University College London Hospital NHS Foundation Trust, UK.
Foot Ankle Int. 2012 Aug;33(8):669-74. doi: 10.3113/FAI.2012.0669.
Reconstruction of a flatfoot commonly involves a calcaneal Medial Displacement Osteotomy (MDO) to correct hindfoot valgus in combination with soft tissue procedures. We compared fixation of an MDO using either a single, large cannulated screw versus a locking step-plate in load to failure in a cadaveric model.
Eight matched pairs of cadaveric limbs were loaded using a mechanical testing rig. Two pairs served as non-operated controls. The remaining paired limbs underwent a 10-mm MDO stabilized either with a single 7-mm screw or a step-plate with four locking screws. One pair was used as a pilot study and the remaining five pairs were loaded up to 4500 N to failure.
In the five pairs loaded to failure, the median (with 95% CI) maximum force were 1779 N (1099-2312) and 826 N (288-1607) for the plate and screw, respectively (p = 0.043). With single screw fixation, the tuberosity fragment consistently failed by rotation and angulation into varus. With plate fixation, failure occurred as the screws cut through the internal surfaces of the tuberosity and body with no failure at the screw-plate interface.
In this cadaveric model, a locked step-plate supported a significantly higher maximum force than a single large cannulated screw.
The magnitude of the load supported by the locking step-plate suggests that allowing early weightbearing post-operation may be safe in clinical practice before union of the osteotomy.
平足症的重建通常涉及跟骨内侧移位截骨术（MDO），以纠正后足外翻，并结合软组织手术。我们比较了在尸体模型中，使用单根大空心螺钉与锁定阶梯板固定 MDO 在失效负荷下的固定效果。
8 对匹配的尸体肢体使用机械测试装置进行加载。两对作为非手术对照。其余配对肢体接受 10mm 的 MDO 固定，分别使用单根 7mm 螺钉或带有 4 根锁定螺钉的阶梯板。一对用于初步研究，其余五对加载至 4500N 失效。
在五对加载至失效的配对肢体中，最大力的中位数（95%置信区间）分别为 1779N（1099-2312）和 826N（288-1607），用于板和螺钉（p=0.043）。使用单螺钉固定时，结节碎片始终通过旋转和成角进入内翻而失效。使用板固定时，螺钉穿过结节和体部的内表面断裂，而在螺钉-板界面没有失效。
在这个尸体模型中，锁定阶梯板支撑的最大力明显高于单根大空心螺钉。
锁定阶梯板所承受的负荷大小表明，在截骨术愈合之前，临床实践中术后早期负重可能是安全的。
