Speed of sound in bone at the tibia: is it related to lower limb bone mineral density in spinal-cord-injured individuals?

Abstract

A cross-sectional study evaluating BMD at the hip and tibia, and SOS at the radius and mid-tibia in individuals with spinal cord injury (SCI) and a subgroup of non-SCI individuals. To investigate the speed of sound (SOS) in bone in relation to bone mineral density (BMD). Kinesiology Department, McMaster University, Ontario, Canada. In 14 individuals with SCI and 10 non-SCI individuals, proximal femur and tibia BMD were measured using dual energy X-ray absorptiometry, and radius and tibia SOS were measured with an ultrasonometer. T-scores were calculated using healthy reference databases. Inter-relationships between measurement techniques were determined using Pearson's correlation coefficients. P-values less than 0.05 were considered statistically significant. : The average ages of the SCI and non-SCI groups were 33+/-9 and 27+/-6 years, respectively. Lesion level ranged from C4 to T12 and average time postinjury was 12 years, with a range of 1.6-25 years. Using the WHO criteria for osteoporosis, nine of 14 SCI subjects were osteoporotic at the hip, with the remainder in the osteopenic range. Tibia SOS T-scores were in the osteoporotic range for one subject with SCI, and two were in the osteopenic range. Among non-SCI individuals, one male had a tibia SOS T-score of -1.4, all others were within the normal range. Hip BMD and tibia SOS were significantly correlated (r=0.46, P<0.01). Hip BMD and tibia BMD were more strongly correlated (r=0.80, P<0.0005). Tibia BMD was not significantly correlated with SOS at the tibia (r=0.35, P=0.09). Radius SOS T-scores were positive and not significantly correlated with any lower limb variable. Lower-limb bone mass is reduced in spinal cord-injured individuals, but SOS at the mid-tibia is not. It remains to be determined whether ultrasound measurements can predict fracture in the SCI population.