Raducha Jeremy E, Nacca Christopher R, Crisco Joseph J, Evans Andrew R
Department of Orthopaedics, Warren Alpert Medical School of Brown University, Providence, RI, USA.
Department of Orthopaedics, Warren Alpert Medical School of Brown University, Providence, RI, USA; University Orthopedics Incorporated, Providence, RI, USA.
Clin Biomech (Bristol). 2022 Apr;94:105352. doi: 10.1016/j.clinbiomech.2021.105352. Epub 2021 Apr 13.
To potentially limit peri-implant fractures our institution commonly implements a "stress-taper" fixation construct in which the screw lengths towards the proximal end of a construct are incrementally decreased, in order to avoid a focal stress-riser when loaded. To assess this construct, we asked: 1) Does the stress taper strategy increase torsional strength than the bicortical locking construct when biomechanically tested in a cadaveric femur model? 2) Does it fail in a less comminuted fracture pattern?
Seven matched pairs of cadaveric femora were randomly assigned to one of two distal femur fixation groups: plating with stress taper strategy or bicortical fixation. Specimens were first cyclically loaded, then axially rotated to failure under 800 N of compression. Peak torque at failure, degrees of rotation at failure, and energy to failure were calculated and compared using paired t-tests. Fractures were categorized with the assistance of fluoroscopy according to the Orthopedic Trauma Association classification, 32.
There was significantly greater peak torque (110.6 ± 49.7 Nm vs. 80.6 ± 35.2 Nm), rotation at failure (23.8 ± 5.3° vs 18.9 ± 4.5°) and energy to failure (25.3 ± 15.7 J vs. 14.1 ± 8.3 J) in the stress-taper group as compared to the bicortical group (p = 0.0424), (p = 0.0213) and (p = 0.0460), respectively. 6/7 fractures in the stress-taper group were classified 32 A1 with 1/7 classified A2. 5/7 fractures in the bicortical group were classified B1 and 2/7 classified A2.
'Stress taper fixation' in distal femurs may be protective against peri-implant fractures compared to traditional bicortical fixation. The 'stress taper' concept can increase torsional failure strength in an in vitro model.
为了潜在地限制植入物周围骨折，我们机构通常采用一种“应力渐变”固定结构，即朝着结构近端的螺钉长度逐渐减小，以避免加载时出现局部应力集中。为了评估这种结构，我们提出以下问题：1）在尸体股骨模型中进行生物力学测试时，应力渐变策略与双皮质锁定结构相比，是否能提高扭转强度？2）它在骨折粉碎程度较轻的骨折模式中是否失效？
将七对匹配的尸体股骨随机分配到两个股骨远端固定组之一：采用应力渐变策略的钢板固定组或双皮质固定组。首先对标本进行循环加载，然后在800N的压缩力下轴向旋转直至失效。计算失效时的峰值扭矩、失效时的旋转度数和失效能量，并使用配对t检验进行比较。在荧光透视的辅助下，根据骨科创伤协会分类32对骨折进行分类。
与双皮质组相比，应力渐变组的峰值扭矩（110.6±49.7 Nm对80.6±35.2 Nm）、失效时旋转度数（23.8±5.3°对18.9±4.5°）和失效能量（25.3±15.7 J对14.1±8.3 J）显著更高（p = 0.0424）、（p = 0.0213）和（p = 0.0460）。应力渐变组7例骨折中有6例分类为32 A1，1例分类为A2。双皮质组7例骨折中有5例分类为B1，2例分类为A2。
与传统的双皮质固定相比，股骨远端的“应力渐变固定”可能对植入物周围骨折具有保护作用。“应力渐变”概念可在体外模型中提高扭转失效强度。
