Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Canada.
Department of Physical Medicine and Rehabilitation Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.
J Bone Miner Res. 2015 Aug;30(8):1422-30. doi: 10.1002/jbmr.2474. Epub 2015 May 21.
Spinal cord injury (SCI) is characterized by marked bone loss and a high rate of low-energy fracture around regions of the knee. Changes in the mechanical integrity of bone after SCI are poorly defined, and a better understanding may inform approaches to prevent fractures. The purpose of this study was to quantify reductions in torsional stiffness and strength at the proximal tibia as a function of time since SCI. Sixty adults with SCI ranging from 0 to 50 years of duration and a reference group of 10 able-bodied controls received a CT scan of the proximal tibia. Measures of integral bone mineral were calculated for the total proximal tibia, and localized measures of cortical and trabecular bone mineral were calculated for the epiphysis, metaphysis, and diaphysis. Torsional stiffness (K) and strength (T(ult)) for the total proximal tibia were quantified using validated subject-specific finite element models. Total proximal tibia measures of integral bone mineral, K, and T(ult) decreased exponentially (r(2) = 0.52 to 0.70) and reached a new steady state within 2.1 to 2.7 years after SCI. Whereas new steady-state values for integral bone mineral and K were 52% to 56% (p < 0.001) lower than the reference group, the new steady state for T(ult) was 69% (p < 0.001) lower than the reference group. Reductions in total proximal tibia measures occurred through a combination of trabecular and endocortical resorption, leaving a bone comprised primarily of marrow fat rather than hydroxyapatite. These findings illustrate that a short therapeutic window exists early (ie, 2 years) after SCI, during which bone-specific intervention may attenuate reductions in mechanical integrity and ultimately prevent SCI-related fragility fracture.
脊髓损伤（SCI）的特征是明显的骨丢失和膝关节周围高能骨折发生率高。SCI 后骨机械完整性的变化定义不明确，更好地了解这一点可能有助于预防骨折。本研究的目的是定量评估 SCI 后近端胫骨扭转刚度和强度随时间的变化。60 名 SCI 成人，病程从 0 到 50 年不等，以及 10 名健康对照组接受了近端胫骨 CT 扫描。计算了整个近端胫骨的骨矿物质积分，以及骺、干骺端和骨干的皮质和松质骨矿物质的局部积分。使用经过验证的个体特异性有限元模型，对整个近端胫骨的扭转刚度（K）和强度（T(ult)）进行了定量评估。整个近端胫骨的骨矿物质积分、K 和 T(ult) 呈指数下降（r²=0.52 至 0.70），在 SCI 后 2.1 至 2.7 年内达到新的稳定状态。尽管新的稳定状态下的骨矿物质积分和 K 比对照组低 52%至 56%（p<0.001），但 T(ult)的新稳定状态比对照组低 69%（p<0.001）。整个近端胫骨测量值的减少是通过松质骨和内皮质吸收的组合发生的，导致骨骼主要由骨髓脂肪而不是羟磷灰石组成。这些发现表明，在 SCI 后早期（即 2 年内）存在一个短暂的治疗窗口，在此期间，针对骨骼的干预可能会减轻机械完整性的降低，并最终预防 SCI 相关的脆性骨折。
