ULTRASOUND BONE DENSITOMETRY AND DUAL-ENERGY X-RAY ABSORPTIOMETRY IN PATIENTS WITH SPINAL-CORD INJURY - A CROSS-SECTIONAL STUDY

Bone is lost following spinal cord injury (SCI) and in the long-term m ay become osteopenic and liable to fracture. Two non-invasive techniqu es, ultrasound bone densitometry (USBD) and dual energy X-ray absorpti ometry (DXA), have been applied to monitor bone changes after spinal i njury. 31 SCI patients were scanned using an ultrasound bone densitome ter, to give measurements of speed of sound (SOS), broadband ultrasoun d attenuation (BUA) and 'stiffness'. The time since injury of these pa tients ranged between 5 weeks to 36 years with a mean of 5.87+/-10.21 years. Ultrasonic properties at the calcaneus of these patients were s ignificantly lower than the healthy reference population, and a rapid decline in ultrasound properties occurred in the first 3 months. The f all continued up to 54 months but at a slower rate. The normal linear relationship between SOS and BUA was not altered by SCI. Eighteen pati ents had DXA measurements at the lumbar spine and the right proximal f emur. Bone mineral density (BMD) at the femoral neck was significantly lower than the normal reference population (P<0.05). SOS and 'stiffne ss' correlated significantly with BMD at the lumbar spine, Ward's tria ngle, the femoral neck, the greater trochanter and the intertrochanter ic site (P<0.05). BUA correlated significantly at all these sites with the exception of the trochanter. A negative correlation was found bet ween the ultrasonic properties at the calcaneus and BMD at the lumbar spine which is in contrast to the positive relationship in normal subj ects. There was a tendency for BMD to increase at the lumbar spine aft er the first 12 months after injury, although this trend was not signi ficant overall. The 'stiffness' at the calcaneus and BMD at the femora l neck were lower than the reference population following 12 months si nce injury. These results show that bone deficit at the calcaneus occu rs rapidly and to a severe degree after SCI, and that ultrasound has a n important role to play in the assessment of bone status in these pat ients.