Computer-assisted surgery improves rotational positioning of the femoral component but not the tibial component in total knee arthroplasty.

PURPOSE: Computer-assisted surgery (CAS) may facilitate better positioning of total knee arthroplasty (TKA) along the coronal and lateral axes; however, there are doubts as to its usefulness in the rotational plane.

METHODS: This is a prospective study of 95 TKAs comparing two groups: the CAS group and the standard equipment group. The series comprises 95 cases. A radiography of the lower limb and computer tomographies (CTs) of the femoral condylar region, the proximal end of the tibia and the ankle were performed to measure rotational angulation. A month after TKA surgery, the radiography and the CTs were repeated to analyze the position of the prosthetic components in the rotational plane.

RESULTS: In the coronal axis, both CAS and mechanical technique improved femoro-tibial alignment, but when there are preexisting deformities ≥4°, CAS obtains better results. A strong correlation (R = 0.94, p = 0.001) was observed between the mean rotational axis measured with CT in the tibial plateau and that measured from the axis of the ankle. The mean initial femoral rotation of the complete series was 6.7° and 2.7° at 1-month follow-up (p < 0.001). In the standard instrumentation group, the femoral rotation went from 6.8° to 2.3°, whereas in the CAS group the femoral rotation went from 6.5° to 3.1° (p = 0.039), which is very close to the ideal 3° angle of external rotation. Tibial rotation changed by 5.28° for the entire patient population, but no differences were found when comparing CAS and standard instrumentation.

CONCLUSION: CAS improves frontal alignment in TKA, especially in the presence of preoperative deformities. In the femoral component, navigation most closely replicated the ideal 3° external rotation of the femoral component, but tibial rotation did not differ when comparing CAS to standard instrumentation.

LEVEL OF EVIDENCE: II.