Radiological evaluation of coronal femoral and tibial morphology and coronal limb alignment in windswept deformity of the knee

Windswept deformity (WSD) of the knee, involving valgus deformity in one knee and varus deformity in the other, is uncommon and not well understood. This study aimed to clarify the radiological characteristics of WSD patients with osteoarthritis. WSD knees with Kellgren–Lawrence stage 3 or 4 osteoarthritis in 36 patients were radiologically evaluated. Mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle (MPTA), arithmetic hip–knee–ankle (aHKA) angle, and joint line obliquity were measured. Comparisons in radiological measurements were made with 47 patients with bilateral valgus and 135 patients with bilateral varus knee osteoarthritis (control groups). Among WSD patients, 75% had valgus deformity in the right knee, while 25% had it in the left knee. The mLDFA in valgus WSD knees was significantly lower than that in varus WSD knees (85.1 ​± ​2.2° vs. 87.3 ​± ​2.3°; p < ​0.001), whereas the MPTA in varus WSD knees was significantly lower than that in valgus WSD knees (83.9 ​± ​0.5° vs. 87.8 ​± ​0.5°; p ​< ​0.001). The calculated aHKA angle indicated that valgus and varus WSD knees corresponded to constitutional valgus and varus alignments, respectively. Compared with the control groups, the mLDFA in valgus WSD knees was significantly higher than that in bilateral valgus knees (85.1 ​± ​0.4° vs. 83.5 ​± ​0.3°; p ​= ​0.003), whereas the mLDFA in varus WSD knees was significantly lower than that in bilateral varus knees (87.4 ​± ​0.4° vs. 88.5 ​± ​0.2°; p ​= ​0.008). WSD is more frequently associated with right knee valgus deformity in the Japanese population. Significant side-specific differences in coronal femoral and tibial morphology and constitutional limb alignment were observed in WSD. • The right knee is more frequently involved in valgus deformity in windswept deformity (WSD) patients. • Valgus and varus WSD knees show constitutional valgus and varus, respectively. • WSD patients show side differences in bony anatomy and constitutional alignment.