Biomechanical assessment of a novel bone lengthening plate system - A cadaveric study

Background Although many types of external fixators have been developed for distraction osteogenesis, all have some drawbacks. We recently developed a novel bone lengthening plate to overcome these problems. The purpose of this study is to conduct biomechanical analyses using cadavers to assess the stability of the bone lengthening plate in relation to distraction length and femoral bone mineral density. Methods We used human cadaveric femurs (n = 18) to assess the effects of distraction length and bone mineral density on the biomechanical stability of the bone lengthening plate. After establishing control (n = 6, 0 mm lengthening) and experimental groups (n = 12, 30 mm lengthening), we measured biomechanical stability (structural stiffness, ultimate load, and displacement) under a compressive load. The experimental group was subdivided into a group with normal bone mineral density (n = 6) and a group with osteoporosis (n = 6), and the biomechanical stability of these groups was compared. Finding Structural stiffness differed significantly between the control (417.6 N/mm) and combined experimental groups (185.6 N/mm, p = 0.002). Ultimate load also differed significantly between the control (1327.8 N) and combined experimental (331.4 N, p = 0.002) groups. Bone mineral density was unrelated to structural stiffness (p = 0.204), ultimate load (0.876), or displacement (0.344). In all cases, failure of the bone lengthening plate occurred at the longitudinal connectors, such as the connecting columns between the upper and lower plates, and the lengthening shaft of the bone lengthening plate. Interpretation The biomechanical stability of the bone lengthening plate was affected by the lengthening length but not by bone mineral density. In addition, biomechanical stability during lengthening was most strongly influenced by the longitudinal connectors.