Optimal plaster conformation derived using a custom-made jig to obtain maximum strength of protective plaster of Paris for hand surgery.

BACKGROUND: Surgical repair of soft tissue trauma in the upper limb frequently requires postoperative immobilization to prevent tension across repaired tendons, vessels, or nerves. A plaster of Paris backslab, placed on either the volar or the dorsal surface, is frequently used, as it is inexpensive and easy to apply.
METHODS: In an effort to improve upon the strength of plaster of Paris backslabs, we designed a custom-made jig to subject angled backslabs (n = 5 per group) of various designs to a torsional force. We tested 10-layered backslabs with 0, 1, or 2 ridges and 15-layered backslabs without ridges.
RESULTS: We demonstrate that the addition of longitudinal reinforcing ridges on the convex surface of backslabs can improve simple backslabs in terms of breaking strength, plaster stiffness, and failure load. The optimal design employs a single, centrally placed ridge, which provides the maximum support in the axis of the net force acting across the angle, the fulcrum of angle backslabs. The formation of two parallel longitudinal ridges does not offer any additional support.
CONCLUSIONS: Backslabs can be strengthened significantly by placement of a single reinforcing ridge. This allows plaster weight and thickness to be kept to a minimum, reducing the setting time of the plaster and contributing to patient comfort. These findings demonstrate the ideal construction of angled plaster of Paris backslabs for the protection of soft tissue repairs.