Park Maxwell C, Jun Bong J, Park Chong J, Ahmad Christopher S, ElAttrache Neal S, Lee Thay Q
Southern California Permanente Medical Group, Woodland Hills Medical Center, Department of Orthopaedic Surgery, 5601 De Soto Avenue, Los Angeles, CA 91365, USA.
Am J Sports Med. 2007 Nov;35(11):1931-9. doi: 10.1177/0363546507304139. Epub 2007 Jul 19.
Biomechanical testing without humeral motion is a standard method for evaluating rotator cuff repair constructs. This cannot elucidate the effects of dynamic external rotation on the repair, which is a common postoperative motion.
Biomechanical properties and gap formation of rotator cuff repairs will be different when dynamic external rotation is allowed to occur during loading.
Controlled laboratory study.
In 6 matched pairs of human cadaveric shoulders, a commonly used single-row rotator cuff repair was performed. In 6 shoulders, a materials testing machine and a custom testing apparatus that permits cyclic rotation (0 degrees -30 degrees ) were employed (group 1). In contralateral shoulders, the apparatus was fixed to prevent humeral rotation (group 2). All repairs were cyclically loaded from 0 to 60 N at a displacement rate of 1 mm/s for 30 cycles. The constructs were then loaded to failure. Repair strength, gap formation, and strain were compared between groups.
Cyclic loading revealed no difference in linear stiffness between testing conditions. Hysteresis was significantly greater when dynamic external rotation was allowed to occur. With load to failure, there were no differences in yield or ultimate load. Anterior tendon gap formation was greater at end rotation (30 degrees of humeral external rotation) and at yield load, and strain on the posterior tendon was less with dynamic external rotation. With dynamic external rotation, gap formation and tendon strain were significantly greater in the anterior region of the supraspinatus tendon compared with the posterior region.
External rotation using postoperative physiologic loads affects gap formation and tendon strain between anterior and posterior supraspinatus tendon regions. Previous testing models without humeral rotation may underestimate gap formation and anterior tendon strain and overestimate posterior tendon strain.
Understanding regional differences with respect to these variables, depending on quality of repair, may provide the surgeon a framework from which to prescribe guidelines for postoperative rehabilitation.
在无肱骨运动情况下进行生物力学测试是评估肩袖修复结构的标准方法。但这无法阐明动态外旋对修复的影响，而动态外旋是常见的术后动作。
在加载过程中允许动态外旋时，肩袖修复的生物力学特性和间隙形成会有所不同。
对照实验室研究。
在6对匹配的人体尸体肩部标本上，进行常用的单排肩袖修复。在6个肩部标本中，使用材料试验机和允许循环旋转（0度至30度）的定制测试装置（第1组）。在对侧肩部，将装置固定以防止肱骨旋转（第2组）。所有修复均以1毫米/秒的位移速率从0至60牛进行循环加载，持续30个循环。然后将结构加载至破坏。比较两组之间的修复强度、间隙形成和应变。
循环加载显示测试条件之间的线性刚度无差异。允许动态外旋时，滞后现象明显更大。加载至破坏时，屈服载荷或极限载荷无差异。在前屈终末（肱骨外旋30度）和屈服载荷时，前侧肌腱间隙形成更大，且动态外旋时后侧肌腱的应变更小。与后侧区域相比，动态外旋时，冈上肌腱前侧区域的间隙形成和肌腱应变明显更大。
使用术后生理负荷进行外旋会影响冈上肌腱前后区域之间的间隙形成和肌腱应变。先前无肱骨旋转的测试模型可能会低估间隙形成和前侧肌腱应变，并高估后侧肌腱应变。
根据修复质量了解这些变量的区域差异，可为外科医生提供一个框架，据此制定术后康复指南。
