Abstract
Malalignment in total knee replacement (TKR) is frequently associated with early failure and poor functional results. It has been suggested that errors in tibial and femoral alignment of > 3° occurs in at least 10% of TKR. Since 1999 we have been using a computer-based alignment system (Orthopilot;Aesculap,Tuttlingen,Germany) for TKR in more than 300 implants. The aim of this retrospective study is to present our experience in comparison with traditional alignment systems for TKR.
Patients receiving TKR with different alignment systems were enrolled in the study and assigned to three different groups. In group A (38 cases) TKR was performed using a computer-assisted alignment system, in group B (40 cases) TKR was performed using a totally intramedullary alignment system and in group C (37 cases) TKR was performed using a totally extramedullary alignment system. The criteria for inclusion were a diagnosis of primary osteoarthritis, a pre-operative mechanical frontal axis (MFA) ranging from 165° to 195°, and a pre-operative knee flexion deformity not exceeding 10° calculated according to pre-operative radiographs. The radiographs were assessed for the alignment of the femoral and tibial component and the lower limb alignment, considering the lateral femoral component angle (FCA), the medial tibial component angle (TCA), respectively.
The surgical time was statistically longer in the computer-assisted group. The results did not show statistically significant differences in FCA, TCA and MFA among the three groups. However, in the extramedullary aligned group there was a statistically higher percentage of TKRs with both an abnormal FCA and MFA compared to the computer-based alignment group. Furthermore, in the computer-based alignment group all the implants were aligned within 4° of an ideal MFA.
Our results demonstrate the significant improvement in the accuracy of implant alignment using a computer-assisted system compared to an extramedullary one. Furthermore, we underline how stressing the knee during all the phases of the registration process for the navigated implant can demonstrate how much of the deformity can be corrected and thus guide the soft-tissue release.
