Bone loss at the os calcis compared with bone loss at the knee in individuals with spinal cord injury.

BACKGROUND/OBJECTIVE: The objective of this study was to document acute bone loss at the os calcis and compare it with bone loss at the knee following spinal cord injury (SCI) as a potential proxy for bone loss in individuals with SCI.

METHODS

Bone mineral density (BMD) was measured by dual energy x-ray absorptiometry (DEXA) at the knee and os calcis, which also was assessed by ultrasound in 6 individuals--5 with complete SCI and 1 with incomplete SCI--at means of 33.5 and 523 days following injury.

RESULTS

Bone mineral was progressively greater as measured from proximal to distal sites. The net average BMD of the knee declined 24% (P = 0.017). The distal femur lost 27% (P = 0.038) and the proximal tibia lost 32% (P = 0.015), whereas the os calcis lost 38% (P = 0.001) as measured by DEXA and 49% (P < 0.001) as estimated from ultrasound. The mean loss of 24% at the knee was significantly different from the loss percentages at the os calcis as measured by both techniques: DEXA (P = 0.036) and ultrasound (P = 0.043). Differences between annualized loss rates at the knee and the os calcis measured by both techniques also were significant: DEXA (P = 0.032) vs ultrasound (P = 0.038). However, annualized loss rates demonstrated the same trend for differential loss at the sites examined in the 5 individuals with complete injuries but not for the 1 participant with an incomplete injury. The loss rates were similar for the complete and incomplete participants at the os calcis, but not at the knee.

CONCLUSION

The BMD of the os calcis declined 38% by DEXA and 49% by ultrasound compared with 24% at the knee when measured 1 to 1.5 years after injury. BMD of the os calcis and distal femur measured by DEXA in persons with complete SCI were highly correlated (r = 0.84, P < 0.0001).