相关疾病：
骨折Solution: Far Cortical Locking
Far Cortical Locking Reduces Construct Stiffness While Maintaining Construct Strength
解决办法：对侧皮质锁定
对侧皮质锁定能在降低固定装置刚度的同时保持固定装置的力量
Several strategies to reduce the stiffness of locked-plate constructs have been proposed, including the use of thinner plates, increasing the plate elevation from the bone surface, using slotted holes in the near cortex, and increasing the plate span14,42-44. However, either a reduction in stiffness is gained at the cost of construct strength or stiffness remains insufficient to promote bone-healing by callus formation. Far cortical locking was introduced as an alternative strategy to reduce the stiffness of a locked-plate construct without reducing its strength13. Farcortical- locking screws lock into the plate and the far cortex of a diaphysis and have a reduced midshaft diameter to bypass the near cortex (Fig. 4, a). Therefore, far-cortical-locking screws have an increased working length, allowing for elastic cantilever bending of the screw shaft within a controlled motion envelope (Dd) in the near cortex. Analogous to external fixators, farcortical- locking constructs derive flexible fixation and parallel interfragmentary motion from elastic flexion of screw shafts (Fig. 4, b and c). Under elevated loading, contact of the farcortical- locking screw shaft at the near cortex provides additional support and load-sharing with the near cortex. The ability of far-cortical-locking screws to reduce the stiffness of a locked-plate construct while retaining its strength was formally evaluated in a bench-top study of surrogates of normal and osteoporotic bone13.
目前研究者已经有很多种降低锁定钢板装置刚度的方法，包括使用更薄的钢板，增加钢板与骨质表面的距离，在同侧皮质使用滑动螺钉孔，以及增加钢板固定范围。但是，固定装置刚度的降低或者是以固定力量的降低为代价，或者是刚度降低过度以致不足以促进骨痂形成并最终形成骨折愈合。而对侧皮质固定被作为另外一个能在降低锁定钢板装置刚度同时又能保持其固定力量的方法被发展出来。对侧锁定螺钉装置固定骨折时锁固定钢板以及骨干的对侧皮质，而其螺杆的直径相对变小而并不固定于钢板同侧骨皮质（图4A）。如此一来，对侧锁定螺钉的工作长度相应增加，并允许螺钉干在同侧皮质钉孔中进行一定的范围（Dd）内的弹性变形弯曲活动。与外支架固定相似的是，对侧皮质锁定装置能将螺钉干的弹性变形转化为弹性固定以及骨折块的对称性移动（图4B，C）。当负荷增加时，对侧锁定螺钉的钉干变形导致其与同侧骨皮质接触，从而提供进一步的支撑以及并与同侧皮质之间产生应力分担。此前的实验研究在正常及骨质疏松性骨质中均已经证明了对侧锁定螺钉装置能在降低固定装置刚度的同时保持其强度。
Methods
Locked-plate constructs and far-cortical-locking constructs were tested in a diaphyseal bridge-plate configuration under axial compression, torsion, and bending. Generic 4.5-mm locking plates and screws made of titanium alloy were used in all constructs. The far cortical locking was done with locking screws that had a smooth shaft with a 3.2-mm diameter to bypass the near cortex. Plates were applied at a 1-mm elevation from the bone with three screws placed proximally in the first, third, and fifth screw holes from the fracture site and with one hole left empty over the 10-mm osteotomy gap. First, the stiffness of the locked-plate and far-cortical-locking constructs was determined in each principal loading mode in surrogates of a non-osteoporotic femoral diaphysis. Subsequently, the constructs were tested to failure in each loading mode under progressive dynamic loading to determine their strength. Finally, failure tests were repeated in a validated model of an osteoporotic femoral diaphysis45 to determine construct strength in a worst-case scenario of bridge-plate fixation in osteoporotic bone. Each loading mode and construct was tested in five specimens.
方法
对以锁定钢板装置以及对侧锁定装置组成的骨干桥接钢板结构分别在轴向，旋转及弯曲应力下进行测试。所有固定装置均使用以钛合金制成的通用型4.5mm锁定钢板及相应的螺钉。对侧皮质锁定螺钉的钉干直径为3.2mm，与同侧骨皮质无直接接触固定。钢板离骨质距离为1mm，近侧骨折段以三枚螺钉固定，分别经第1，3，5三个钉孔安放，而位于10mm的截骨间隙处有1个钉孔空置。首先于非骨质疏松性人工股骨干上测试锁定钢板和对侧皮质锁定装置在每种主要负荷模式下的刚度。随后，以逐步增大的动力性负荷测试两种固定装置直到固定失败，从而测定其固定强度。最后，以一种已经被证明有效的骨质疏松性股骨干模型进行同样的测试，以此来测定在骨质疏松情况下固定装置的强度。所有负荷模式及固定装置均分别重复测试5次。
Results
The stiffness of the far-cortical-locking constructs was 88% lower than that of the standard locked-plate constructs under axial compression up to 400 N. At elevated loading, nearcortex support of the far-cortical-locking screws provided a sixfold increase in stiffness. The resulting biphasic stiffness of the far-cortical-locking constructs (Fig. 5, a) resembled the progressive-stiffening behavior characteristic of Ilizarov external fixators. In torsion and bending, the far-cortical-locking constructs provided a 58% and 29% reduction in stiffness, respectively, compared with that of the locked-plate constructs.
结果
当轴向负荷为400N时，对侧皮质锁定装置的刚度比标准锁定钢板装置的刚度低88%。随着负荷的增加，同侧皮质的支撑使对侧锁定螺钉固定装置的刚度增加6倍。对侧皮质锁定螺钉固定装置所表现出来的双相刚度表现（图5A）与ILIZAROV外固定支架逐步增加的刚度特性相类似。在扭转及弯曲应力下，与锁定钢板固定装置相比，对侧锁定螺钉固定装置的强度分别降低了58%和29%。
Interfragmentary motion of the far-cortical-locking constructs in response to 200 N of loading was nearly parallel (0.51 mm and 0.59 mm at the near and far cortices, respectively). Under the same loading, locked-plate constructs yielded less motion, and motion was significantly smaller at the near cortex (0.02 mm) than at the far cortex (0.05 mm, p < 0.01).
在200N负荷作用下，对侧皮质锁定螺钉固定装置固定的骨折块间移动向乎是平行的（钢板同侧及对侧移动距离分别为0.51mm和0.59mm）。在同样的负荷下，锁定钢板固定装置固定的骨折块间移动程度明显减小，且钢板同侧移动度（0.02mm）显著小于对侧皮质移动度(0.05mm) (p < 0.01)。
In the non-osteoporotic diaphysis, the strength of the farcortical- locking constructs was 7% lower in compression, 54% higher in torsion, and 21% higher in bending compared with that of the locked-plate constructs. In the osteoporotic diaphysis, the strength of the far-cortical-locking constructs was 16% lower in compression, 9% higher in torsion, and 20% higher in bending compared with that in the locked-plate constructs.
在非疏松性骨干，与锁定钢板装置相比，对侧皮质锁定螺钉固定装置在轴向、扭转及弯曲负荷下的固定强度分别降低7%，增加54%，增加21%。而在骨质疏松性骨干，三种负荷下的固定强度分别为降低16%，增加9%，增加20%。
Conclusions
The results of this study demonstrate that far-cortical-locking constructs combine three key factors aimed at promoting secondary bone-healing with locking plates: stiffness reduction, parallel interfragmentary motion, and progressive stiffening. Far-cortical-locking screws reduce the initial stiffness of a locked-plate construct to that of an external fixator. Farcortical- locking constructs deliver nearly parallel interfragmentary motion within the 0.2 to 1-mm range9,29-31, which is known to promote callus formation. Progressive stiffening of far-cortical-locking constructs provides a low initial stiffness, enabling interfragmentary motion under reduced postoperative weight-bearing, while increased secondary stiffness provides progressive stabilization at elevated loads. The far-cortical- locking constructs retained at least 84% of the axial strength of the locked-plate constructs and were up to 54% stronger in torsion and up to 21% stronger in bending than the locked-plate constructs. The considerable strength increase in torsion and bending may be attributed to evenly distributed load-sharing among all of the far-cortical-locking screws (Fig. 5, b). In contrast, the end-screw of a standard locked construct induces a stress riser, which reduces the construct strength in bending and torsion46. In summary, far-cortical-locking constructs resemble ‘‘internal fixators’’ that combine the benefits of fixed-angle stabilization with flexible fixation for promotion of fracture-healing by callus formation.
结论
本研究结果证明对侧皮质锁定钢板装置综合了三个着眼于以锁定钢板促进二期骨折愈合的关键因素：低刚度，骨折块对称性移动以及逐步增加的固定强度。对侧皮质锁定螺钉使得锁定钢板装置的刚度降低到了与外固定支架相似的水平。而且对侧皮质锁定装置能获得骨折块间范围在0.2mm到1mm之间几乎对称的移动度，而该移动范围已知有助于促进骨痂形成。而对侧皮质锁定装置渐进性增加的固定强度使得术后初始强度较低，这允许术后低度负重下骨折块之间的移动，而在负荷增加的情况下，随之增加的固定强度对也提供了进一步的稳定性。对侧皮质锁定装置保持了锁定钢板装置至少84%的轴向强度，而扭转强度及弯折强度增加最高分别达54%及21%。明显增加的扭转和弯折强度可能与在所有对侧锁定螺钉上平均分布的负荷有关（图5B）。与此相反的是，标准锁定钢板装置的末端螺钉会产生应力集中带，这将降低固定装置在弯折和扭转应力下的强度。总之，对侧皮质锁定螺钉固定装置与“内固定支架”相似，集中了角度稳定装置以及弹性固定的优点，从而有利于促进骨痂形成导致的骨折愈合。
