Effect of Footprint Preparation on Tendon-to-Bone Healing: A Histologic and Biomechanical Study in a Rat Rotator Cuff Repair Model

Purpose: To compare the histologic and biomechanical effects of 3 different footprint preparations for repair of tendon-to-bone insertions and to assess the behavior of bone marrow-derived cells in each method of insertion repair. Methods: We randomized 81 male Sprague-Dawley rats and green fluorescent protein-bone marrow chimeric rats into 3 groups. In group A, we performed rotator cuff repair after separating the supraspinatus tendon from the greater tuberosity and removing the residual tendon tissue. In group B, we also drilled 3 holes into the footprint. The native fibrocartilage was preserved in groups A and B. In group C, we excavated the footprint until the cancellous bone was exposed. Histologic repair of the tendon-to-bone insertion, behavior of the bone marrow-derived cells, and ultimate force to failure were examined postoperatively. Results: The areas of metachromasia in groups A, B, and C were 0.033 +/- 0.019, 0.089 +/- 0.022, and 0.002 +/- 0.001 mm(2)/mm(2), respectively, at 4 weeks and 0.029 +/- 0.022, 0.090 +/- 0.039, and 0.003 +/- 0.001 mm(2)/mm(2), respectively, at 8 weeks. At 4 and 8 weeks postoperatively, significantly higher cartilage matrix production was observed in group B than in group C (4 weeks, P = .002; 8 weeks, P < .001). In green fluorescent protein-bone marrow chimeric rats in group B, bone marrow-derived chondrogenic cells infiltrated the fibrocartilage layer. Ultimate force to failure was significantly higher in group B (19.7 +/- 3.4 N) than in group C (16.7 +/- 2.0 N) at 8 weeks (P = .031). Conclusions: Drilling into the footprint and preserving the fibrocartilage improved the quality of repair tissue and biomechanical strength at the tendon-to-bone insertion after rotator cuff repair in an animal model.