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

Abstract

Study design: 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. Objectives: To investigate the speed of sound (SOS) in bone in relation to bone mineral density (BMD). Setting: Kinesiology Department, McMaster University, Ontario, Canada. Methods: 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. Results: 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. Conclusion: 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.