Edwards W Brent, Schnitzer Thomas J, Troy Karen L
Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Canada.
J Bone Miner Res. 2014 Sep;29(9):2074-9. doi: 10.1002/jbmr.2227.
Bone loss after spinal cord injury (SCI) is associated with an increased risk of fracture resulting from minor trauma. Proximal femoral fractures account for approximately 10% to 20% of the fractures in this population and are among the most serious of injuries. Our purpose was to quantify changes to proximal femoral strength in patients with acute SCI. Thirteen subjects received dual-energy X-ray absorptiometry (DXA) and clinical computed tomography (CT) scans at serial time points during acute SCI separated by a mean of 3.5 months (range 2.6 to 4.8 months). Areal bone mineral density (aBMD) at the proximal femur was quantified from DXA, and proximal femoral strength was predicted using CT-based finite element (FE) modeling in a sideways fall configuration. During the acute period of SCI, femoral neck and total proximal femur aBMD decreased by 2.0 ± 1.1%/month (p < 0.001) and 2.2 ± 0.7%/month (p < 0.001), respectively. The observed reductions in aBMD were associated with a 6.9 ± 2.0%/month (p < 0.001) reduction in femoral strength. Thus, changes in femoral strength were some 3 times greater than the observed changes in aBMD (p < 0.001). It was interesting to note that in just 3.5 months of acute SCI, reductions in strength for some patients were on the order of that predicted for lifetime declines owing to aging. Therefore, it is important that therapeutic interventions are implemented soon after SCI in an effort to halt bone loss and decrease fracture risk. In addition, clinicians utilizing DXA to monitor bone health after SCI should be aware of the potential discrepancy between changes in aBMD and strength.
脊髓损伤（SCI）后的骨质流失与因轻微创伤导致骨折的风险增加有关。股骨近端骨折约占该人群骨折的10%至20%，是最严重的损伤之一。我们的目的是量化急性SCI患者股骨近端强度的变化。13名受试者在急性SCI期间的连续时间点接受了双能X线吸收法（DXA）和临床计算机断层扫描（CT），平均间隔3.5个月（范围2.6至4.8个月）。通过DXA对股骨近端的骨密度（aBMD）进行量化，并使用基于CT的有限元（FE）模型在侧方跌倒配置下预测股骨近端强度。在SCI急性期，股骨颈和整个股骨近端的aBMD分别以每月2.0±1.1%（p<0.001）和2.2±0.7%（p<0.001）的速度下降。观察到的aBMD降低与股骨强度每月降低6.9±2.0%（p<0.001）相关。因此，股骨强度的变化比观察到的aBMD变化大约大三倍（p<0.001）。有趣的是，在急性SCI的短短3.5个月内，一些患者的强度下降幅度与因衰老导致的终生下降幅度相当。因此，在SCI后尽快实施治疗干预以阻止骨质流失并降低骨折风险非常重要。此外，利用DXA监测SCI后骨骼健康的临床医生应意识到aBMD变化与强度之间的潜在差异。
