Objective: To provides an objective tool to evaluate rotator cuff function in rats.
Methods: Sixty adult male Sprague Dawley rats, weighing (281.21 ± 20.12) g, were involved in this experiment. Botulinum toxin A (6 U/kg) was injected into the infraspinatus of 12 rats in Botox group. Infraspinatus tendons of 12 rats in tear group were cut by microinvasive method. Infraspinatus tendons of 12 rats in sham-operation group were exposed but not cut. No any treatment was performed on the 12 rats in normal control group. One shoulder joint of each rat was selected randomly as treatment side. After 7 days, cadence, rate of stand phase, support pressure, swing speed, stand speed, and stride length of rats in those 4 groups were measured. Treatment side and contralateral side ratio of each gait parameter was caculated. If parameters of Botox group and tear group both showed significant differences compared with those of normal control group and sham-operation group, the gait parameter was brought into rating scale as an item. Each item was assigned from 1 point to 5 points according to gait parameter. The chronic rotator cuff injury model was established in 12 rats of verification group and rating scale was used to evaluate rotator cuff function each week for 8 weeks after surgery.
Results: All gait parameters of tear group were significantly less than those of Botox group (P < 0.05), and Botox group was significantly less than sham-operation group and normal control group (P < 0.05), but no significant difference was found between sham-operation group and normal control group (P > 0.05). All gait parameters were brought into rating scale as items. All items were rated from 1 point to 5 points, so the total score was 30 points and the lowest score was 6 points. Thirty points meant normal function of infraspinatus (rotator cuff function was normal), and 6 points meant complete loss of infraspinatus function (rotator cuff function was severely damaged). Rotator cuff functional scores of rats in verification group were 27.00 ± 1.86, 23.75 ± 2.83, 21.33 ± 1.92, 18.17± 2.37, 13.17 ± 1.64, 11.67 ± 2.50, 8.17 ± 1.27, 6.50 ± 0.67 from the 1st week to the 8th week respectively.
Conclusion: The rating scale of rat rotator cuff function may reflect the severity of rotator cuff injury and the functional status of rotator cuff to some extent in rats.