Malrotation of the fixed-bearing posterior stabilized total knee prosthesis causes a postoperative rotational mismatch between the femur and tibia.

PURPOSE

This study aimed to identify factors associated with rotational mismatch after total knee arthroplasty (TKA) using fixed-bearing posterior stabilized prosthesis and to evaluate the impact of the rotational mismatch on clinical outcomes.

METHODS

This retrospective cohort study included 159 cases that underwent TKA. Whole-leg computed tomography images were obtained 2 weeks after TKA, with three-dimensional measures of alignment. Rotational alignment of the femoral and tibial components and rotational mismatch between components and between the femur and tibia bones were evaluated. The new Knee Society Score (KSS) was obtained at the final outpatient visit, which was defined as the final follow-up timepoint. Predictive factors were identified for rotational mismatch of the lower extremity and poor new KSS.

RESULTS

The mean follow-up period was 42 ± 16 months. Rotational mismatch ≥ 10° between bones was identified in 56 cases (35%), with a mean mismatch angle of 5.0° ± 9.1° of external rotation of the tibia relative to the femur. Rotational mismatch ≥ 10° between components was identified in three cases (2%; mean 0.3° ± 3.6° of internal tibial rotation). A multivariate regression analysis showed that component malrotation was predictive of post-operative rotational mismatch between bones (p < 0.01) and rotational mismatch ≥ 10° associated with poor new KSS (odds ratio 4.22; p < 0.01).

CONCLUSION

Malrotation of the fixed-bearing posterior stabilized TKA causes a rotational mismatch between the femur and tibia bones. Excessive rotational mismatch between bones greater than 10° is a risk factor for poor postoperative functional outcome. Precise component positioning is essential for improving TKA outcomes.

LEVEL OF EVIDENCE

III.