussion

Despite advances in proper component positioning in THA, acetabular cup malalignment remains a concern. The advent of computer navigation systems to aid cup alignment has offered a more reproducible and accurate alternative.³^,⁸^,¹²^,¹³ However, widespread acceptance of such systems requires validation based on post-operative studies, often at six-week follow-ups and beyond. Early migration of implant components is known to occur within the first few weeks following THA, possibly adding an error to the post-operative accuracy assessment studies. Our objective was therefore to assess the potential error in such studies caused by early implant component migration within the first six weeks of THA.

Acetabular cup inclination and anteversion are the target measurements for intra-operative navigation systems. It is important to note that navigation systems may determine inclination and anteversion angles based on radiographic, anatomic, or operative coordinate systems.²² Slight differences in absolute measurements may be found between each system, but relative changes in inclination and anteversion over time would remain unaffected. This study is not a comparison of measurements by computer navigation systems, or a description of contributing factors in early implant migration. Rather, we aimed to assess the presence of a potential error caused by implant component migration which may attribute to erroneous reporting of computer navigation systems accuracy for cup position when comparisons are made postoperatively. Consequently, factors such as bone quality, implant sizing, or reaming technique are not considered in our analysis. Similarly, whilst the inclusion of screws may affect implant fixation,²³ our study does not aim to explain the causes of migration and screw count is only described for transparency regarding the surgical approach. Comparing cup alignment between intra-operative and six-week follow up measurements, we found a mean difference of 1.6° with a maximum of 11.1° for inclination and 4.2° with a maximum of 15.3° for anteversion. Total rotation of acetabular cups between day of surgery and the six-week follow-up was 1.95° with a maximum rotation of 4.98°. Our results therefore show that substantial cup migration may occur within the first few weeks of THA, which may partially confound attempts to measure cup placement accuracy. No correlation was found between cup migration and the change in anteversion or inclination angle, potentially due to the uncertainty of radiographically measuring cup inclination and anteversion. Notably, as the accuracy differences between systems become smaller, the impact of measurement errors (including from cups migrating when it is assumed that they have not) will have a greater effect.

Previous studies validating computer navigation systems based on post-operative follow-ups have reported a range of results. Ybinger et al.¹³ reported an average mean difference of 3.5° ± 4.4° for inclination and 6.5° ± 7.3° for anteversion between intra-operative computer navigation measurements and post-operative computer tomographs taken after the completion of patient rehabilitation. Dorr et al.¹² reported mean differences of 4.4° and 4.1° for inclination and anteversion when compared to post-operative computer tomographs. Vigdorchik et al.³ compared intra-operative computer navigation angles with six-week post-operation radiographs and found absolute mean differences of 4.1° ± 2.7° for inclination and 5.3° ± 4.4° for anteversion. Based on our findings, we hypothesize that part of the difference reported is due to in vivo acetabular cup movement, rather than navigation errors. As such, the accuracy and precision of computer navigation systems may be higher than previously reported.

4.1

4.1 Limitations

This study has limitations. First, we used anteroposterior radiographs to measure acetabular cup position. The gold standard for measuring cup position is done using CT scans; however, 2-dimensional radiographic measurements using the methods described by Lewwinek et al.¹ are widely used and provide relatively accurate and reliable measurements of inclination and anteversion.²⁴^,²⁵ It is also important to note that fluoroscopy and plain radiographs differ in terms of radiation exposure, image quality, and anatomical visualization though, any error attributed to the difference in modality is considered minimal. Next, as cup inclination and anteversion are not perfectly lined up with the axes of RSA, we were not able to extract explicit data regarding cup orientation using this method. Still, RSA provides migration tracking at an accuracy of 0.5°, making it a valuable tool to report overall rotation of the cup, and we also examined the effect of total rotation across all three axes. Our study may have been underpowered (power = 0.72) to detect statistically significant differences between cup angle measurements intra-operatively and at 6 weeks post-operation. Increasing the sample in future studies may help improve sensitivity to detect small measurement differences. Nevertheless, we aimed to report the possibility of migration error being added to validation experiments, and such experiments have comparable sample sizes.

5 Conclusion

In conclusion, this study demonstrated that early migration of acetabular cups may introduce an error in studies reporting computer navigation accuracy in acetabular cup placement based on post-operative imaging follow-ups.

CRediT authorship contribution statement

Shahnaz Taleb: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Data curation, manuscript writing. Jennifer S. Polus: Validation, Resources, manuscript revision. Brent Lanting: Conceptualization, Resources, manuscript revision, Supervision. Matthew G. Teeter: Conceptualization, manuscript revision, Supervision, Funding acquisition.

Consent

Patients were enrolled and informed consent was collected pre-operatively between January 2018 and July 2019 in a manner approved by our institutional research ethics board.

Ethical statement

This study was part of a larger prospective randomized clinical trial (NCT03558217) approved by our institutional research ethics board and adheres to the Helsinki Declaration of the World Medical Association (WMA) – Ethical Principles for Medical Research Involving Human Subjects.

Funding sources

This study is supported by a Starts Career Development Award from the Arthritis Society. ST is supported in part by a Queen Elizabeth II Graduate Scholarship in Science and Technology and Mitacs through the Mitacs Accelerate program.

References

Lewinnek G.E., Lewis J.L., Tarr R., et al . Dislocations after total hip-replacement arthroplasties. 1978
[Google Scholar]
Bhaskar D., Rajpura A., Board T., . Current concepts in acetabular positioning in total hip arthroplasty. Indian J Orthop. 2017;51:386.
[Google Scholar]
Vigdorchik J.M., Sculco P.K., Inglis A.E., et al . Evaluating alternate registration planes for imageless, computer-assisted navigation during total hip arthroplasty. J Arthroplast. 2021;36:3527-3533.
[Google Scholar]
Moskal J.T., Capps S.G., . Improving the Accuracy of Acetabular Component Orientation: Avoiding Malposition. 2010
[Google Scholar]
D’lima D.D., Urquhart A.G., Buehler K.O., et al . The Effect of the Orientation of the Acetabular and Femoral Components on the Range of Motion of the Hip at Different Head-Neck Ratios. 2000
[Google Scholar]
Berry D.J., . Unstable total hip arthroplasty: detailed overview. Instr Course Lect. 2001;50:265-274.
[Google Scholar]
Kennedy J.G., Rogers W.B., Soffe K.E., et al . Effect of acetabular component orientation on recurrent dislocation, pelvic osteolysis, polyethylene wear, and component migration. J Arthroplast. 1998;13:530-534.
[Google Scholar]
Ryan J.A., Jamali A.A., Bargar W.L., . Accuracy of computer navigation for acetabular component placement in THA. Clin Orthop Relat Res. 2010;468:169.
[Google Scholar]
Jolles B.M., Genoud P., Hoffmeyer P., . Computer-assisted cup placement techniques in total hip arthroplasty improve accuracy of placement. Clin Orthop Relat Res. 2004;426:174-179.
[Google Scholar]
Saxler G., Marx A., Vandevelde D., et al . The accuracy of free-hand cup positioning - a CT based measurement of cup placement in 105 total hip arthroplasties. Int Orthop. 2004;28:198.
[Google Scholar]
Leenders T., Vandevelde D., Mahieu G., et al . Reduction in variability of acetabular cup abduction using computer assisted surgery: a prospective and randomized study. Comput Aided Surg. 2002;7:99-106.
[Google Scholar]
Dorr L.D., Malik A., Wan Z., et al . Precision and bias of imageless computer navigation and surgeon estimates for acetabular component position. 2007:92-99.
[Google Scholar]
Ybinger T., Kumpan W., Hoffart H.E., et al . Accuracy of navigation-assisted acetabular component positioning studied by computed tomography measurements. Methods and results. J Arthroplast. 2007;22:812-817.
[Google Scholar]
Moon J.K., Jung J.W., Kim Y., et al . Acetabular cup migration after primary cementless total hip arthroplasty in rheumatoid arthritis and its influencing factors: a comparative study with osteoarthritic hip. Int Orthop. 2020;44:1047-1053.
[Google Scholar]
Perelgut M.E., Polus J.S., Lanting B.A., et al . The effect of femoral stem collar on implant migration and clinical outcomes following direct anterior approach total hip arthroplasty. Bone Joint J. 2020;102:1654-1661.
[Google Scholar]
Polus J.S., Perelgut M.E., Vasarhelyi E.M., et al . Femoral stem migration after direct lateral and direct anterior total hip arthroplasty: a prospective cohort study. Can J Surg. 2022;65:E487-E495.
[Google Scholar]
Perelgut M., Lanting B., Teeter M., . Does hip femoral stem design impact implant migration and patient recovery following a primary direct anterior total HIP arthroplasty? Orthopaedic Proceed. 2020;102-B
[Google Scholar]
Ilchmann T., . Radiographic assessment of cup migration and wear after hip replacement. Acta Orthop Scand Suppl. 1997;68
[Google Scholar]
Kärrholm J., Gill R.H.S., Valstar E.R., . The history and future of radiostereometric analysis. Clin Orthop Relat Res. 2006;448:10-21.
[Google Scholar]
Campbell D., Mercer G., Nilsson K.G., et al . Early migration characteristics of a hydroxyapatite-coated femoral stem: an RSA study. Int Orthop. 2011;35:483.
[Google Scholar]
Hopkins W.G., . Measures of reliability in sports medicine and science. Sports Med. 2000;30:1-15.
[Google Scholar]
Murray D.W., . The definition and measurement of acetabular orientation. J Bone Joint Surg Br. 1993;75:228-232.
[Google Scholar]
Polus J.S., Vasarhelyi E.M., Lanting B.A., et al . Acetabular cup fixation with and without screws following primary total hip arthroplasty: migration evaluated by radiostereometric analysis. HIP Int 2023
[Google Scholar]
Herrlin K., Peitersson H., Selvik G., . COMPARISON OF TWO-AND THREE-DIMENSIONAL METHODS FOR ASSESSMENT OF ORIENTATION OF THE TOTAL HIP PROSTHESIS. 1988
[Google Scholar]
Lee G.C., Lee S.H., Kang S.W., et al . Accuracy of planar anteversion measurements using anteroposterior radiographs. BMC Muscoskelet Disord. 2019;20
[Google Scholar]