Background Loss of plaster integrity is linked to failure to maintain fracture reduction and pain. Adding plaster layers makes the construct more cumbersome. This biomechanical study applied the engineering principle of the reinforcement strut to pragmatically designed dorsal wrist backslabs to investigate the effect on flexural strength.

Methods Ridged and non-ridged 8-layered casts were created using an investigator's wrist (n = 24). Failure load was recorded in simulated wrist flexion and extension. Failure of the cast was defined by the point of plastic deformation. Force was compared using student's t-test and effect size.

Results There was no significant difference in backslab dimensions. Ridged casts had a 1.6 times greater failure load in extension compared to non-ridged casts (p < 0.001; Cohen d = 3.42). In flexion, ridged cast failure load was not significantly stronger than in non-ridged (1.15 times, p = 0.16). Variance in failure load was greater in ridged casts (p = 0.003).

Conclusions Adding a longitudinal ridge to dorsal wrist backslabs increases its strength in wrist extension but not in flexion. The benefit conferred by the ridge likely varied due to minor random differences in ridge height. The present technique may be a simple, lightweight and cost effective method of increasing the strength of wrist backslabs without needing to layer additional reinforcement plaster.