Kane Patrick, Vopat Bryan, Heard Wendell, Thakur Nikhil, Paller David, Koruprolu Sarath, Born Christopher
Department of Orthopaedics, Rhode Island Hospital, 593 Eddy Street, Providence, RI, 02903, USA,
Clin Orthop Relat Res. 2014 Aug;472(8):2492-8. doi: 10.1007/s11999-014-3594-x. Epub 2014 Apr 24.
Intertrochanteric hip fractures pose a significant challenge for the orthopaedic community as optimal surgical treatment continues to be debated. Currently, varus collapse with lag screw cutout is the most common mode of failure. Multiple factors contribute to cutout. From a surgical technique perspective, a tip apex distance less than 25 mm has been suggested to decrease the risk of cutout. We hypothesized that a low-center lag screw position in the femoral head, with a tip apex distance greater than 25 mm will provide equal, if not superior, biomechanical stability compared with a center-center position with a tip apex distance less than 25 mm in an unstable intertrochanteric hip fracture stabilized with a long cephalomedullary nail.
QUESTIONS/PURPOSES: We attempted to examine the biomechanical characteristics of intertrochanteric fractures instrumented with long cephalomedullary nails with two separate lag screw positions, center-center and low-center. Our first research purpose was to examine if there was a difference between the center-center and low-center groups in cycles to failure and failure load. Second, we analyzed if there was a difference in fracture translation between the study groups during loading.
Nine matched pairs of femurs were assigned to one of two treatment groups: low-center lag screw position and center-center lag screw position. Cephalomedullary nails were placed and tip apex distance was measured. A standard unstable four-part intertrochanteric fracture was created in all samples. The femurs were loaded dynamically until failure. Cycles to failure and load and displacement data were recorded, and three-dimensional (3-D) motion was recorded using an Optotrak(®) motion tracking system.
There were no significant differences between the low-center and center-center treatment groups regarding the mean number of cycles to failure and mean failure load. The 3-D kinematic data showed significantly increased motion in the center-center group compared with the low-center group. At the time of failure, the magnitude of fracture translation was statistically significantly greater in the center-center group (20 ± 2.8 mm) compared with the low-center group (15 ± 3.4 mm; p = 0.004). Additionally, there was statistically significantly increased fracture gap distraction (center-center group, 13 ± 2.8 versus low-center group, 7 ± 4; p < 0.001) and shear fracture gap translation (center-center group, 12 ± 2.3 mm; low-center group, 6 ± 2.7 mm; p < 0.001).
Positioning of the lag screw inferior in the head and neck was found to be at least as biomechanically stable as the center-center group although the tip apex distance was greater than 25 mm.
Our findings challenge previously accepted principles of optimal lag screw placement.
转子间髋部骨折对骨科界构成重大挑战，因为最佳手术治疗方案仍存在争议。目前，拉力螺钉穿出伴内翻塌陷是最常见的失败模式。多种因素导致螺钉穿出。从手术技术角度来看，建议尖顶距小于25 mm以降低螺钉穿出风险。我们假设，在使用长髓内钉固定的不稳定转子间髋部骨折中，股骨头内拉力螺钉低中心位置（尖顶距大于25 mm）与尖顶距小于25 mm的中心-中心位置相比，将提供同等甚至更好的生物力学稳定性。
问题/目的：我们试图研究使用长髓内钉并采用两种不同拉力螺钉位置（中心-中心和低中心）固定的转子间骨折的生物力学特性。我们的首要研究目的是检验中心-中心组和低中心组在失效循环次数和失效载荷方面是否存在差异。其次，我们分析了研究组在加载过程中骨折移位是否存在差异。
将九对匹配的股骨分配到两个治疗组之一：低中心拉力螺钉位置组和中心-中心拉力螺钉位置组。置入髓内钉并测量尖顶距。在所有样本中制造标准的不稳定四部分转子间骨折。对股骨进行动态加载直至失效。记录失效循环次数、载荷和位移数据，并使用Optotrak®运动跟踪系统记录三维（3-D）运动。
低中心治疗组和中心-中心治疗组在平均失效循环次数和平均失效载荷方面无显著差异。三维运动学数据显示，与低中心组相比，中心-中心组的运动显著增加。在失效时，中心-中心组（20±2.8 mm）的骨折移位幅度在统计学上显著大于低中心组（15±3.4 mm；p = 0.004）。此外，骨折间隙牵张（中心-中心组为13±2.8，低中心组为7±4；p < 0.001）和剪切骨折间隙移位（中心-中心组为12±2.3 mm；低中心组为6±2.7 mm；p < 0.001）在统计学上也显著增加。
尽管尖顶距大于25 mm，但发现头颈部拉力螺钉低位放置在生物力学稳定性上至少与中心-中心组相当。
我们的研究结果挑战了先前公认的最佳拉力螺钉放置原则。
