Development and biomechanical evaluation of a new biodegradable intramedullary implant for osteosynthesis of midshaft fractures of small hollow bones

BACKGROUND Up to date there is no intramedullary, biodegradable osteosynthesis commercially available to treat non-comminuted midshaft fractures of small hollow bones applying not only a stable osteosynthesis but an additional axial compression to the fracture site. OBJECTIVE AND METHODS Therefore we (1) designed different implant profiles and simulated the inner tension/volume using CAD. (2) Thereafter we manufactured a prototype with the best volume/tension-ratio using 70:30 poly-(L-lactide-co-D, L-lactide) (PLLA/PDLLA) and poly-e-caprolactone (PCL) by injection moulding. Both materials are resorbable, licensed for medical use and show a slow degradation over at least one year. (3) The implants were tested in a universal testing machine (Zwick/RoellZ010) using a 3-point-bending-setup. (4) We compared the implants with different types of commercially available Ti6Al4V 6-hole 2, 3 mm-plates including interlocking systems (Leibinger Set, Stryker) (each group n= 6) using a 4-point-bending-test-setup with artificial metacarpal bones (Sawbones®). RESULTS The 3-point-bending-test-results showed that mean failure-force of PCL-tubes was 57.94 ± 4.28 N whereas the PLLA/PDLLA-tubes had an approximately four-fold higher value of 227.24 ± 1.87 N (p< 0.001). Additionally, the 4-point-bending-test-results showed that the maximum load of PLLA/PDLLA tubes (61.97 ± 3.58 N) was significantly higher than the strongest 6-hole metacarpal plate (22.81 ± 0.76 N) (p< 0.001). CONCLUSION The study showed that the new type of biodegradable, intramedullary tension-osteosynthesis made of PLLA/PDLLA is even more stable than common plate osteosynthesis in a small-hallow-bone-model. Further in vivo investigation should be performed to evaluate the surgical technique and long-term healing process of the bone and biodegradation process of the implant.