Osteogenesis imperfecta (OI) is a genetic disorder characterised by skeletal fragility, recurrent fractures, and progressive deformities. The Fassier-Duval (FD) telescopic intramedullary nail is commonly used in paediatric OI patients for stabilising long bones while accommodating bone growth. Despite its clinical benefits, the FD nail is often associated with substantial complications, particularly bending failure and nail migration attributed to insufficient distal fixation. The aim of this research was to quantify the bending stability provided by the FD nail under clinically relevant loading conditions and to develop design modifications to improve the distal fixation mechanism.
Biomechanical analysis was conducted to assess the bending stresses and stiffness of the FD nail under physiological loading. Calculations demonstrated that the nail undergoes plastic deformation, contributing minimally to the overall bending stiffness of the bone–nail composite construct. Consequently, the compromised OI bone remains the primary load-bearing structure, underscoring the negligible mechanical bending stability of current FD nails.
To address the distal fixation mechanism, three modified fixation concepts were developed and prototyped: a corkscrew-shaped male end, a screw threaded male end coupled with a partially threaded interlocking pin, and a K-wire secured with a clamp cap. Pull-out testing using synthetic bone models showed a substantial increase in fixation strength compared to current FD fixation methods. The screw-threaded male end combined with an interlocking pin provided the most consistent mechanical stability, while the K-wire secured with a clamp cap achieved the highest mean pull-out force, although with greater variability.
Overall, the results highlight the critical role of secure distal anchorage components for achieving fixation strength. Additionally, the findings suggest that the nail’s primary function is to serve as an internal growth guide for longitudinal growth, rather than to act as a load-bearing implant capable of restoring mechanical stability. Collectively, this research provides biomechanical insights into bending stability and proposes improved distal fixation designs that have the potential to reduce nail migration.