Effect of the starting point of half-pin insertion on the insertional torque of the pin at the tibia

Abstract

Purpose: The authors have observed a failure to achieve secure fixation in elderly patients when inserting a half-pin at the anteromedial surface of the tibia. The purpose of this study was to compare two methods for inserting a half-pin at tibia diaphysis in elderly patients.

Materials and methods: Twenty cadaveric tibias were divided into Group C or V. A half-pin was inserted into the tibias of Group C via the conventional method, from the anteromedial surface to the interosseous border of the tibia diaphysis, and into the tibias of Group V via the vertical method, from the anterior border to the posterior surface at the same level. The maximum insertion torque was measured during the bicortical insertion with a torque driver. The thickness of the cortex was measured by micro-computed tomography. The relationship between the thickness of the cortex engaged and the insertion torque was investigated.

Results: The maximum insertion torque and the thickness of the cortex were significantly higher in Group V than Group C. Both groups exhibited a statistically significant linear correlation between torque and thickness by Spearman's rank correlation analysis.

Conclusion: Half-pins inserted by the vertical method achieved purchase of more cortex than those inserted by the conventional method. Considering that cortical thickness and insertion torque in Group V were significantly greater than those in Group C, we suggest that the vertical method of half-pin insertion may be an alternative to the conventional method in elderly patients.

Keywords: Fracture; diaphysis; external fixation; tibia.

Fig. 1

Cross-section of the right tibia diaphysis. A, anterior border; I, interosseous border; M, medial border.

Fig. 2

Schanz screw (5.0×120-mm; thread length=40 mm).

Fig. 3

Orientation of Schanz screws inserted by the conventional method and vertical method. C, conventional method, from the anteromedial surface to the interosseous border; V, vertical method, from the anterior border to the posterior surface.

Fig. 4

Torque driver for measuring the insertion torque of the Schanz screws.

Fig. 5

Cortical thickness at the cross-section of the tibia diaphysis. A, anterior border of the tibia; M, medial border; I, interosseous border. Blue arrow: cortical thickness in Group C. Red arrow: cortical thickness in Group V.