Histological and biomechanical evaluation of biologic adjuvants in a murine tendon-bone healing model

Abstract

Background. The purpose of this study was to compare subacromial bursa to concentrated bone marrow aspirate (cBMA) in a murine, tendon-bone healing model. The authors hypothesized that subacromial bursa would show similar biomechanical, histological, and cell survivability to that of cBMA. Methods. Thirty-nine NSG mice were included in the study. All mice underwent simulated patella tendon avulsion injuries and were divided into one of three treatment groups: subacromial bursa, cBMA, or fibrin clot only. Subacromial bursa and cBMA were obtained from a single patient during primary arthroscopic rotator cuff repair (male, age: 57 years). All mice were sacrificed at 2 weeks for biomechanical, histologic, and immunohistochemistry evaluation. Biomechanical analysis included load to failure and stiffness, with the contralateral knees used as controls. Human PCR analysis was performed to confirm survivability in the bursa and cBMA groups. Results. With respect to the contralateral intact limb, treatment with subacromial bursa significantly increased load to failure (66% of intact) compared to fibrin only (47.87% of intact, P=0.018). cBMA was found to restore tendon strength to 49.9% to its intact side, however no significant difference was found when compared to bursa (P=0.06). No significant difference in stiffness was found between groups. Human nuclear antigen was positive in 75% of the bursa treated mice compared to only 25% of the cBMA specimens. Conclusions. Subacromial bursa tissue demonstrated significant improvement in tendon strength compared to fibrin clot treatment (acellular control) at 2 weeks. Increased human cell survivability was also demonstrated using bursal tissue compared to cBMA.