Dynamic Interfragmentary Compression Through a Tibial Intramedullary Nail Compared to Backslapping Alone: A Biomechanical Analysis

OBJECTIVES: To investigate the amount of interfragmentary compression obtained in a transverse tibia fracture model with backslapping alone (BS) versus the intramedullary nail's dynamic internal compression (IC) mechanism and if that compression is maintained after loading. METHODS: A transverse diaphyseal tibia synthetic fracture model was used. Specimens were allocated to four groups (n=5/group) that received one of two intramedullary nails (A or B) and obtained compression either with the IC device or with BS alone. Specimens underwent sinusoidal loading for 135,000 cycles of 700N @3Hz to simulate three months of weightbearing. Interfragmentary pressure measurements were measured at initial compression, procedure completion (pre-cycling) and after loading (post-cycling). Compression at each stage was compared between BS and IC groups as well as between stages. Outcomes were also compared between Nails A and B. RESULTS: There was significantly greater initial (1097N vs 167N, p<0.001) and pre-cycling (391N vs 103N, p<0.001) compression generated with IC compared to BS. The IC group also maintained greater compression than the BS group post-cycling (377N vs 75N, p<0.001). Both groups experienced significant loss of compression between initial and pre-cycling timepoints and during the cycling process (p<0.05 for all). On subanalysis, Nail B was able to generate significantly more initial compression than Nail A with the IC device (1523N vs 382N, p=0.001) and maintain it post-cycling (412N vs 205N, p=0.032). Conversely, Nail A was able to generate and maintain significantly more compression than Nail B at all three time-points with the BS technique (p<0.05 for all). CONCLUSIONS: Intramedullary IC devices generated and maintained greater interfragmentary fracture compression than traditional BS techniques alone. However, some compressive force was lost after loading regardless of compression technique utilized. Differences in compressive force were observed between nail manufacturers with both techniques, which may suggest that nail geometry and instrumentation may contribute to fracture compression. LEVEL OF EVIDENCE: V.