PURPOSE: Plating of serial rib fractures in flail chest injuries reduces the mortality associated with prolonged ventilation. However, rib plating is a highly invasive procedure and posterior fractures are difficult to access. This study investigated the durability and fixation strength of intramedullary rib splints for less-invasive fixation of posterior rib fractures. Tested was the hypothesis that splint constructs can withstand a loading history that spans the post-operative healing phase in osteoporotic ribs. Furthermore the effect of splint size on construct performance was investigated.
METHODS: A fracture was induced in six pairs of human osteoporotic ribs (ribs 4 to 9, female, 71 years). Fractures were stabilized with narrow splints (NS, 4 mm width) and wide splints (WS, 5 mm width) on the contralateral ribs. The 1 mm thick and 95 mm long titanium splints were inserted anterior to the fracture. Constructs were subjected to a dynamic loading of 360,000 cycles with a 200 Nmm bending moment, corresponding to respiration during a 3-week healing period at an exaggerated five-fold physiologic bending load. Finally, constructs were loaded to failure.
RESULTS: Exaggerated dynamic loading caused no construct failures and resulted in average subsidence of the construct by 0.3±0.2 mm (NS) and 0.5±0.2 mm (WS). The residual bending strength after 360,000 loading cycles was slightly higher in NS constructs (1340±159 Nmm) than in WS constructs (1163±154 Nmm) (p=0.04). NS constructs failed by splint bending whereas WS constructs failed by rib splitting.
CONCLUSION: Both constructs withstood five-fold physiological dynamic loading and maintained residual strength higher than 25 times the physiological bending load. The higher residual strength of NS constructs may be attributed to the higher splint flexibility that decreases stress concentrations and preserves rib elasticity. These results were obtained in a worst-case combination of exaggerated loading in osteoporotic ribs. Rib splints may provide a less-invasive alternative for posterior rib fractures.
CLINICAL IMPLICATIONS: Findings suggest that the fixation strength of the rib splints is sufficient to endure respiration during the post-operative healing period.
DISCLOSURE: Michael Bottlang, Grant monies (from sources other than industry) Financial support for research provided by the Legacy Research Foundation.; Other Lincensing fees received from Synthes CMF.; Product/procedure/technique that is considered research and is NOT yet approved for any purpose. This research describes a novel intramedullary splint for fixation of rib fractures. This splint has not yet been approved by the NIH and is not commerically available.