Zderic Ivan, Oh Jong-Keon, Stoffel Karl, Sommer Christoph, Helfen Tobias, Camino Gaston, Richards Geoff, Nork Sean E, Gueorguiev Boyko
AO Research Institute Davos, Davos, Switzerland.
Department of Orthopaedic Surgery, Guro Hospital, Korea University Medical Center, Seoul, Republic of Korea.
J Orthop Trauma. 2018 Feb;32(2):67-74. doi: 10.1097/BOT.0000000000001008.
To investigate biomechanically in a human cadaveric model the failure modes of the proximal femoral locking compression plate and explore the underlying mechanism.
Twenty-four fresh-frozen paired human cadaveric femora with simulated unstable intertrochanteric fractures (AO/OTA 31-A3.3) were assigned to 4 groups with 6 specimens each for plating with proximal femoral locking compression plate. The groups differed in the quality of fracture reduction and plating fashion of the first and second proximal screws as follows: (1) anatomic reduction with on-axis screw placement; (2) anatomic reduction with off-axis screw placement; (3) malreduction with on-axis screw placement; (4) malreduction with off-axis screw placement. The specimens were tested until failure using a protocol with combined axial and torsional loading. Mechanical failure was defined as abrupt change in machine load-displacement data. Clinical failure was defined as 5 degrees varus tilting of the femoral head as captured with optical motion tracking.
Initial axial stiffness (in N/mm) in groups 1 to 4 was 213.6 ± 65.0, 209.5 ± 134.0, 128.3 ± 16.6, and 106.3 ± 47.4, respectively. Numbers of cycles to clinical and mechanical failure were 16,642 ± 10,468 and 8695 ± 1462 in group 1, 14,076 ± 3032 and 7449 ± 5663 in group 2, 8800 ± 8584 and 4497 ± 2336 in group 3, and 9709 ± 3894 and 5279 ± 4119 in group 4. Significantly higher stiffness and numbers of cycles to both clinical and mechanical failure were detected in group 1 in comparison with group 3, P ≤ 0.044.
Generally, malreduction led to significantly earlier construct failure. The observed failures were cut-out of the proximal screws in the femoral head, followed by either screw bending, screw loosening, or screw fracture. Proper placement of the proximal screws in anatomically reduced fractures led to significantly higher construct stability. Our data also indicate that once the screws are placed off-axis (>5 degrees), the benefit of an anatomic reduction is lost.
在人体尸体模型中对股骨近端锁定加压钢板的失效模式进行生物力学研究，并探讨其潜在机制。
将24对新鲜冷冻的人体尸体股骨模拟不稳定型转子间骨折（AO/OTA 31-A3.3），分为4组，每组6个标本，用股骨近端锁定加压钢板进行固定。各组在骨折复位质量及第一枚和第二枚近端螺钉的置入方式上有所不同，如下：（1）解剖复位且螺钉沿轴置入；（2）解剖复位且螺钉偏心置入；（3）复位不良且螺钉沿轴置入；（4）复位不良且螺钉偏心置入。使用轴向和扭转联合加载方案对标本进行测试直至失效。机械失效定义为机器载荷-位移数据的突然变化。临床失效定义为通过光学运动跟踪捕捉到股骨头内翻倾斜5度。
第1至4组的初始轴向刚度（单位：N/mm）分别为213.6±65.0、209.5±134.0、128.3±16.6和106.3±47.4。第1组临床和机械失效的循环次数分别为16,642±10,468和8695±1462，第2组为14,076±3032和7449±5663，第3组为8800±8584和4497±2336，第4组为9709±3894和5279±4119。与第3组相比，第1组的刚度以及临床和机械失效的循环次数均显著更高，P≤0.044。
一般来说，复位不良会导致内固定装置显著更早失效。观察到的失效情况是股骨头内近端螺钉穿出，随后出现螺钉弯曲、螺钉松动或螺钉断裂。在解剖复位的骨折中正确置入近端螺钉可显著提高内固定装置的稳定性。我们的数据还表明，一旦螺钉偏心置入（>5度），解剖复位的益处就会丧失。
