Background: Although the use of hip arthroscopy continues to increase, capsular management remains a controversial topic. Purpose: To investigate the biomechanical effect of capsulotomy and capsular repair techniques on hip joint kinematics in varying combinations of sagittal and coronal joint positions. Study Design: Controlled laboratory study. Methods: Eight fresh-frozen hemi-pelvises (78.3 ± 6.0 years of age; 4 left, 6 male) were dissected of all overlying soft tissue, with the exception of the hip joint capsule. The femur was potted and attached to a load cell, while the pelvis was secured to a custom-designed fixture allowing static alteration of the flexion-extension arc. Optotrak markers were rigidly attached to the femur and pelvis to track motion of the femoral head with respect to the acetabulum. After specimen preparation, 7 conditions were tested: (1) intact, (2) after portal placement (anterolateral and midanterior), (3) interportal capsulotomy (IPC) (35 mm in length), (4) IPC repair, (5) T-capsulotomy (IPC +15-mm longitudinal incision), (6) partial T-repair (repair of longitudinal incision with IPC left open), (7) full T-repair. All conditions were tested in 15° of extension (–15°), 0°, 30°, 60°, and 90° of flexion. Additionally, all flexion angles were tested in neutral, as well as in specimen-specific maximum abduction and adduction, resulting in 15 testing positions. Internal rotation (IR) and external rotation (ER) moments of 3 N·m were manually applied to the femur via the load cell at each position. Rotational range of motion and joint kinematics were recorded. Results: In the neutral coronal plane, T-capsulotomy significantly increased IR/ER rotational range of motion compared with intact state at −15° (55.96°± 6.11° vs 44.92°± 7.35°, P < .001), while IPC significantly increased rotation compared with the portal state at 0° (60.09°± 6.82° vs 51.68°± 10.35°, P = .004). No statistically significant increases were found in mediolateral joint translation after IPC or T-capsulotomy. Similarly, no statistically significant increases were noted in anteroposterior translation after IPC or T-capsulotomy. Complete capsular repair restored near native joint kinematics, with no significant differences in rotation or translation between any complete capsular repair groups and the intact state, regardless of joint position. Conclusion: Universally, across all conditions, complete capsular repair after interportal or T-capsulotomy restored rotational range of motion and joint translation to values observed in the native joint. Clinical Relevance: Where feasible, complete capsular closure should be performed, especially after T-capsulotomy. However, further clinical evaluation is required to determine whether adverse kinematic parameters of an unrepaired capsule are associated with reduced patient-reported outcomes.

Purpose To noninvasively characterize the ligament strain in the hip capsule using a novel CT-based imaging technique. Methods The superior iliofemoral ligament (SIFL), inferior iliofemoral ligament (IIFL), ischiofemoral ligament (IFL) and pubofemoral ligament (PFL) were identified and beaded in seven cadavers. Specimens were mounted on a joint motion simulator within an O-arm CT scanner in − 15°, 0°, 30°, 60°, and 90° of flexion. 3 Nm of internal rotation (IR) and external rotation (ER) were applied and CT scans obtained. Strains were calculated by comparing bead separation in loaded and unloaded conditions. Repeated-measures ANOVA was used to evaluate differences in strain within ligaments between hip positions. Results For the SIFL, strain significantly decreased in IR at 30° (p = 0.045) and 60° (p = 0.043) versus 0°. For ER, there were no significant position-specific changes in strain (n.s.). For the IIFL, strain decreased in IR and increased in ER with no significant position-specific differences. For the IFL, strain increased with IR and decreased with ER with no significant position-specific differences. Finally, in the PFL there was a significant flexion angle-by-load interaction (p < 0.001; ES = 0.566), with peak strains noted at 60˚, however pair-wise comparisons failed to identify significant differences between positions (n.s.). Strain decreased in ER, with no significant position-specific differences. Conclusion The SIFL and IIFL limit hip external rotation with greater effect in higher flexion angles, while the IFL and PFL limit hip internal rotation. Following hip arthroscopy, consideration should be given to restricting external rotation as traditional capsulotomies cause injury to the SIFL and IIFL.

Background: Several techniques for hip capsular reconstruction have been described to address gross instability or microinstability due to capsular deficiency. However, objective biomechanical data to support their use are lacking. Purpose: To compare the kinematic effect of 2 capsular reconstruction techniques (iliotibial band [ITB] graft and Achilles tendon graft). Kinematic effect encompassed rotational range of motion (ROM) as well as joint translation in the coronal, sagittal, and axial planes. Study Design: Controlled laboratory study. Methods: 8 paired, fresh-frozen hemi-pelvises (16 hips) were tested on a custom-designed joint motion simulator in the intact state and after capsulectomy. Pairs were randomly allocated to either ITB or Achilles reconstruction and retested. Testing was performed at 0°, 45°, and 90° of flexion. Internal-external rotation (IR-ER) torques and abduction-adduction torques of 3 N·m were applied to the femur via a load cell at each position, and rotational ROM and joint translation in the coronal, sagittal, and axial planes were recorded. Results: At 45° and 90°, there was a significant effect of the condition of the hip on the total IR-ER ( P = .004, effect size [ES] = 0.305; and P < .001, ES = 0.497; respectively). At 45°, mean ± SD total rotation was significantly greater for the capsulectomy (59.7°± 15.9°) state compared with intact (53.3°± 13.2°; P = .007). At 90°, reconstruction significantly decreased total rotation to 49.0°± 18.9° compared with a mean total rotation of 52.8°± 18.7° after capsulectomy ( P = .02). No difference was seen in the total abduction-adduction of the hip between conditions. Comparisons of the 2 different reconstruction techniques showed no significant differences in total IR-ER or abduction-adduction ROM or joint translation in the coronal, sagittal, or axial planes. For translation, at both 0° and 45° there was a statistically significant effect of the condition on the medial-lateral translation ( P = .033; ES = 0.204). Reconstruction, independent of technique, was successful in significantly decreasing ( P = .030; P = .014) the mean medial-lateral translation at 0° and 45° of hip flexion from 5.2 ± 3.8 mm and 5.6 ± 4.0 mm to 2.8 ± 1.9 mm and 3.9 ± 3.2 mm, respectively. Conclusion: The integrity of the native hip capsule played a significant role in rotational stability, where capsulectomy significantly increased rotational ROM. Both ITB and Achilles reconstruction techniques restored normal rotational ROM of the hip at 90° of flexion as well as coronal plane stability at 0° and 45° of hip flexion. No differences were seen between ITB and Achilles reconstruction techniques. Clinical Relevance: Both capsular reconstruction techniques provide comparable joint kinematics, restoring rotation and translation to normal values with the exception of rotational ROM at 45°, which remained significantly greater than the intact state. The most significant results were the rotational stability at 90° of hip flexion and coronal plane stability at 0° and 45° of hip flexion, which were significantly improved compared with the capsulectomy state.

While 3D motion capture (MoCap) has enabled the high-resolution analysis of human movement, major limiting factors of these systems are their high cost and restriction to laboratory settings. This limits the generalizability of data captured in a controlled environment to movements performed during sport. The development of algorithms to support portable markerless MoCap systems provide a low-cost functional alternative to measure kinematics during sport-specific movement tasks in a real-world setting, with minimal invasiveness. PURPOSE: Assess the accuracy of a custom, portable, and markerless MoCap system in capturing lower limb joint kinematics during functional motor tasks compared to a gold-standard 3D MoCap system. METHODS: 15 subjects (12 females; age: 20±1 year) performed three motor tasks (8 trials each): walking, running, and cutting in a laboratory. The portable MoCap system comprised of 5 high-definition 2D cameras and proprietary pose-estimation software (wrnchAI ver 1.2.2) to capture lower limb landmark points and establish joint positions. Subjects were outfitted with 29 retroreflective markers for concurrent capture via a 10-camera Vicon 3D MoCap system. We extracted bilateral summary variables of ankle, knee, and hip angles in the sagittal and frontal planes. To assess the agreement between systems, coefficient of multiple determination (R 2 ), root mean squared error (RMSE), and mean joint angle estimation error (MEE) were calculated per trial. RESULTS: R 2 values revealed a strong relationship (range: 0.64-0.94). RMSE and MEE results indicate a strong to moderate accuracy (RMSE range: 0.83°-8.15°, MEE range: 0.86° -9.40°). See Table 1 for summary of results. CONCLUSION:The findings indicate the portable MoCap system with wrnchAI software effectively captured lower limb kinematics during functional motor tasks. Overall, portable MoCap technology can provide a cost-effective tool to assess athletes in a natural sport environment.Summary of R^2, RMSE, MEE results across conditions reported as mean ± standard deviation.

While 3D motion capture (MoCap) has enabled the high-resolution analysis of human movement, major limiting factors of these systems are their high cost and restriction to laboratory settings. This limits the generalizability of data captured in a controlled environment to movements performed during sport. The development of algorithms to support portable markerless MoCap systems provide a low-cost functional alternative to measure kinematics during sport-specific movement tasks in a real-world setting, with minimal invasiveness. PURPOSE: Assess the accuracy of a custom, portable, and markerless MoCap system in capturing lower limb joint kinematics during functional motor tasks compared to a gold-standard 3D MoCap system. METHODS: 15 subjects (12 females; age: 20±1 year) performed three motor tasks (8 trials each): walking, running, and cutting in a laboratory. The portable MoCap system comprised of 5 high-definition 2D cameras and proprietary pose-estimation software (wrnchAI ver 1.2.2) to capture lower limb landmark points and establish joint positions. Subjects were outfitted with 29 retroreflective markers for concurrent capture via a 10-camera Vicon 3D MoCap system. We extracted bilateral summary variables of ankle, knee, and hip angles in the sagittal and frontal planes. To assess the agreement between systems, coefficient of multiple determination (R 2 ), root mean squared error (RMSE), and mean joint angle estimation error (MEE) were calculated per trial. RESULTS: R 2 values revealed a strong relationship (range: 0.64-0.94). RMSE and MEE results indicate a strong to moderate accuracy (RMSE range: 0.83°-8.15°, MEE range: 0.86° -9.40°). See Table 1 for summary of results. CONCLUSION:The findings indicate the portable MoCap system with wrnchAI software effectively captured lower limb kinematics during functional motor tasks. Overall, portable MoCap technology can provide a cost-effective tool to assess athletes in a natural sport environment.