Shear movement at the fracture site delays healing in a diaphyseal fracture model

Abstract

This study tested the hypothesis that interfragmentary axial movement of transverse diaphyseal osteotomies would result in improved fracture healing compared to interfragmentary shear movement. Ten skeletally mature merino sheep underwent a middiaphyseal osteotomy of the right tibia, stabilized by external fixation with an interfragmentary gap of 3 mm. A custom made external fixator allowed either pure axial ( n = 5) or pure shear movement ( n = 5 ) of 1.5 mm amplitude during locomotion by the animals. The movement of the osteotomy gap was monitored weekly in two sheep by an extensometer temporarily attached to the fixator. After 8 weeks the sheep were killed, and healing of the osteotomies was evaluated by radiography, biomechanical testing, and undecalcified histology. Shear movement considerably delayed the healing of diaphyseal osteotomies. Bridging of the osteotomy fragments occurred in all osteotomies in the axial group (lOO%), while in the shear group only three osteotomies (60%) were partially bridged. Peripheral callus formation in the shear group was reduced by 36% compared to the axial group (p < 0.05). In the axial group bone formation was considerably larger at the peripheral callus and in between the osteotomy gaps but not in the intramedullary area. The larger peripheral callus and excess in bone tissue at the level of the gap resulted in a more than three times larger mechanical rigidity for the axial than for the shear group (p < 0.05). In summary, fixation that allows excessive shear movement significantly delayed the healing of diaphyseal osteotomies compared to healing under axial movement of the same magnitude.

Implant Material and Design Alter Construct Stiffness in Distal Femur Locking Plate Fixation: A Pilot Study

“…Axial stiffness values obtained by the two titanium implants were more than 30% smaller and may thus provide a different mechanical stimulus for fracture healing. Although axial micromotion at the fracture site is known to stimulate healing, torsional motion induces shear at the fracture site and may be more critical for successful fracture healing [1]. Torsional stiffness again was largest for the steel plate with the AxSOS design.…”

A new angle stable nailing concept for the treatment of distal tibia fractures

“…The applied osteosynthesis must keep the interfragmentary strain within optimal limits to avoid excessive movement and strain. Mainly torsional and sheer stresses have proven to delay bone healing [15,16]. The significant reduction in torsional movements could represent a relevant advantage in the treatment of distal tibia fractures.…”

What Are the Biomechanical Properties of the Taylor Spatial Frame™?

“…There is general consensus that a certain level of axial strain is desirable and necessary to stimulate bone healing with, among others, Kenwright and Goodship [22], as early as 1989, reporting increased callus mineralization and fracture stiffness in ovine tibial fractures with approximately 16% axial strain compared with more rigid fixation, although this was seen to deteriorate in quality somewhat with increased strains of up to 66% [10,13,17,22,34,36]. Likewise, although there is less agreement on this, it generally is considered that shear strain, whether linear or rotational, is detrimental to bone healing and should be limited where possible [3,8,10,29,36]. Relating this to the current study, given the nonclinically representative nature of the models tested and infinite variability of possible fracture patterns, it is not possible to extrapolate the precise change in mechanical behavior that would be produced at a specific fracture site by use of a TSF.…”