Tsai Andrew G, Ashworth Timothy J, Marcus Randall, Akkus Ozan
Case Western Reserve University, School of Medicine, Department of Orthopaedics,10900 Euclid Avenue, Cleveland, OH USA 44106.
University of North Carolina, School of Medicine, Department of Orthopaedics,101 Manning Drive, Chapel Hill, NC USA 27514.
Iowa Orthop J. 2017;37:23-28.
Iatrogenic subtrochanteric fractures of the femur can occur postoperatively following placement of screws in the lateral femoral cortex. Drilling holes below the lesser trochanter is generally avoided to prevent fatigue failure; however, there is little biomechanical evidence to support this recommendation. We hypothesized that hole placement below the level of the lesser trochanter will not accelerate fatigue failure compared to holes at the level of the lesser trochanter.
Twelve matched-pairs of male fresh-frozen cadaveric femurs were used for biomechanical testing. A single screw hole was drilled through the lateral femoral cortex either at the level of the lesser trochanter (proximal-hole group) or below the lesser trochanter (distal-hole group). Each femur was cycled to failure using a physiologically-relevant loading model. Paired t-test was used to evaluate for a difference in cycles to failure between groups.
There was no statistical difference in cycles to failure between the groups with the hole drilled at or below the lesser trochanter.
The traditional recommendation to avoid drilling holes below the level of the lesser trochanter is based mainly on experience and case reports in the literature. The results of this study indicate that placing holes below the level of the lesser trochanter, in and of itself, may not pose any additional risk of fracture. Other important factors need to be considered, such as tapering of the lateral femoral cortex.
There are often situations where the patient's anatomy and facture pattern is more conducive to placing a screw distal to the lesser trochanter. This study may allow surgeons greater flexibility in placing screws more distally in the lateral femoral cortex by demonstrating the safety of doing so, at least in the population studied.
股骨转子下医源性骨折可在股骨外侧皮质置入螺钉后发生。一般避免在小转子下方钻孔以防止疲劳失效；然而，几乎没有生物力学证据支持这一建议。我们假设，与在小转子水平钻孔相比，在小转子水平以下钻孔不会加速疲劳失效。
使用12对匹配的男性新鲜冷冻尸体股骨进行生物力学测试。在小转子水平（近端孔组）或小转子下方（远端孔组）通过股骨外侧皮质钻一个单螺钉孔。使用生理相关加载模型使每个股骨循环至失效。采用配对t检验评估两组之间失效循环次数的差异。
在小转子处或小转子下方钻孔的两组之间，失效循环次数没有统计学差异。
避免在小转子水平以下钻孔的传统建议主要基于文献中的经验和病例报告。本研究结果表明，在小转子水平以下钻孔本身可能不会带来任何额外的骨折风险。还需要考虑其他重要因素，如股骨外侧皮质的逐渐变细。
在很多情况下，患者的解剖结构和骨折类型更有利于在小转子远端置入螺钉。本研究通过证明这样做的安全性，至少在所研究的人群中，可能会使外科医生在股骨外侧皮质更向远端置入螺钉时具有更大的灵活性。
