Relationship between neuropathy proximal to the suprascapular nerve and rotator cuff tear in a rodent model.

BACKGROUND: Rotator cuff tears are believed to coexist with cervical spine lesions. In cases of preexisting neuropathy, such as cervical spine lesions, fatty degeneration has likely already occurred due to the neuropathy. In these cases, rotator cuff tear is thought to occur easily because of preexisting extensive fatty degeneration and degeneration of the tendons due to neuropathy. This study aimed to evaluate the effects of paralysis due to neuropathy proximal to the suprascapular nerve on the supraspinatus and infraspinatus tendons using a rat model of brachial plexus paralysis.

METHODS: This study included fifteen, 8-week-old Sprague-Dawley rats. The left shoulder was included in the paralysis group and the contralateral shoulder constituted the sham group. Biomechanical testing (evaluated maximum tear force, maximum displacement and Young's modulus) (n = 10) and histological analyses (n = 5) (using the Bonar scale) were performed at 12 weeks postoperatively to confirm the degeneration of the tendon.

RESULTS: The mean maximum tear force was significantly lower in the paralysis group than in the sham group (P = 0.008), indicating that rotator cuff tears occurred with a lower force in the paralysis group. Additionally, the average Young's modulus was significantly greater in the paralysis group than in the sham group (P = 0.003), indicating that the rotator cuff muscle became hard and inflexible in the paralysis group. The Bonar scales of the histological analyses were significantly higher in the paralysis group (total score = 7.04 ± 0.61) than the sham group (total score = 0) (p < 0.0001).

CONCLUSIONS: If neuropathy of proximal to the suprascapular nerve, such as cervical spine or brachial plexus lesion, exists, weakness and degeneration of the rotator cuff tendon and stiffness of the rotator cuff muscle develop. Neuropathy is likely a cause of rotator cuff tears.