外固定针结构与远侧皮质骨折的关系

The structure of external fixation pin and the fracture of distal cortex

目的分析外固定针结构与其拧入骨干时引起远侧皮质骨折间的关系。方法成人新鲜尸体胫骨11根,取包埋后胫骨中段为针拧入测试区,确定进针点和方向。按针尖、针杆直径及螺纹的不同,将固定针分为4组(A、B、C、D)。通过MTS机动力轴,在扳手上施以持续纵向压力100N,操作者以≤3Nm的扭矩顺时针以25～30圈/min拧入固定针。观察胫骨近、远侧皮质的骨折情况。结果①A组(直径6mm)与B组(直径5mm)非自攻型固定针间所致骨折发生率没有显著性差异(P>0.05);②在螺距和直径相同前提下(C组与B组),自攻型较非自攻型针更易造成骨折(P<0.05);③对于自攻型固定针,D组(螺距1mm)固定针较C组(螺距2mm)骨折几率显著性降低(P<0.05);④远侧骨皮质较近侧骨皮质更易发生骨折(P<0.05)。结论自攻型外固定针拧入时易导致远侧骨皮质骨折,减少螺距和牙深可降低骨折发生率。

Objective To analyze the relationship between the structure of external fixation pin and the fracture of distal cortex. Methods 11 fresh human tibial specimens were prepared. The insertion points and the angles of pin were determined before operation. According to different structures, the pins were classified into 4 groups(A, B, C, D). With a spanner, the manipulator circumrotated the pins into the bone with ≤3Nm torque and a velocity of 25 to 30 round/min under 100N axial compression under MTS. The fractures of proximal cortex or distal cortex were noted respectively. All data were analyzed with ANOVA. Results The different diameters (group A: 6mm; group B: 5mm) of pins could not lead to the different rates of cortex fracture significantly(P >0.05)under the drilling preparation. The self tapping pins (group C) could cause fracture more frequently than normal pins with the same pitch and diameter (group B)(P< 0.05). The rate of fracture decreased significantly as a result of decrease of the pins pitch and thread depth (P< 0.05). The fracture occurred more frequently on distal cortex than on proximal cortex(P< 0.05). Conclusions The self tapping pins can cause fractures of distal cortex more frequently. Decrease of pitch and thread depth of pins is helpful in decreasing the incidence of the cortex fracture.