Thera-Step and the Hypertonic Lower Leg

Louis J. Haberman, C.P.O.

Introduction and History

The complexities in management of the hypertonic lower limb have long been acknowledged. Conventional (metal) orthotic designs are ill-conceived for the more involved hypertonic patient with accompanying spasticity. Lacking a total-contact fit, appropriate contours, proper positioning and specific pressures, these devices may actually worsen the patient's condition. Traditional physical therapy modalities provide no long lasting benefits for the hypertonic patient. Medications prescribed for these patients have questionable effectiveness. These drugs are depressants which do not contribute positively to the rehabilitation of an already depressed patient.

Lehneis¹ and Marx were among the first to consider the potential benefits to be derived from the utilization of total-contact plastic orthoses. Neurodevelopmental Techniques (NDT) as described by Bobath and Bobath,³ and consideration of primitive pathological reflexes as identified by Baird⁴ and others, have offered additional understanding and appreciation of the roles of proper positioning and appropriate pressure distribution within a molded ankle foot orthOs's.

In response to this information, new and exciting treatments and orthoses have been developed. Cusick⁵ demonstrates that significant reductions in excess tone and tightness and biomechanical correction can be achieved via serial casting. In 1986, Ford, Gratz and Shamp⁶ presented the Neurophysiological Ankle-Foot Orthosis (NAAFO) which incorporates many of the aforementioned concepts into its design.

Thera-Step a markedly different, yet conceptually similar orthosis to the NA-AFO, was successfully fit in 1977 to a closed head injury patient. The original design had been modified over the years after several hundred fittings to arrive at its present configuration (Figure 1) . Thera-Step was formally presented in 1984 at the ACPOC Mceting in Baltimore, Maryland, and has been recognized by the United States Patent Office in granting it U.S. Patent Number 4,554,912.

Hypertonicity

The hypertonic limb lacks the ability to inhibit or shut off input to specific muscle groups. In the foot and ankle this often resuIts in the adoption of an equinovarus position. Hypertonicity may be divided into three classifications: spasticity; clonus; and rigidity.

Spasticity, by definition, is resistance to motion in one direction. This phenomena may be best illustrated by manually moving an equinus foot towards neutral. The ability to move the foot from equinus or varus would indicate a "dynamic" versus a "fixed" deformity, according to Bleck.⁷ The "dynamic" nature of this type patient should readily enable the orthotist to optimally position the lower limb for the inhibitive cast. Spasticity may also be divided into three classifications: mild; modcrate; and severe.

Mild spasticity may be characterizcd by a neutral hindfoot at hcel strike and midstance with the potential for supination of the forefoot. Clinical experience has indicated that mild spastidty can be suecessfully managed by various devices. A flexible trim-line molded plastic orthosis (MAFO) cast in dorsi-flexion, a conventional AFO with double-action ankle joints, or a tone-inhibiting device will provide the necessary stability and assistance required for the mildly spastic patient.

A word of caution: patients exhibiting mild spasticity may manifest increased levels of spasticity at various times and under varying circumstances. If these neurological changes become significant, the flexible MAFO and/or the conventional AFO may become unusable. It is, therefore, strongly urged that the orthotist seek out the opinion and recommendations of the physician, physical therapist and patient's family. The physical therapist is probably in the best p0-sition to provide information relating to neurological and physiological changes.

Moderate spasticity places the hindfoot in varus with accompanying forefoot supination At mid-stance and toe-off forefoot supination and plantar-flexion are reduced due to weight transmission through the foot. The moderately spastic patient would be best served by provision of a tone-inhibiting orthsis.

Severe spasticity places the entire foot in equinus. The hindfoot is in varus and the forefoot is inverted. Internal rotation is often seen as the fifth metatarsal head is the only point of contact with the floor. The severely spastic patient absolutely requires a tone-reducing (inhibiting) orthosis. Pre-orthotic intervention by those skilled in neurodevelopmental techniques and serial casting should prove helpful in obtaining a negative cast within the correct parameters for optimum results:

Clonus is characterized by a series of alternating contractions and partial relaxations that can be elicited by an external stimuli. Clonus may be mild and intermittent or quite severe and continuous. Mild clonus with no significant spasticity may be successfully treated utilizing a MAFO with flexible trim lines cast in dorsiflexion. Marked clonus with accompanying mild to moderate spasticity should be treated utilizing a tone-inhibiting device.

Rigidity, as its name implies, is resistance to movement in both directions. It is beyond the skills of the orthotist to treat such patients in an effective manner and thus beyond the scope and intent of this article.

What should a tone-inhibiting orthosis do? It should:

Provide three-point pressure systems to biomechanically correct calcaneal varus and forefoot supination. The correction of this pathomechanical state will reestablish a heel to toe gait.
Provide a significant reduction or elimination of hypertonicity. Achieving a relaxed state will prevent irritation of the involved limb within the orthosis and shoe.
Reduce energy expenditure, thus increasing endurance.
Permit unrestricted movement of the hip and knee, but not recurvatum.
Be comfortable.
Maintain total contact with the involved limb at all times.
Provide a precise and narrow range of motion at the foot/ankle complex. Excessive movement of the ankle component in the direction of plantar flexion will encourage resumption of hypertonicity.
Offer increased contact pressure to specific zones of the limb to facilitate neurological and biomechanical changes.

Design and Construction

The Thera-Step orthosis is a total-contact device and may be compared, in that regards, to a well fitting prosthesis. The orthosis is constructed of 3/16" Copolymer. This material offers the right combination of rigidity and controlled flexibility.

There are two distinct, yet complimentary, three-point pressure systems applied to the limb by Thera-Step. The hindfoot varus and forefoot supination are controlled by an appropriately relieved and padded malleolar area; a higher medial wall; an extended projection proximal to the medial malleolus and an extended trim line over the first tarsal of the foot (Figure 2 and Figure 3 ). The equinus component is controlled by a well-contoured footplate, a broad proximal posterior section, and the patient's footwear. The downward and posteriorly directed force provided by the shoe vamp is assisted by the provision of a diagonal Velcro closure. Increased contact-pressure is provided uniformly throughout the orthosis. The footplate incorporates substantial contouring from the distal aspect of the calcaneus to an area just proximal to the metatarsal heads. The apex of the plantar modification is approximately 1" proximal to the metatarsal heads. The base of the fifth metatarsal head rarely requires plaster build-up as the substantial plantar modifications tend to reduce contact there. The navicular must be free of undesirable contact and is appropriately relieved. The orthosis is trimmed well behind the medial malleolus which encourages plastic deformation in the direction of valgus during mid-stance and toe-off. The orthosis is initially molded over a Pelite pad which covers a large area about the lateral malleolus. After molding, the pad is replaced with Plastazote or PPT foam. A firm, yet comfortable contact-pressure must be maintained at all times at this location. By design, Thera-Step provides positive neurological input and biomechanical correction for the hypertonic lower limb.

Experience and Results

As of this writing, Thera-Step orthoses have been fit to more than 600 patients over a 12 year period. The great majority of these patients - 346 - are diagnosed as having sustained cerebral vascular accidents. There have also been 110 head trauma, 142 multiple sclerosis and 61 cerebral palsy patients fitted with Thera-Step.

Patients wearing Thera-Step for the first time immediately report that enhanced stability and confidence is evident during gait. The foot/ankle complex is maintained in a neutral and relaxed attitude throughout the gait cycle. Many patients state that their toes cease clawing within minutes, hours or days of receiving their Thera-Step and have transitioned to a flexible MAFO due to significant reduction in excess tone. Others no longer require an orthosis of any kind. It is impossible to say, at this time, whether the Thera-Step orthosis or a natural series of events occurred to permit such a change. Sixteen percent of this patient population are now deceased.

Acceptance of the device has been nothing short of remarkable. There have been two rejections. A marked change in leg volume of one patient necessitated the addition of foam lining in the orthosis for maintenance of the total contact fit. The padding distressed the patient and he subsequently rejected the orthosis despite its continued benefits. The second rejection, a multiple sclerosis patient with bi-lateral involvement, occurred due to the patient's perception of extreme confinement. All pressures were appropriate and no evidence of hypertonicity was present when the orthoses were worn. It is believed that sensory confusion (as related to fit and function) was responsible for the rejection.

Contraindications

While Thera-Step can be routinely used to benefit most patients with upper motor neuron lesions, there are two exceptions: uncontrolled, fluctuating edema and fixed equinovarus.

The provision of an appropriately fitting anti-edema stocking will most often solve the edema problem. Fixed equinovarus must be altered, if possible, with the intervention of NDT and serial casting by those skilled in the art. When the foot-ankle is once again "dy namic," the orthotist can then appropriately position the limb for maximum tone inhibition.

Thera-Step and Footwear

As footwear is considered to be a component of the orthosis, its selection should be carefully scrutinized. The following shoe types will complement the Thera-Step design: sneakers (low profile or high top), extra-depth oxfords, Hush Puppies and Rock-ports (laced).

The footwear selected should fit both feet appropriately. A laced shoe maintains the foot in the shoe more effectively than a slip-on and facilitates donning. The heel height should not exceed 1".

Casting

Perhaps the single most important element in successfully fitting the hypertonic patient is the cast impression. It is assumed that at this point the patient's lower limb can be placed into a tone-inhibiting and biomechanically correct position. The patient should be seated in a firm chair with armrests. The foot must easily reach the floor and be plantargrade. Once the casting position is established, the patient must not alter his/her position in the chair. Any such movements will certainly change the pre-determined knee flexion and dorsiflexion angles No contoured footboards are required. The pre-casted position of the lower limb should be as follows (Figure 4 and Figure 5 ):

Hip at 90-95° of flexion;
Knee at 100-110° of flexion;
Foot/ankle at 5-10° of dorsiflexion;
Induce moderate ankle valgus.

Identify and mark the following landmarks (Figure 6 and Figure 7 ):

Fibular head
Lateral malleolus and 2" proximal to it
Achilles tendon
Apex of posterior calcaneus
Navicular
Base of the fifth metatarsal head
Medial malleolus
First tarsal
Proximal and distal aspects, medial side of first metatarsal head

Carefully establish and mark the distal trimline for the footplate (Figure 8) . Place surgical tubing over the cast sock and have the patient maintain the hose on the center of the knee. Without tension, apply two roles of elastic plaster bandage followed by two rolls of standard plaster bandage for reinforcement. Massage the plaster well with hands as it sets. Restore the predetermined tone-inhibiting position. Hold the foot/ankle in a valgus position with one hand while using the heel of the hand to inhibit forefoot supination. Use the other hand to provide a firm downward force from the top of the knee (Figure 9) . As the plaster sets, recheck the position of the ankle, knee and hip. The position of the casted limb should be identical to that of the pre-casted limb. Finally, index the cast, remove from patient and staple together. The finished orthosis should provide the wearer with uniform total-contact, comfort, reduction/elimination of excess tone and maintenance of the foot and ankle in a biomechanically correct attitude (Figure 10 and Figure 11 ).

Fabrication

The modified model is prepared for drape molding in the usual manner. The model should not be dry. The Pelite malleolar pad is placed on the model in the pre-determined location and maintained there by the application of two nylon stockings. The copoly mer material is molded under full vacuum and allowed to cool for over 24 hours. After trimming, the Pelite pad is removed. The orthosis is then sanded and buffed smooth. The tarsal and medial mid-calf projections are beveled from the inside out. The ankle loop and keeper must be installed with a #9 copper rivet before the ankle pad is inserted. The new malleolar pad is fabricated of Plastazote or PPT foam, and is beveled slightly from the underside so as to create a smooth transition inside the orthosis after it is bonded in place. Properly locate and install the padded Velcro closures.

Summary

Thera-Step, a tone-inhibiting orthosis, incorporates the biomechanical and neurophysiological concepts suggested by prominent researchers. The foot and ankle is casted in a relaxed (non-tonal) state and this position is maintained by two distinct, yet complimentary, three point pressure systems. The design allows for one-handed donning. There is evidence that reducing or eliminating excess tone and tightness in the foot and ankle often results in tone reduction in more proximal articulations. Thera-Step differs from other tone-inhibiting devices in that it does not permit plantar flexion and does not require extreme dorsiflexion to perform its tasks. This in no way diminishes the efficacy of alternative designs, but merely illustrates a different approach. Based on extensive clinical experience and long-term observation, it is suggested that the Thera-Step design consistently achieves its goals in significantly reducing and/or eliminating spasticity in patients with upper motor neuron disorders.