Department of Orthopaedic Surgery
Stellenbosch University

Page 4 Cast Modifications   Home   << Start

Plaster Casts and Splints

Windows in casts

There are times when it is necessary to inspect wounds under casts, and making windows to do so seems reasonable. If at the time of cast application such a window is known to be necessary, it is a good plan to apply a large bolus of dressings over the wound, so that it sticks out. One may then take a sharp knife and cut around the periphery of this wad, leaving an oval hole. A rectangular hole cut with a saw makes the cast weak, because the corners act as stress risers. The cast might reasonably be reinforced by a dorsal fin to make up for the weakness of the open section. If the window is made to inspect a wound - plaster it closed again after the inspection to avoid a fracture in your cast. If a tibial wound needs regular access eg a skin graft or flap over a open fracture consider an alternative to a window such as exoskeletal fixation.

Windows in casts are hazardous if left open, especially if there is any tendency for the limb to swell. The soft tissue may herniate through the hole, becoming grossly edematous, and the skin tends to break down from the pressure produced by the margins of the defect. To avoid this complication, we generally cut a piece of felt or sponge rubber to the size of the hole and bandage this snugly in place over the dressings with an elastic bandage to provide uniform compression.

Wedging of a cast

After an attempted closed reduction and the application of a circular cast, there may be some residual varus or valgus angulation or posterior bow. Under these circumstances, it is quite permissible to make a transverse cut two thirds of the way around the cast (leaving a hinge opposite the convexity of the angulation)
Agulated tibia
Angulated Fracture
Cutting the plaster
Cutting the POP
and open up the cut until the angulation is adequately corrected. The cut edges of the cast must then be everted with molders, or, if these are not available, pliers. Little blocks of wood or corks to are placed hold the wedge open. Make sure these do not exert pressure on the unserlying skin. We generally pack some sheet wadding in the defect and repair the cast while holding the limb in the corrected position. To gain the greatest mechanical advantage, the wedge should be made at the point where the central long axes of both fragments intersect; this point can be ascertained by drawing the appropriate lines on the x-ray film. Wedging can correct angulation but not shortening or rotation. We find the greatest use for wedging in fractures of the tibia, where the correction tends to be comparatively small. If large corrections are to be made, a combination of an opening wedge on the concave side and closing wedge on the convex side is safer, because a large opening wedge will elongate the cast and apply undue pressure on the dorsum of the foot. However, if large corrections are necessary, we usually apply a new cast.
Cast is wedged open
Cast is corrected to predetermined angle
Post reduction Xray
Post reduction

Splitting a plaster cast

A cast is rigid and cannot compensate for swelling of the limb. If there is any danger of swelling ie most fresh fractures the cast must be split. Avoid circular casts in fresh fractures about the elbow and knee
- rather use an back-slab as the initial plaster.
Use a plaster saw or shears to split the cast( and cut through all padding too). In a forearm fracture make the cut on the Ulnar border. If loss of reduction is feared after the swelling subsides the cut can be railroaded. (a 25 mm track is cut out) A week later a bandage can be applied over the plaster to compress it over the shrunken limb.