The Neutral Position Casting Technique
Prior to applying the plaster splints, always pre-position the patient and briefly hold the foot to establish the proper casting position. It is important to make any significant patient positioning adjustments before applying the plaster splints. Attempting to position the patient after the plaster splints have been applied may result in a casting error. For that reason, the patient positioning procedures and foot gripping technique will be described in detail before the plaster application process is described.
Patient and Chair Positioning
Place the patient in the supine casting position. The patient should be as comfortable and relaxed as possible. In a treatment room setting, the backrest of the casting chair should be reclined at to a comfortable angle (approximately 30 to 60 degrees from vertical). The seat should be inclined about ten degrees so that the knee can be slightly flexed to reduce hamstring tension and promote comfort (see figure 5).
Adjust the chair so that leg rest and tibia are parallel to the floor. The tibia may be placed in a slightly declined position (ie. the distal aspect may be slightly lower than the proximal aspect). Important: The tibia should not be declined much beyond a five degree angle to the floor, as doing so will result in an increased dorsiflexion force acting on the foot as the foot is lifted into the casting position. Never incline the tibia or leg rest (ie. never place the distal aspect of the tibia higher than the proximal aspect of the tibia). Inclining the tibia can result in a plantarflexion force acting on the forefoot during casting. This may cause the MTJ to become supinated due to simultaneous plantarflexion and adduction of the forefoot on the rearfoot when the foot is held in the casting position. This casting error is commonly referred to as supination of the oblique axis of the MTJ and it is one of the more common casting errors.
The chair or table should be raised so that the patient’s toes are only a few inches below the height of the practitioners chin when the foot is held in the casting position. This will place the practitioner’s arm and shoulder in a very comfortable position during casting. If it is not possible to raise the casting chair high enough, it may be necessary for the practitioner to sit while casting in order to avoid having to incline the tibia or bend at the waist while casting. Bending at the waist while casting is not only fatiguing and uncomfortable but tends to result in casting errors due to improper alignment of the foot by the practitioner. If it is necessary to sit while casting, be sure to achieve the same relationship between the practitioner’s upper body and the patient’s foot that is described herein for casting while standing.
Foot and Leg Positioning
- Grasp the lateral aspect of the forefoot and apply a mild dorsiflexion force. Rotate the entire foot until the long axis of the foot is approximately vertical (ie. parallel to the patient’s sagittal plane).
- It may be necessary to internally or externally rotate the leg in order to bring the long axis of the foot into a vertical position. If necessary, have the patient shift their weight onto their opposite hip in order to internally rotate the leg to the point where the foot is vertical when the STJ is in the neutral position. The patient must be able to fully relax and should not actively assist in maintaining their foot and leg position. If excessive external leg rotation occurs when the patient relaxes, it may be necessary to support the hip on the side being casted with a sand bag, wedge, or pillow to prevent excessive external leg rotation.
- With the STJ in the neutral position, fully pronate the MTJ and apply a dorsiflexion force to the plantar surface of the forefoot to create dorsiflexion motion at the ankle joint. Increase and decrease the amount of dorsiflexion force on the forefoot and look for any evidence of STJ motion or tibial rotation. Rotate the tibia as necessary so that dorsiflexion of the foot occurs with the least amount of STJ motion or tibial rotation. It may be necessary to adjust the position of the hip. Be sure that the patient is completely relaxed from the hip down and that they do not attempt to assist in positioning their foot or leg, except when instructed to do so. Contrary to popular belief, the frontal plane position of the patella is not important during casting. The goal is to create stability between the foot and leg so that the MTJ will remain fully pronated while the STJ is held in the neutral position during casting. The patella may assume any position provided the STJ remains in the neutral position and the MTJ is fully pronated. On rare occasion, it may be necessary to have an assistant stabilize the leg during casting to prevent leg rotation or STJ motion if it can not be prevented by other means.
- The ankle should remain lax and the foot should be in a plantarflexed position at the ankle joint. The foot will remain approximately 10 to 20 degrees plantarflexed at the ankle joint during casting. Due to the plantarflexed position of the foot and passive tension in the achilles tendon, gently lifting the forefoot during casting will create a midtarsal joint pronation and ankle joint dorsiflexion force. No additional force is typically required to pronate the MTJ during casting. It is not necessary to create a perpendicular relationship between the foot and leg. Attempting to do so may cause the STJ to pronate, resulting in a casting error.
- Instruct the patient to completely relax and inform them not to converse during casting so that they can focus on relaxation. Promote total relaxation of the entire body and especially the leg. Instruct the patient to “Totally relax your leg from the hip down”. Many patients find it easier to relax when they close their eyes and they should be made comfortable in doing so. Be observant and confirm that the foot is not being held up by contraction of the anterior tibial muscle. If you observe that the patient is attempting to assist you by holding their foot up, instruct them to “just let your foot drop”. It is important to observe and feel for patient assistance throughout the entire casting process. Assistance by the patient can cause inversion of the forefoot on the rearfoot or what is commonly referred to as supination about the longitudinal axis of the MTJ. A false forefoot varus can be the result of insufficient patient relaxation or inadvertent inversion of the forefoot by the practitioner. Without the patient’s knowledge, you can check to see if they are assisting you by very slightly reducing your lift on the forefoot. This will decrease the resulting dorsiflexion force on the forefoot during casting which should result in instantaneous and very slight plantarflexion motion of the entire foot at the ankle joint. If you do not notice immediate plantarflexion of the entire foot, then gently instruct the patient to “relax and let your foot fall, let me do the work”. Check again for relaxation. Be sure to complete this simple check immediately after final positioning of the foot but before the splints begin to set so that the foot can be repositioned if necessary.
