Mazzaferro Sandro, Diacinti Daniele, Proietti Emanuela, Barresi Giusi, Baldinelli Matteo, Pisani Daniela, D'Erasmo Emilio, Pugliese Francesco
Department of Clinical Science, University La Sapienza of Rome, Italy.
Nephrol Dial Transplant. 2006 Feb;21(2):466-71. doi: 10.1093/ndt/gfi206. Epub 2005 Oct 18.
Bone mineral density (BMD) is widely employed to evaluate the risk of fractures, but more than mineral content is bone quality that accounts for bone strength. In fact, occasionally, subjects with normal or only mildly reduced BMD also experience pathologic fractures. In metabolic bone disease, like renal transplantation, the agreement between fractures and BMD is less predictable. We assessed the prevalence of vertebral fractures by means of a new, DEXA-based method (morphometric absorptiometry, MXA) and compared its concordance with the two mostly employed radiological techniques (Visual semi-quantitative, SQ, and morphometric radiography, MRX) in an asymptomatic population of transplanted patients. Moreover, the association of bone fractures with low BMD values was examined.
Fifty-three renal transplant patients underwent spinal radiographs and BMD measurements by DEXA. In order to obtain a morphometric assessment, a lateral DEXA scan was performed.
Patients with vertebral fracture were 17/53 (32%) with both SQ and MRX, and 12/53 (23%) with MXA (chi(2) = n.s.). A single fracture was detected in 9/53 patients (17%) with SQ and MRX, and in 4/53 (7.5%) with MXA; multiple fractures were 8/53 (15%) with any technique. With SQ as the standard reference, predictive indexes were excellent with MRX (invariably 100%) and quite good with MXA (sensitivity 70.6%; specificity 100%). Of the total of 689 vertebrae, 49 were fractured with SQ, 54 with MRX and 41 with MXA. Mild deformities were present in 21 (SQ), 26 (MRX) and 13 (MXA) vertebral bodies, respectively, while moderate-severe deformities were 28 with any technique. Again, with SQ as standard reference, predictive indexes were good (MRX: sensitivity 100%, specificity 99.2%; MXA: sensitivity 83.7%, specificity 100%). When we classified patients according to BMD T-score values, SQ and MRX recognized fractures in 4/18 normal (22%), 10/22 osteopenic (45%) and 3/13 osteoporotic (23%). With MXA 3/18 (17%) normal, 6/22 (27%) osteopenic and 3/13 (23%) osteoporotic were fractured. The lower performance of MXA was very likely due to the poor quality of images from the upper thoracic spine of obese subjects.
Prevalence of vertebral fractures in renal transplant patients is quite high and randomly associated with reduced BMD. A surveillance of the spine by Rx, implemented with vertebral morphometry, is therefore warranted to recognize the disease. (MXA is a reliable alternative technique, especially in more severely affected individuals.) MXA, although less sensitive than the conventional techniques because of possible technical biases, is very specific, and can be proposed for follow-up purposes in this population of patients.
骨密度（BMD）被广泛用于评估骨折风险，但决定骨强度的不仅是矿物质含量，还有骨质量。事实上，偶尔会出现骨密度正常或仅轻度降低的受试者发生病理性骨折的情况。在代谢性骨病中，如肾移植，骨折与骨密度之间的相关性较难预测。我们采用一种基于双能X线吸收法（DEXA）的新方法（形态计量吸收法，MXA）评估了移植患者无症状人群中椎体骨折的患病率，并将其与两种最常用的放射学技术（视觉半定量法，SQ，和形态计量X线摄影，MRX）的一致性进行了比较。此外，还研究了骨折与低骨密度值之间的关联。
53例肾移植患者接受了脊柱X线摄影和DEXA骨密度测量。为了获得形态计量评估结果，进行了一次脊柱侧位DEXA扫描。
椎体骨折患者中，SQ和MRX检测出17/53例（32%），MXA检测出12/53例（23%）（χ²检验，无显著差异）。SQ和MRX在9/53例患者（17%）中检测出单发骨折，MXA在4/53例（7.5%）中检测出单发骨折；任何技术检测出多发骨折的比例均为8/53例（15%）。以SQ作为标准参考，MRX的预测指标极佳（始终为100%），MXA的预测指标相当不错（敏感性70.6%；特异性100%）。在总共689个椎体中，SQ检测出49个骨折椎体，MRX检测出54个，MXA检测出41个。轻度畸形分别出现在21个（SQ）、26个（MRX）和13个（MXA）椎体中，而任何技术检测出的中度至重度畸形均为28个。同样，以SQ作为标准参考，预测指标良好（MRX：敏感性100%，特异性99.2%；MXA：敏感性83.7%，特异性100%）。当我们根据骨密度T值对患者进行分类时，SQ和MRX在4/18例正常患者（22%）、10/22例骨量减少患者（45%）和3/13例骨质疏松患者（23%）中检测出骨折。MXA在3/18例（17%）正常患者、6/22例（27%）骨量减少患者和3/13例（23%）骨质疏松患者中检测出骨折。MXA表现较差很可能是由于肥胖受试者上胸椎图像质量不佳。
肾移植患者椎体骨折的患病率相当高，且与骨密度降低无明显关联。因此，采用椎体形态计量学进行脊柱X线检查以识别该病是必要的。（MXA是一种可靠的替代技术，尤其适用于病情较重的个体。）MXA虽然由于可能存在的技术偏差比传统技术敏感性稍低，但特异性很强，可用于该患者群体的随访。
