Meniscal damage, meniscal extrusion, varus–valgus malalignment, and medial–lateral laxity are local factors that may be present in primary knee osteoarthritis . Varus malalignment increases loading of the medial tibiofemoral compartment during gait by increasing the external adduction moments (force toward the sagittal plane) acting on the knee during the late-stance phase of the gait cycle [14,15]. In TKA, gold standard is restoration of neutral mechanical axis, considered critical for long-term success. A tibial cut made at 90° compared to the tibial mechanical axis allows long survival of the tibial component in terms of aseptic loosening [16–18].
In this study, we aimed to discriminate factors that contribute to arthritic varus and to the global limb malalignment. We observed several of our patients with varus angulation of their tibia, contributing to the global limb malalignment. In literature different observations are reported about morphology to varus arthritic knee. Bellemans et al. previously demonstrate that the strongest parameter that influences HKA in healthy knees with constitutional varus is MPTA . Similarly, in our study, the deformity of the proximal tibia was the most important factor related to the varus osteoarthritic knee (Figure 2A). Varus malalignment determines a medial overload that results in a tibial cartilage wearing with secondary subchondral bone collapse. Correcting intra-operatory by cutting the most lateral tibial plateau with the guide aligned 90° from mechanical axis of the tibia, we observed a restoration of neutral limb alignment. Moreover, tibial cuts measured pre-operatively were predictable of what have been measured during surgery.
Weiping et al. observed that femorotibial geometric alignment referred to increased mLDFA and decreased MPTA was one of the two potential components giving the major contribution to varus deformity of the lower extremity in knee osteoarthritis. In our population, the conformation of the distal femur had a minor impact in the contribution of varus knee than the geometry of the proximal tibia. At the same time, observing the correlation diagram between mLDFAs and HKAs, millimetric augment of varus grade on the distal femur corresponds linearly to HKA varus grade augmentation (Figure 2B). Bellemans  observed a good correlation of these two parameters also in constitutional knees.
Thienpont et al. suggest that the mean varus alignment of the lower limb (178° HKA°) is rather a result of lateral soft tissue laxity with joint line opening (JLCA of 3°) on the lateral side in varus knees. Despite in our population we found a median JLCA of 5°, it wasn’t significantly related to the amount of varus osteoarthritic deformity as it was for the MPTA. Moreover, the amount of JLCA didn’t change the definitive tibial plateau cuts’ thickness. Tibial cuts had major thickness on the lateral side than in the medial side. That was directly related to the grade of varus deformity and so on the grade of MPTA (Figure 3A, B). Secondary to these observations, the majority of correction during TKA should be obtained on the lateral tibial plateau, in order to correct tibial deformity. A JLCA >2° could be more related to the amount of medial soft tissue release needed to balance the knee in extension once the mechanical alignment of the tibia has already been restored through the tibial cut. This is definitively important in order to get a neutral, well balanced, HKA. Indeed, not so much intra-articular deformity correction can be obtained on the femoral side compared to the tibial side associated with soft tissue release in extension on the concave side (medial collateral ligament in extension).
Cho et al.  in a selected Asiatic population, found that lateral femoral bowing shows a tendency to increase his value directly proportional to the grade of varus knee deformity. In our European population, we also found an increase of femoral bowing according to the degree of varus knee deformity (Figure 2E), but not statistically significant and with mean values at the edge of normal parameters (4,6-7,8°). Therefore, diaphyseal femoral deformity had not such a strong impact both on HKA and on osteoarthitis progression in knee varus deformity, compared to what was found in Asiatic population (Table 1).
Finally, Issin et al. shows that abnormal forces applied to ankle may cause collapse in distal lateral tibial metaphysis and decrease LDTA in varus knees and that medial neck shaft angle may decrease due to possible abnormal loading angles to the femoral neck in some individuals with varus gonarthrosis. In our series different grades of HKA were associated with variable LDTA values showing a completely dissociated correlation between those parameters (Figure 2D). The same was observed for MNSA (Figure 2F).
The limitations to this study include the nature of retrospective analysis. We used standard full leg standing radiographs, which are the standard for alignment assessment, but may not be as accurate and reproducible as 3D computer tomography or biplanar radiographs. Furthermore, the use of bipodal weight-bearing view without the augment of the unipodal view cannot be helpful to evaluate the presence of ligament imbalance. The rotational position of the lower extremities might influence the outcome of the measurements. We performed varus-valgus stress radiograph only in case of clinical varus positive stress at 0° and/or 30°. We did not compare the grade of medial compartment release to JLCA values. Another limitation is the lack of explanation for the patho-etiology and the natural course of tibia vara. Furthermore, we don't have consecutive images to document the natural progression of this condition overtime.
According to our findings the major contributor to osteoarthritic varus knee malalingment on radiological evaluation is related to proximal tibia deformity. As a clinical consequence, performing TKA requests consciousness of lower limb alignment. Pre-operative planning could be mandatory to investigate the exact position of deformity. During performing TKA, the majority of the correction should therefore be made on tibial cut.