Impact on bone and muscle area after spinal cord injury

Abstract

Spinal cord injury (SCI) causes inactivation and consequent unloading of affected skeletal muscle and bone. This cross-sectional study investigated correlations of muscle and bone in spinal cord-injured subjects compared with able-bodied subjects. Thirty-one complete SCI paraplegics were divided according to the neurological level of injury (NLoI) into group A (n=16, above thoracic 7 NLoI, age: 33±16 years, duration of paralysis (DoP): 6±6 years) and group B (n=15, thoracic 8-12, age: 39±14 years, DoP: 5.6±6 years), compared with 33 controls (group C). All were examined with peripheral quantitative computed tomography at 66% of tibia length (bone and muscle area, bone/muscle area ratio). In able-bodied subjects, muscle area was correlated with bone area (P<0.001, r=0.88). Groups A and B differed significantly from the control group in terms of bone and muscle area (P<0.001). In paraplegics, less muscle per unit of bone area (bone/muscle area ratio) was found compared with controls (P<0.001). Bone area was negatively correlated with the DoP in the total paraplegic group (r=-0.66, P<0.001) and groups A and B (r=-0.77, P=0.001 vs r=-0.52, P=0.12, respectively). Muscle area and bone/muscle ratio area correlations in paraplegic groups with DoP were weak. Paraplegic subjects who performed standing and therapeutic walking had significantly higher bone area (P=0.02 and P=0.013, respectively). The relationship between bone and muscle was consistent in able-bodied subjects and it was predictably altered in those with SCI, a clinical disease affecting bone and muscle.

Figure 1

Schematic presentation of the correlation between bone area and DoP. A linear correlation between bone area (cortarea) and duration of paralysis (DoP) in 66% in the total paraplegic group was found to fit our data. Bone area was negatively correlated with the DoP in the total paraplegic group (r²=0.364, r=−0.66, P<0.001, bone area=379.9−7.12 × DoP).

Figure 2

Peripheral quantitative computed tomography (pQCT) in 66% of the tibia in SCI vs control. Figures represent pQCT of the tibia slice (a) in spinal cord-injured subjects with paraplegia and (b) in controls (scanner XCT 3000, Stratec Medizintechnik). Areas in black and red represent cortical and trabecular bone, respectively, whereas areas in grey represent fat. (a) pQCT of the tibia from a spinal cord-injured paraplegic thoracic (T)₁₂ 24-year-old man, slice: 66%. (b) pQCT of the tibia from a control subject, 30-year-old man, slice: 66%.