Henschel Julia, Tsai Stanley, Fitzpatrick Daniel C, Marsh J Lawrence, Madey Steven M, Bottlang Michael
1Biomechanics Laboratory, Legacy Research Institute, Portland, Oregon 2Slocum Orthopaedics, Eugene, Oregon 3Dept. of Orthopaedics and Rehabilitation, University of Iowa Hospital and Clinics, Iowa City.
J Orthop Trauma. 2017 Oct;31(10):531-537. doi: 10.1097/BOT.0000000000000879.
Decreasing the stiffness of locked plating constructs can promote natural fracture healing by controlled dynamization of the fracture. This biomechanical study compared the effect of 4 different stiffness reduction methods on interfragmentary motion by measuring axial motion and shear motion at the fracture site.
Distal femur locking plates were applied to bridge a metadiaphyseal fracture in femur surrogates. A locked construct with a short-bridge span served as the nondynamized control group (LOCKED). Four different methods for stiffness reduction were evaluated: replacing diaphyseal locking screws with nonlocked screws (NONLOCKED); bridge dynamization (BRIDGE) with 2 empty screw holes proximal to the fracture; screw dynamization with far cortical locking (FCL) screws; and plate dynamization with active locking plates (ACTIVE). Construct stiffness, axial motion, and shear motion at the fracture site were measured to characterize each dynamization methods.
Compared with LOCKED control constructs, NONLOCKED constructs had a similar stiffness (P = 0.08), axial motion (P = 0.07), and shear motion (P = 0.97). BRIDGE constructs reduced stiffness by 45% compared with LOCKED constructs (P < 0.001), but interfragmentary motion was dominated by shear. Compared with LOCKED constructs, FCL and ACTIVE constructs reduced stiffness by 62% (P < 0.001) and 75% (P < 0.001), respectively, and significantly increased axial motion, but not shear motion.
In a surrogate model of a distal femur fracture, replacing locked with nonlocked diaphyseal screws does not significantly decrease construct stiffness and does not enhance interfragmentary motion. A longer bridge span primarily increases shear motion, not axial motion. The use of FCL screws or active plating delivers axial dynamization without introducing shear motion.
降低锁定钢板结构的刚度可通过对骨折进行可控的动力化来促进自然骨折愈合。这项生物力学研究通过测量骨折部位的轴向运动和剪切运动，比较了4种不同刚度降低方法对骨折块间运动的影响。
将股骨远端锁定钢板应用于模拟股骨干骺端骨折。短桥接跨度的锁定结构作为非动力化对照组（锁定组）。评估了4种不同的刚度降低方法：用非锁定螺钉替换骨干锁定螺钉（非锁定组）；在骨折近端有2个空螺钉孔的桥接动力化（桥接组）；使用远皮质锁定（FCL）螺钉进行螺钉动力化；以及使用主动锁定钢板进行钢板动力化（主动组）。测量骨折部位的结构刚度、轴向运动和剪切运动，以表征每种动力化方法。
与锁定对照组结构相比，非锁定组结构具有相似的刚度（P = 0.08）、轴向运动（P = 0.07）和剪切运动（P = 0.97）。与锁定组结构相比，桥接组结构的刚度降低了45%（P < 0.001），但骨折块间运动以剪切为主。与锁定组结构相比，FCL组和主动组结构的刚度分别降低了62%（P < 0.001）和75%（P < 0.001），并显著增加了轴向运动，但未增加剪切运动。
在股骨远端骨折的替代模型中，用非锁定骨干螺钉替换锁定螺钉不会显著降低结构刚度，也不会增强骨折块间运动。较长的桥接跨度主要增加剪切运动，而非轴向运动。使用FCL螺钉或主动钢板可实现轴向动力化，而不会引入剪切运动。
