Acetabular Depth is Your Friend: Adequate Rim Resection in Femoroacetabular Impingement Surgery Remains a Challenge

Joshua Sapong Knudsen, FRACS (Ortho), MBChB, NEW ZEALAND Matthew J. Brick, MBChB, FRACS, NEW ZEALAND

ISAKOS eNewsletters   Current Perspective 2026   rating

Introduction

Femoroacetabular impingement (FAI) is characterised by abnormal contact between the acetabulum and the femur during functional range of motion^1-3. This mechanical conflict leads to progressive joint dysfunction and is a recognised precursor to secondary osteoarthritis (OA). FAI may involve cam-type morphology (femoral neck abnormality), pincer-type morphology (acetabular overcoverage), or a combination of both (observed in the majority of clinical cases). Hip arthroscopy aims to eliminate bony impingement and address secondary chondrolabral pathology, thereby improving function and potentially altering the degenerative trajectory of the joint^1-3.

The Challenge of Adequately Performing the Rim Resection in FAI Surgery

Pincer-type FAI is broadly defined as acetabular overcoverage. A common radiographic threshold is a lateral center-edge angle (LCEA) of >39° on a standardised anteroposterior (AP) pelvic radiograph^1-3. Pincer-type morphology may be focal or global. Focal pincer morphology is characterized by localised overcoverage, frequently anterior, and is often associated with acetabular retroversion (indicated by the crossover sign on AP radiographs without pelvic tilt), and Global pincer morphology is characterized by generalised overcoverage³. Both morphologies result in “collision” impingement, typically manifesting as labral-dominant damage, peripheral chondral lesions, and often a “contrecoup” lesion on the posteroinferior acetabulum. We have yet to learn how pincer lesions develop, but we have noted that pincer lesions are most frequently observed in young to middle-aged female patients.

The primary surgical objective is to resolve mechanical impingement through osteoplasty, often including acetabuloplasty, followed by labral preservation (remodelling or repair) and capsular management with use of repair or plication depending on the patient’s needs^1-3. Addressing the impingement is critical; as noted by Philippon et al. residual deformity is the primary driver for revision hip arthroscopy. Early in the history of hip arthroscopy, Matsuda et al. and Shao et al. demonstrated that arthroscopic treatment of focal and global pincer lesions was both safe and effective; however, historical data have often shown inferior outcomes for patients with pincer morphology as compared with those with isolated cam morphology^1,2. Other investigators have raised concerns about outcomes following acetabuloplasty. Specifically, Palmer et al.  reported poorer clinical results following rim resection, and Gupta et al. identified acetabuloplasty as a predictor of conversion to total hip arthroplasty (THA). Chandrasekaran et al. further demonstrated that patients with “overcoverage" (LCEA, >40°) who underwent acetabuloplasty had lower Harris Hip Scores and higher THA conversion rates than those with normal coverage (LCEA, 25° to 40°)².

Bhatia et al. provided a biomechanical rationale for these high failure rates⁴. In a cadaveric model, those investigators demonstrated that increased rim resection depth correlated with a precipitous rise in peak contact pressure, with resections of 6 and 8 mm increasing pressure by 300% and 400%, respectively. The Multicentre Osteoarthritis Study (MOST) demonstrated that an increase in joint contact pressure was highly associated with accelerated OA development, although that study pertained to knee patients. Similarly, Colvin et al. demonstrated a correlation between the amount of rim resection and subluxation of the hip, with 4 and 5-mm resection resulting in subluxation in 30% and 70% of their hip models, respectively.

The relationship between linear resection and angular change is significant and important in real-life practice. Philippon et al. found that the initial 1 mm of resection reduces the LCEA by 2.4°, with each subsequent millimetre resulting in a 0.6° change. Ju et al. proposed the following predictive formula: ΔLCEA = 1.8 + (0.64 × rim resection in mm)⁵.

The previously noted discrepancy in pincer outcomes may be related to over-resection. In the study by Chandrasekaran et al., the correction of the mean LCEA was much larger in the overcovered (pincer) group (from 45° to 28°) than in the control group (from 31° to 28°)². The standard deviations in both groups implied that some patients may have had correction of the LCEA to <25 deg°, which is borderline dysplastic².  In contrast, Brick et al., found no significant difference in outcomes after more conservative correction of acetabular overcoverage¹. In their prospectively collected database, 114 overcovered hips were matched with normal covered hips in a 1:1 fashion and were followed for 2 years. In the pincer group, mean LCEA was corrected from 44° to 34°, whereas in the comparison group, it was corrected from 33° to 31° . Thus, the postoperative LCEAs in both groups were higher than those reported by Chandrasekaran et al., and the degree of the correction was much more conservative in the pincer group. Despite this conservative correction, the reoperation rates did not differ significantly between the two groups, implying the successful elimination of FAI¹.  The variability in postoperative LCEA also differed between those two studies. Chandrasekaran et al. described standard deviations of 5.31° in the overcovered group and 4.07° in the control group, compared with values of 3.5° and 3.0° for the respective groups in the study by Brick et al.^1,2. The combination of the higher postoperative LCEA and smaller standard deviation in the study by Brick et al. suggests that those investigators did not inadvertently create a borderline dysplastic hip postoperatively.

Ju et al.  assessed the relationship between depth of acetabuloplasty and patient-reported outcomes at 2 years in patients with global pincer FAI⁵. That retrospective review included 41 hips with global pincer morphology (LCEA, >40°; Tönnis angle, <0° ), splitting them into a low-resection (<3 mm) to high-resection (>3 mm) groups. While both groups improved, the low-resection group—which maintained a postoperative LCEA of approximately 42°—showed superior trends. Notably, the chondrolabral junction was preserved in the low-resection group. However, the high-resection group included one patient who underwent debridement of the labrum and one who underwent reconstruction⁵. Thus, in that study, it is difficult to isolate the effect of resection depth from potential effects of the difference in labral treatment.

In a study of patients with extreme pincer morphology (LCEA, >45°; Tönnis angle, ≤0°), White et al. demonstrated significant improvement following circumferential labral reconstruction and measured acetabuloplasty³ . By targeting a postoperative LCEA in the mid-30° range, (average, 35.4°), they achieved high satisfaction and a low (2%) THA conversion rate at 2 years³.

The Femoral Osteoplasty Plays a Critical Role as Well

Although the present article is focused on acetabular work in the treatment of FAI, the acetabulum is rarely treated in isolation. FAI, as the name implies, involves both the acetabulum and the femur, and a large number of patients present with involvement of both sides of the joint^1-5. Our improving ability to consistently optimise femoral morphology has likely contributed to the growing body of evidence highlighting that, despite higher postoperative LCEAs, low reoperation rates and improvement in postoperative function can be achieved. Based on approximately 5,000 procedures performed over 20 years, the senior author’s practice has evolved toward favoring femoral-sided bony correction in patients with mixed cam/pincer morphology with preoperative LCEAs in the high-30° range. Even in the presence of a relatively deep acetabulum, a stable functional labrum is left alone in favour of femoral-side correction when possible.

Summary and Future Perspectives

In this article, we have highlighted the evolving management of pincer morphology from aggressive rim resection, aimed at bringing the socket depth to the middle of the normal range, to a more conservative acetabuloplasty targeting the upper limit of the normal range. Current evidence suggests that aiming for a postoperative LCEA in the mid-to-high 30° range yields outcomes comparable to those for other FAI morphologies while avoiding the risks of iatrogenic instability and increased contact pressures. The surgical goal should be to eliminate mechanical impingement while preserving acetabular depth and optimising the soft-tissue structures of the hip, including labral function and capsular repair.

This evolution of optimal management of pincer FAI has been guided by multiple small-scale studies. However small studies are inherently more prone to bias with confounding variables difficult to control. There is a need for larger databases. Hip arthroscopy has well-established short to medium term benefits but the potential for long-term effects lend itself to the need for high-quality long-term registries. A limitation in current pincer description is our ongoing use of a 2-dimensional imaging (Pelvis X-rays) to describe a 3-dimensional issue. As 3D Imaging and impingement modelling becomes routine this may improve our ability to describe FAI preoperatively, remodel intra operatively (with intraoperative 3D Guidance) and measure our work post operatively. Incorporating accurate pre- and post-operative data into long term registries will further improve our management of pincer patients

References

1. Brick CR, Bacon CJ, Brick MJ. Importance of Retaining Sufficient Acetabular Depth: Successful 2-Year Outcomes of Hip Arthroscopy for Patients With Pincer Morphology as Compared With Matched Controls. The American Journal of Sports Medicine [Internet]. 2020 [cited 2026 May 23];48(10):2471–80. Available from: https://journals.sagepub.com/doi/pdf/10.1177/0363546520937301
2. Chandrasekaran S, Darwish N, Chaharbakhshi EO, Suarez-Ahedo C, Lodhia P, Domb BG. Minimum 2-Year Outcomes of Hip Arthroscopic Surgery in Patients With Acetabular Overcoverage and Profunda Acetabulae Compared With Matched Controls With Normal Acetabular Coverage. The American Journal of Sports Medicine [Internet]. 2017 [cited 2026 May 23];45(11):2483–92. Available from: http://journals.sagepub.com/doi/pdf/10.1177/0363546517708769
3. White BJ, Spears H, McKaughan Q, Constantinides SM. Treatment of severe pincer-type femoroacetabular impingement with arthroscopic significant acetabular rim correction and circumferential labral reconstruction improves patient-reported outcome measures. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 2023;39(1):41–50.
4. Bhatia S, Lee S, Shewman E, Bush-Joseph CA, Salata MJ, Nho SJ. Effects of Acetabular Rim Trimming on Hip Joint Contact Pressure. Orthopaedic Journal of Sports Medicine [Internet]. 2015 [cited 2026 May 23];3(3_suppl). Available from: https://journals.sagepub.com/doi/pdf/10.1177/2325967115S00006
5. Ju X, He Z, Dang H, Zhang X, Zhang Z, Xu Y, et al. Relationship between the Depth of Acetabuloplasty and Outcomes of Hip Arthroscopy in Patients with Global Pincer Femoroacetabular Impingement: Study with a Minimum Follow‐Up Period of 2 Years. Orthopaedic Surgery [Internet]. 2023 [cited 2026 May 23];15(6):1571–8. Available from: https://onlinelibrary.wiley.com/doi/pdf/10.1111/os.13739

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