Huxel Kellie C, Swanik C Buz, Swanik Kathleen A, Bartolozzi Arthur R, Hillstrom Howard J, Sitler Michael R, Moffit Dani M
Athletic Training Department, Indiana State University, Terre Haute, IN 47809, USA.
J Bone Joint Surg Am. 2008 Jan;90(1):154-62. doi: 10.2106/JBJS.F.01133.
The complex interactions between capsuloligamentous structures and muscle-recruitment strategies that maintain glenohumeral stability remain unclear. The purposes of the present study were to determine whether stiffness regulation and muscle-activation strategies differed under varying joint positions and levels of contraction in the shoulder and to determine the relationship between generalized joint laxity, glenohumeral joint laxity, and joint stiffness.
Forty healthy, physically active subjects with a mean age (and standard deviation) of 25.2 +/- 4.6 years, a mean height of 174.7 +/- 6.7 cm, and a mean mass of 73.1 +/- 13.8 kg were tested. Shoulder stiffness and the activation of muscles (including the rotator cuff and the anterior deltoid) were measured at two levels of internal rotation torque (0% and 50% of maximum) and two joint positions (0 degrees and 90% of maximum external rotation) before and after a 5 degrees external rotation perturbation. Generalized laxity and glenohumeral joint laxity (in the anterior, posterior, and inferior directions) were also assessed.
Stiffness was 77% greater at 50% of maximum internal rotation torque than at 0% of maximum internal rotation torque (p < 0.001) but was not significantly different between joint positions (p = 0.73). From 0% to 50% of maximum internal rotation torque, preparatory and reactive recruitment of the subscapularis increased significantly more (p < 0.05) than those of the other muscles. Also, subscapularis preparatory activity was 36% greater in 0 degrees of external rotation than in 90% of maximum external rotation (p < 0.01). Generalized joint laxity (as indicated by a score of >/=4) was present in 20% of the subjects. Glenohumeral joint laxity (as indicated by a grade of >/=2) was present in the anterior, posterior, and inferior directions in 13%, 15%, and 15% of the subjects, respectively. No correlation existed between passive stiffness and generalized or glenohumeral laxity (r = -0.12 to 0.29; p = 0.08 to 0.48).
Moderate levels of muscle contraction can significantly increase glenohumeral joint stiffness and stability. Preactivation of the subscapularis appears to be the primary dynamic stabilizer with the arm in 0 degrees of external rotation. However, with the arm in 90% of maximum external rotation (the apprehension position), less subscapularis activity is observed and the maintenance of stability may shift toward other musculoskeletal structures because joint stiffness does not change. A relationship between generalized joint laxity, glenohumeral laxity, and stiffness was not observed in healthy subjects.
关节囊韧带结构与维持盂肱关节稳定性的肌肉募集策略之间的复杂相互作用仍不明确。本研究的目的是确定在不同的关节位置和肩部收缩水平下，刚度调节和肌肉激活策略是否存在差异，并确定全身关节松弛度、盂肱关节松弛度与关节刚度之间的关系。
对40名健康、有体育锻炼习惯的受试者进行测试，他们的平均年龄（及标准差）为25.2±4.6岁，平均身高为174.7±6.7厘米，平均体重为73.1±13.8千克。在5°外旋扰动前后，于两个内旋扭矩水平（最大扭矩的0%和50%）和两个关节位置（最大外旋的0°和90%）测量肩部刚度和肌肉（包括肩袖肌群和三角肌前部）的激活情况。还评估了全身松弛度和盂肱关节松弛度（前、后和下方方向）。
最大内旋扭矩的50%时的刚度比最大内旋扭矩的0%时大77%（p<0.001），但关节位置之间无显著差异（p = 0.73）。从最大内旋扭矩的0%到50%，肩胛下肌的预激活和反应性募集比其他肌肉增加得更显著（p<0.05）。此外，外旋0°时肩胛下肌的预激活活动比最大外旋90%时高36%（p<0.01）。20%的受试者存在全身关节松弛度（评分≥4）。分别有13%、15%和15%的受试者在盂肱关节的前、后和下方方向存在盂肱关节松弛度（分级≥2）。被动刚度与全身或盂肱关节松弛度之间无相关性（r = -0.12至0.29；p = 0.08至0.48）。
适度的肌肉收缩可显著增加盂肱关节的刚度和稳定性。肩胛下肌的预激活似乎是手臂处于外旋0°时的主要动态稳定器。然而，当手臂处于最大外旋90%（恐惧位）时，观察到肩胛下肌的活动较少，并且由于关节刚度不变，稳定性维持可能会转向其他肌肉骨骼结构。在健康受试者中未观察到全身关节松弛度、盂肱关节松弛度与刚度之间的关系。
