Osteoporosis affects component positioning in computer knee arthroplasty

Although computer-assisted navigation in total knee arthroplasty (TKA) has many advantages, undetected tracker pin movement can result in poor lower limb alignment and component position. Osteoporosis may be an underlying cause of tracker pin movement. The present prospective case-control study compared 6-month radiographic outcomes in 44 osteoporotic and 56 non-osteoporotic knees undergoing navigation TKAs. Osteoporotic knees were defined as those having a T-score of -2.5 or less either in the femoral neck or lumbar spine or both. At postoperative 6 months' follow-up, the average coronal tibial component position was greater valgus in osteoporotic group than in nonosteoporotic group (non-osteoporotic = varus 0.7 degrees +/- 1.8 degrees; osteoporotic = valgus 1.2 degrees +/- 3.4 degrees; p = 0.041). Multiple linear regression analysis showed that being in the osteoporotic group was a predictor of tibial coronal component position (beta = 0.321, p = 0.039). In addition, preoperative lumbar spine bone mineral density was found to be a predictor of coronal and sagittal alignments of the tibial component (beta = 0.406, p = 0.015, beta = 0.463, p = 0.007). The present study found that osteoporosis affected tibial component position in computer-assisted navigation TKA. Clinicians should be particularly aware of the possibility of undetectable tracker pin movement during navigation TKA in osteoporotic knees. (C) 2011 Elsevier B.V. All rights reserved.