BACKGROUND: In the early stage following spinal cord injury, a series of changes in metabolism and secretion take place, such as accelerated bone resorption and decreased bone formation. Determination of the biochemical markers of bone metabolism early after spinal cord injury may help understand the metabolic changes and facilitate risk evaluation for osteoporosis on such occasion.OBJECTIVE: To study the earlychanges of bone mass and bone metabolism indices in guinea pigs with spinal cord injury and evaluate the impact of spinal cord injury on bone metabolism.DESIGN: Randomly controlled animal experiment. SETTING: Department of Rehabilitation Medicine, Zhongshan Hospital of Fudan UniversityMATERIALS: The experiment was conducted in the Institute of Rehabilitation Medicine, Zhongshan Hospital of Fudan University in March 2004. Twenty-three male guinea pigs with body weight of 427-710 g (averaging 570 g) were provided by the Experimental Animal Center,Zhongshan Hospital of Fudan University and divided into experimental group (n=10) and normal control group (n=13). All the guinea pigs were kept under the same environment and fed with standard food for two weeks.METHODS: Small microsurgery scissors was used to induce a 1.5-mm transverse incision of the spinal cord, with the bleeding carefully managed and the wound closed. Thirty minutes after surgery, the guinea pigs recovered consciousness with bilateral lower limb paralysis (hypertonic paraplegia) and loss of superficial and deep sensations, but without urinary and fecal incontinence. The animals in the control group had sham operation. After housing in the same environment with standard food for 2 weeks, urine,serum and shinbone samples were collected from the animals for measurement of serum bone alkaline phosphatase (BALP), urinary pyridinoline (Pyd)/creatinine (Cr) and Ca/Cr. t test and H test were used for comparison of the samples between the two groups.parison of biochemical markers for bone formation between the two groups.RESULTS: Ten animals were analyzed in each group. No significant difference was observed in the BMD and bone dry weight between the two groups (P ＞ 0.05), but the bone ash weight of experimental group was remarkably lower than that of the control group [(0.284±0.050) vs (0.361±0.064) mg, t=3.254, P ＜ 0.05). The experimental group had significantly lower serum BALP than the control group [(0.640±0.240)vs (1.328±0.606) U/L, H=9.499, P ＜ 0.05), but higher urinary Pyd/Cr [(0.206±0.080) vs (0.117±0.037), P ＜ 0.01) and Ca/Cr [(0.003±0.003)vs (0.002±0.002), P ＜ 0.05] than the control group (H=9.676, 4.124,P ＜ 0.05).CONCLUSION: After the spinal cord injury, bone resorption remarkably increases and the function of the osteoblasts is inhibited. Bone metabolic abnormalities can occur in the early stage of spinal cord injury, and the biochemical indices for bone metabolism are sensitive in evaluating the risks for osteoporosis after spinal cord injury.