Characteristics of terminal hemimelia: What is the difference between terminal hemimelia and classic fibular hemimelia?

Purpose: Fibular hemimelia has denoted a spectrum of postaxial longitudinal deficiency with fibular aplasia/hypoplasia; the term "terminal hemimelia" is reserved for patients with postaxial longitudinal deficiency having a normal fibula. We aimed to delineate the characteristics of terminal hemimelia. Methods: In total, 30 patients with postaxial longitudinal deficiency who had a normal or hypoplastic fibula and visited our institution between 1992 and 2022 were reviewed. Patients were divided into terminal hemimelia and classic fibular hemimelia groups, and their demographic characteristics and clinical and radiographic findings were compared. Results: Femoral shortening, knee valgus, and tibial spine hypoplasia were less common in terminal hemimelia (n = 13) than in classic fibular hemimelia (n = 17) (p = 0.03, p < 0.001, and p = 0.003, respectively). None of the patients in the terminal hemimelia group exhibited knee instability, whereas 12% of patients with classic fibular hemimelia did. Ball-and-socket ankle and absence of lateral rays were commonly observed in both groups. However, tarsal coalition was observed less frequently in terminal hemimelia (p = 0.004). All terminal hemimelia patients exhibited a painless plantigrade foot without ankle instability. Despite limb-length discrepancy at maturity averaging 40.4 mm for terminal hemimelia and 67.0 mm for classic fibular hemimelia (p < 0.001), patients with terminal hemimelia, except for one, exhibited > 20 mm of limb-length discrepancy. However, 46% of them underwent limb-length equalization procedures, mostly single-stage tibial lengthening, at a mean age of 11.2 years. Conclusion: Terminal hemimelia may present with a milder phenotype than classic fibular hemimelia. It mainly overlaps with the symptoms of fibular hemimelia below the ankle joint and manifests as limb-length discrepancy. However, a considerable number of patients with terminal hemimelia required limb-length equalization procedures, for example single-stage tibial lengthening. Level of evidence: level IV.