Objective The aim of this study was to evaluate the effect of bidirectional insertion on axial pullout strength of tapered run out (TRO), traditional negative profile (TNP) and positive profile (PP) pins.

Study Design Cadaveric adult canine tibiae were harvested. Tapered run out pins (Group 1) were inserted unidirectionally to the desired position; bidirectionally past the desired position, then withdrawn to the desired position (Group 2); and bidirectionally as described for Group 2, repeated twice (Group 3). Traditional negative profile pins (Group 4–6) and PP pins (Group 9–11) were placed in the same manner. Tapered run out (Group 7), TNP (Group 8) and PP pins (Group 12) were driven unidirectionally such that the shaft of the pin violated the cis-cortex. A servohydraulic testing machine extracted the pins and measured axial peak pullout strength.

Results Positive profile pins had significantly greater pullout strength than TRO and TNP pins placed unidirectionally to the desired position. Method of insertion had no effect on peak pullout strength of TNP pins. TRO and PP pins inserted unidirectionally to the desired position had significantly greater peak pullout strengths than insertion bidirectionally or if the shaft of the pin violated the cis-cortex.

Conclusion The authors recommend that pins used for external skeletal fixation should be placed unidirectionally to the desired position with fluoroscopic guidance, intra-operative depth gauge measurements or measurements from preoperative radiographs. Repositioning pins results in loss of peak pullout strength with TRO and PP pins.

目的 本研究的目的是评估双向插入对锥形跳动（TRO）、传统负轮廓（TNP）和正轮廓（PP）销轴向拔出强度的影响。

研究设计 收获尸体成年犬胫骨。锥形跳动销（第 1 组）单向插入所需位置；双向经过所需位置，然后撤回到所需位置（第 2 组）；和双向如第 2 组所述，重复两次（第 3 组）。传统的负剖面销（4-6 组）和 PP 销（9-11 组）以相同的方式放置。锥形跳动（第 7 组）、TNP（第 8 组）和 PP 针（第 12 组）被单向驱动，使得针的轴违反了顺式皮层。伺服液压试验机提取销钉并测量轴向峰值拉拔强度。

结果 与单向放置到所需位置的 TRO 和 TNP 引脚相比，正轮廓引脚的拔出强度显着提高。插入方法对 TNP 引脚的峰值拔出强度没有影响。TRO 和 PP 针单向插入所需位置的峰值拔出强度明显大于双向插入或针的轴违反顺式皮层的情况。

结论 作者建议，用于外部骨骼固定的针应单向放置到所需位置，并通过透视引导、术中深度计测量或术前 X 光片测量。重新定位销会导致 TRO 和 PP 销失去峰值拔出强度。