title: 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 (100%), 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.
authors.affiliation: Department of Orthopaedic Research and Biomechanics, University of Ulm, Helmholtzstr. 14, 89081 Ulm, Germany. peter.augat@medicin.uni-ulm.de
authors.forename: Peter
authors.initials: P
authors.lastname: Augat
authors.forename: Johannes
authors.initials: J
authors.lastname: Burger
authors.forename: Sandra
authors.initials: S
authors.lastname: Schorlemmer
authors.forename: Thomas
authors.initials: T
authors.lastname: Henke
authors.forename: Manfred
authors.initials: M
authors.lastname: Peraus
authors.forename: Lutz
authors.initials: L
authors.lastname: Claes
mesh_terms: D000818:Animals; D002146:Bony Callus / Q000000981:diagnostic imaging / Q000503:physiopathology*; D019245:Compressive Strength; D004195:Disease Models, Animal; D016267:External Fixators; D005260:Female; D005592:Fracture Fixation / Q000379:methods*; D017102:Fracture Healing / Q000502:physiology*; D011859:Radiography; D033081:Shear Strength; D012756:Sheep; D013977:Tibia / Q000000981:diagnostic imaging / Q000293:injuries / Q000503:physiopathology*; D013978:Tibial Fractures / Q000000981:diagnostic imaging / Q000503:physiopathology*; D019415:Torque