Hooke, Alex W

Purpose To determine the relationship between cam morphology of the hip and ipsilateral sacroiliac motion compared to the native hip in a cadaveric model. Methods A simulated cam state was created using a 3‐dimensional printed cam secured to the head‐neck junction of 5 cadaveric hips. Hips were studied using a computed tomography–based optic metrology system and a 6 degree‐of‐freedom robot to exert an internal rotation torque at 3 different torque levels (6 N‐m, 12 N‐m, 18 N‐m). Outcomes included translational and rotational movement about 3 axes and composite (total) translational motion at the ipsilateral sacroiliac (SI) joint. Statistical analysis included a linear mixed model regression with repeated measures. Results The presence of a simulated cam was associated with medial motion in the coronal plane ( P = .03) and posterior motion in the sagittal plane ( P < .01) but not composite motion ( P = .37). Motion in the axial plane was in an inferior direction ( P = .08). Cam morphology significantly changed rotation in the sagittal plane ( P < .01) but not in the coronal ( P = .63) or axial plane ( P = .18). Composite motion was related to the amount of torque applied to the hip ( P < .01). The amount of torque applied to the hip was related to rotation in the coronal plane ( P < .01), axial plane ( P < .01), and sagittal plane ( P < .01) with increased effects as torque increased. Torque was not associated with translation movement in any of the anatomic planes. Conclusions The presence of simulated cam morphology is associated with motion in a more medial, inferior, and posterior direction at the ipsilateral SI joint relative to a native state. Increasing torque affects the magnitude of translation, but not its direction, which in this study is primarily influenced by cam morphology. Clinical Relevance This biomechanical connection between cam‐type femoroacetabular impingement syndrome and the ipsilateral SI joint provides insight into SI joint dysfunction in patients with femoroacetabular impingement syndrome.

Purpose To investigate the gliding resistance dynamics between the supraspinatus (SSP) tendon and the coracoacromial arch, both before and after subacromial decompression (anterolateral acromioplasty) and acromion resection (acromionectomy). Methods Using 4 fresh‐frozen cadaveric shoulders, acromion shapes were classified (2 type I and 2 type III according to Bigliani). Subacromial bursa and coracoacromial ligament maintenance replicated physiologic sliding conditions. Gliding resistance was measured during glenohumeral abduction (0° to 60°) in internal rotation (IR) and external rotation (ER). Peak gliding resistance between the SSP tendon and the coracoacromial arch was determined and compared between intact, anterolateral acromioplasty, and acromionectomy. Results Peak SSP gliding resistance during abduction in an intact shoulder was significantly higher in IR than in ER (4.1 vs 2.1 N, P < .001). The mean peak SSP gliding resistance during 0° to 60° glenohumeral abduction in IR in the intact condition was significantly higher compared with the subacromial decompression condition (4.1 vs 2.8 N, P = .021) and with the acromionectomy condition (4.1 vs 0.9 N, P < .001). During 0° to 60° glenohumeral abduction in ER, mean peak SSP gliding resistance in the intact condition was not significantly different compared with the subacromial decompression condition (2.1 vs 2.0 N, P = .999). The 2 specimens with a hooked (i.e. type III) acromion showed significantly higher mean peak SSP gliding resistance during glenohumeral abduction in IR and ER when compared with the 2 specimens with a flat (i.e. type I) acromion (IR: 5.8 vs 3.0 N, P = .006; ER: 2.8 vs 1.4 N, P = .001). Conclusions In this cadaveric study, peak gliding resistance between the SSP tendon and the coracoacromial arch during combined abduction and IR was significantly reduced after anterolateral acromioplasty and was significantly higher in specimens with a hooked acromion. Clinical Relevance The clinical benefit of subacromial decompression remains unclear. This study suggests that anterolateral acromioplasty might reduce supraspinatus gliding resistance in those with a hooked acromion and in the typical “impingement” position.