Properties of a hybrid plaster-fibreglass cast

OBJECTIVE: To examine the suitability of a plaster-fibreglass hybrid cast f or orthopedic applications, comparing them to plaster of Paris (POP) and fi breglass constructs. METHOD: Groups of 10 standardized hybrid, POP and fibreglass casts were stu died. An Instron servohydraulic system was used to test the casts in 3-poin t bending and shear. OUTCOME MEASURES: Strength, stiffness, weight, thickness and cost of the 3 types of cast, and shear strength at the interface between the POP and fibr eglass in the hybrid casts. RESULTS: The hybrid casts were twice as strong as the POP constructs, were stiffer and weighed 14% less but were thicker and cost 2.5 times more. They were almost as strong as and less than half the cost of the fibreglass con structs but were thicker, not as stiff, and weighed 42% more. The shear str ength of the POP-fibreglass interface in the hybrid casts was higher than t he 3-point bending strength of this construct by a factor of 3. CONCLUSIONS: Plaster-fibreglass hybrid casts should be considered for ortho pedic use on the basis of their strength, stiffness, weight and cost, combi ned with their ackno vi ledged advantages of good moulding ability and wate r resistance.