To review the biomechanical principles that guide fracture fixation with plates and screws; specifically to compare and contrast the function and roles of conventional unlocked plates to locked plates in fracture fixation. We review basic plate and screw function, discuss the design rationale for the new implants, and examine the biomechanical evidence that supports the use of such implants.
Systematic review of the per reviewed English language orthopaedic literature listed on PubMed (National Library of Medicine online service).
Papers selected for this review were drawn from peer review orthopaedic journals. All selected papers specifically discussed plate and screw biomechanics with regard to fracture fixation. PubMed search terms were: plates and screws, biomechanics, locked plates, PC-Fix, LISS, LCP, MIPO, and fracture fixation.
The following topics are discussed: plate and screw function-neutralization plates and buttress plates, bridge plates; fracture stability-specifically how this effects gap strain and fracture union, conventional plate biomechanics, and locking plate biomechanics.
Locked plates and conventional plates rely on completely different mechanical principles to provide fracture fixation and in so doing they provide different biological environments for healing. Locked plates may increasingly be indicated for indirect fracture reduction, diaphyseal/metaphyseal fractures in osteoporotic bone, bridging severely comminuted fractures, and the plating of fractures where anatomical constraints prevent plating on the tension side of the bone. Conventional plates may continue to be the fixation method of choice for periarticular fractures which demand perfect anatomical reduction and to certain types of nonunions which require increased stability for union.
"Over the last ten years, locking plates for use in femoral neck fractures have been introduced (Aminian et al. 2007, Berkes et al. 2012, Lin et al. 2012, Nowotarski et al. 2012, ). Locking plate technology was first introduced to bridge and stabilize long bone fractures as an alternative to compression plate fixation (Egol et al. 2004). In femoral neck fractures, bridging the fracture is impossible due to the anatomy. "
"This difference was highly significant in mediolateral cantilever bending but less obvious under axial compression, where the good fracture reduction with optimal cortical support probably prevented larger differences . This finding is consistent with similar outcomes of previous studies (Egol et al., 2004; Miller and Goswami, 2007) and may be explained with the angular stability of the locked screw-plate connection which does not allow for any slipping or change in the angulation so that screw loosening and pullout can be prevented. Consequently, it ultimately leads to a stiffer construct and higher pullout resistance. "
"Furthermore, locking plates enable the use of biological fixation techniques that emphasise preservation of blood supply and functional reduction over anatomic reduction and interfragmentary compression. However, in the absence of anatomic reduction and interfragmentary compression, locked plating constructs rely on secondary bone healing  , induced by interfragmentary motion in the millimetre range    and can be enhanced by passive or active dynamisation  . "
[Show abstract][Hide abstract] ABSTRACT: The dynamic locking screw (DLS) in association with minimally invasive plate osteosynthesis (MIPO) in a bridging construct for simple metadiaphyseal long bone fractures enables modulation of the rigidity of the system and facilitates the development of early and triplanar bone callus.Twenty patients affected by distal tibial fracture were treated with MIPO bridging technique and DLS at the proximal side of the fracture. Time of consolidation, quality of the reduction, complications and American Orthopaedic Foot and Ankle Society (AOFAS) score were monitored and the results compared with those from a control group treated with only standard screws on both fracture sides. Student t-test for independent samples was used for the comparison of means between the two groups. Chi-square test was used for the comparison of proportions. A multiple logistic regression model was constructed to assess the possible confounding effects. Performance was considered significant for p < 0.05. The mean healing time was 17.6 ± 2.8 weeks in the group treated with standard screws and 13.5 ± 1.8 weeks in the group treated with DLS (t = 5.5, p < 0.0001). The DLS was associated with early healing and triplanar bone callus.
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