Maugars Y, Berthelot J M, Delécrin J, Trécant M, Passuti N, Daculsi G, Prost A
Service de Rhumatologie, CHU de Nantes.
Rev Chir Orthop Reparatrice Appar Mot. 1995;81(4):326-32.
We emphasize the opportunity of an in vivo bone mass measurement with an easy and accurate technique for orthopedic practice. At the present time, Dual Energy X Ray Absorptiometry (DEXA) is the most used technique, and is a safe and short examination. It can assess the quantity of mineral of any region of the body with a remarkable reproducibility (1 to 3 per cent). New machines are improved, and they permit many practical applications beyond the osteoporosis field. Thus, in orthopedics, we can distinguish several interesting topics. Peripheral risk of fracture can be evaluated because of good correlation between bone mineral content and biomechanical properties of bone. Even if a peripheral fracture occurs after a fall, low bone mineral density plays an important role, as in the case of femoral neck fractures in elderly patients. In traumatological practice, a DEXA with a specialized advice has to be requested if the traumatism cannot fully explain the occurrence of the peripheral fracture. Low bone mineral density defines an osteoporotic state, with the possibility of selecting adequate therapy. The good reproducibility of the measurement allows early estimation of bone loss following a period of immobilization. Varying models of osteosynthesis can be compared in vivo, to evaluate a decrease of "stress shielding" bone resorption. The role of stiffness of an implant on regional bone mineral content can be assessed. Likewise, periprosthetic bone mineral content can be measured in various regions, and followed over time. Specific software allows the exclusion of the region where the metallic prosthesis is projected. The reproducibility of this peripheral bone mineral content is 2 to 3 per cent, which individually allows an estimation of variations of more than 5 per cent. It will be possible to evaluate in vivo the influence of various parameters of the prosthesis on bone mineral content in controlled studies, such as the role of the shape, the position, the structure, the coating. Mineral content of biomaterials and bone grafts are taken into account. Focusing the X Ray beam allows ultrahigh resolution. Precise measurements of very small parts of bone such as rodent tibia or vertebra are possible. The good reproducibility (2 per cent) authorizes the evaluation of various parameters which modify bone remodeling, such as immobilization or activity, ovariectomy. Preventive or curative therapeutics which change bone mass can be evaluated in animal pre clinical studies. There are other methods of measurement of bone mineral content. Digitalization of radiographs is not sufficiently accurate and CT Scan generate high levels of radiation. The DEXA is actually the best compromise for an accurate and reproducible measurement of the bone mineral content in vivo. This method will certainly be an important tool in orthopedics for several clinical or animal investigations in the future.
我们强调，对于骨科实践而言，采用简便且准确的技术进行体内骨量测量具有重要意义。目前，双能X线吸收法（DEXA）是应用最为广泛的技术，它安全且检查时间短。该方法能够以极高的重复性（1%至3%）评估身体任何部位的矿物质含量。新型设备不断改进，其应用范围已超越骨质疏松领域，涵盖了诸多实际应用。因此，在骨科领域，我们可以区分出几个有趣的研究方向。由于骨矿物质含量与骨生物力学特性之间存在良好的相关性，所以可以评估外周骨折风险。即便外周骨折是因跌倒所致，低骨矿物质密度仍起着重要作用，老年患者股骨颈骨折便是如此。在创伤科实践中，如果创伤无法充分解释外周骨折的发生，就需要进行专业指导下的DEXA检查。低骨矿物质密度可定义为骨质疏松状态，据此能够选择合适的治疗方法。测量的良好重复性有助于早期评估固定一段时间后骨量的丢失情况。可以在体内比较不同的骨合成模型，以评估“应力遮挡”性骨吸收的减少情况。还可以评估植入物刚度对局部骨矿物质含量的影响。同样，可以测量假体周围不同区域的骨矿物质含量，并进行长期跟踪。特定软件能够排除金属假体投影所在的区域。外周骨矿物质含量测量的重复性为2%至3%，这足以单独评估超过5%的变化情况。在对照研究中，有可能在体内评估假体的各种参数对骨矿物质含量的影响，比如形状、位置、结构、涂层的作用等。同时，还会考虑生物材料和骨移植的矿物质含量。聚焦X射线束可实现超高分辨率，能够精确测量非常小的骨部位，如啮齿动物的胫骨或椎骨。良好的重复性（2%）使得我们能够评估各种影响骨重塑的参数，如固定或活动、卵巢切除等。在动物临床前研究中，可以评估改变骨量的预防或治疗性疗法。还有其他测量骨矿物质含量的方法，如X线片数字化不够准确，而CT扫描会产生高水平辐射。实际上，DEXA是体内准确且可重复测量骨矿物质含量的最佳选择。在未来，这种方法必将成为骨科领域多项临床或动物研究的重要工具。
