Background

Cancellous screw fixation is often used in fracture fixation. When this screw is over-tightened, damage to the bone and other non-linear processes such as fracture and construct failure would be involved. The objectives of this study were (1) to determine the reduction in pull-out strength when a cancellous screw spins and (2) to determine how much pull-out strength can be restored by revising with a larger diameter screw.

Methods

A biomechanical study using synthetic polyurethane foam (320 kg/m³) was performed to assess (1) the pull-out strength of a 6.5 mm cancellous screw, (2) the pull-out strength of a loosened 6.5 mm cancellous screw and (3) the pull-out strength of a loosened 6.5 mm cancellous screw revised with a 7.3 mm cancellous screw.

Findings

The baseline pull-out strength of the 6.5 mm cancellous screw was 2213.91 ± 200.51 N. There was a 79.1% (463.79 ± 99.95 N) reduction in pull-out strength once spinning occurs (p = 0.027). When a spinning 6.5 mm cancellous screw was revised to a 7.3 mm cancellous screw, the pull-out strength increased to 1313.65 ± 93.23 N, 59.3% of the baseline pull-out strength (2213.91 ± 200.51 N) (p = 0.027).

Intepretation

A loosened 6.5 mm cancellous screw results in a 79.1% reduction in pull-out strength. Revising a loosened cancellous screw by inserting a larger 7.3 mm diameter screw partially improves the pull-out strength to 59.3% of the baseline. Surgeons should consider the use of “two-finger tight” torque when inserting a screw to avoid stripping.

中文翻译：

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用更大的螺钉修正松动的松质螺钉不会恢复原始的拔出强度——一项生物力学研究

背景

松质螺钉固定常用于骨折固定。当该螺钉拧得过紧时，会涉及对骨骼的损害以及其他非线性过程，例如骨折和构造失败。本研究的目的是 (1) 确定松质螺钉旋转时拔出强度的降低和 (2) 确定通过修改更大直径的螺钉可以恢复多少拔出强度。

方法

使用合成聚氨酯泡沫 (320 kg/m ³ ) 进行了一项生物力学研究，以评估 (1) 6.5 mm 松质螺钉的拔出强度，(2) 松开的 6.5 mm 松质螺钉的拔出强度和 ( 3) 用 7.3 mm 松质螺钉修正了松动的 6.5 mm 松质螺钉的拔出强度。

发现

6.5 mm 松质螺钉的基线拔出强度为 2213.91 ± 200.51 N。一旦发生旋转，拔出强度会降低 79.1% (463.79 ± 99.95 N) ( p  = 0.027)。将旋转的 6.5 mm 松质螺钉修改为 7.3 mm 松质螺钉时，拔出强度增加到 1313.65 ± 93.23 N，是基线拔出强度 (2213.91 ± 200.51 N) 的 59.3% ( p  = 0.027)。

解释

松动的 6.5 mm 松质螺钉会导致拔出强度降低 79.1%。通过插入直径为 7.3 mm 的较大螺钉来修正松动的松质螺钉，部分地将拔出强度提高到基线的 59.3%。外科医生在插入螺钉时应考虑使用“双指拧紧”扭矩以避免剥离。