Correlation of Shear to Compression for Progressive Fracture Obliquity

Abstract

The accompanying shear force at the point of bone opposition is an important factor inherent to tibial fracture stability during axial loading. We determined at which angle of fracture obliquity shearing becomes a dominant force after stabilization with circular external fixation, and how modifications to the external fixator can reduce this effect. We constructed tibial fracture models with a successively increasing fracture angle obliquely (from 0°to 60°) to determine the stability in the classic Ilizarov frame and subsequent frame modifications during axial loading (maximum, 1000 N). Stability was determined by measuring the fracture line displacement for each fracture obliquity model after an applied axial load. Fracture line displacement was recorded as coordinate component changes as measured by an ultrasonic digitizer. We defined construct stability as less than 2 mm of fracture line migration with loading. More than 3500 data points were collected for this study. The classic Ilizarov construct successfully stabilized fractures with up to 30°of fracture obliquity, after which divergent instability occurs. The addition of proximal and distal perpendicular half-pins provides little benefit. Arced wires provided stability up to 40°fracture obliquity. A formal steerage pin construct provided stability for all fracture models (up to 60°of fracture obliquity) with all applied loads (up to 1000-N axial load).

Influence of Mechanical Force on Bone Matrix Proteins in Ovariectomised Mice and Osteoblast-like MC3T3-E1 Cells

“…Mechanical forces from exercise appear to increase the expression of periostin and semaphorin-3A, which in turn jointly promote activation and differentiation of osteoblasts through Wnt/β-catenin signalling. Actual exercise produces complex mechanical effects such as repetitive compression or shearing forces (42). Therefore, it is unknown whether other types of mechanical stimulation cause a phenomenon similar to what we observed.…”

Radius and ulna fracture repair with the IMEX miniature circular external skeletal fixation system in 37 small and toy breed dogs: A retrospective study

“…Removal of the MCESF led to a fracture developing at the original fracture site. Wire tract osteolysis and subsequent implant loosening may result from excessive axial motion of the bone segments and high shear forces across the short oblique fracture . Four dogs subsequently fractured the ipsilateral antebrachium at a different location from the original fracture and long term after MCESF removal.…”

“…Wire tract osteolysis and subsequent implant loosening may result from excessive axial motion of the bone segments and high shear forces across the short oblique fracture. 29,48,49 Four dogs subsequently fractured the ipsilateral antebrachium at a different location from the original fracture and long term after MCESF removal. Although we could not document any anomaly to explain these fractures, toy breeds are prone to stress protection after external skeletal or plate fixation, leading to osteopenia.…”

Reconstruction of massive uncontained glenoid defects using a combined autograft-allograft construct with reverse shoulder arthroplasty: preliminary results

“…In trauma surgery, shear angles exceeding 30 from the plane of compression create instability and are detrimental to bone healing. 45 Our technique allows axial compression with a shear angle of less than 30 for stable fixation and reduction of micromotion to allow integration.…”