Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic, 200 First Street, SW, Rochester, MN 55905, USA.
Am J Sports Med. 2010 Mar;38(3):600-7. doi: 10.1177/0363546509350074. Epub 2009 Dec 4.
Tightness of the posteroinferior capsule is assumed to be the cause of internal rotation loss in baseball pitchers. Although the relationship between posterior capsule and subacromial impingement has been recognized, this relationship during the baseball-pitching motion is unclear.
Contact pressure during baseball-pitching motion increases with posterior capsule tightness.
Controlled laboratory study.
Eight fresh-frozen shoulders were used. The peak contact pressure and area on the coracoacromial arch were measured on a custom-designed shoulder experimental device capable of 6 degrees of freedom motion. Simultaneously, the sites of peak pressure on the coracoacromial arch and humerus were observed from various angles. The posteroinferior capsule tightness was simulated by plicating the capsule in the region from 6 to 8 o'clock. The static testing positions correlated to the early cocking, late cocking, acceleration, deceleration, and follow-through phases of the pitching motion.
The peak contact pressure during the follow-through phase (0.63 + or - 0.50 MPa) significantly increased with posteroinferior capsule tightness (1.00 + or - 0.65 MPa) (P = .014). Additionally, the contact area on the coracoacromial ligament during the follow-through phase (0.98 + or - 0.67 cm(2)) significantly increased with posteroinferior capsule tightness (1.47 + or - 0.91 cm(2)) (P < .001). The site of the peak contact pressure did not change between the 2 conditions.
Our findings demonstrate that posteroinferior capsule tightness leads to higher contact pressure under the subacromial arch and increased contact area, particularly on the coracoacromial ligament during the follow-through phase.
This tightness may affect risk of injury of the rotator cuff and its surrounding tissues by increasing subacromial contact during pitching.
人们认为后下盂唇紧张是导致棒球投手内旋受限的原因。尽管已经认识到后下盂唇与肩峰下撞击之间的关系，但在棒球投球运动中这种关系尚不清楚。
在棒球投球运动中，随着后下盂唇紧张度的增加，接触压力也随之增加。
对照性实验室研究。
使用 8 个新鲜冷冻的肩部标本。在一个可以进行 6 自由度运动的定制肩部实验装置上测量喙肩弓上的峰值接触压力和面积。同时，从不同角度观察喙肩弓和肱骨上的峰值压力点。通过在 6 点至 8 点区域皱缩盂唇来模拟后下盂唇紧张度。静态测试位置与早期挥棒、晚期挥棒、加速、减速和随球动作相关。
在随球动作的随球阶段，后下盂唇紧张度为 1.00 ± 0.65 MPa 时的峰值接触压力（0.63 ± 0.50 MPa）显著增加（P =.014）。此外，在随球阶段，喙肩弓韧带的接触面积（0.98 ± 0.67 cm²）随后下盂唇紧张度增加（1.47 ± 0.91 cm²）而显著增加（P <.001）。在这两种情况下，峰值接触压力的位置没有改变。
我们的发现表明，后下盂唇紧张度导致在随球阶段，肩峰下弓下的接触压力更高，接触面积更大，尤其是喙肩弓韧带的接触面积更大。
这种紧张度可能会增加投球时肩峰下的接触，从而影响肩袖及其周围组织受伤的风险。
