Intramedullary limb lengthening (LL) is now achievable through motorized intramedullary devices. While this technology mitigates some complications of external-fixation-based lengthening, many complications common to all lengthening procedures persist. New challenges and complications exclusive to this newer technology are also presented. The LL surgeon should be aware of and ready to respond to complications involving device malfunctions, poor local bony and soft-tissue biology, patient compliance, neurovascular compromise, joint instability, regenerate problems, and others. While technology will continue to evolve, study of and adherence to foundational principles of LL will minimize risks and optimize patient outcomes.

IntroductionVarious methods based on bony landmarks are used to determine patellar height. This study analyzed five methods for patellar height measurement on lateral knee radiographs, namely, the Insall–Salvati, Koshino–Sugimoto, Blackburne–Peel, modified Insall–Salvati, and Caton–Deschamps methods.MethodsOverall, 425 pediatric participants (221 males, 204 females; age range 5–18 years) were included and were divided equally into three age groups (A, 5–10 years; B, 11–13 years; and C, 13–18 years). For the comparison of the applicability of each method, the applicable probabilities for each age group and sex-based differences were analyzed using logistic regression techniques. Intra-rater reliability and inter-rater variability were analyzed by two trained raters.ResultsThe Koshino–Sugimoto method was applicable to all patients. The 80% applicable age of female patients was lower than that of male patients for the Blackburne–Peel (male = 11.9, female = 11) and Caton–Deschamps (male = 11.9, female = 11.1) methods. However, in the Insall–Salvati (male = 12, female = 12.1) and modified Insall–Salvati (male = 12.6, female = 13.1) methods, the 80% applicable age in male patients was lower than that in female patients. The Koshino–Sugimoto method showed the highest variability in group B, while the Insall–Salvati showed the highest variability in group C. In terms of intra-observer reliability, the Caton–Deschamps method showed the same reliability as the Insall–Salvati method, in group C.ConclusionsOur results demonstrated differences in the reliability, variability, and applicability of patellar height measurement methods according to age group. The applicability of patellar height measurement methods also differed according to sex. Therefore, based on age group and sex, different methods should be used for patellar height measurement in pediatric patients.