| Summary: | Objective: The purpose of this study was to investigate the effect of hyaluronic acid (HA) in the tendon–bone healing process after rotator cuff repair in a rabbit model. Methods: In vitro, rat bone marrow stromal cells (rBMSCs) were cultured in media for cartilage-related and inflammation-related gene expression levels examination at 1.0 mg/mL of HA. In vivo, 48 New Zealand white rabbits underwent rotator cuff repair surgery, and they were randomly divided into three groups: (1) control group (n = 16), (2) microfracture (MF) group accepting MF treatment (n = 16) and (3) MF/HA group accepting MF with HA treatment (n = 16). Four rabbits from each group were sacrificed at 6 and 12 weeks postoperatively for histological evaluation and biomechanical testing. Results: In vitro experiments reveal that HA significantly decreased inflammation-related mRNA expression (IL-1, TNFα) compared with the control group. At 6 weeks after surgery, there was no significant difference of load-to-failure between groups. At 12 weeks after surgery, the mean failure load of the MF/HA group was significantly higher than that of the control group (100.5 ± 10.1 N vs. 68.0 ± 6.2 N; p = 0.0115). The mean failure load of the MF group appeared higher than that of the control group, whereas there was no significant difference (p > 0.05). Histologically, more chondrocytes were clustered at the tendon–bone interface, and more extracellular matrixes were produced in the MF/HA group. The interface of the MF/HA group appeared similar with the normal tendon–bone interface. Conclusion: HA may play a crucial role in the acceleration of tendon-to-bone healing which might be through inhibiting inflammation. Rotator cuff repair using MF along with HA led to better tendon–bone healing and a subsequent increase of biomechanical strength at the repair site. The translational potential of this article: HA injection is very common for patients with rotator cuff disease because of its antiinflammatory action and adhesion prevention preoperatively. The HA injection during surgery provides an antiinflammatory effect during tendon–bone healing process and leads to better tendon–bone healing postoperatively. Keywords: Rotator cuff repair, Tendon bone healing, Hyaluronic acid, BMSCs
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