Huang Shier-Chieg, Lin Chen-Chiang, Lin Jinn
Department of Orthopedic Surgery, National Taiwan University Hospital Yun-Lin Branch, Yun-Lin County, Taiwan.
J Trauma. 2009 Feb;66(2):436-42. doi: 10.1097/TA.0b013e318154013b.
Proximity of the distal locking screw to the fracture site potentially can cause implant failure in locked nailing of distal femoral fractures. In this biomechanical study, we investigated the effects of nail-cortical contact and nail purchase in the distal subchondral bone on fixation stability and implant strain.
Using fiberglass artificial femurs, we fixed five different distal femoral osteotomies with specially manufactured locked nails representing different conditions of nail-cortical contact. In each condition, six femur-nail constructs were loaded on the femoral head axially with 700 N; then we measured the fixation stability and strain at the superiormost distal locking screw and nail hole. The tests were conducted both with and without nail purchase in distal subchondral bone.
When there was no nail-cortical contact, the load transmitted to the distal femoral fragment was completely borne by the nail and the distal locking screws. Low fixation stability and high strain on the distal screw and nail hole resulted. Greater nail-cortical contact increased the fixation stability and decreased strains on the distal screw and nail hole. Purchase of the nail tip in distal subchondral bone significantly increased the fixation stability and decreased nail hole strain except in the situation of long nail-cortical contact. The screw strain was significantly reduced in all conditions, and the reduction in strain was significantly greater than that associated with the nail hole, 32% +/- 8% versus 15.7% +/- 2.5% (p = 0.002).
In locked nailing of distal femoral fractures, the prime factor determining fixation stability and implant strain is nail-cortical contact. In situations without nail-cortical contact, a longer nail with purchase in the subchondral bone of the distal femur is recommended.
在股骨远端骨折的锁定髓内钉固定中，远端锁定螺钉靠近骨折部位可能会导致植入物失效。在这项生物力学研究中，我们调查了钉-皮质接触以及钉尖在远端软骨下骨中的把持力对固定稳定性和植入物应变的影响。
我们使用玻璃纤维人工股骨，用特制的锁定髓内钉固定五种不同的股骨远端截骨模型，这些髓内钉代表了不同的钉-皮质接触情况。在每种情况下，对六个股骨-髓内钉结构在股骨头处以700 N的轴向力加载；然后我们测量最上方远端锁定螺钉和钉孔处的固定稳定性和应变。测试分别在有和没有钉尖把持远端软骨下骨的情况下进行。
当没有钉-皮质接触时，传递到股骨远端骨折块的负荷完全由髓内钉和远端锁定螺钉承担。结果导致固定稳定性低，远端螺钉和钉孔处的应变高。更大的钉-皮质接触增加了固定稳定性，并降低了远端螺钉和钉孔处的应变。除了长钉-皮质接触的情况外，钉尖把持远端软骨下骨显著增加了固定稳定性并降低了钉孔应变。在所有情况下，螺钉应变均显著降低，且应变降低幅度显著大于钉孔，分别为32%±8%和15.7%±2.5%（p = 0.002）。
在股骨远端骨折的锁定髓内钉固定中，决定固定稳定性和植入物应变的主要因素是钉-皮质接触。在没有钉-皮质接触的情况下，建议使用更长的、能把持股骨远端软骨下骨的髓内钉。
