THE EFFECT OF INCREASING BONE LOSS ON PRIMARY STABILITY OF METAPHYSEAL SLEEVES IN REVISION TOTAL KNEE ARTHROPLASTY

Approximately 20% of primary and revision Total Knee Arthroplasty (TKA) patients require multiple revisions, bone loss may worsen and present an increasing challenge at each operation. The aims of this study were to investigate the effect of increasing bone loss on primary stability of metaphyseal sleeves and suggest a critical bone loss limit after which the sleeve may not be stable. A two phase experiment was performed on biomechanical testing sawbones and human cadaveric tibiae. Sleeves were inserted into the tibia and a standard axial pull-out (0 – 10mm) force and torque (0 - 30°) tests were carried out. For the sawbone experiment, the peak pull-out force with no defect was 160N, for small defect (15mm) was 133N, medium defect (25mm) 108N and large defect (35mm) 56N. The peak torque with no defect was 17.8Nm, for small was 13.4Nm, medium 13.3Nm and large 11.1Nm. The only significant reduction of force was for the large defect. For the cadaveric experiment only the no defect, medium and large were tested. The mean peak pull-out force with no defect was 208N, medium 150N and large 50N. The peak torque with no defect was 13.6Nm, medium 9.9Nm and large 4.7Nm. The only significant reduction in force was observed in the large group. For the scenarios examined, up to 25mm radial defect may be acceptable, between 26-35mm may be the “critical limit” for bone loss making the implant unstable. This is the first study in the literature to quantify this critical limit in any arthroplasty.