Tibial component alignment in total knee arthroplasty may improve by setting extra-medullary instrumentation to the proximal tibia only

Current instrumentations in TKA is not entirely satisfactory since a varus malalignment of tibial component has been reported in 2% to 40% of cases. This result may partially be due to tibial torsion, which cause a lateral shift of the anterior projection of the mechanical axis at the ankle joint compared to a-p axis of proximal tibia. In this study we investigated the accuracy of a new surgical technique in which the influence of tibial torsion on the alignment of the tibial component is bypassed by positioning the extramedullary rod in line with the proximal tibia only, with no references at the ankle joint. MATERIALS AND METHODS: Eighty-six consecutive patients (94 knees) who underwent conventional TKA were included in the study. The extramedullary guide for the tibial cut was set at the proximal tibia, in line with an anterior projection of mechanical axis connecting the posterior tibial notch with the medial 1/3 of the tibial tuberosity in both groups. At the distal tibia, extramedullary rod was set, in the first 47 knees (group 1), to a point located 5 mm medially to the center of the intermalleolar distance, while in the second 47 knees (group 2), it was left free to rotate in the axial plane according to the proximal tibial alignment. Mechanical femorotibial angle(MFT) and tibial component alignment was assessed postoperatively on long standing radiographs. RESULTS: The mean MFT angle was 3.4°± 1.9 in group 1 (range -3° to 7°; 95% CI, 2.9°- 3.8) and 2.7° ± 1.8 in group 2 (range -2° to 6.5°; 95% CI, 2.2 - 3.1) (p=0.07). A MFT angle in the normal range was found in 36 knees (77%) in group 1 and 40 (85%) in group 2 (p=0.2). A malalignment of the tibial component >3° in the coronal plane was present in 16 knees of group 1 (34%); in 2 of them it was greater than 4°. In group 2, two knees showed a malalignment of the tibial component>3° (4%) (p=0.0001 vs group 1), none of whom greater than 4°. DISCUSSION: A major issue in achieving a correct coronal alignment of tibial component in TKA is tibial torsion, which causes a rotational mismatch between proximal and distal epiphysis . If the extramedullary rod is not translated medially at the ankle joint to compensate for tibial torsion, a varus tibial cut is likely to occur. In keeping with this, a varus malalignment of the tibial component is the most frequent error found when extramedullary systems are used . CONCLUSIONS: Our results demonstrated that malalignment of tibial component in coronal plane may be reduce using a surgical technique in which he possible effects of tibial torsion are bypassed setting the extramedullary rod in line with proximal tibial references only