Hip Joint Torsional Loading Before and After Cam Femoroacetabular Impingement Surgery

Abstract

Background:Surgical management of cam femoroacetabular impingement (FAI) aims to preserve the native hip and restore joint function, although it is unclear how the capsulotomy, cam deformity, and capsular repair influence joint mechanics to balance functional mobility.Purpose:To examine the contributions of the capsule and cam deformity to hip joint mechanics. Using in vitro, cadaveric methods, we examined the individual effects of the surgical capsulotomy, cam resection, and capsular repair on passive range of motion and resistance of applied torque.Study Design:Descriptive laboratory study.Methods:Twelve cadaveric hips with cam deformities were skeletonized to the capsule and mounted onto a robotic testing platform. The robot positioned each intact hip in multiple testing positions: (1) extension, (2) neutral 0°, (3) flexion 30°, (4) flexion 90°, (5) flexion-adduction and internal rotation (FADIR), and (6) flexion-abduction and external rotation. Then the robot performed applicable internal and external rotations, recording the neutral path of motion until a 5-N·m of torque was reached in each rotational direction. Each hip then underwent a series of surgical stages (T-capsulotomy, cam resection, capsular repair) and was retested to reach 5 N·m of internal and external torque again after each stage. During the capsulotomy and cam resection stages, the initial intact hip’s recorded path of motion was replayed to measure changes in resisted torque.Results:Regarding changes in motion, external rotation increased substantially after capsulotomies, but internal rotation only further increased at flexion 90° (change +32%, P = .001, d = 0.58) and FADIR (change +33%, P < .001, d = 0.51) after cam resections. Capsular repair provided marginal restraint for internal rotation but restrained the external rotation compared with the capsulotomy stage. Regarding changes in torque, both internal and external torque resistance decreased after capsulotomy. Compared with the capsulotomy stage, cam resection further reduced internal torque resistance during flexion 90° (change −45%, P < .001, d = 0.98) and FADIR (change −37%, P = .003, d = 1.0), where the cam deformity accounted for 21% of the intact hip’s torsional resistance in flexion 90° and 27% in FADIR.Conclusion:Although the capsule played a predominant role in joint constraint, the cam deformity provided 21% to 27% of the intact hip’s resistance to torsional load in flexion and internal rotation. Resecting the cam deformity would remove this loading on the chondrolabral junction.Clinical Relevance:These findings are the first to quantify the contribution of the cam deformity to resisting hip joint torsional loads and thus quantify the reduced loading on the chondrolabral complex that can be achieved after cam resection.

Hip Joint Capsular Anatomy, Mechanics, and Surgical Management

“…Translations of the hip joint center should be further examined to help characterize microinstability over the series of surgical stages 17,20,49 . In addition, the balance between capsular repair and plication should be compared with established objective measures to minimize iatrogenic instability in hips with pathology 6,19 .…”

“…Since surgical management of FAI and other common hip pathologies in young adults can be effective in minimizing the risks of adverse cartilage loading and degeneration 19,61,64,65,70 , more research needs to be done to examine where changes occur first (i.e., subchondral bone, cartilage, or capsule) in response to varying joint morphology and mechanics. This is certainly the case for the zona orbicularis.…”

“…Although it has been well established that surgically resecting the cam morphology can delay the pathomechanical process of subchondral bone stiffening 60 , 61 , cartilage degeneration 62 , 63 , and adverse loading 64 , 65 , it was elusive how much the actual morphology or any of the individual surgical stages contributed to these aspects. In what we believe is the only documented in vitro cadaveric study that has examined a well-represented pathological cohort with cam morphologies, Ng et al evaluated a large group of hip specimens with moderate-to-high alpha angles (representative of the symptomatic cam population) from young, male donors 19 . The study examined how the capsulotomy, cam resection, and capsular repair affected passive range of motion and torque loading (Fig.…”

“…The effects of these factors are evident in the many cases of iatrogenic instability arising in patients with milder deformities who underwent overcorrection, resulting in ineffective labral seals and load distributions 76 , 89 - 91 , which were further compounded by a deficient capsule 92 . As capsular repair can substantially decrease external rotation during deep hip flexion, complete capsular repair or augmentation may be most effective for larger capsulotomies or overresected cams 18 , 85 ; however, it should be cautiously performed to avoid overtightening the joint 19 .…”

“…More importantly, how the hip capsule is managed during surgical interventions (preservation and arthroplasty) and its effects on joint function are increasingly recognized [5][6][7][8] . Several recent laboratory studies have provided new insights into functional mobility and stability of the hip joint that should be carefully considered during surgery [9][10][11][12][13][14][15][16][17][18][19][20] . The purpose of this review was to provide a comprehensive summary of the functional anatomy and material characteristics of the hip capsule and the effects of different capsular management techniques during arthroscopic and arthroplasty procedures on joint function.…”