Comparison of Force Causing Breakage of Short Leg Posterior Slabs Done by Edge-folded and Edge-trimmed Types

Abstract

Comparison of Force Causing Breakage of Short Leg Posterior Slabs Done by Edge-folded and Edge-trimmed Types

Damrong Thapanakulsak MD

Department of Orthopedics, BMA Medical College and Vajira Hospital

Objective: To compare the force causing breakage of the short leg posterior slabs done by edge-folded and edge-trimmed methods.

Study design: Experimental study.

Subjects: Five short leg posterior slabs with edge-folded heels and 5 short leg posterior slabs with edge-trimmed heels.

Methods: All short leg posterior slabs were prepared by molding each gypsum cast, measured 6 inches wide x 21 inches long x 10 layers thick, over a short leg model. The edges of the slab were either folded or perpendicularly trimmed the redundancy along the heel before molding. The slab was allowed to dry for 3 days before measuring its thickness. Forces, generated from the compressing machine were applied to each slab at 3 points until the slabs were broken. The forces causing slab breakage and thickness at the heel of two types of the slabs were compared.

Main outcome measures: Forces causing slab breakage and thickness at the heel of the slabs.

Results: Median thickness at the heel of the edge-folded slab was significantly thicker than that of the edged-trimmed slab, 15.1 mm. and 10.2 mm. respectively (p-value = 0.009). However, the median forces causing the edge-folded slab to be broken was significantly lesser than that to the breakage of edged-trimmed one, 655 newton and 1680 newton respectively (p-value = 0.003).

Conclusion: Short leg posterior slabs with edge-trimmed heels are tougher than ones with edge-folded heels despite less thickness at the heel of the slabs.

Vajira Med J 2009 ; 53 : 267-271