Tejwani Nirmal C, Park Samuel, Iesaka Kazuho, Kummer Fred
Department of Orthopaedics, NYU-Hospital for Joint Diseases, New York, NY 10016, USA.
J Orthop Trauma. 2005 Jul;19(6):380-3. doi: 10.1097/01.bot.0000155312.12510.bd.
To examine the effects of locked distal screws in retrograde nails used in unstable osteopenic distal femur fractures.
Biomechanical testing of paired human cadaveric femurs.
Seven matched pairs of embalmed, moderately osteopenic cadaver femurs were instrumented with 12-mm intramedullary nails in a statically locked, retrograde fashion. One femur of each pair had locked distal screws and the other femur had unlocked distal screws. A 2.5-cm gap of bone was cut nine centimeters from the distal condyles to simulate an unstable fracture. The locked distal screw nails were compared to unlocked distal screw nails for collapse of the fracture gap, medial-lateral and anterior-posterior translation of the nail within the fracture site, and fracture angulation. The femurs were axially loaded, cycled, and then loaded to failure.
Motion at the fracture site with axial cyclic loading and site of failure when loaded to failure.
After cycling, both locked distal screw and unlocked distal screw nails demonstrated several millimeters medial and anterior translation within the fracture site and approximately 1 mm collapse of the fracture gap. Although no statistically significant differences were found, the locked distal screw nails had less anterior and medial translation, angulation, and collapse of the fracture gap after cycling. Loads to failure were similar for both locked distal screw and unlocked distal screw nails. It was noted that proximal femur failure occurred at the level of the proximal screw hole in the nail at the subtrochanteric level in 7 (4 locked distal screws and 3 unlocked distal screw groups) of the 14 samples. Four other samples failed through the intertrochanteric region (2 locked distal screw and 2 unlocked distal screw groups) and the remainder within the distal fragment by fracture of the femur along the medial cortex.
Although most differences in fixation stability were not significant, the locked distal screw nails exhibited less fracture collapse and anterior and medial translation of the nail at the fracture site than the unlocked distal screw nails. The degree of varus angulation after cyclic loading was also less for the locked distal screw nails. The length of the nail chosen should avoid having proximal locking screws distal to the lesser trochanter, thus averting proximal femur stress risers and fractures.
研究锁定远端螺钉在不稳定型骨质疏松性股骨远端骨折逆行髓内钉固定中的作用。
配对新鲜人尸体股骨的生物力学测试。
七对经过防腐处理、中度骨质疏松的尸体股骨，以静态锁定、逆行方式植入12毫米髓内钉。每对股骨中，一根股骨使用锁定远端螺钉，另一根股骨使用非锁定远端螺钉。从股骨远端髁突处9厘米远的位置截去2.5厘米长的一段骨，以模拟不稳定骨折。比较锁定远端螺钉组与非锁定远端螺钉组在骨折间隙塌陷、骨折部位髓内钉的内外侧及前后移位以及骨折成角情况。对股骨施加轴向载荷、循环加载，然后加载直至破坏。
轴向循环加载时骨折部位的位移以及加载至破坏时的破坏部位。
循环加载后，锁定远端螺钉组和非锁定远端螺钉组在骨折部位均出现数毫米的内侧及前方移位，骨折间隙塌陷约1毫米。尽管未发现统计学上的显著差异，但锁定远端螺钉组在循环加载后骨折部位的前方及内侧移位、成角以及骨折间隙塌陷程度较小。锁定远端螺钉组和非锁定远端螺钉组的破坏载荷相似。注意到14个样本中有7个（4个锁定远端螺钉组和3个非锁定远端螺钉组）在股骨转子下水平髓内钉近端螺钉孔处发生股骨近端破坏。另外4个样本在转子间区域破坏（2个锁定远端螺钉组和2个非锁定远端螺钉组），其余样本在远端骨折块内，股骨沿内侧皮质发生骨折。
尽管在固定稳定性方面的大多数差异不显著，但锁定远端螺钉组相比非锁定远端螺钉组，骨折塌陷程度较小，骨折部位髓内钉的前方及内侧移位也较小。循环加载后内翻成角程度锁定远端螺钉组也较小。所选用髓内钉的长度应避免小转子远端有近端锁定螺钉，从而避免股骨近端应力集中及骨折。
