Repair of a Rotator Cuff Tendon Defect Using an Acellular Human Dermal Graft in a Large Primate Model (SS-44)

Abstract

A large primate model which resembles human shoulder anatomy, mechanics, and immunogenicity was used to evaluate the use of an acellular dermal human graft for rotator cuff tendon defect repair and augmentation. A rotator cuff defect was created in two groups of baboons. In one group, the defect was repaired with the acellular human dermal graft, while the other group did not have a repair. All grafted specimens healed, the nongrafted defects failed to heal. The graft was successful at restoring tendon integrity at defects sites and demonstrated a favorable histological appearance including neovascularization and graft incorporation into native tendon. Evaluate an acellular human dermal graft for rotator tendon defect repair and augmentation in a large primate model which closely resembles the human shoulder anatomy, mechanics, and immunogenicity. A primate rotator cuff injury model was developed and consisted of full thickness bilateral defects in the infraspinatus and subscapularis tendons. Ten adult female skeletally mature baboons were divided into two groups. In one group (n=5), the defects were repaired using a non-cross-linked human acellular dermis graft (GraftJacket Regenerative Tissue Matrix, Wright Medical). A patch of graft material was cut to cover the tendon width and length and sutured with nonabsorbable suture. At the bone insertion site, the patch was secured to the residual tendon and periosteum by suture placed through superficial bone tunnels. In the other group (n=5), the defects were created, but no graft was applied. The subscapularis tendon was used for histological study, and the infraspinatus tendon was used for mechanical testing (not reported here). The right and left shoulders were operated on 6 weeks apart. After euthanasia at 12 weeks, one 6-week and one 12-week shoulder was available from each animal. Clinical assessment included: (1)grasping for food, limb extension forward, limb extension to shoulder level, limb extension overhead; (2) radiographs under sedation preoperatively, then 0, 6, 12 weeks postoperatively; (3) Passive range of motion measurements under sedation preoperatively, then at 0, 6 12 weeks postoperatively. The subscapularis tendon of each joint was studied histologically using sections stained with H and E, Masson's trichrome and Verhoeff-van Gieson to determine healing of the model defect, incorporation of the graft material into the native tendon, and any immunogenic response to the implanted material. All incisions healed. Progressive improvement in limb function was observed in both groups. At necropsy, all grafted tendons were intact. Grossly, grafted tendons were thickened by residual graft material and fibrous tissue, and the defects were no longer present. In contrast, non-grafted tendons had normal to thinner dimensions, and the central defects were still visible grossly or covered only by a thin membrane. Radiographically, there were no differences between the groups. All shoulders had a smooth ROM with no crepitus or instability. ROM differences from preoperative values were seen in both groups with peak loss occurring at 6 weeks, returning toward, but not completely, to preoperative values at 12 weeks. Histologically, in the grafted group, tendon continuity was re-established with incorporation of the graft into the substance of the tendon. The 12 week grafted specimens were characterized by a greater degree of incorporation and remodeling with collagen fibers oriented in the long axis of the tendon and decreased cellular infiltrate compared to the 6 week specimens. The untreated tendon defects failed to heal after 12 weeks. The acellular human dermal matrix was successful in restoring tendon integrity at defect sites and is supported by the favorable histological appearance. There was no impedance to wound healing from the acellular graft material. The large primate rotator cuff defect model replicated well the human rotator cuff condition.