Tibial Component Alignment May Improve By Setting The Extramedullary Instrumentation To The Proximal Tibia Only

BACKGROUND: A proper alignment of total knee arthroplasty (TKA) was found to influence knee biomechanics and long term survival of the implants. However, using standard instrumentation, varus-valgus malalignment of tibial component greater than 3° has been reported in 2% to 40% of cases. A major issue in achieving a correct coronal when extramedullary instrumentation are used for tibial cut, is tibial torsion, i.e., the axial rotation of the tibia along its longitudinal axis. As tibial torsion causes a rotational mismatch between proximal and distal ephiphysis, the anterior projection of mechanical axis at the distal tibia is externally rotated compared to the proximal one, whereby if the centre of intermalleolar axis is used ad distal reference for the extarmedullary road, a varus tibial cut is likely to occur. OBJECTIVE: 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 guide in line with the proximal tibia only MATERIAL AND METHODS : Eighty-six patients (94 knees) with primary or secondary osteoarthritis of the knee who underwent underwent TKA were analysed. There were 49 women and 37 men with a mean age of 72 years (range 53-86 years). In the first 43 patients (47 knees) a standard procedure was used (group 1) while in the second 43 patients (47 knees) operated on in the following year, a modified surgical technique was performed (group 2). In particular, the extramedullary guide was set in line with the proximal alignment on the TT (medial 1/3), leaving the extramedullary rod locked in neutral alignment (varus-valgus= 0) in the malleolar clamp, without align it to any anatomical landamark. Limb and components alignment, including femoro-tibial alngke (FTA), femoro-tibial mechanical axis and femur and tibia component alignmnet was assessed on postoperative long-leg radiographs taken 3 months after surgery. A FTA between 2° to 8° of valgus and a component and FT mechanical axis alignment of 0± 3° of varus/valgus were considered within the normal range. RESULTS: A FTA within the normal range was found in 39 (83%) knees in gr 1 and in 41 (87%) of group 2 (p= 0.3). The mean FT mechanical axis was 3.4°± 1.9 in group 1 and 2.7 ± 1.8 in group 2 (p=0.07). Femoral component alignment averaged 2.1° ± 2.4 in group 1 and 1.7 ± 2.1 in group 2 (p=0.3) Tibial component alignment in the coronal plane averaged -2° ± 1.9 in group 1 and - 0.6° ± 1.8 in group 2 (p=0.0001). A varus malalignmnet of the tibial component (>3°) in the coronal plane was present in 16 and in 2 knees of group I and II, respectively (p=0.0008). CONCLUSIONS: The results of this study showed that, by setting the extramedullary road to the anterior projection of the mechanical axis at the proximal tibia and maintaining the same axial orientation of extramedullary road at the ankle joint, the effects of tibial torsion on the distal alignment of the extramedullary systems may be neutralized. This was found to improve the percentage of patients with neutral alignment and reduce significantly the rate of malalignment in varus of tibial component.