The lateral proximal tibia is a reliable indicator of knee skeletal maturity on full-length standing radiographs of the lower limb: A study in a Japanese population.

Abstract

Leg-length discrepancy and genu varum/valgum are typically assessed using full-length standing radiographs of the lower limb (FLSR), and guided growth surgery is performed when indicated. Accurate assessment of skeletal maturity is essential for predicting surgical outcomes. However, no standardized system currently exists to evaluate skeletal maturity around of the knee based on FLSR. Between 2012 and 2024, 345 cases underwent FLSR. After excluding those with prior lower limb surgery or premature epiphyseal closure, 172 cases (344 limbs; 79 boys, 93 girls) were analyzed. Skeletal maturity was assessed at the medial and lateral distal femur and proximal tibia. The proportion of evaluable limbs, intra-rater reliability, and inter-rater reliability (evaluated by two orthopaedic surgeons) were compared. Maturity was classified into five stages: Stage 0 (epiphysis is not reaching the metaphysis), Stage 1 (epiphysis is reaching metaphysis without capping), Stage 2 (complete capping without physeal fusion), Stage 3 (complete capping with active physeal fusion), and Stage 4 (complete physeal fusion). Cases with overlapping metaphysis and epiphysis were defined as indeterminate. The proportion of evaluable limbs was the highest at the lateral proximal tibia (LPT), followed by the lateral distal femur, medial proximal tibia, and medial distal femur. The LPT demonstrated excellent intra-rater reliability (ICC = 0.976) and consistently high inter-rater reliability. Left-right staging discrepancies were least frequent at the LPT, and no LPT cases were indeterminate. Although skeletal maturity advanced with age, substantial individual variation was observed. The LPT showed perfect evaluability and consistently superior reliability, making it the most dependable site for assessing knee skeletal maturity on FLSR. IV.