Background: Osteoporosis increases the revision rate of rotator cuff repair (RCR). Weak fixation might not be the only cause of high RCR failure rates. The biological mechanism associated with tendon-to-bone healing after RCR in osteoporosis should be investigated.
Hypothesis: (1) Osteoporosis would impair rotator cuff healing through the high osteoclastic activity at the repaired interface. (2) Risedronate would promote rotator cuff healing by reducing osteoclastic activity at the repaired interface.
Study design: Controlled laboratory study.
Methods: A total of 84 female Sprague Dawley rats were randomly treated using ovariectomy or sham surgeries to establish osteoporotic and nonosteoporotic rat models. After confirming osteoporosis, a chronic rotator cuff tear model was created and RCR was performed. Postoperatively, osteoporotic rats were randomly divided into osteoporosis (OP) and osteoporosis with risedronate administration (OP+RIS) groups. Nonosteoporotic rats were used as the control (CON) group. Osteoclastic activity was measured at 1 and 3 weeks after RCR, and histologic analysis of the tendon-to-bone interface, bone morphometric evaluation, and biomechanical tests were performed at 4 and 8 weeks.
Results: At the early healing stages of 1 and 3 weeks after RCR, the OP group showed the highest osteoclast density at the repaired interface. Compared with the OP group, risedronate administration significantly decreased osteoclast density in the OP+RIS group. At 8 weeks, histologic scores were greater in the OP+RIS group than in the OP group but still lower than in the CON group. Histologic scores at 8 weeks were negatively correlated with osteoclast density at the early healing stage. Additionally, the OP+RIS group showed better bone morphometric parameters and biomechanical properties than did the OP group.
Conclusion: Osteoporosis impaired rotator cuff healing, which might be related to the high osteoclast density at the repaired interface at the early healing stage. Postoperative risedronate administration decreased osteoclast density and enhanced rotator cuff healing in osteoporotic rats, although the effect was inferior to that in nonosteoporotic rats.
Clinical relevance: Postoperative risedronate administration can be considered a potential therapy to enhance rotator cuff healing in patients with postmenopausal osteoporosis. However, this needs to be verified in a clinical setting.
Keywords: bisphosphonate; osteoclast; osteoporosis; risedronate; rotator cuff repair; tendon-to-bone healing.