Below knee cast stresses and intra-cast pressures during normal walking

Twenty-one tests on 13 volunteer subjects were used to quantify cast stresses and intra-cast pressures in below knee casts during normal walking. A microcomputer and force plate system were used to study the gait with various cast configurations. It was found that stresses were high where expected but also in less obvious locations, i.e. anterior and posterior aspects of the upper part of the cast. The data suggest that, irrespective of the design of the cast (as long as it is well fitting), control of rotation will be sufficient. This also validates the use of an articulating ankle component in most situations, although this type of cast provides less rotation control. If a fixed ankle is used then the casting material should be concentrated around the junction of foot and shank cylinders and less on the shank (only sufficient to provide rigidity). Comparison of different materials indicates that use of modern casting materials requires more emphasis on splint construction details than when using conventional plaster of Paris.