PT Classroom - Serial Casting with Anterior Cut-Out to Increase Dorsiflexion ROM ׀ by Nancy Hylton, PT, LO

Serial Casting with Anterior Cut-Out to Increase Dorsiflexion ROM

In In our more than 30 year history using AFOs in children with Cerebral Palsy at Children’s Therapy Center of Kent, Washington, we have found that a minumum of 90 degrees of ankle ROM into dorsiflexion is needed for optimal Dynamic AFO fit. Full weight bearing over the affected limb and the ankle movement permitted by this style of AFO will encourage the acquisition of the additional 10 degrees of tibial motion over the foot necessary for typical progression in mid-stance. Occasionally, children with Cerebral Palsy, especially very active hemiplegic or diplegic patients, arrive for orthotic consultation with limited functional ankle dorsiflexion, R2 (maximum ankle dorsiflexion reached by the examiner) greater than 90 degrees with knee extended. This increased muscle tightness and functional shortening is most often associated with periods of rapid long bone growth and the inability of the muscle to stay on active stretch long enough for the muscle to adapt its length to the new bone length.

The plantarflexor group is one that typically can become shortened in this situation, restricting the typical movement needed to advance the body over the foot in walking. Increased dynamic tension in the plantarflexor group can be a compensation for different primary deficits, including medial-lateral ankle and rearfoot instability, and unpredictability of knee control and fear of knee collapse during weight bearing. The first instance is related to the normal ankle and rearfoot stabilizing function of the soleus in weight bearing, and the second to the a primary function of the gastrocnemius as a knee extension stabilizer in weight bearing. In a person with motor control deficits, these functions can cause excessive concentric activation of the muscles and over-flow to other groups in an attempt to stabilize the ankle or knee. Typically, eccentric muscle control is used to manage these functions.

Serial casting is an established therapeutic tool to assist functional muscle growth and soft tissue tension reduction associated with rapid long-bone growth in Cerebral Palsy. Serial casting is designed to put specific muscle group on active prolonged stretch to stimulate adaptive muscle growth to re-establish more optimal length-tension relationships. In children with Cerebral Palsy, the eccentric and isometric muscle contractions associated with active stretch and prolonged stretch appear to be more difficult than concentric muscle contractions. This and problematic increased dynamic tension puts children with spastic cerebral palsy at higher risk for decreased muscle growth adaptation during and after long-bone growth spurts.

Our particular style of short-leg serial cast incorporates an anterior cut-out which permits an additional 5 to 10 degrees of motion into dorsiflexion within the cast in weight bearing. Very precise use of ¼ inch thick casting felt permits a very tight fit with good protection for bony prominences. The use of an initial layer of soft cast (3M Soft-cast) provides compression which quiets hypertonus and initial positioning of the foot and ankle. This is followed by a layer more rigid fiberglass cast (Delta-lite Rigid) for durability and final positioning. The anterior opening is cut-out approximately 3 inches above the ankle bend and permits excellent stabilizing and seating of the heel with controlled motion into dorsiflexion. Protection of the tibia is provided by an extra 1/4th inch felt cast padding at the edge of the cut-out. The heel, malleoli and dorsum of the foot are protected during the movement into dorsiflexion by the very precise use 1/4th inch thick casting felt mentioned above.

As a key component of our style of serial casting, children are encouraged use active weight-bearing and balancing exercises order to use the muscles in a lengthened range and to strengthen more typical movement and weight-bearing strategies in the casted leg. Therapists and parents understand that this time in the cast is a “window of opportunity” to develop more typical sensori-motor strategies and strength, so children are encouraged to be as active as possible to take maximum advantage of the time in the cast. This combination of active or active assisted weight-bearing strategies and anterior cut-out to permit additional motion into dorsiflexion, appears to produce more rapid improvements in functional range of motion and less post-casting weakness in the children. A standard canvas cast boot with flat rubber sole is use to maximize traction and balance during weight bearing.