Effect of a single subacromial prednisolone injection in acute rotator cuff tears in a rat model.

PURPOSE: This study examined the early effect of a subacromial steroid injection on injured rotator cuff tendon.

METHODS: Forty rats were allocated into two groups: a steroid injection (group 1) and no injection as control (group 2). A full-thickness defect was made at the unilateral infraspinatus tendon in both groups. A single dose of methylprednisolone was injected in steroid group. The tendon was harvested at 1, 3, 7, 14, and 42 days after surgery; gene expression and immunohistochemical study were performed for type-I/III collagen, tumour necrosis factor (TNF)-α, and extracellular matrix molecules.

RESULTS: The type-III to type-I collagen ratio was at 7 days higher in the steroid group than that in the control group and decreased to the control level at 14 days and was maintained until 42 days. The general expression of the MMPs and TIMPs between two groups showed similar pattern regardless of the steroid injection. The gene expression of aggrecan and fibronectin in the steroid group was significantly higher than that in the control group (p < 0.05) at 3 days after surgery. They decreased to the equal level with control group at 7 days after surgery. Both groups showed no significant difference between aggrecan and fibronectin until 42 days after surgery (n.s.).

CONCLUSIONS: A subacromial steroid injection may alter the collagen composition and extracellular matrix and interfere with the healing process in an acute tear of rat infraspinatus tendon at the early phase after the injection. However, these alterations seem to become normalized after the early inflammatory healing phase.