Objective

The purpose of this study was to examine the effect of insertion angles on the pullout strength of connected pins using a synthetic model simulating a hand bone.

Material and methods

The material consisted of Sawbones® (20 mm × 20 mm × 60 mm), fixation pins secured to a connecting rod much like an external fixator, an electric drill (speed 1,290 rpm) and a tensile testing machine. The Sawbones® were drilled with different pin diameters (1.2 mm, 1.5 mm, and 1.8 mm) and insertion angles (100°, 110° and 120°). A vertical displacement of 1 mm/min was applied until the pins were extracted (maximum force).

Results

The pullout strength increased with the insertion angle of the connected pins. It also increased with their diameter. Regardless of the pin diameter, the load-displacement curve during the pullout test had 4 sections (peak 1, ascending slope, peak 2, descending slope) that corresponded to the combined frictional force and contact force between the pins and Sawbones®.

Discussion

Our study findings showed that, theoretically, for wrist or hand fractures treated with connected pins, the larger the diameter and insertion angle, the better the mechanical holding power of the pins.

Level of evidence

I, experimental study.

中文翻译：

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手部手术中连接针的拔出强度：针直径和插入角度的影响

客观的

本研究的目的是使用模拟手骨的合成模型检查插入角度对连接销的拔出强度的影响。

材料与方法

该材料包括 Sawbones®（20 毫米 ×  20 毫米 × 60 毫米）、固定在连杆上的固定销（很像外固定器）、电钻（速度 1,290 rpm）和拉伸试验机。Sawbones® 钻有不同的针直径（1.2 毫米、1.5 毫米和 1.8 毫米）和插入角度（100°、110° 和 120°）。施加 1 毫米/分钟的垂直位移，直到拔出销钉（最大力）。

结果

拔出强度随着连接销的插入角度而增加。它也随着直径的增加而增加。无论销直径如何，拉出测试期间的载荷-位移曲线有 4 个部分（峰值 1，上升斜率，峰值 2，下降斜率）对应于销与 Sawbones® 之间的组合摩擦力和接触力。

讨论

我们的研究结果表明，理论上，对于使用连接针治疗的手腕或手部骨折，直径和插入角度越大，针的机械保持力越好。

证据等级

一、实验研究。