Does having shorter tibias increase the likelihood of developing knee osteoarthritis? An observational cross-sectional radiographic analysis

Background The crural index, a fundamental property of the human skeletal system, is the ratio of the total length of the tibia to that of the femur. This study aimed to investigate the correlation between the crural index and knee osteoarthritis (OA). Methods This observational cross-sectional study included patients with preoperative weight-bearing full-length radiographs who were divided into two groups according to the Kellgren–Lawrence grading system. After rigorous screening based on the inclusion and exclusion criteria, 92 and 125 patients were included in the control and knee OA groups, respectively. The crural index, hip-knee-ankle angle (HKA), the deviation of the HKA from 180° (|HKA-180|), mechanical axis deflection (MAD), mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle (MPTA), arithmetic HKA (aHKA), and |aHKA| were compared between the two groups. In addition, linear regressions of the crural index were performed to assess their correlations. Results The crural index was significantly smaller in the knee OA group than in the control group (crural index: 79.49 ± 2.39 versus 82.14 ± 2.22, respectively; p < 0.001). The crural index correlated well with both |HKA-180| (R² = 0.54, p < 0.05) and MAD (R² = 0.57, p < 0.05). Conclusions Patients with OA of the knee have a much smaller crural index, which was closely related to the knee alignment.