title: Reasons why dynamic compression plates are inferior to locking plates in osteoporotic bone: a finite element explanation.
abstract: While locking plate fixation is becoming increasingly popular for complex and osteoporotic fractures, for many indications compression plating remains the standard choice. This study compares the mechanical behaviour of the more recent locking compression plate (LCP) device, with the traditional dynamic compression plates (DCPs) in bone of varying quality using finite element modelling. The bone properties considered include orthotropy, inhomogeneity, cortical thinning and periosteal apposition associated with osteoporosis. The effect of preloads induced by compression plating was included in the models. Two different fracture scenarios were modelled: one with complete reduction and one with a fracture gap. The results show that the preload arising in DCPs results in large principal strains in the bone all around the perimeter of the screw hole, whereas for LCPs large principal strains occur primarily on the side of the screw proximal to the load. The strains within the bone produced by the two screw types are similar in healthy bone with a reduced fracture gap; however, the DCP produces much larger strains in osteoporotic bone. In the presence of a fracture gap, the DCP results in a considerably larger region with high tensile strains and a slightly smaller region with high compressive strains. These findings provide a biomechanical basis for the reported improved performance of locking plates in poorer bone quality.
authors.affiliation: a School of Engineering, The University of Edinburgh , Edinburgh EH9 3JL, Scotland , UK.
authors.forename: Alisdair R
authors.initials: AR
authors.lastname: MacLeod
authors.forename: A Hamish R W
authors.initials: AH
authors.lastname: Simpson
authors.forename: Pankaj
authors.initials: P
authors.lastname: Pankaj
mesh_terms: D001860:Bone Plates; D001842:Bone and Bones / Q000601:surgery*; D019245:Compressive Strength; D020342:Finite Element Analysis; D050723:Fractures, Bone / Q000601:surgery; D006801:Humans; D008962:Models, Theoretical; D010024:Osteoporosis / Q000601:surgery*; D013314:Stress, Mechanical; D013977:Tibia / Q000601:surgery
keywords: dynamic compression plate; locking compression plate; preload; principal strains; screw