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 in- creasing
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.