Biomechanical comparison of two extensor mechanism reconstruction techniques

Extensor mechanism disruption is a debilitating complication that can occur following total knee arthroplasty. High primary repair failure rates have made reconstruction the treatment of choice. The literature describes two methods of reconstruction with synthetic mesh, however these methods have not been biomechanically compared.

Synthetic mesh constructs were implanted in six matched pairs of cadaveric tibiae using the tuberosity technique, where mesh is anchored at the tuberosity, and the intramedullary technique, where the mesh is cemented within the medullary canal underneath the tibial component. During biomechanical testing, joint reaction forces were applied to the tibial base plate while axial tensile loads were applied to the mesh construct to measure stiffness, yield force, and ultimate force to failure. Displacements of the tibial tray and the point of load were tracked using an infrared motion analysis system.

There were significant differences between the two constructs. Overall, the intramedullary technique was 3 times stiffer (107 ± 11 N/mm vs 42 ± 12 N/mm, P = 0.03) and 54% stronger (1143 ± 31 N vs 741 ± 85 N, P = 0.03) than the trough technique. There was also an increased yield strength (729 ± 9 N vs 542 ± 78 N, P = 0.03). Failure of the trough method occurred at the mesh insertion site whereas failure of the intramedullary technique was between the insertion site and patellar level.

This study shows a potential biomechanical advantage when implanting under the tibial base plate. While our model does not incorporate soft tissue ingrowth, it does compare insertion techniques where ingrowth has minimal effects.