Effects of Various Modified Heel Slab Techniques on the Strength of Short Leg Posteri

Abstract

Effects of Various Modified Heel Slab Techniques on the Strength of Short Leg Posterior Slab

Damrong Thapanakulsak MD

Deparment of Orthopedics, Faculty of Medicine Vajira Hospital, University of Bangkok Metropolis

Objective: To study the strength of short leg posterior slabs done by edge-folded, edge-cut-folded, edge-cut-tangential, edge-cut-off and edged-cut-folded-back heel techniques by comparing the forces causing breakage in 3-point-bending loads.

Methods: Five types of short leg posterior slabs were prepared as the following: short leg posterior slabs with edge-folded heels (group 1), with edge-cut-folded heels (group 2), with edge-cut-tangential heels (group 3), with edge-cut-off heels (group 4), and with edge-cut-folded-back heels (group 5). There were 20 slabs in each group or altogether 100 slabs. Each slab was prepared by molding each gypsum bandage, measuring 6 inches wide x 21 inches long x 10 layers thick, over a short leg model. In group 1, the redundant edges of slabs were folded along the medial and lateral aspects of the heel before molding. In group 2, the redundant edges of slabs were perpendicularly cut and folded along the medial and lateral aspects of the heel before molding. In group 3, the redundant edges of slabs were tangentially cut off along the medial and lateral aspects of the heel before molding. In group 4, the redundant edges of slabs were cut off 6 cm along the medial and lateral aspects of the heel before molding. In group 5, the redundant edges of slabs were perpendicularly cut proximally and distally at 6 cm away from the medial and lateral aspects of the heel and folded back along the heel before molding. Each slab was air-dried for 3 days before its thickness and height of the edges over the heel were measured. The strength of each slab was tested by measuring the forces, generated from the compressing machine, causing breakage in 3-point-bending loads.

Results: The edge-folded slabs (group 1) had the thickest edge compared to other groups (p-value < 0.001) with mean thickness of 13.5 ฑ 0.8 mm while the edge-cut-folded slabs (group 2) had the highest edge with mean height of 72.1 ฑ 2.3 mm (p-value < 0.001). The edge-cut-folded slabs (group 2) were the strongest type with the greatest force causing slab breakage in 3-point-bending loads of 1200.3 ฑ 300.8 newton (p-value < 0.001).

Conclusion: The strength of short leg posterior slabs with edge-cut-folded heels was the best among the five modified heel slabs.

Keywords: short leg posterior slab, strength, modified heel