Abstract
Title
3D distribution of cortical bone thickness in the proximal humerus, implications for fracture management.
Introduction
CT imaging is commonly used to gain a better understanding of proximal humerus fractures. the operating surgeon however has a limited capacity to evaluate the internal bone geometry from these clinical CT images. our aim was to use clinical CT in a novel way of accurately mapping cortical bone geometry in the proximal humerus. we planned to experimentally define the cortico-cancellous border in a cadaveric study and use CT imaging software to map out cortical thickness distribution in our specimens.
Methodology
With ethical approval we used fifteen fresh frozen human proximal humeri. These were stripped of all soft tissue and transverse CT images taken with a GE VCT Lightspeed scanner. The humeral heads were then subsequently resected to allow access to the methaphyseal area. Using currettes, cancellous bone was removed down to hard cortical bone. Another set of CT images of the reamed specimen were then taken. Using Mimics imaging software[Materialise, Leuven] and a CAD interface, 3-matic [Materialise, Leuven], we built 3D model representations of our intact and reamed specimens. We first had to define an accurate CT density threshold for visualising cortical contours. We then analysed cortical thickness distribution based on that experimented threshold.
Results
we were able to statistically determine the CT threshold, in Hounsfield Units, that represents the cortico-cancellous interface in the proximal humerus. Our 3D colour models provide an accurate depiction of the distribution of cortical thickness in the proximal humerus.
Discussion/Conclusions
Our Hounsfield value for the cortico-cancellous interface in the proximal humerus agrees with a similar range of 400 to 800 HU reported in the literature for the proximal femur. Knowledge of regional variations in cortical bone thickness has direct implications for basic science studies on osteoporosis and its treatment, but is also important for the orthopaedic surgeon since our decision for treatment options is often guided by local bone quality.
