The purpose of this study was to identify the procedural steps in a total knee arthroplasty (TKA) in which technical errors occur and to quantify the magnitude of these errors. Forty-nine consecutive TKAs were performed using a traditional exposure and manual instrumentation. An image-free computer navigation system (OrthoPilot; Aesculap AG, Tuttlingen, Germany) was used to measure and compare femoral and tibial alignment at specific procedural points during the TKA; this data was then used to evaluate possible sources of error in the procedure. The femoral cut tended to be made in hyperextension, the tibial cut tended to be made in hyperextension and valgus, and the tibial component tended to be implanted in valgus. This study identified specific points during the performance of a TKA where technical errors occur. This information suggests technical considerations that can help a surgeon achieve more reproducible, durable, and successful outcomes for his or her patients.