Gerber Christian, Meyer Dominik C, Frey Eric, von Rechenberg Brigitte, Hoppeler Hans, Frigg Robert, Jost Bernhard, Zumstein Matthias A
Department of Orthopaedics, University of Zurich, Balgrist, Zürich, Switzerland.
J Shoulder Elbow Surg. 2009 Mar-Apr;18(2):163-71. doi: 10.1016/j.jse.2008.09.003. Epub 2008 Dec 18.
Chronic rotator cuff tears are associated with irreversible architectural muscle changes and a high rate of repair failure. The changes observed in man and their irreversibility with a single stage repair can be reproduced in sheep. It was the purpose of this experiment to test the hypothesis that slow, continuous elongation of a retracted musculotendinous unit allows reversal of the currently irreversible structural muscle changes.
The infraspinatus tendon of 12 sheep was released using a greater tuberosity osteotomy and allowed to retract for 4 months. Then, a new device was mounted on the scapular spine and used to extend the infraspinatus muscuculotendinous unit transcutaneously by 1 mm per day. Thereafter, the tendon was repaired back to the greater tuberosity. We assessed the muscular architecture using magnetic resonance imaging, macroscopic dissection, histology, and electron microscopy. Fatty infiltration (in Hounsfield units 1/4 HU) and muscular cross-sectional area (in % of the control side) were monitored with computed tomography at tendon release, initiation of elongation, repair, and at sacrifice.
Sixteen weeks after tendon release, the mean tendon retraction was 29 +/- 6 mm (14% of original length, P = .008). In 8 sheep, elongation was achieved as planned (group I), but in 4, the elongation failed technically (group II). The mean traction time was 24 +/- 6 days with a mean traction distance of 19 +/- 4 mm. At sacrifice, the mean pennation angle in the infraspinatus of group I was not different from the control side (29.8 degrees +/-7.5 degrees vs. 30 degrees +/-6 degrees , P = .575). In group II, the pennation angle had increased from 30 degrees +/-6 degrees to 55 degrees +/-14 degrees (P = .035). There was no fatty infiltration at the time of tendon release. After retraction, there was a significant increase in fatty infiltration of the infraspinatus muscle and a decrease of its cross-sectional area to 57% of the contralateral side (P = .0001). During traction, the degree of fatty infiltration remained unchanged (36 HU to 38 HU, P = .381), and atrophy improved to a muscle square area of 78% of the contralateral side (P = .0001) in group I. In group II, an increase of fatty infiltration was measured from 36 HU to 28 HU; however, this increase was not significant (P = .144). Atrophy did not change in group II (57-55%, P = .946). At sacrifice, the remaining muscle mass was 64% in group I and 46% in group II (P = .019).
Our preliminary results document, that continuous elongation of a retracted, fatty infiltrated and atrophied musculotendinous unit is technically feasible.
In the sheep, continuous elongation can lead to restoration of normal muscle architecture, to partial reversal of muscle atrophy, and to arrest of the progression of fatty infiltration.
Basic science level 2; Prospective comparative therapeutic study.
慢性肩袖撕裂与不可逆的肌肉结构改变以及高修复失败率相关。在人类中观察到的这些改变及其单阶段修复的不可逆性在绵羊中可以重现。本实验的目的是验证以下假设：缓慢、持续地延长回缩的肌腱肌肉单元可使目前不可逆的肌肉结构改变发生逆转。
通过大结节截骨术松解12只绵羊的冈下肌腱，使其回缩4个月。然后，在肩胛冈上安装一种新装置，用于经皮每天将冈下肌腱肌肉单元延长1毫米。之后，将肌腱重新修复至大结节处。我们使用磁共振成像、大体解剖、组织学和电子显微镜评估肌肉结构。在肌腱松解、开始延长、修复以及处死时，用计算机断层扫描监测脂肪浸润（以亨氏单位1/4 HU表示）和肌肉横截面积（以对侧的百分比表示）。
肌腱松解16周后，肌腱平均回缩29±6毫米（为原始长度的14%，P = 0.008）。在8只绵羊中，按计划实现了延长（I组），但在4只中，延长在技术上失败（II组）。平均牵引时间为24±6天，平均牵引距离为19±4毫米。处死时，I组冈下肌的平均羽状角与对侧无差异（29.8度±7.5度对30度±6度，P = 0.575）。II组中羽状角从30度±6度增加到55度±14度（P = 0.035）。肌腱松解时无脂肪浸润。回缩后，冈下肌脂肪浸润显著增加且其横截面积减小至对侧的57%（P = 0.0001）。在牵引过程中，I组脂肪浸润程度保持不变（36 HU至38 HU，P = 0.381），萎缩改善至肌肉横截面积为对侧的78%（P = 0.0001）。II组中，脂肪浸润从36 HU增加至28 HU，但这种增加不显著（P = 0.144）。II组萎缩无变化（57 - 55%，P = 0.946）。处死时，I组剩余肌肉质量为64%，II组为46%（P = 0.019）。
我们的初步结果表明，对回缩、脂肪浸润和萎缩的肌腱肌肉单元进行持续延长在技术上是可行的。
在绵羊中，持续延长可导致正常肌肉结构的恢复、肌肉萎缩的部分逆转以及脂肪浸润进展的停止。
基础科学2级；前瞻性对比治疗研究。
