Surgical treatment of femoroacetabular impingement improves hip kinematics: a computer-assisted model.

BACKGROUND: Femoroacetabular impingement (FAI) is now recognized as the most common cause of early osteoarthritis in the nondysplastic hip. While the surgical treatment of FAI has demonstrated favorable clinical outcomes, the ability of an osteoplasty to reliably improve hip kinematics and range of motion remains unknown.

PURPOSE: This study used computer-assisted 3-dimensional (3D) analysis to assess differences in hip range of motion before and after the arthroscopic surgical treatment of symptomatic FAI.

STUDY DESIGN: Case series; Level of evidence, 4.

METHODS: Ten patients with symptomatic, focal cam and/or pincer impingement lesions underwent high-resolution computed tomography scans and computer-assisted 3D modeling of the involved hip before and after corrective arthroscopic surgery by the senior author. Cam location, alpha angle, neck-shaft angle, femoral version, and acetabular version at 12-o'clock through 3-o'clock positions were measured. The model was subsequently dynamized to define the preoperative and postoperative range of motion and location of impingement with hip flexion, internal rotation, and internal rotation at 90° of hip flexion. Statistical analysis of preoperative and postoperative hip flexion and internal rotation at 90° of hip flexion was performed using paired t tests with P < .05 defined as significant.

RESULTS: The cam lesion was located between 12 o'clock and 5 o'clock in all cases. Mean preoperative alpha angle was 59.8° (range, 36°-76°). Mean femoral version was 12.5° (range, -15° to 32°). Mean preoperative hip flexion was 107.40° ± 11.6°, and mean internal rotation at 90° of hip flexion was 19.10° ± 13.0°. The location of impingement was unique in each case and not predictable based on simple radiographic measures (ie, alpha angle) alone. Corrective femoral and rim osteoplasty resulted in significant improvements in both hip flexion (3.8°; P = .002) and internal rotation (9.3°; P = .0002). Mean postoperative alpha angle was 36.4° (range, 22°-46°).

CONCLUSION: Focal cam and/or rim osteoplasty can reliably improve hip kinematics and range of motion in patients with symptomatic FAI, particularly the limitation of internal rotation in a flexed position. Computed tomography-based computer modeling can localize regions of anticipated mechanical impingement in symptomatic patients. A complete osteoplasty in these defined regions, through an arthroscopic or open approach, predictably improves range of motion and may help to eliminate the recurrent mechanical collision and secondary chondral injury associated with FAI.