Internal impingement—or entrapment of the undersurface of the rotator cuff tendon against the glenoid during overhead activities—is believed to contribute to articular-sided tears. However, little is known about internal impingement outside athletic populations. Therefore, the objectives of this study were to (1) describe glenoid-to-footprint distances and proximity centers during dynamic, in vivo motion in asymptomatic individuals, and (2) determine the extent to which these measures differed between individuals with and without a rotator cuff tear. Shoulder kinematics were assessed in 37 asymptomatic individuals during scapular plane abduction using a high-speed biplane radiographic system. Glenoid-to-footprint distances and proximity center locations were calculated by combining the kinematics with computerized tomography-derived bone models. Glenoid-to-footprint contact was presumed to occur when the minimum distance was less than the estimated labral thickness. The condition of the supraspinatus tendon (intact, torn) was assessed using ultrasound. Minimum distances and proximity centers were compared over humerothoracic elevation angles (90°, 110°, 130°, 150°) and between supraspinatus pathology groups using two-factor mixed model analysis of variances. Glenoid-to-footprint minimum distances decreased consistently across elevation angles (p < 0.01) without a significant difference between groups. Contact was estimated to occur in all participants. Proximity centers were generally located on the anterior half of the rotator cuff footprint and on the posterosuperior glenoid. Statement of Clinical Significance: Internal impingement during overhead motions may be a prevalent mechanism of rotator cuff pathology as contact appears to be common and involves the region of the rotator cuff footprint where degenerative rotator cuff tears are thought to originate.

中文翻译：

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无症状个体肩胛平面外展期间肩袖内部撞击的体内评估

内部撞击——或在头顶活动期间肩袖肌腱的下表面卡住关节盂——被认为是导致关节侧撕裂的原因。然而，对于运动人群之外的内部撞击知之甚少。因此，本研究的目的是 (1) 描述无症状个体在动态体内运动期间关节盂到足迹的距离和接近中心，以及 (2) 确定这些措施在有和没有症状的个体之间的差异程度肩袖撕裂。使用高速双平面放射照相系统在肩胛平面外展期间对 37 名无症状个体的肩部运动学进行了评估。通过将运动学与计算机断层扫描衍生的骨骼模型相结合，计算出关节盂到足迹的距离和接近中心位置。当最小距离小于估计的盂唇厚度时，假定发生关节盂与足迹接触。使用超声波评估冈上肌肌腱的状况（完整、撕裂）。使用双因素混合模型方差分析比较肱胸仰角（90°、110°、130°、150°）和冈上肌病理组之间的最小距离和邻近中心。Glenoid-to-footprint 最小距离跨仰角持续下降（150°) 和冈上肌病理组之间使用双因素混合模型方差分析。Glenoid-to-footprint 最小距离跨仰角持续下降（150°) 和冈上肌病理组之间使用双因素混合模型方差分析。Glenoid-to-footprint 最小距离跨仰角持续下降（p  < 0.01) 组间无显着差异。据估计，接触发生在所有参与者中。邻近中心通常位于肩袖印迹的前半部分和后上关节盂上。临床意义声明：头顶运动期间的内部撞击可能是肩袖病理学的普遍机制，因为接触似乎很常见，并且涉及肩袖足迹区域，据认为退行性肩袖撕裂起源于此。