Marrow stimulation improves meniscal healing at early endpoints in a rabbit meniscal injury model

Purpose To critically evaluate the effect of marrow stimulation (MS) on the extent of healing and the local biological environment after meniscal injury in ligamentously stable knees in a rabbit model. Methods A reproducible 1.5-mm cylindrical defect was created in the avascular portion of the anterior horn of the medial meniscus bilaterally in 18 New Zealand White rabbits (36 knees). In right knees (MS knees), a 2.4-mm Steinman pin was drilled into the apex of the femoral intercondylar notch and marrow contents were observed spilling into the joint. Left knees served as controls. Rabbits were killed in 3 groups (n = 6 rabbits each) at 1, 4, and 12 weeks with meniscal harvest and blinded histomorphometric and histologic evaluation using an established 3-component tissue quality score (range, 0 to 6). One-week specimens were also evaluated for the presence of proregenerative cytokines using immunohistochemistry. Results The mean proportion of the avascular zone defect bridged by reparative tissue was greater in MS knees than in controls at each endpoint (1 week, 55% v 30%, P  = .02; 4 weeks, 71% v 53%, P  = .047; 12 weeks, 96% v 77%, P  = .16). Similarly, there was a consistent trend toward superior tissue quality scores in knees treated with MS compared with controls (1 week, 1.8  v 0.3, P  = .03; 4 weeks, 4.3 v 2.8, P  = .08; 12 weeks, 5.9 v 4.5, P  = .21). No statistically significant differences, however, were observed at the 12-week endpoint. Increased staining for insulin-like growth factor I, transforming growth factor-β, and platelet-derived growth factor was observed in regenerated tissue, compared with native meniscal tissue, in all specimens at 1 week. Staining density for all growth factors was similar, however, in reparative tissue of MS and control knees. Conclusions The results of this study suggest that marrow stimulation leads to modest improvements in quality and quantity of reparative tissue bridging a meniscal defect, particularly during the early recovery period. Clinical Relevance Clinical evaluation of marrow stimulation techniques designed to enhance healing in isolated meniscus repair surgery may be indicated.