The degree of external rotation produced by the gap technique in total knee arthroplasties (TKA) was measured and compared with other methods.

Thirty-nine TKA patients (52 cases) were enrolled in this study. The transepicondylar axis (TEA) and the perpendicular line to the anteroposterior axis (APA) were drawn on the images of the computerized tomographs (CT). After resecting the posterior condyles using the gap technique, the maximal depths of the resected fragments were measured, and the resected lines (RL) were drawn on the same CT images. The differences in the angles between the RLs and the TEAs, the perpendicular lines to the APAs, and the lines that were externally rotated 3o from the posterior condylar axes, were evaluated.

The posterior condylar axes formed 5.1±2.5 ° angles with the RLs, 5.3±1.6 ° angles with the TEAs, and 4.5±2.1 ° angles with the lines that were perpendicular to the APAs. The RLs showed similar TEAs, and the APAs (0.2±2.6 ° and 0.6±3.0 °, respectively). However, the lines of 3 ° external rotation (2.1±2.5 °) were significantly different.

A more ideal flexion gap could be obtained with the TEAs compared with other methods. However, resections of the posterior condyles using the gap technique might be more effective than with the TEAs due to the individual variations and errors in obtaining symmetric flexion gaps with this value.