Biomechanical evaluation of interlocking nail and locking compression plating for stabilization of ovine critical-sized segmental tibia defects

BACKGROUND: Segmental large volume bone loss resulting from fracture or osseous neoplasia is a major challenge to orthopedic surgeons and there is an ongoing quest to identify treatments that optimize healing. To advance treatment, large animal translational models—such as the ovine critical-sized tibia defect model—are instrumental for testing of novel scaffolds for bone regeneration. However, little standardization in the implants utilized for defect stabilization has been determined and current commercially available implants may be inadequate to replicate the strength of the native tibia. We hypothesize that a 10-mm interlocking nail (ILN) would be stiffer in axial, bending, and torsional loading than its 8-mm counterpart and would be stiffer in axial and torsional loading compared to a 4.5-mm broad locking compression plate (LCP). METHODS: Tibias were harvested from 24 ovine hind limbs from skeletally mature ewes euthanized for reasons unrelated to this study and were randomized to treatment group. An ex vivo comparison of a novel 10-mm angle-stable non-tapered ILN was compared to a commercially available 8-mm angle-stable tapered ILN and a broad LCP in an ovine critical-sized (5-cm) tibia defect model. Axial stiffness, torsional stiffness, and bending stiffness were determined in control intact tibia and tibial constructs in the three treatment groups. Following implantation, radiography was performed in all limbs and tibia length and cortical and medullary cavity diameter were measured. Comparisons between groups were assessed with a one-way analysis of variance. Significance was set at P<0.05. RESULTS: The 10-mm ILN in tibia containing a 5-cm ostectomy gap most closely replicated the structural properties of intact tibia compared with other constructs. The 10-mm ILN had significantly stronger torsional (P<0.001) and bending (P=0.002) stiffness than the 8-mm ILN, and was significantly stronger than the LCP in axial (P=0.04) and torsional (P=0.01) stiffness. CONCLUSIONS: A 10-mm ILN used to stabilize an ovine critically-sized tibia defect most closely mimicked the structural properties of the intact tibia when compared to a 8-mm ILN or broad LCP. Further in vivo testing will aid in determining which stabilization method is best suited for testing of novel tissue engineering and bone healing studies.