Weil Yoram A, Gardner Michael J, Mikhail George, Pierson Glen, Helfet David L, Lorich Dean G
Orthopaedic Trauma Service, Hospital for Special Surgery, 535 E. 70th Street, New York, NY, USA.
Arch Orthop Trauma Surg. 2008 Feb;128(2):227-34. doi: 10.1007/s00402-007-0497-2. Epub 2007 Nov 6.
Intramedullary nails for fixation of extracapsular hip fractures have gained popularity recently. Although clinically successful, they are not devoid of complications. An infrequently reported complication is the medial migration of the femoral neck element (FNE) of the implant into the pelvis. The purpose of this study was to create a biomechanical model simulating this effect based on a clinical case radiographic analysis.
Eight clinical cases of medial migration were available for radiographic analysis. Medial migration was quantified and the fractures were classified. A biomechanical model was built comprising two fixtures containing the nail and FNE respectively. A pivot between the two fixtures, representing a deficient femoral calcar, simulated an unstable fracture type. Two pivot points were used for each nail. The constructs were tested using sinusoidal loading (40-800 N at 2 Hz) and medial migration was assessed. Five different nail designs (TFN, PFN, PFN-a, Gamma-3 and IMHS) were tested (overall 75 tests).
All the five implants demonstrated medial migration to a similar distance. The TFN required the highest number of cycles (3127 +/- 2569) and the IMHS the lowest (58.8 +/- 3.6) although this difference did not reach statistical significance (P = 0.07). Changing the pivot point for the medial calcar did not alter the results significantly. All eight clinical cases demonstrated an unstable intertrochanteric fracture pattern (AO/OTA 32A2).
Discrete biomechanical conditions are required to reproduce medial migration of the FNE in cephalomedullary devices.
用于固定髋关节囊外骨折的髓内钉近来越来越受欢迎。尽管在临床上取得了成功，但它们并非没有并发症。一种较少报道的并发症是植入物的股骨颈部件（FNE）向骨盆内侧移位。本研究的目的是基于临床病例的影像学分析创建一个模拟这种效应的生物力学模型。
有8例内侧移位的临床病例可供影像学分析。对内侧移位进行量化并对骨折进行分类。构建了一个生物力学模型，包括两个分别包含髓内钉和FNE的固定装置。两个固定装置之间的一个枢轴，代表股骨距缺损，模拟不稳定骨折类型。每个髓内钉使用两个枢轴点。使用正弦加载（2赫兹下40 - 800牛）对结构进行测试，并评估内侧移位情况。测试了五种不同的髓内钉设计（TFN、PFN、PFN - a、Gamma - 3和IMHS）（共75次测试）。
所有五种植入物的内侧移位距离相似。TFN所需的循环次数最多（3127 ± 2569），IMHS最少（58.8 ± 3.6），尽管这种差异未达到统计学显著性（P = 0.07）。改变股骨距内侧的枢轴点对结果没有显著影响。所有8例临床病例均表现为不稳定的转子间骨折类型（AO/OTA 32A2）。
需要特定的生物力学条件来重现头髓内固定装置中FNE的内侧移位。
