Modified Alendronate Mitigates Mechanical Degradation of the Rotator Cuff in an Osteoporotic Ovine Model

Abstract

Background: Osteoporosis is an independent risk factor for failure after arthroscopic rotator cuff repair. Since rerupture rates after rotator cuff repair are associated with decreased bone mineral density and bone microarchitecture, adaptations of biomechanical properties of the rotator cuff enthesis in patients with osteoporosis remain unclear. Additionally, the effects of osteogenic therapy carrier drugs used for the treatment of osteoporosis on rotator cuff structure and properties have not been previously documented. Purpose: To investigate the changes to soft tissue biomechanics and insertional structure secondary to osteoporosis with and without an osteogenic therapy carrier (ie, modified alendronate). Study Design: Controlled laboratory study. Methods: Biomechanical, histopathological, and microcomputed tomography analyses were performed on 20 shoulders obtained from 10 osteoporotic sheep randomly allocated to modified bisphosphonate (ie, alendronate) or control (ie, osteoporotic without treatment) groups; 6 shoulders from healthy sheep were utilized for comparison purposes. Results: Tendons from the control group exhibited a 57% decrease in undeformed Young modulus as compared with the healthy group ( P = .010). Tendons from the modified bisphosphonate treatment group exhibited a 229% increase in initial Young modulus as compared with the control group ( P = .010). Marked changes within the tendon insertional organization were noted in both the control and the modified bisphosphonate treatment group samples as evidenced by increased interdigitation of the bone–mineralized fibrocartilaginous junction. The control samples exhibited a markedly paucicellular insertion, whereas the modified bisphosphonate treated tendons exhibited a hypercellular insertional region as compared with the healthy group. Both groups exhibited significantly ( P < .01) decreased bone quality underlying the infraspinatus insertion, as evidenced by all microcomputed tomography outcome parameters. Conclusion: This work illuminates changes to rotator cuff tendon secondary to osteoporosis. Specifically, it revealed decreased tendon modulus and altered insertional structure in the osteoporotic samples. Secondarily, these data revealed increases in tendon modulus accompanied by increased cellularity within the tendon insertion region after systemic modified bisphosphonate injections. Clinical Relevance: Bisphosphonate treatment may have a positive effect on the healing of the enthesis after rotator cuff repair.