Arthroscopic Femoral and Acetabular Osteoplasties Alter the In Vivo Hip Kinematics of Patients With Femoroacetabular Impingement.

Purpose: Three-dimensional (3D)-two-dimensional (2D) fluoroscopic image registration was used to measure 3D hip kinematics before and after hip arthroscopy in patients with femoroacetabular impingement (FAI). Methods: In total, 24 subjects diagnosed with FAI (21 unilateral, 3 bilateral) were prospectively recruited. A clinical impingement test was performed on both hips while the patient was awake and then while anaesthetized, and in the operative hip after arthroscopic osteoplasties and labral repair. Fluoroscopy was used to image the hip during the impingement tests. Images were analyzed using 3D-2D image registration to calculate joint kinematics. The examiner's hand was instrumented with a glove to measure internal rotation torque applied to the hip during each test. Results: Internal rotation increased by 3.7° (standard error [SE] 0.95°) after surgery (P = .001). Maximum displacement of the femoral head out of the acetabulum was 4.0 mm (SE 0.5 mm) in the operative group before surgery and 1.8 mm (SE 0.3 mm) after surgery (P < .001). This was due to a decrease in lateral displacement by 1.3 mm (SE 0.4 mm, P = .002) and proximal displacement by 0.8 mm (SE 0.3 mm, P = .013). Internal rotation torque was greater in the operative hips when anaesthetized compared with when awake, by 5 Nm (SE 1.2 Nm, P < .001), and greater in the contralateral hips than the operative hips when awake by 8.4 Nm (SE 1.4 mm, P < .001). Conclusions: Arthroscopic osteoplasty and labral repair increased hip range of motion and reduced femoral head displacement from the acetabulum during the IR90 provocation test (i.e., hip flexion to 90°, maximum internal rotation) in patients with FAI. This suggests that the impinging acetabular rim acted as a fulcrum before surgery and may have caused edge loading that was reduced after surgery. Level of Evidence: Level IV case series, therapeutic study.

Validation of a method to measure three-dimensional hip joint kinematics in subjects with femoroacetabular impingement.

INTRODUCTION: A kinematic measurement method combining dynamic motion and imaging, which captures the behaviour of the hip at terminal motion, may offer improved diagnostic accuracy and enhance our understanding of the mechanics of femoroacetabular impingement (FAI). METHODS: 3 embalmed cadaveric hip/pelvis specimens with implanted Roentgen Stereophotogrammetric Analysis (RSA) beads were mounted on a custom rig and imaged with a fluoroscope in four poses to simulate a clinical impingement examination: in hip extension and in three positions: near impingement, early impingement and late impingement while simulating a flexion/adduction/internal rotation manoeuvre. Hip joint kinematics were measured using 2 methods and compared: RSA (gold standard) and a custom 3-dimensional to 2-dimensional (3D-2D) image registration method which matches 3D models developed from CT to 2D fluoroscopic images. RESULTS: Using RSA as the gold standard, bias and precision of hip joint rotations measured using 3D-2D registration demonstrated maximums of 1.64° and 3.96°, respectively. However, if the single outlier was removed, bias and precision were 0.55° and 1.38°. Bias and precision of translations had maximums of 0.51 mm and 0.77 mm, respectively. CONCLUSIONS: This 3D to 2D registration method may offer a clinically useful solution for dynamic assessment of hip impingement. If 5-mm translation and 10° of rotation represent a clinically significant difference in hip kinematics, the method's accuracy of approximately 1 mm displacement and 1° rotation should enable detection of significant clinical differences.