Estimating Skeletal Maturity Using Knee Radiographs During Preadolescence: The Epiphyseal:Metaphyseal Ratio

Background: Though skeletal maturity is most relevant during adolescence, it has utility in treatment of younger patients in some circumstances. Accurate estimation of skeletal maturity using knee radiographs would be useful when treating limb length discrepancy and other general medical conditions in preadolescent patients. Currently, a quick, accurate, and reproducible method of estimating skeletal maturity in preadolescents is lacking. Methods: Serial anteroposterior knee radiographs taken at historical growth study visits leading up to the chronological age associated with 90% of final height (an enhanced skeletal maturity standard as compared with peak height velocity) were analyzed in 75 children. Epiphyseal and metaphyseal widths of the distal femur, proximal tibia, and proximal fibula were measured and the epiphyseal:metaphyseal ratio was calculated. Greulich and Pyle (GP) bone ages were also assigned by an experienced pediatric endocrinologist using left hand radiographs. Stepwise linear regression and generalized estimating equation analyses were used to make a skeletal maturity model incorporating demographics (age+sex) and knee epiphyseal:metaphyseal ratios. Results: A total of 258 left knee radiographs from 39 girls (mean age 8.6 y, range: 2.9 to 13 y) and 36 boys (mean age 10.6 y, range: 3.8 to 15 y) were included. The demographics+ratios model had similar prediction accuracy (0.49 vs. 0.48 y, P =0.84) and rate of outliers (11% vs. 9%, P =0.11) as the demographics+GP model. The demographics+ratios model outperformed all other models evaluated, including a demographics-only model ( P <0.001 for all). Conclusions: When combined with chronological age and sex, epiphyseal:metaphyseal ratio measurement in the knee allows for skeletal maturity estimation comparable to using the GP technique. Clinical Relevance: We have defined a knee skeletal maturity system that could be applied in treatment of orthopaedic conditions in preadolescents where a knee radiograph is already obtained, avoiding the need for an additional hand radiograph.