Executive Editor: Chris Colton

Authors: Florian Gebhard, Phil Kregor, Chris Oliver

Distal femur 33-B3.2/3 Long leg cast - hinged knee brace

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Glossary

1 Principles top

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Common deformity

It is recognized that perfect realignment of a displaced distal femoral fracture will be impossible with a long leg cylinder splint. However, it helps to bring the fracture out to length and to correct some of the common hyperextension deformity.

Note: If the splint is not able to control the length adequately, this would be an indication for tibial skeletal traction, when a spanning external fixator could not be made available for provisional stabilization.

The surgeon applying the long leg splint must remember that the common deformity of a supracondylar femoral fracture (A- or C-type fractures) is shortening and hyperextension of the distal fragment. In order to counteract the hyperextension, either a bolster can be placed under the supracondylar region, or preferably the knee can be sufficiently flexed by bringing the leg off the end or side of the table.

In order to maintain the length of the fracture in the long leg splint care must be taken to provide good supracondylar molding.

2 Preparation top

Material

To apply the long leg circular cast, the following materials are needed:

  • A stockinette, or tubular gauze bandage
  • Scissors
  • Cotton wool, or dedicated under-cast padding
  • Plaster-of-Paris bandages, which come in rolls of varying widths
  • Plaster slabs, generally five layers thick, and available in differing widths
  • Water, or another wetting agent

The water should be tepid, or lukewarm, with an ideal temperature between 22° and 25° C.

It should be noted that colder water, or a bandage that is wetter, will allow for an increased working time, while warmer water, or a bandage that is drier, reduces the working time.


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Patient positioning

The patient should be lying supine, with the ankle over the edge of the table. The foot should be plantigrade.

The patient’s knee should be flexed to approximately 20-35°, which will relax the gastrocnemius muscle. This will reduce the hyperextension.

The buttock on the side of the injury should be elevated from the table with a bolster, if possible.

3 Reduction top

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The long leg cast is generally applied several weeks after the fracture has occurred. Nonetheless, the surgeon should be aware of the tendency of the fracture to shorten and to fall into hyperextension. Manual traction, as depicted, can counteract the tendency for shortening, as previously described. A bolster placed beneath the supracondylar region will counteract hyperextension deformity.

4 Padding top

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Leg support

After reduction, an assistant supports the leg, and checks to ensure that there is no rotation of the fracture, by verifying that the second toe, patella and superior iliac spine remain in line.

The distal edge of the cast will be located at the level of the metatarsal heads, while the toes should remain free.

The proximal edge lies just below the greater trochanter on the lateral side, and just below the groin on the medial side.

Take care to avoid pressure over the fibular head and neck area, to prevent pressure on the common peroneal nerve that could cause neurapraxia, or nerve damage.


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Stockinette application

Apply a stockinette and cut it slightly longer than the final cast will be.


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Cotton wool padding

Starting at the distal border, gently wind on the cast padding, once around the foot and then around the ankle several times in a figure-of-eight. Make sure that the edge does not cut into the 90° bend of the ankle.


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Wind the cast padding towards the knee, with an overlap of 50%.

The overlap creates a double layer of padding, which is sufficient in most cases.

The cotton wool extends slightly beyond the planned length of the cast, so that when the end of the stockinette is folded over, the end of the cast will be padded.


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Additional padding

Apply additional cast padding over the patella, the malleoli and over the heel, to protect the pressure points against pressure sores.

It should be kept in mind that, when more padding is applied, there will be less support to the injury site.

5 Plaster application top

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Plaster bandage

Dip the plaster bandage into the water and remove the excess moisture by gently squeezing the bandage.

Starting with the bottom of the foot, wrap the plaster bandage around the ankle in a figure-of-eight.


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Pass the bandage over the heel and then towards the knee with a 50% overlap, in the same manner as the cotton wool.

In this case a 200 mm wide plaster bandage is used. A 150 mm wide bandage may also be used, however, it will take longer to apply.


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Additional plaster bandage

Apply a second plaster bandage beginning over where the first one ended.

It continues proximally towards the planned upper edge of the cast and then returns towards the ankle.

As additional plaster bandages are required, they should begin with the end of the previous one, in order to ensure even thickness of the cast.


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Gaining cast strength

To strengthen the cast, apply plaster slabs to both the anterior and posterior aspects.

A third slab may also be applied to reinforce the proximal edge.


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Forming the proximal end of the cast

Fold the loose end of the stockinette over the proximal edge of the cast.

Starting just below the proximal edge add another plaster bandage. This will secure the loose end of the stockinette and the plaster slabs.


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Knee flexion

You may now place a pillow under the patient’s leg, although the knee should continue to be supported manually.

Knee flexion of 20-35° will relax the gastrocnemius, as previously discussed. This can be accomplished by a bolster or pillow underneath the supracondylar region, or by bringing the leg off the side, or end, of the table.


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Forming the distal end of the cast

Note the extra plaster covering the toes. This ensures adequate support for the metatarsal heads.

Remove the excess plaster with the scissors and fold the stockinette over the distal end of the cast.


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Apply another plaster bandage to secure the ankle and the loose end of the stockinette at the distal edge.

As before, apply it in a figure-of-eight around the ankle.

Attempts should be made to ensure that the foot is at 90° to the lower leg. If the foot drops into equinus, it will be difficult to correct a soft-tissue deformity later.


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Final molding

While the plaster is still soft, mold it gently to the curve of the tibia and around the knee. In addition, a supracondylar mold is important for the cast to control the length of the limb.

Check to ensure that there is no rotation of the fracture, by verifying that the second toe, patella and superior iliac spine remain in line.

To ensure that the foot is plantigrade, apply gentle pressure to the sole of the forefoot.

The pressure should be continued until the plaster hardens. However, the plaster will not achieve full strength for 36 hours.


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Completed cast

The application of the long leg circular cast is now complete.

v1.0 2008-12-03