Related Experiment Video
Updated: May 24, 2026
In Vivo Quantification of Hip Arthrokinematics during Dynamic Weight-bearing Activities using Dual Fluoroscopy
Published on: July 2, 2021
Alterations in internal rotation and alpha angles are associated with arthroscopic cam decompression in the hip
Bryan T Kelly1, Asheesh Bedi, Catherine M Robertson
1Center for Hip Pain and Preservation, Hospital for Special Surgery, New York, NY, USA.
Background:
Symptomatic labral tears of the hip are associated with bony abnormalities of the femoral head and acetabulum, resulting in impingement. These patients have characteristic internal rotation limitations, which can result in compensatory athletic injury patterns around the hip, pelvis, and lumbar spine.
Hypothesis:
Patients undergoing arthroscopic cam decompression will have improvement in internal rotation after decompression. Patients with decreased femoral neck anteversion will have decreased preoperative internal rotation of the hip and show less improvement after cam decompression.
Study Design:
Cohort study; Level of evidence, 3.
Methods:
Patients undergoing arthroscopic decompression of cam and pincer lesions of the hip and treatment of labral injury were evaluated for range of motion and bony anatomy by preoperative computed tomography and pre- and postoperative radiographs. Patients were excluded for age older than 40 years, arthritic changes of the joint, and revision setting.
Results:
Fifty-five patients (56 hips) were treated with selective labral debridement with functional labral preservation (33/56) or selective labral debridement with labral refixation (23/56) and cam decompression. Fifty-one of the 56 had resection of associated pincer lesions. Patients were divided into femoral anteversion subgroups: normal (5°-20°, 34 patients), increased (>20°, 8 patients), and decreased (<5°, 13 patients). Mean patient age was 24.7 ± 6.3 years (range, 14-39 years). Alpha angle, a measure of the head-neck offset, decreased from 68.0° ± 10.0° preoperatively to 43.4° ± 4.0° after decompression (P < .001). Internal rotation of the hip increased from 9.9° ± 6.6° preoperatively to 27.6° ± 6.4° after decompression (P < .001) and 30.1° ± 5.3° at 3 months (P < .001). Hip flexion was not significantly different immediately after decompression but was significantly improved from 115.7° ± 13.3° preoperatively to 127.9° ± 6.6° at 3 months postoperatively (P < .003). Although improvement in internal rotation after decompression increased independent of femoral version, patients with abnormal version had altered internal rotation with increased values associated with increased anteversion (15.7° ± 5.4°/34.3° ± 6.7°) and decreased with relative retroversion (7.1° ± 8.3°/25.2° ± 4.9°; P < .05).
Conclusion:
Arthroscopic decompression results in improvement of the radiographic alpha angle and normalization of internal rotation in impingement-related disease of the hip. Internal rotation improvements can be achieved even in the setting of femoral retroversion.
