70.7 Windowing casts and wedging them

Windows

If a patient has an open fracture, a soft tissue injury, or osteomyelitis, you may occasionally need to make a window in his cast, so that his lesions can be dressed. Fortunately, most wounds and sinuses don’t need a dressing, because plaster readily absorbs pus and blood. Avoid a window when you can because: (1) if a patient walks about, his tissues may swell and herniate through it, so that his wound will not heal, and (2) windows which are not closed and strengthened can weaken a cast so much that it bends with each step he takes.

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Figure 70.7: ALTERATIONS TO A CAST. A, if a cast is pressing on a patient’s heel, you can open it with a saw, and then repair the cut with plaster bandages. B, to E, the easiest way to make a window is to put some dressings over the lesion, make the cast, saw off the bulge, and then repair the cast. Kindly contributed by John Stewart.

Wedges

If a patient’s fractured forearm or lower leg is angulated inside a cast, you can straighten it in two ways, provided the fragments have not yet united: (1) You can open or close a wedge in the cast. This is not as easy as it looks because you may make a wrinkle inside the cast which will cause a pressure sore. So wedging needs care and skill! (2) You can wait until his fracture is healed enough not to displace, but is still soft enough to be bent. This is 3 to 6 weeks after the injury in an adult, and sooner in a child. You can then remove the old cast, straighten the patient’s limb under anaesthesia, and apply a new cast. If you don’t have X–rays, always use this method. Changing a cast is safer than wedging it, but if you are very short of plaster you may have to wedge it.

Opening a wedge is easier; it lengthens a cast slightly, and if the fragments are overlapped, it helps to distract them. Closing a wedge by cutting a piece out of a cast and then closing up the gap is more difficult, and is less often necessary. It closes up the fragments a little, so it is useful if they are distracted.

AVOID WINDOWS IF YOU CAN DON’T LET WEDGES CAUSE PRESSURE SORES

WINDOWING A CAST

Make the windows as small as is conveniently possible, as in Fig. 70-7. Put a firm ball of cotton wool over the lesion where you want a window, and make the cast over it. While the cast is still soft, hold a knife parallel to the patient’s skin, and cut off the swelling over the wool, so as to make the window. Or, cut a square hole in a dry cast with a plaster saw.

Prevent the tissues of the lesion herniating through the window by raising the limb and by applying a firm pressure dressing through the window. This acts like a piston in a cylinder and helps to prevent herniation. Dress the wound and plaster over the window to strengthen the cast.

WEDGING A CAST

Study the X–rays and plan the geometry of what you intend to do carefully. Draw a line round the cast where you want to cut.

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Figure 70.8: OPENING A WEDGE. Obtain some small blocks of wood to hold the wedge open. Cut through the whole circumference of the cast except for 2 or 3 cm on its convex side, so as to leave a hinge on which it can bend (A, and B). Make the cut about 2 cm proximal to the fracture (C), so that if there is a wrinkle inside the cast, it will not be directly over the fracture, where it may erode the skin. Use a saw or plaster knife. Cut down to the padding, and not into the limb! Carefully bend the cast the way you want it- If necessary hold it open with a block of wood (D), but make sure that the block is clear of the skin. Then repair the cast with a few turns of plaster bandage (E). X–ray the limb to check alignment. Kindly contributed by Peter Bewes.

OPENING A WEDGE is better than trying to close one, because you are less likely to make a wrinkle inside a cast that will cause a pressure sore. Do this as in Fig. 70-8.

CLOSING A WEDGE On the side of the cast which is to be made concave, mark out a wedge about 1 to 3 cm across at its widest part. Cut out the wedge, and gently bend the cast so as to close the wedge. Repair the cast with some turns of plaster bandage. X–ray the limb to check alignment.

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Figure 70.9: THE GEOMETRY OF WEDGING. A, the angulation that requires correction. B, if the wedge is far from the fracture a small movement will correct the displacement. B, if the wedge is near or over the fracture, a larger movement is necessary. Kindly contributed by Peter Bewes.

If more than one wedge is needed in different planes, replace the cast. CAUTION! Wedge a limb, especially an arm, with care—it can precipitate Volkmann’s ischaemic contracture. Watch the circulation in the limb carefully afterwards.