Changes of basic bone turnover parameters in short-term and long-term patients with spinal cord injury

The bone mineral density (BMD), the cross- links (PYD, DPD and NTx) and the bone specific alcaline phosphatase (BAP) was investigated in a cross-sectional study in 62 male patients with spinal cord injury (SCI), n = 28 short-term (0–1 year after SCI) and n = 34 long-term SCI patients (> 5 years after SCI). Knowledge about this parameters are necessary to find an adequate therapy for this special kind of osteoporosis. Immobilisation osteoporosis in SCI patients is a well-known problem that may lead to pathological fractures. Little is known regarding the extend of the osteoporosis as well as the causative factors. Measurements of the BMD in the proximal femur and the lumbar spine were performed with dual-energy-X-ray-absorptiometry (DEXA), of the osteoblast marker BAP (bone specific alkaline phosphatase) from serum and the osteoclast markers PYD (pyridinoline), DPD (desoxy-pyridinoline) and NTx (N-telopeptide of collagen type I) from urine. We found a significant decrease of BMD in the proximal femur and no relevant change in the lumbar spine compared to an age- and sex correlated control group (Z-score) in short-term and long-term SCI patients. There was a significant bone loss at the proximal femur between short and long-term SCI patients, whereas at the lumbar spine the BMD even slightly increases. Bone resorption (cross-links) was increased in both groups, though in long-term SCI patients it is significantly decreased compared to short-term SCI patients (DPD from 211.7 u/g creatinine to 118.1 u/g creatinine; NTx from 215.1 nmol/mmol creatinine to 83,6 nmol/mmol creatinine). The bone formation marker BAP is slightly below normal range in both groups (12.3 U/l in short-term, 9.7 U/l in long- term SCI patients). Only the proximal femur is affected by the immobilisation osteoporosis of SCI patients, therefore the BMD measurements in these patients should be performed at the lower limb. The problem of the immobilisation osteoporosis in SCI patients is the striking increase of bone resorption and the missing reaction of the bone formation.