Novel intramedullary-fixation technique for long bone fragility fractures using bioresorbable materials.

Almost all of the currently available fracture fixation devices for metaphyseal fragility fractures are made of hard metals, which carry a high risk of implant-related complications such as implant cutout in severely osteoporotic patients. We developed a novel fracture fixation technique (intramedullary-fixation with biodegradable materials; IM-BM) for severely weakened long bones using three different non-metallic biomaterials, a poly(l-lactide) (PLLA) woven tube, a nonwoven polyhydroxyalkanoates (PHA) fiber mat, and an injectable calcium phosphate cement (CPC). The purpose of this work was to evaluate the feasibility of IM-BM with mechanical testing as well as with an animal experiment. To perform mechanical testing, we fixed two longitudinal acrylic pipes with four different methods, and used them for a three-point bending test (N = 5). The three-point bending test revealed that the average fracture energy for the IM-BM group (PLLA + CPC + PHA) was 3 times greater than that of PLLA + CPC group, and 60 to 200 times greater than that of CPC + PHA group and CPC group. Using an osteoporotic rabbit distal femur incomplete fracture model, sixteen rabbits were randomly allocated into four experimental groups (IM-BM group, PLLA + CPC group, CPC group, Kirschner wire (K-wire) group). No rabbit in the IM-BM group suffered fracture displacement even under full weight bearing. In contrast, two rabbits in the PLLA + CPC group, three rabbits in the CPC group, and three rabbits in the K-wire group suffered fracture displacement within the first postoperative week. The present work demonstrated that IM-BM was strong enough to reinforce and stabilize incomplete fractures with both mechanical testing and an animal experiment even in the distal thigh, where bone is exposed to the highest bending and torsional stresses in the body. IM-BM can be one treatment option for those with severe osteoporosis

IM-BM procedures.

<p>View of the distal femur (B1) and bone cross section schema (B2) after CPC injection. PLLA: PLLA woven tube; PHA: PHA fiber mat; CPC: calcium phosphate cement.</p

Representative postoperative radiographs.

<p>Representative postoperative radiographs in the IM-BM group (PLLA + CPC + PHA) at week 0 (a) and week 8 (b). (b) The fracture site obtained complete bony union (arrow). Representative postoperative radiographs in the Kirschner wire group at week 0 (c) and week 1 (d). (d) Cutout happened at the fracture site (arrowhead). Representative postoperative radiograph in the PLLA + CPC group at week 0 (e). (e) It showed CPC leakage from the fracture site. Representative postoperative radiograph in the CPC group at week 1 (f). (f) It showed fracture displacement.</p

Histologic cross sections of specimens from the IM-BM group.

<p>Histologic cross sections of specimens from the IM-BM group (PLLA + CPC + PHA) stained with hematoxylin and eosin. (a) A PHA fiber mat layer surrounded the CPC, and the PLLA tube was not degraded at week 20. (b) At week 52, the PLLA tube seemed to have degraded gradually. (c) Multinucleated giant cell (arrowhead) and neovascularization were observed in the PHA fiber mat layer at week 52. PHA fiber (arrow). PL: PLLA woven tube; PH: PHA fiber mat C: CPC; B: bone cortex; BM: bone marrow.</p

Result of mechanical testing.

<p>A representative stress–strain curve 10 min after the CPC injection in group 1 (double arrow) and group 4 (arrow).</p