Proposed Referential Index to Resect Femoroacetabular Cam-Type Impingement During Arthroscopy Using a Cadaveric Hip Model.

Purpose: To establish a reference index for the simple identification of the optimum resection point for cam-type impingement on arthroscopy.

Methods: Twelve cadaveric left hips with a 20° to 40° center-edge angle, without osteoarthritis, were examined (mean age, 85 ± 10.1 years). The pelvis was fixed such that the anterior pelvic plane and femur were parallel to the table. The resection line for impingement was first defined on the femoral head surface 5 mm distal to the acetabular labrum, from the 9-o'clock (anterior) to 12-o'clock (superior) position. Next, we measured the hip flexion angle necessary for the head-neck junction to reach the resection line. After positioning the wire on the femoral head surface along the resection line from the 9- to 12-o'clock area of the femoral head, we measured the target alpha angle on radiographs at 0°, 15°, 30°, 45°, and 60° of hip flexion using the frog-leg 45/45/30 view (45° of flexion, 45° of abduction, and 30° of external rotation) and Dunn 45 view (45° of flexion, 20° of abduction, and neutral rotation).

Results: The mean hip flexion angle at which the head-neck junction reached the resection line was 31° ± 4.6°. For 0°, 15°, 30°, 45°, and 60° of hip flexion, the mean target alpha angle was 75.5° ± 5.5°, 65.3° ± 5.6°, 56.3° ± 5.8°, 49.0° ± 6.6°, and 42.6° ± 5.8°, respectively, using the frog-leg 45/45/30 view and 75.0° ± 6.0°, 65.8° ± 6.2°, 57.2° ± 7.3°, 50.7° ± 6.9°, and 44.2° ± 5.8°, respectively, using the Dunn 45 view. There were no significant differences between the 2 radiographic techniques (P = .82, P = .84, P = .76, P = .57, and P = .52, respectively).

Conclusions: A description of the degree of hip flexion during cam resection can affect the final alpha angle when using the labrum as a reference for resection.

Clinical Relevance: The described index allows systematic navigation of cam lesions during arthroscopy for femoroacetabular impingement patients using the hip flexion angle.