Abstract
High energy bone fractures resulting from impact trauma are often accompanied by subcutaneous soft tissue injuries, even if the skin remains intact. There is evidence that such closed soft tissue injuries affect the healing of bone fractures, and vice versa. Despite this knowledge, most impact trauma studies in animals have focussed on bone fractures or soft tissue trauma in isolation. However, given the simultaneous impact on both tissues a better understanding of the interaction between these two injuries is necessary to optimise clinical treatment. The aim of this study was therefore to develop a new experimental model and characterise, for the first time, the healing of a complex fracture with concurrent closed soft tissue trauma in sheep. A pendulum impact device was designed to deliver a defined and standardised impact to the distal thigh of sheep, causing a reproducible contusion injury to the subcutaneous soft tissues. In a subsequent procedure, a reproducible femoral butterfly fracture (AO C3-type) was created at the sheep’s femur, which was initially stabilised for 5 days by an external fixator construct to allow for soft tissue swelling to recede, and ultimately in a bridging construct using locking plates. The combined injuries were applied to twelve sheep and the healing observed for four or eight weeks (six animals per group) until sacrifice. The pendulum impact led to a moderate to severe circumferential soft tissue injury with significant bruising, haematomas and partial muscle disruptions. Posttraumatic measurements showed elevated intra-compartmental pressure and circulatory tissue breakdown markers, with recovery to normal, pre-injury values within four days. Clinically, no neurovascular deficiencies were observed. Bi-weekly radiological analysis of the healing fractures showed progressive callus healing over time, with the average number of callus bridges increasing from 0.4 at two weeks to 4.2 at eight weeks. Biomechanical testing after sacrifice showed increasing torsional stiffness between four and eight weeks healing time from 10% to 100%, and increasing ultimate torsional strength from 10% to 64% (relative to the contralateral control limb). Our results demonstrate the robust healing of a complex femur fracture in the presence of a severe soft tissue contusion injury in sheep and demonstrate the establishment of a clinically relevant experimental model, for research aimed at improving the treatment of bone fractures accompanied by closed soft tissue injuries.
Highlights
High energy bone fractures resulting from impact trauma are often accompanied by subcutaneous soft tissue injuries, even if the skin remains intact
Our results demonstrate the robust healing of a complex femur fracture in the presence of a severe soft tissue contusion injury in sheep and demonstrate the establishment of a clinically relevant experimental model, for research aimed at improving the treatment of bone fractures accompanied by closed soft tissue injuries
High energy bone fractures resulting from impact trauma, such as those sustained by pedestrians hit by a motor vehicle, are often accompanied by subcutaneous soft tissue injuries, even if the skin remains intact
Summary
High energy bone fractures resulting from impact trauma, such as those sustained by pedestrians hit by a motor vehicle, are often accompanied by subcutaneous soft tissue injuries, even if the skin remains intact. Clinical experience and experimental research has provided evidence that the healing of bone fractures is influenced by the state of the surrounding tissue [1,2,3]. The muscles and periosteum that surround bone are important for the re-vascularisation of the fracture callus, but these tissues are known as a source for osteoprogenitor cells that are essential for bone formation during fracture healing [3,4,5]. A better understanding of the interplay between bone fracture healing and the surrounding soft tissue is essential for the development of better treatment modalities for bone fractures with concurrent soft tissue injuries. The experimental trauma should reflect a clinically observed injury pattern, whilst at the same time allow for a high level of standardisation, which is required to limit the variability and reduce the necessary sample size
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