Bone mineral density after spinal cord injury: assessment of hip and knee measurements

Bone loss is most common around the knee region in spinal cord injury (SCI) population. However, bone mineral density (BMD) measurement and T score in the knee region, which indicate osteoporosis, are not clear. This study aimed to examine BMD, T and Z scores at hip and knee including femoral neck (FN), total hip (TH), proximal tibia (PT), and distal femur (DF) in individuals with SCI, to investigate the relationship between BMD of the knee and hip, and to define DF and PT T scores thresholds that predict osteoporosis at the hip.

This cross-sectional study used dual-energy x-ray absorptiometry to assess BMD in 94 SCI individuals. The medial and lateral parts of the PT and DF were defined as PT-1 and PT-2, DF-1 and DF-2, respectively. T and Z scores of PT and DF were calculated with a tool recommended by ISCD.

All knee BMD values showed positive correlations with the hip BMD. Applying a PT-1 T-score threshold of - 1.55, the overall specificity was 83.9% and the sensitivity was 84.2% in detecting osteoporosis at FN or TH.

Low hip BMD values are associated with low knee BMD values in SCI individuals. A T score of -1.55 in PT-1 probably indicates osteoporosis of the hip. However, there is a prompt need for standardization of the T-cut off value in the knee region, where the risk of fracture risk is high. Body mass index, time since injury, wheelchair use, and injury severity were associated with bone loss in the PT-1.