Prevalence of Tibia Valga Morphology in Valgus Knees and its Implications for Primary Total Knee Arthroplasty

Abstract Introduction Tibia valga, an extra-articular valgus deformity of the tibia, is common in valgus knees and can result in component misplacement and early total knee arthroplasty (TKA) failure. However, the prevalence and importance of tibia valga in TKA has been seldom reported. This study aims to describe the prevalence and characteristics of tibia valga morphology in valgus knees and describes implications for surgical planning in primary TKA. Methods We prospectively examined pre-operative weightbearing whole-body EOS digital radiographs of patients with knee osteoarthritis listed for TKA between December 2018 and December 2020. Hip-knee-ankle angle (HKA), mechanical lateral distal femoral angle (mLDFA), mechanical medial proximal tibial angle (mMPTA), joint line convergence angle (JLCA) and tibial morphology with centre of rotation of angulation of tibia (CORA-tibia) were measured and analysed. Results In 830 knees, 253 (30%) and 577 (70%) were classified as valgus and varus respectively. In valgus knees, 89 knees (35%) had tibia valga. Median CORA-tibia was 2.8 o (range 0.2-10.9 o ). Tibia valga knees had no difference in mLDFA, higher HKA (5.0 o versus 3.0 o , p=0.002) and mMPTA (89.6 o versus 88.1 o , p<0.01), and lower JLCA (2.1 o versus 2.3 o , p<0.01) compared to non-tibia valga knees. Tibia valga deformity was weakly positively correlated with valgus HKA (ρ=0.23, p<0.001) and mMPTA (ρ=0.38, p<0.001). In varus knees, there were 52 cases of tibia valga (9%) with median CORA-tibia of 3.0 o (range 0.5-5.5 o ). Tibia valga knees had higher mMPTA (87.0 o versus 85.2 o , p<0.05) and no difference in HKA, mLDFA and JLCA. CORA-tibia was weakly positively correlated with mMPTA. Conclusions Tibia valga is common in valgus knees, occurring in 35% of this population. Extra-articular tibial rather than distal femoral anatomy contributes most to valgus HKA. To detect the deformity, full leg-length radiographs should be acquired pre-operatively. Intramedullary instrumentation should be used cautiously in knees with tibia valga when performing TKA.