A BIOMECHANICAL ANALYSIS OF THE MATERIAL PROPERTIES OF THE TRUFIT CB PLUG FOR OSTEOCHONDRAL DEFECTS OF THE KNEE

We performed a study to evaluate the material properties of a new cylindrical scaffold plug licensed for the treatment of osteochondral defects as prior to the removal of a core of normal femoral condylar bone, it is imperative that the biomechanical properties of replacement implant material are known. TruFit CB plugs (Smith and Nephew) are resorbable material composed of polylactide-co-glycolide (PLG) copolymer, calcium-sulfate, polyglycolide (PGA) fibres and surfactant. The implants are 7mm, 9mm and 11mm cylindrical plugs. The stress/strain relationships of both the dual layer implant and the base layer material were examined. Compressive load testing at selected strain rates was performed in both confined and unconfined models in a substitute body fluid filled chamber. Compressive failure was found to occur between 40–60% strain with maximum stresses at failure for the dual layer implants occurring at 5.5MPa (7mm), 5.8MPa (9mm) and at 8.5MPa (11mm). The mechanical strength under constrained loading conditions is higher than in unconstrained loading (compressive stress required to develop 5 percent strain being 0.6MPa unconfined to 1.1MPa confined for 7mm; 0.6MPa to 1.4MPa for 9mm and 1.0MPa to 3.2MPa for 11mm implants). This demonstrates the importance of a close press fit. The modulus of elasticity was calculated at 50 MPa (7mm), 60 MPa (9mm) and 80 MPa (11mm). The larger the plug size, the higher the strength shown under test conditions at all strain rates. Prior to this study, the material properties of this implant have not been characterized. The Young’s moduli of the implants are in keeping with previous estimated values for successful regeneration of cartilage within a synthetic scaffold. The biomechanical properties described in this study will help to guide surgeons in TruFit CB use and guide the rehabilitation programmes of those patients who have had osteochondral lesions treated with TruFit CB scaffold plugs.