Meyers Nicholaus, Sukopp Matthias, Jäger Rudolf, Steiner Malte, Matthys Romano, Lapatki Bernd, Ignatius Anita, Claes Lutz
Institute of Orthopedic Research and Biomechanics, Center of Musculoskeletal Research Ulm, University Hospital Ulm, Ulm, Baden-Württemberg, Germany.
Department of Orthodontics, University Hospital Ulm, Ulm, Baden-Württemberg, Germany.
PLoS One. 2017 Apr 28;12(4):e0176735. doi: 10.1371/journal.pone.0176735. eCollection 2017.
Rat models are widely used in preclinical studies investigating fracture healing. The interfragmentary movement at a fracture site is critical to the course of healing and therefore demands definition in order to aptly interpret the experimental results. Estimation of this movement requires knowledge of the fixation stiffness and loading. The characteristic loading for the rat femur has been estimated, but the stiffness of fixation used in rat studies has yet to be fully described. This study aimed to determine the 6 degree of freedom stiffness of four commonly used implants, two external fixators (RatExFix and UlmExFix), a locking plate, and a locking intramedullary nail, in all degrees of freedom and estimate the interfragmentary movement under specific physiological loads. The external fixator systems allow the greatest movement. Mounted 45° anterolateral on the femur, the RatExFix allows an average of 0.88 mm of motion in each anatomic direction while the stiffer UlmExFix allows about 0.6 mm of motion. The nail is far stiffer than the other implants investigated while the plate allows movement of an intermediate magnitude. Both the nail and plate demonstrate higher axial than shear stiffness. The relatively large standard deviations in external fixator shear motion imply strong dependence on bone axis alignment across the gap and the precise orientation of the specimen relative to the loading. The smaller standard deviation associated with the nail and plate results from improved alignment and minimization of the influence of rotational positioning of the specimen due to the reduced implant eccentricity relative to the specimen axis. These results show that the interfragmentary movement is complex and varies significantly between fixation devices but establishes a baseline for the evaluation of the results of different studies.
大鼠模型广泛应用于骨折愈合的临床前研究。骨折部位的骨折块间移动对愈合过程至关重要，因此需要明确其定义以便恰当地解释实验结果。估计这种移动需要了解固定刚度和负荷情况。已对大鼠股骨的特征性负荷进行了估计，但大鼠研究中使用的固定刚度尚未得到充分描述。本研究旨在确定四种常用植入物（两种外固定器（大鼠外固定器和乌尔姆外固定器）、一块锁定钢板和一根锁定髓内钉）在所有自由度下的六自由度刚度，并估计在特定生理负荷下的骨折块间移动。外固定器系统允许的移动最大。大鼠外固定器安装在股骨前外侧45°位置，在每个解剖方向上平均允许0.88毫米的移动，而刚度较大的乌尔姆外固定器允许约0.6毫米的移动。髓内钉比其他研究的植入物刚度大得多，而钢板允许中等程度的移动。髓内钉和钢板的轴向刚度均高于剪切刚度。外固定器剪切运动中相对较大的标准差意味着强烈依赖于骨折间隙处的骨轴对齐以及标本相对于负荷的精确方向。与髓内钉和钢板相关的较小标准差是由于植入物相对于标本轴的偏心度降低，从而改善了对齐并将标本旋转定位的影响降至最低。这些结果表明，骨折块间移动很复杂，在不同固定装置之间差异很大，但为评估不同研究结果建立了一个基线。
