Frictional Properties of the Meniscus Improve After Scaffold-augmented Repair of Partial Meniscectomy: A Pilot Study

Background To prevent further degeneration, it is desirable to fill a meniscal defect with a supportive scaffold that mimics the mechanics of native tissue. Degradable porous scaffolds have been used, but it is unclear whether the tissue that fills the site of implantation is mechanically adequate, particularly with respect to frictional performance. Questions/purposes We therefore determined the frictional behavior of native and engineered meniscal replacement tissue from in vivo implantation over time. Methods We evaluated boundary and mixed-mode friction coefficients of tissue generated in porous polyurethane scaffolds used to augment the repair of the meniscus of 13 skeletally mature sheep after partial meniscectomy. Implants were removed for evaluation at 3, 6, and 12 months. The friction coefficient, aggregate modulus, and hydraulic permeability were evaluated for tissue harvested from native meniscus adjacent to the implants, native meniscus from the intact contralateral knee, and repair tissue from the site of the scaffold implantation. The equilibrium friction coefficient (mu(eq)) was measured in the presence of a lubricant bath of either phosphate-buffered saline (PBS) or equine synovial fluid (ESF). Results Boundary mu(eq) in PBS of engineered meniscus improved with time and was similar to native tissue after 6 months. ESF enhanced lubrication for all samples at nearly all time points demonstrating the efficacy of ESF as a joint lubricant for repair tissue as well as native meniscus. Modulus increased and permeability decreased with implantation, likely as a result of tissue ingrowth. Conclusions Promoting tissue ingrowth into porous scaffolds is a potential strategy for improving friction performance in meniscal repair.