A rat traumatized shoulder model for the study of post-surgical adhesions

A third of patients after open reduction and plating of proximal humerus fractures require subsequent plate removal principally because of adhesions which occur between the deep surface of the deltoid and fracture fixation zone and limit shoulder motion. A rat model of post-surgical shoulder adhesions was developed using a deltoid split approach commonly used in proximal humerus fracture surgery, with trauma induced by a straight diamond nasal rasp to the undersurface of the deltoid and supraspinatus tendon and adjoining proximal humerus. Using the model, the traumatized limb of 12 animals treated with an alginate mimetic injected into the wound before closure and 9 untreated animals were immobilized for 9 ± 1 days and then their passive range of shoulder flexion-extension measured, followed by histopathology examination. The total passive range of shoulder flexion-extension of 120 degrees in the alginate treated group was greater than the 84 degrees in the untreated group (p = 0.0043). The mean periosteal fibrotic capsule width in the injured area of untreated animals (515 ± 449 μm) was greater than that of animals treated with alginate (186 ± 180 μm, p = 0.003). Untreated animals had severe, grade 4 fibrosis and collagen deposition, and granulation tissue, while treated animals had mild grade 1 responses. The animal model developed produced limited shoulder motion and associated fibrotic changes. It can be used to evaluate potential treatments designed to prevent adhesions that develop after plating of proximal humeral fractures.