Bone Loss at the Os Calcis Compared with Sone Loss at the Knee in Individuals with Spinal Cord Injury

Abstract

Background/Objective: The objective of this study was to document acute bone loss at the os calcis and compare it with bone lossat 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, whichalso was assessed by ultrasound in 6 individuals-5 with complete SCI and 1 with incomplete SCI-at means of 33.5 and 523 daysfollowing injury.

Results: Bone mineralwas progressively greater as measured from proximal to distal sites. The net average BMD of the knee declined24% (P = 0.017). The distalfemurlost 27% (P = 0.03 8) and the proximal tibia lost 32% (P = 0 .015) , whereas the os calcis lost3 8% (P = 0.001) as measured by DEXA and 49% (P<0.001) as estimated from ultrasound. The mean loss of 24'7'o at the kneewas significantly different from the loss percentages at the os calcis as measured by both techniques: DEXA (P = 0.036) andultrasound (P = 0.043). Differences between annualized loss rates at the knee and the os calcis measured by both techniques alsowere significant: DEXA (P = 0.032) vs ultrasound (P = 0.038). However, annualized loss rates demonstrated the same trend fordifferentiallass 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 3 8% by DEXA and 49% by ultrasound compared with 24% at the knee whenmeasured 1 to 1.5 years after injury. BMD of the os calcis and distal femur measured by DEXA in persons with complete SCI werehighly correlated (r = 0.84, P < 0.0001 ).