Biomechanical comparison of bioresorbable F-u-HA/PLLA screw and tension band wire fixation in medial malleolar fractures

Abstract

The authors have recently reported that forged composites of raw particulate unsintered hydroxyapa- tite/poly-L-lactide (F-u-HA/PLLA) screws are useful for the treatment of medial malleolar fracture. However, the biome- chanical properties of these screws have not yet been fully elucidated. The aim of the present study was to compare the biomechanical properties of F-u-HA/PLLA screws with those of tension band wiring (TBW) using medial malleolar fracture models obliquely oriented at 45° angles in synthetic tibial bones. Fractures were fixed using two 4.5-mm-diameter partial thread F-u-HA/PLLA screws, two 4.5-mm-diameter full thread F-u-HA/PLLA screws, or TBW. The fracture models were tested parallel to the distal joint surface and parallel to the fracture line. The compression load at 1, 2, 3, 4 and 5 mm of fracture displacement was assessed. The compression load parallel to the distal joint surface at 3, 4 and 5 mm of fracture displacement was significantly higher in the partial thread screw group than in the TBW group (P<0.01). Additionally, the compression load parallel to the distal joint surface at 4 and 5 mm was significantly higher in the full thread screw group than in the TBW group (P<0.001). However, the TBW group exhibited a higher compression load at 1 mm compared to the full thread group (P<0.05). As regards the compression load parallel to the fracture line, the compression load at 3, 4 and 5 mm of fracture displacement was markedly higher in the partial thread screw group than in the TBW group (P<0.01); likewise, the compression load at 4 and 5 mm of displacement was significantly higher in the full thread screw group than in the TBW group (P<0.001). On the whole, these results strongly suggest that F-u-HA/PLLA screw fixation, particularly partial thread screw fixation, has good biomechanical strength and provides adequate stability for the treatment of medial malleolar fractures.