Assessment of tibial fracture healing using dual energy X-ray absorptiometry

Abstract

The assessment of fracture healing is largely a matter of clinical judgement, often based on observing x-rays showing the formation of bridging callus or obscuration of the fracture line and an impression of fracture stiffness obtained by manual loading. In circumstances where these assessment methods are compromised, for example in fractures stabilised using either external fixation or intramedullary nailing, the determination of healing can be problematic. Dual Energy X-ray Absorptiometry (DXA) provides a quick, non-invasive and quantitative method of measuring bone density, which could enable the change in mineral content at a healing site to be monitored. This study evaluated the viability of using DXA to assess the healing of tibial fractures stabilised using intramedullary nails and external fixators. Trials have been undertaken on a Lunar DPX-L scanner situated at South Cleveland Hospital, Middlesbrough. Aluminium and hydroxyapatite phantoms have been used to determine the accuracy, sensitivity and reproducibility of the DXA measurements. Small fracture gaps of less than 0.05 mm were detectable on both simulated transverse and oblique fractures. BMD values which one might expect at a fracture site could be accurately measured down to 0.16 g cm(^-2)14 Patients with tibial fractures (6 with intramedullary nails and 8 with external fixators) have been measured at 4 week intervals following trauma. The bone mineral density (BMD) at regions of interest along the fractured tibial shaft were compared to the non-fractured contra-lateral. Anatomical landmarks were used to relocate the regions of interest between scans and good reproducibility of results (coefficient of variation = 3.36 %) was obtained. After an initial fall in the first month, the BMD at the fracture site gradually increased to the original unfractured value by approximately the fifth month post-fracture. Proximal and distal to the trauma site there was a gradual decrease in BMD in all of the patients, which persisted for about 5 months post-fracture.