不同长度锁钉固定桡骨远端不稳定骨折的生物力学比较

Biomechanical comparison of unstable distal radius fractures fixed by locking screws with different length

目的比较不同长度锁定螺钉固定桡骨远端骨折的术后稳定性及不同时期骨痂和远端螺钉的应力分布情况,为桡骨远端骨折螺钉长度的选择提供生物力学依据。方法分别建立含骨折断面和骨痂的桡骨远端不稳定骨折的三维有限元模型,并用掌侧锁定钢板和不同长度锁钉固定,通过赋予骨痂不同材料属性来模拟骨折术后不同时期。分析术后不同时期骨痂和远端螺钉的应力分布情况,同时根据骨折断面最大轴向位移计算整个固定系统的压缩刚度。结果对于相同轴向载荷,75%长度以上单皮质螺钉固定时压缩刚度与双皮质螺钉固定相比基本无差异;术后早期骨痂处最大应力随着螺钉长度增加逐渐变小;术后中后期远端螺钉最大应力随着螺钉长度增加逐渐变大,远端双皮质螺钉应力最大。结论采用75%长度以上单皮质锁钉固定桡骨远端不仅可以达到早期稳定性,同时也避免伸肌腱并发症的发生。

Objective To compare the postoperative stability of unstable distal radius fractures fixed by locking screws with different length and analyze the stress distributions of distal screws and callus at different healing periods, so as to provide biomechanical references for choosing appropriate length of screws for treating distal radius fractures. Methods The three-dimensional finite element models of unstable distal radius fractures with fracture section and callus were established, respectively, and fixed by volar locking plates and locking screws with different length. Then different periods of fracture healing were simulated by assigning callus with different material properties. Stress distributions on callus and distal screws at different postoperative periods were analyzed, and compression stiffness of the whole fixation system was calculated according to the maximum axial displacement at fracture section. Results Under the same axial loads, the compression stiffness was basically the same by using unicortical screw with over 75% length or bi-cortical screw. With the screw length increasing, the maximum stress of callus was decreased gradually during the period of early healing; while the maximum stress of distal screws was increasing gradually with the increase of screw length at middle and last period of fracture healing, and the stress of distal bi-cortical screw was the largest. Conclusions Using the unicortical distal locking screws with at least 75% length can not only produce early stability， but also avoid extensor tendon injuries due to dorsal screw prominence.