The Transformer Ankle Foot Orthosis

Orthotists managing the care of children and adults face the challenge of providing an orthosis capable of facilitating the best functional outcomes. The practitioner ultimately chooses the most appropriate design features after performing a dynamic assessment of the individual's mobility pattern, thorough neuromuscular assessment, and measurement of available range of motion. Research has demonstrated, that even subtle shifts in the alignment of the foot and ankle can significantly disrupt or smooth out the gait cycle. (1) This paper introduces the Transformer Ankle Foot Orthosis [*The Transformer is a TCFlex orthosis manufactured by Orthomerica Products.], which utilizes components, trim lines, and total contact foot plate modifications to allow the orthotist to "tune" the orthosis to the most functional position.(1) The adjustable dorsiflexion and plantarflexion stop allows the orthotist to make changes over time as the individual adapts to the settings, gains strength, or requires a different position to improve function.

The proximal trim line is at the proximal aspect of the tibial tubercle and has an anterior tibial wrap to assist with knee extension when a dorsiflexion stop is employed. The hind foot, mid-foot, and forefoot alignment is set to promote the most efficient mobility given any range of motion constraints. The forefoot may be posted to preserve the most appropriate hind foot orientation. The foot is contained within total contact dorsal flaps to control the mid-foot and distribute forces. The dorsal plastic also provides containment to enhance proprioceptive feedback in an aligned position.

The total contact foot plate modifications help maintain the correct alignment by seating the calcaneus in the heel cup using the peroneal arch modification, Carlson modification, and accentuating the medial longitudinal arch. The metatarsal pad placement just posterior to the metatarsal heads unweights the metatarsal heads, and the toe rise pad supports the toes to prevent clawing.(2)

The versatility of the orthosis comes from the use of the design features mentioned above combined with the adjustable dorsiflexion and plantarflexion stop and low profile, free motion, ankle joints. The individual dons the orthosis in the position pre-determined to be appropriate during the patient evaluation. Shoes are also applied, and the individual walks in the orthosis independently or with whatever assistive device is needed. The patient's gait is evaluated from coronal and sagittal views to assess the impact of the preset alignment.

According to researchers at University of Strathclyde, the relationship between the AFO and the footwear can significantly influence the quality of outcome. (3) This is a concept long known and easily practiced with double action/adjustable ankle joints attached to an orthopedic shoe. But it has been less common in thermoplastic, total contact designs. The Transformer offers an opportunity to incorporate the proprioceptive characteristics of total contact designs into a system that can precisely control sagittal plane alignment in both dorsiflexion and plantarflexion.

Adjustable sagittal plane alignment is essential for patients with pathology that vacillates between remission and exacerbation. It is appropriate following achilles tendon lengthening in children or repairs in the adult population. The orthotist can lock the orthosis post-operatively, and free up motion as the soft tissue heals and therapy is initiated. The adjustable sagittal plane alignment gives the orthotist a tool for "tuning" the orthosis to the individual's unique blend of muscle strength, bone and joint pathology, musculotendinous length, balance, and compensatory mechanisms in gait. This tuning is done while the patient wears the appropriate shoe to complement the orthosis. Tuning relates to this orthosis-in-shoe alignment, and takes into account more than just the dorsiflexion and plantarflexion angle.(3)

When "tuning" the orthosis, evaluate the inclination of the AFO/footwear combination. A vertical shank may stabilize the knee, but cause the hip to be unstable. Neurological conditions are sensitive to small changes, and improper positioning may lead to higher energy consumption or even long term deterioration. Appropriate positioning optimizes the ground reaction forces at the knee and hip to influence function. If a patient has poor dorsiflexion range and the AFO dorsiflexes excessively, it can cause too much pull on the gastrocnemius and trigger knee flexion at terminal swing and stance phase. These patients may benefit from alignment in some plantarflexion, with a buildup under the AFO to bring the shaft more anterior. Often the amount of plantarflexion and heel buildup can be reduced over time as the hamstring and dorsiflexors stretch with each step. (3)

The Transformer combines proprioceptive and adjustable alignment features in a total contact ankle foot orthosis. Adult models can be fabricated from higher durometer plastic without the dorsal wraps. Two-stage AFOs can be fabricated for patients with excessive dorsiflexion with a UCBL dorsal wrap inside a more rigid posterior AFO component. This provides reinforcement to the posterior stop and a total contact inner boot to provide proprioceptive and control of the foot and ankle complex. The Transformer's low profile design and dynamic components provide opportunity for fine tuning an orthosis for each phase of the individual's rehabilitation process.

References

1. Owens E, "Shank angle to floor measures of tuned ankle-foot orthosis footwear combinations used with children with cerebral palsy, spina bifida and other conditions." Gait & Posture 16: Supp 1, S132-135. 2002.

2. Lima D, "Overview of the Causes, Treatment, and Orthotic Management of Lower Limb Spasticity". JPO, Vol 2. Num 1. 33-39. 1990.

3. Owen E. "Shank angle to floor measures and tuning of ankle-foot orthosis footwear combinations for children with cerebral palsy, spina bifida and other conditions", Proceedings of ESMAC Seminars 2004.