Factors influencing bone loss in paraplegia

Significant bone loss develops in the first months and continues years after spinal cord injury. A cross - sectional comparative study was performed to evaluate factors influencing bone loss in spinal cord injured men with paraplegia.

We studied 31 paraplegic men in chronic stage (>1.5 years) in comparison with 30 able-bodied men of similar age, height, and weight. The paraplegic men were allocated into 2 subgroups based on the neurological level of injury; high paraplegics (n=16, T4-T7 neurological level of injury) and low paraplegics (n=15, T8-T12 neurological level of injury). The influence of positive and negative factors (spasticity, standing-therapeutic walking, and duration of paralysis) on bone structures was evaluated by pQCT measurement of the total, trabecular and cortical bone mineral density (BMDtot, BMDtrab, BMDcort, respectively) and cortical thickness (THIcort) at the distal tibial epiphysis and the tibial diaphysis at 4% and 38% proximal to the distal end of the tibia. The stress strain index (SSI) was measured at 14% (SSI(2)) and at 38% (SSI(3)) of the tibial diaphysis, and the difference SSI(3) - SSI(2) (δSSI(3-2)) was calculated.

In all paraplegics, bone mineral density parameters were significantly reduced compared to the control group (BMDtot: p<0.0005, BMDtrab: p<0.0005, BMDcort: p=0.029, THIcort: p=0.019, SSI(2): p=0.009, SSI(3): p=0.003, respectively). Paraplegics who used standing frames or long brace orthoses had statistically significant higher bone mass and geometric parameters (BMDtrab: p=0.03, BMDtot: p=0.01, THIcort: p=0.013, respectively), while spasticity did not protect bone. The duration of paralysis was significantly related to trabecular bone loss (r=-0.5, p=0.05) and cortical thickness (r=-0.6, p=0.006) in high paraplegics and to δSSI(3-2) in low paraplegics (r=0.534, p=0.03).

The neurological level of injury adversely affects bone strength in paralyzed lower extremities such as the distal tibia. Standing or therapeutic walking could possibly have a positive effect in cortical and trabecular bone in paraplegia.