Sandra Schorlemmer

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

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 mid‐diaphyseal 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.

Glucocorticoid treatment of ovariectomized sheep affects mineral density, structure, and mechanical properties of cancellous bone.

Thus far, orthopedic research lacks a suitable animal model of osteoporosis. In OVX sheep, 6 months of steroid exposure reduced bone density and mechanical competence. Bone properties and bone formation did not recover for another 6 months. Therefore, steroid‐treated OVX sheep may serve as a large animal model for osteopenic bone.

Temporary distraction and compression of a diaphyseal osteotomy accelerates bone healing

Mechanical strain during callus distraction is known to stimulate osteogenesis. It is unclear whether this stimulus could be used to enhance the healing of a normal fracture without lengthening the bone. This study tested the hypothesis that a slow temporary distraction and compression of a diaphyseal osteotomy accelerates fracture healing. Fourteen sheep underwent a middiaphyseal osteotomy of the right tibia, stabilized by external fixation. An external fixator allowed either a temporary axial distraction (TD group; n = 6) or a constant fixation (C group; n = 8). Distraction began 7 days postoperatively at a rate of 0.5 mm twice per day for 2 days with subsequent shortening of 1.0 mm twice on the third day. The procedure was repeated four times. Fluorochrome labeling was performed postoperatively. After 8 weeks the sheep were sacrificed and healing was evaluated using densitometric, biomechanical, and histological methods. Bending stiffness of the tibiae after 8 weeks was 58% higher in the TD group than in the C group. The volume of the periosteal callus was significantly (p = 0.05) higher in the TD group (3.9 cm3) than in the C group (2.7 cm3). There was 20% more bone in the fracture gap of the TD group than the C group. There was a significantly higher bone formation rate in the TD group than in the C group. This study demonstrated the feasibility of fracture healing stimulation by the temporary application of distraction and compression.

Temporary distraction of a diaphyseal osteotomy accelerates fracture healing

INTRODUCTION: Mechanical strain, which occurs during callus distraction, is known to stimulate osteogenesis. This method is used to close large bone defects as well as to achieve leg lengthening (Ilizarov). Our idea was to use the tissue strain induced bone formation to accelerate the bone healing process of normal fractures. To avoid a lengthening of the fractured bone the distraction was followed by a subsequent reduction and reconstitution of the original fracture gap. The hypothesis was that this temporary distraction enhances the fracture healing process.