Stankewich C J, Chapman J, Muthusamy R, Quaid G, Schemitsch E, Tencer A F, Ching R P
Harborview Biomechanics Laboratory, Department of Orthopedics, University of Washington, Seattle, USA.
J Orthop Trauma. 1996;10(4):248-57. doi: 10.1097/00005131-199605000-00005.
The decision of whether to attempt screw fixation of a femoral neck fracture is based partly on the estimated strength of the fixed bone/implant construct in relation to the loads it will be required to bear. The goal of this study was to determine in vitro the relation of the following biomechanical factors to the strength of internally fixed femoral neck fractures subjected to cyclic and failure loading: (a) square of the density of cancellous bone in the femoral head, (b) percent comminution of the inferior fracture surface, (c) moment arm of the joint force, or distance from the axis of the joint force to the fracture surface, and (d) orientation angle of the fracture surface in the medial/lateral plane relative to the axis of the femoral shaft. Femoral neck fractures were created in each of 38 fresh cadaveric proximal femora using a dropweight or with a materials testing machine. After sustaining a displaced fracture, fixation was achieved using three cannulated cancellous bone screws. The fixed femur was then subjected to 10,000 cycles of a sinusoidially varying load acting on the femoral head, parallel to the femoral shaft, with an initial peak magnitude of 2.2 times body weight, while the hip was flexed, extended, and rotated to mimic some motions of gait. Muscle loading was not simulated. The magnitude of the peak load decreased as the femoral head displaced during cycling. The mean of the peak load for each cycle over the duration of the test was defined as the average load. Following cycling, the bone/screw construct was loaded to failure in the same direction, and this measurement was termed the maximum load. Average and maximum load were then correlated to the four biomechanical factors using a multiple regression analysis. These factors correlated to a high degree with average force (R2 = 0.771; p < 0.0001) and to a lesser but still significant degree with maximum force (R2 = 0.458; p = 0.012), demonstrating that they can be used to estimate the strength of fixation under these loading conditions. The strongest correlation for average force was with fracture angle (p = 0.005) and for failure force was with moment arm length (p = 0.072).
对于股骨颈骨折是否尝试进行螺钉固定的决策，部分取决于固定骨/植入物结构相对于其所需承受负荷的估计强度。本研究的目的是在体外确定以下生物力学因素与承受循环负荷和破坏负荷的内固定股骨颈骨折强度之间的关系：(a)股骨头松质骨密度的平方，(b)骨折下表面的粉碎百分比，(c)关节力的力臂，即从关节力轴到骨折面的距离，以及(d)骨折面在内外平面相对于股骨干轴的取向角度。使用落锤或材料试验机在38具新鲜尸体近端股骨上分别制造股骨颈骨折。在造成移位骨折后，使用三根空心松质骨螺钉进行固定。然后使固定的股骨承受10000次正弦变化负荷循环，负荷作用于股骨头，平行于股骨干，初始峰值大小为体重的2.2倍，同时使髋关节进行屈伸和旋转以模拟步态的一些动作。未模拟肌肉负荷。随着循环过程中股骨头移位，峰值负荷大小降低。将测试持续时间内每个循环的峰值负荷平均值定义为平均负荷。循环结束后，沿相同方向对骨/螺钉结构加载直至破坏，该测量值称为最大负荷。然后使用多元回归分析将平均负荷和最大负荷与四个生物力学因素进行关联。这些因素与平均力高度相关（R2 = 0.771；p < 0.0001），与最大力的相关性较小但仍显著（R2 = 0.458；p = 0.012），表明它们可用于估计这些负荷条件下的固定强度。平均力的最强相关性与骨折角度相关（p = 0.005），破坏力的最强相关性与力臂长度相关（p = 0.072）。
