Femoral component rotations in different gap tensions in total knee arthroplasty: A prospective randomized controlled trial.

BACKGROUND: In total knee arthroplasty (TKA), femoral component rotation is an important factor in the flexion stability and biomechanics of the patellofemoral joint. However, it remains unclear how much tension is appropriate when performing TKA using the gap technique.

METHODS: One hundred fifty TKAs that used the gap technique were randomized into one of the three groups. Gravity group (n=50) included patients who underwent TKA using only the weight of the patient's lower leg. In 20-lbf group (n=50) and 30-lbf group (n=50), a gap-tensioning device was set at 20lbf and 30lbf respectively. The femoral component rotation was measured based on the clinical transepicondylar axis (cTEA) on postoperative CT and any outliers (a femoral component rotation diverging from the cTEA over 3°) were evaluated.

RESULTS: The mean femoral component rotation was -0.82°±2.44° (95% confidence interval [CI], -1.52° to -0.13°) in gravity group, -0.40°±2.22° (95% CI, -1.03° to 0.23°) in 20-lbf group, and 1.37°±2.70° (95% CI, 0.61° to 2.14°) in 30-lbf group. The mean femoral component rotation in 30-lbf group was significantly different from that in gravity group (p<0.001) and 20-lbf group (p<0.001). There were more outliers in 30-lbf group (18% in gravity group, 18% in 20-lbf group, and 36% in 30-lbf group; p=0.043).

CONCLUSIONS: The use of a tensioning device set at 30lbf resulted in an externally rotated femoral component and frequent outliers.