Department of Radiology, University of California and Veterans Administration Medical Centers, San Diego, CA, USA.
J Orthop Sports Phys Ther. 2010 Nov;40(11):729-35. doi: 10.2519/jospt.2010.3279.
Controlled laboratory study.
To measure the architectural properties of rat supraspinatus muscle after a complete detachment of its distal tendon.
Supraspinatus muscles were released from the left humerus of 29 Sprague-Dawley rats (mass, 400-450 g), and the animals were returned to cage activity for 2 weeks (n=12), 4 weeks (n=9), or 9 weeks (n=8), before euthanasia. Measurements of muscle mass, pennation angle, fiber bundle length (sarcomere number), and sarcomere length permitted calculation of normalized fiber length, serial sarcomere number, and physiological cross-sectional area.
Coronal oblique sections of the supraspinatus confirmed surgical transection of the supraspinatus muscle at 2 weeks, with reattachment by 4 weeks. Muscle mass and length were significantly lower in released muscles at 2 weeks, 4 weeks, and 9 weeks. Sarcomere lengths in released muscles were significantly shorter at 2 weeks but not different by 4 weeks. Sarcomere number was significantly reduced at 2 and 4 weeks, but returned to control values by 9 weeks. The opposing effects of smaller mass and shorter fibers produced significantly smaller physiological cross-sectional area at 2 weeks, but physiological cross-sectional area returned to control levels by 4 weeks.
Release of the supraspinatus muscle produced early radial and longitudinal atrophy of the muscle. The functional implications of these adaptations would be most profound at early time points (particularly relevant for rehabilitation), when the muscle remains smaller in cross-sectional area and, due to reduced sarcomere number, would be forced to operate over a wider range of the length-tension curve and at higher velocities, all adaptations resulting in compromised force-generating capacity. These data are relevant to physical therapy because they provide tissue-level insights into impaired muscle and shoulder function following rotator cuff injury.
对照实验室研究。
测量大鼠冈上肌完全切断其远端肌腱后的结构特性。
将 29 只 Sprague-Dawley 大鼠（体重 400-450g）左侧冈上肌从肱骨上释放出来，动物在笼内活动 2 周（n=12）、4 周（n=9）或 9 周（n=8）后安乐死。肌肉质量、羽毛角、纤维束长度（肌节数）和肌节长度的测量允许计算归一化纤维长度、串联肌节数和生理横截面积。
冈上肌的冠状斜切面证实，在 2 周时冈上肌的外科横断，在 4 周时重新附着。在 2 周、4 周和 9 周时，释放肌肉的肌肉质量和长度显著降低。释放肌肉的肌节长度在 2 周时明显缩短，但在 4 周时没有差异。2 周和 4 周时肌节数显著减少，但在 9 周时恢复到对照值。较小的质量和较短的纤维的相反作用导致 2 周时的生理横截面积显著减小，但在 4 周时生理横截面积恢复到对照水平。
冈上肌的释放导致肌肉早期出现放射状和纵向萎缩。这些适应的功能影响在早期时间点最为明显（特别是在康复方面），此时肌肉的横截面积仍然较小，由于肌节数减少，它将被迫在更长的长度-张力曲线范围内和更高的速度下工作，所有这些适应都会导致产生的力量能力受损。这些数据与物理治疗有关，因为它们提供了有关肩袖损伤后肌肉和肩部功能受损的组织水平见解。
