Malrotation in total knee arthroplasty: Effect on tibial cortex strain captured by laser-based strain acquisition

Background. Malrotation of the tibial and femoral components has been recognized to be a clinical complication affecting the performance and durability of total knee arthroplasty. This study used a novel strain acquisition technique to determine the effect of tibio-femoral component malrotation oil tibial torque and strain distribution of the proximal tibial cortex with a cemented fixed-bearing posterior-stabilized knee. Methods. Using electronic speckle pattern interferometry. strain on the proximal tibia Of human cadaveric knees was obtained in response to 1500 N axial loading for neutrally aligned tibial and femoral components. and for 10 degrees internal and external malrotation between the tibial and femoral components. Local strain gage measurements were combined with full-field optical strain measurements to quantify effects on tibial cortex strain and strain distributions caused by the 10 degrees malrotations. In addition. tibial torque was measured for incremental degrees of tibio-femoral malrotation. Findings. Tibio-femoral malrotations as small as 2 degrees caused tibial torque in excess of 4 N m. At 10 degrees malrotation, tibial torque significantly increased to over 8 N m (P < 0.001) as compared to neutrally aligned components. Local strain gage results significantly increased from 500 mu epsilon to 632 mu epsilon compressive strain in response to 10 degrees external malrotation, and to 1000 mu epsilon compressive strain in response to 10 degrees internal malrotation. Full-field optical strain reports yielded the highest strain of 2153 mu epsilon for 10 degrees internal malrotation 30mm below the joint line. Interpretation. Laser-based strain measurement technology provides novel capabilities to capture cortex strain fields. The sensitivity of cortex strain and torsion to small amounts of tibio-femoral nialrotation may explain factors contributing to aseptic implant loosening of the tibial component. (c) 2006 Elsevier Ltd. All rights reserved.