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Challenging Current Practices and Beliefs in using AFOs for Pediatric Patients with Cerebral Palsy


For years pediatric patients diagnosed with cerebral palsy have been managed with standards of practice and beliefs that are now being challenged by new paradigms and research. Clinicians have held to beliefs and practices such as: AFOs should be fabricated to a vertical anatomical alignment in the shoe, AFOs have little or no effect on hip stability, the gastrocnemius (GN) must be strong if the child has an equinus deformity (EQD), accommodating an EQD will not decrease the plantar flexion (PF) contracture, articulating AFOs help reduce PF contractures, AFOs prevent foot deformities and "tone reducing" modifications reduce tone and spasticity. This article will address these existing beliefs of current practice and the new paradigms that have begun to challenge them as myths.

Joint Alignment Myths

One common belief is that the ankle or talocrural joint (TCJ) should be in neutral (90 degrees relative to the floor) resulting in a vertical tibial "neutral" alignment of the AFO when in the shoe. Vertical tibias only exist for a brief moment just prior to midstance in the developed gait and in the pre and early walking patient1. Vertical tibias allow the toddler to explore the frontal plane, stabilize the ankle, build strength and practice weight shifting prior to them learning how to walk and move their tibias in the sagittal plane. In the ambulatory patient a bench alignment in the shoe to verticality will place the weight line too far posterior in relation to the base of support. This posterior displacement will create compensatory flexion at the knees and hips and hyperlordosis of the lumbar spine to achieve and maintain upright stability. The other important factor here is that a predetermined vertical tibia gives no reference to the actual GN length of the patient. This disregard for the GN length can produce a serious negative compensatory pattern for the patient as they reach midstance. Elaine Owen talks extensively about the mutual independence of the patient's actual ankle angle as a measure of the available GN length and the shank to vertical angle (SVA) that is needed to have proper shank kinetics and kinematics during the gait cycle (GC)2. Ignoring the GN length is a significant error in the treatment of any patient with respects to AFO management.

The hip is often neglected when talking about AFO management of the LE. Clinicians often insufficiently address the hip dynamics or the understanding of the influence that distal orthotic alignments can have on hip joint ROM and stability. If tibial advancement is halted to verticality in midstance and is not allowed to achieve a determined degree of inclined SVA, the patient will compensate with hip flexion and possible instability at the hip. Through proper tuning of the AFO with the shoe it is possible to get the ground reaction force (GRF) closer to the knee and hip joint centers. This allows the GRF to move anterior to the knee and posterior to the hip joint axes resulting in correctly timed hip and knee extension at terminal stance. (Figure 1 ) This hip extension moment occurs in opposition to the inguinal ligaments and will result in hip stability and maintenance of hip joint range of motion through the critical phases of weight transfer during walking.

Muscle Myths

As the patient develops GN tightness the belief is that the muscle must be strong to produce and solidify this EQD. It has been shown through muscle strength testing using a dynamometer that all muscle groups tested in children with CP were weaker than those of their nondisabled peers3. When the GN acquires a shortened position, it is unable to generate significant power during the GC. Clinical findings show that the muscles recruited for upright maintenance gradually transform by shortening and stiffening, this results in an already weakened muscle becoming even weaker.

When considering TCJ neutral alignment it is often accepted that if the AFO is set in PF it will capture or increase the existing contracture. There is no evidence of this and in fact serial casting refutes this myth 4 . When casting for an AFO, the orthotist must respect the length that the GN is capable of providing and not force a sagittal plane alignment even if the ankle angle is in residual PF. This respect for the patients GN length will allow them to use the available extensibility of the GN and through proper tuning of the AFO and the shoe, (Figure 2 ) chronic tonic recruitment of the GN at loading response (most commonly as a result of no heel loading and a dorsiflexion moment from a forefoot strike) is relieved. This reeducation allows the GN to be used more optimally during stance phase instead of being recruited (out of phase) for upright stability.

One of the most ubiquitous beliefs is that an articulating AFO with a PF stop and free dorsiflexion will correct an EQD by stretching out the GN during standing and walking. There is no clinical evidence of this outcome and in fact this leads to all the major fitting problems commonly observed in these types of AFOs. This AFO design is incapable of controlling the forces within the plastic when the GN is shortened. As the tibia is halted by the short GN, the calcaneus will be held in relative PF and eventually evert. Once this happens, the talus will drop off the sustentaculum tali and travel "down and in".

This creates an internal rotation as the tibial has no choice but to follow the talus through the bony lock the talocrural joint dictates. Now the foot is no longer congruent and it is in a position of instability with no chance to recover. The clinical telltale signs are; redness over the navicular, medial malleolus, distal 5th metatarsal shaft and base. The AFO is now relegated to trying to halt the resulting foot deformity as the midfoot has substituted for the forefoot rocker.

In fact, it could now be argued that such poorly designed AFOs can create foot deformities rather than prevent them.

The holy grail of beliefs is that "tone reducing" modifications within an AFO help reduce tone and spasticity. In some instances, it is irrefutable that reduced tone is observed with the application of such AFOs, but the cause and effect cannot be proven when referring to these modifications. There is no clinical evidence that these unique bumps and pads reduce tonic reflexes. However if the resistance of rapid elongation of the shortened GN is reduced and its extensibility is increased, the argument could be made that the tone in the muscle has been reduced.4

Myth Busting

The good news is that through the research and clinical practice of therapists and clinicians like; Beverly Cusick, Elaine Owen, Davin Heyd, Bryan Malas, Donald McGovern and others, new paradigms are emerging and old beliefs and practices are becoming myths. It is important for the orthotist to evaluate the CP patient more closely and determine the individuals GN extensibility and available length and incorporate these findings into their AFO design. GN length does matter a lot! Limiting degrees of freedom will increase patient tolerance allowing and encouraging appropriate freedoms that they can participate in during upright standing and walking.

In prosthetics, the importance of alignment during stance is critical. The same holds true in orthotics in that the AFO in combination with the shoe are critical in optimizing the shank kinetics and kinematics of the GC. New research and paradigms should be explored and embraced, and the myths that prevent the achievement of better outcomes should be critically reviewed and dropped. AFOs can do more than pick up the foot during swing, they can be a very effective therapeutic tools for patients diagnosed with cerebral palsy and lower extremity dysfunctions.

Hanger Clinic, Children's Hospital of Wisconsin, Milwaukee, WI

References:

  1. Sutherland D." The Development of Mature Gait ". Gait Posture. 1997;6:163-170.
    Sutherland DH. Olshen RA, Biden EN, Wyatt MP. " The Development of Mature Walking ". London: MacKeith Press;1988.
    Sutherland DH, Olshen RA, Cooper L, Woo S. " The Development of Mature Gait ". J Bone Joint Surg. 1980;62-A:336-353.

  2. Owen E. " Tuning of ankle-foot orthosis combinations for children with cerebral palsy, spina bifida and other conditions ". Proceedings of European Society of Movement Analysis in Adults and Children (ESMAC) Seminar 2004.

  3. Damiano DL, Quinlivan J, Owen BF, Shaf-frey M, Abel MF. " Spasticity versus strength in cerebral palsy: relationships among involuntary resistance, voluntary torque, and motor function ". Eur J Neurol. 2001;8 Suppl 5:40-9. Damiano DL, Martellotta TL, Quinlivan JM, Abel MF. " Deficits in eccentric versus concentric torque in children with spastic cerebral palsy ". Med Sci Sports Exerc. 2001;33(1):117-122.

  4. Cusick B. " Serial casting and other equinus deformity management strategies " Progressive GaitWays, LLC, 2010:35-36.