In the situation of an irreparable meniscus tear, an implant comparable to a normal meniscus is an attractive option. Using a canine model, we assessed the early and late histologic response to a tissue engineered meniscal collagen scaffold (CS). All animals received bilateral arthrotomies, and all joints receiving the CS had an 80% resection of the meniscus. Animals were sacrificed at 3 and 6 weeks, and 12, 13, and 17 months. The CS/tissue complex and host meniscal rim were sectioned for histologic examination with specific focus on the extracellular matrix, angiogenesis, cellular resorption of the scaffold, scaffold appearance, and CS/Host integration. Early histologic samples (3-6 weeks) revealed active angiogenesis and fibrin clots evolving into cellular granulation type tissue. At 12 months, a mature fibrochondrocytic matrix was depositing with gradations of dissolution and integration of the CS implant. Maturing CS/host integration was observed at 18 months. Active cellular resorption of the implant decreased over time. Four cases showed a mild non-specific chronic inflammation and one additional case showed inflammatory engulfment of the scaffold with giant cells at 3 weeks. No evidence of infection either clinically or histologically was observed at any time point. Overall, this histologic analysis demonstrated the active integration of a meniscal like cartilage into a tissue engineered biological scaffold in a canine model.

Level of Evidence: Level V, expert opinion.Keywords: Bosworth fracture dislocation, supination external rotation injury, posterolateral approach of ankle, interposition of extensor digitorum and hallucis longus muscle/tendon

The human knee meniscus is important for the protection of the knee joint from degeneration. Because it is so commonly injured, several methods have been developed to replace damaged meniscal tissue with either transplanted menisci or other synthetic implants. Here we review these different approaches, with a clinical and histological focus on the collagen meniscal implant (CMI or Menaflex), a tissue-engineered bovine collagen product. Clinical trials in patients receiving the CMI have demonstrated good clinical outcomes in follow-ups as long as 10 years. We review the findings of second-look biopsies of implanted CMI constructs; they demonstrate the fibrochondrocytic ingrowth of tissue mimicking a native meniscus. Integration of the CMI to host meniscus is also confirmed. The histologic inflammation occasionally observed around the graft appears to be of little clinical significance. We conclude that tissue-engineered menisci from bovine collagen are safe in the time period examined and that they hold promise for future repair of the meniscus in appropriate individuals.

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