Effect of preoperative deformity on postoperative leg axis in total knee arthroplasty: a prospective randomized study

Computer-assisted surgery-total knee arthroplasty (CAS-TKA) has been suggested to afford greater precision than conventional TKA; however, it is unclear whether this is influenced by preoperative angular deformity. This prospective study was conducted to determine the effect of preoperative angular deformity on the postoperative mechanical axis. Sixty patients underwent stage bilateral TKA; CAS-TKA was performed on one side and conventional TKA on the other side. It was demonstrated that severity of preoperative angular deformity affected the resulting alignment in conventional TKA, but not in CAS-TKA. The mechanical axis of the leg was within 3 degrees of the planned axis in 83% of CAS-TKA but only 32% of conventional TKA cases when the preoperative angular deformity was > 12 degrees (P < 0.01). When the preoperative angular deformity was < 12 degrees, the mechanical axis of the leg was within 3 degrees of the planned axis in 90% of CAS-TKA but only 69% of conventional TKA (P < 0.025). This study thus concluded that the resulting alignment in conventional TKA is influenced by large preoperative angular deformity. Consistent results in alignment can be achieved with CAS-TKA, though preoperative angular deformity still played a role in predicting the postoperative mechanical axis. CAS-TKA achieves better postoperative alignment than conventional TKA in both severe and mild preoperative angular deformity.