View Options - Click to expand
Print Options - Click to expand
E-Mail Options - Click to expand

A Review of Thermoplastic Ankle-Foot Orthoses Adjustments/Replacements in Young Cerebral Palsy and Spina Bifida Patients

Terry J. Supan, CPO
Christopher F. Hovorka, CO

ABSTRACT

A retrospective study was performed to determine how long a thermoplastic ankle-foot orthosis (AFO) will fit appropriately and when subsequent adjustment and replacement are indicated. Clinical records of cerebral palsy and spina bifida patients ages birth to 21 years who used six types of thermoplastic AFOs from 1982 to 1992 were reviewed. Neuromusculoskeletal functional status appears to determine the AFO design prescribed and its replacement. Adjustments to thermoplastic AFOs primarily involve heat flaring to alter plastic contours and provide sufficient space for donning, doffing and pressure relief over regions of bony prominence. Further research is necessary to confirm the results obtained in this study.

Introduction

Within the field of orthotics, no known published studies have addressed the nature and frequency of adjustments and subsequent replacement of orthoses prescribed for the lower limb. A retrospective review was designed to provide data to document the timing of orthotic intervention in a neuromusculoskeletally maturing patient population. Numerous factors of thermoplastic ankle-foot orthosis (AFO) adjustment and replacement were derived from the review of this data.

Methodology

A database was created using a spreadsheet on the Apple Macintosh computer. Medical files of 198 patients wearing thermoplastic AFOs from communities of central Illinois and northeastern Missouri treated at Southern Illinois University School of Medicine, Orthotic/Prosthetic Services (SIUO/P) between July 6, 1982, and June 30, 1992, were recorded. Only patients diagnosed with cerebral palsy or spina bifida between birth and 21 years of age were chosen for this review for two reasons. First, the majority of lower-limb musculoskeletal growth and development was completed by the twenty-first year of life, which ensured a patient population undergoing musculoskeletal growth without the need for radiographic confirmation (1,2). Second, patients diagnosed with cerebral palsy or spina bifida were the two most prevalent patient referral groups for orthotic treatment of the lower limb at this institution.

Thermoplastic AFOs were reviewed since these orthoses were prescribed frequently at SIUO/P over the 10-year period for the two diagnosis groups, which provided a considerable amount of data for this review. The only exception was a modular thermoplastic knee-ankle-foot orthosis (KAFO) incorporating separate AFO and removable thigh sections, which was used by patients fully assembled for nocturnal use and disassembled for AFO daytime use (see Figure 1 ).

Supramalleolar orthoses (SMOs) with trimlines terminating within the immediate region of the malleoli were excluded from this study. No unique contours (i.e., tone-reducing modifications) were incorporated into the AFOs studied. Lower-limb orthotic treatment objectives for both the cerebral palsy and spina bifida patients treated in this review were similar. The primary orthotic objective was to achieve optimum foot and ankle joint positioning to reduce or terminate progression of contractures and secondarily, when indicated, to provide for stable body weight transfers and safe ambulation.

Patient demographics were tabulated consisting of the patient's medical record number, name, gender, date of birth, diagnosis and treated limb. Orthosis variables, such as the orthosis type and dates of new adjustments and replacements to patients' AFOs, were recorded.

The type of orthosis was labeled and classified according to the Health Care Financing Administration (HCFA) Common Procedure Coding System devised by the American Orthotic and Prosthetic Association in conjunction with the American Medical Association (3). The frequency of regional adjustments to orthoses by heat flaring of the thermoplastics was studied. Heat flaring consisted of changing the shape of the thermoplastic to reduce excess pressure where it contacted the patient's limb. These adjustments were performed during a clinic or office visit and deemed appropriate when skin irritation was reported by the patient, his or her family, or health-care workers involved with the patient's care.

An adjustment legend was created that divided the AFOs into 10 corresponding anatomical lower-leg sections described by the corresponding bony anatomy and its related soft tissues and vessels (see Figure 2 ). The foot section of the AFOs was divided into four quadrants. Section A, the medial forefoot, contained the first, second and medial half of the third metatarsals and phalanges. Section B, the lateral forefoot, contained the lateral half of the third and the entire fourth and fifth metatarsals and phalanges. Section C, the medial rearfoot, contained the medial half of the calcaneous, medial half of the talus, the navicular, the medial cuneiform, the middle cuneiform and the medial half of the lateral cuneiform. Section D, the lateral rearfoot, contained the lateral half of the calcaneous and talus, the entire cuboid and the lateral half of the lateral cuneiform.

The ankle section of the AFOs was divided into medial and lateral halves encompassing the malleoli. Section E, the medial ankle, contained the medial malleolus extending to the midline of the distal leg anteriorly and posteriorly, and Section F, the lateral ankle, contained the lateral malleolus extending to the distal leg's midline anteriorly and posteriorly. The proximal two-thirds of the leg extending from proximal to the malleoli up to the knee was known as the leg section and was divided into four quadrants. Section G, the medial and anterior quadrant, extended from the anterior midline encompassing the medial two-thirds of the tibia.

Section H, the lateral and anterior quadrant, extended from the anterior midline to the lateral midline encompassing primarily the fibula. Section I, the medial and posterior quadrant, contained superficially a large part of the medial gastrocnemius and soleus tissue extending from the medial midline to the posterior midline. Section J, the lateral and posterior quadrant, contained the remaining lateral aspect of the gastroenemius and soleus tissue from the lateral midline to the posterior midline.

Only three of the six thermoplastic orthoses (solid, floor-reaction and articulated AFOs) were reviewed according to the site of heat flare modifications performed because these devices were used predominantly among the patient population. The other three orthoses (articulated floor-reaction, Thermoplastic Elastomer (TPE) and dorsiflexion assist AFOs) were not considered in this aspect of the study because they were rarely heat flared (4). The articulated floor-reaction AFO was used only for a short time during the study, and the other two devices (TPE and dorsiflexion-assist AFOs) were prescribed infrequently with little or no documented heat flare adjustments performed.

The replacement of thermoplastic AFOs was recorded according to re- placement criteria based on either a physiologic change in the patient or change in the structure of the AFO (see Table 1 ). All patients were treated with an initial orthosis and as many as four subsequent replacements for both the cerebral palsy and spina bifida patient groups.

Results

Patient Distribution by Diagnosis

Of the 198 patients reviewed, there were 112 males and 86 females. One hundred sixty-seven of these patients (84 percent) were diagnosed with one of three spastic types of cerebral palsy: diplegia (38 percent), hemiplegia (22 percent) or quadriplegia (19 percent) (see Figure 3 ). A small group (5 percent) of patients was diagnosed with a variety of other types of cerebral palsy and was categorized as miscellaneous types. Thirty-one of the 198 patients (16 percent) were diagnosed with spina bifida, of which 30 patients were diagnosed with a myelomeningocele and one patient with a meningocele (see Figure 4 ). Eighteen of the 31 spina bifida patients (58 percent) had their spinal cord defect within the lumbar level followed in order by 23 percent unspecified (seven patients), 13 percent sacral (four patients) and 6 percent thoracic levels (two patients).

Distribution of Orthosis Type

Six types of thermoplastic AFOs were used to treat the patients (see Figure 5 ). A total of 254 devices were prescribed, 83 percent for patients with cerebral palsy and 17 percent for those with spina bifida. For patients with cerebral palsy, the solid AFO was pre- scribed for the majority (58 percent) followed by the articulated (26 percent), floor-reaction (9 percent), dorsiflexion-assist (4 percent), articulated floor-reaction (2 percent) and TPE (1 percent) devices (see Figure 6 ).

Patients with spastic quadriplegia usually were treated with a solid AFO while those with spastic diplegia or hemiplegia were usually treated with either a solid or articulated AFO. All other types of cerebral palsy were treated less frequently and with other types of devices.

The remaining 17 percent or 43 AFOs were prescribed for patients with spina bifida. Within this group, 44 percent were treated with the floor-reaction AFO, followed by the solid (42 percent), articulated floor-reaction (12 percent) and dorsiflexion-assist (2 percent) devices. The majority (58 percent) of the spina bifida patients were ambulatory, with their neural tube defect within the lumbar regions (see Figure 7 ).

Replacement Timelines

The number of patients treated with replacement orthoses reduced considerably with each successive AFO replacement. In addition, there was a wide range in age for the group of patients fit with an initial AFO, which reduced tremendously with each subsequent replacement (see Figure 8a , Figure 8b , Figure 8c , and Figure 8d ). Beyond the usual reasons (surgery, transfer of care, etc.), patients underwent subsequent replacement of orthoses for one of two causes. First, the older children no longer required replacement orthoses due to the lack of growth, or the patient's existing orthoses were discontinued. Second, the younger patients did not require as many replacement orthoses since they had not yet outgrown their existing orthosis. This had a greater effect on the data of the female patients than on those of the male patients. The group mean age of female patients actually declined from the first to the second replacement orthosis (see Figure 8b and Figure 8d ). In all groups, males were older than their female counterparts except for females with spina bifida who were older at their third and fourth AFO replacements. Overall, males with cerebral palsy had their orthoses replaced an average of 0.9-year (10.8 months) intervals while those with spina bifida had theirs replaced an average of 1.51-year intervals.

Distribution of Adjustments Performed

to Orthoses by Patient Diagnosis and Type of Device The reporting of heat flare adjustments by anatomic location was the single most common recorded modification to a thermoplastic AFO over the 10year review. The three types of AFOs used by patients diagnosed with cerebral palsy (solid, floor-reaction and articulated) and those patients diagnosed with spina bifida using the solid or floor-reaction AFOs displayed many differences in the frequency of adjustments performed (see Figure 9a , Figure 9b , and Figure 9c ).

Solid and articulated AFOs were most often adjusted at the foot, ankle and proximal leg. Most adjustments were performed at the foot's navicular region except for spina bifida patients. The fewest adjustments were performed at the proximal leg region. Patients using the floor-reaction AFO had the greatest number of adjustments at the proximal leg and fewest adjustments at the foot and ankle. The floor-reaction AFO had more combined adjustments in the calf of the proximal leg and the fewest adjustments at the ankle.

Discussion

Distribution of Orthosis Type by Patient Diagnosis

When this distribution is compared to the neuromusculoskeletal function of those patients with cerebral palsy, some generalizations may be made. Patients, such as the spastic quadriplegic group, required control of the foot, ankle and knee offered by the solid AFO or modular thermoplastic KAFO with removable thigh shell. These individuals, most of whom were nonambulatory, were prescribed those de vices for prevention of joint contracture or lower-limb joint stabilization during transfers (e.g., from wheelchair to bed).

The spastic diplegic and hemiplegic groups generally displaying less neuromusculoskeletal involvement of the limbs were prescribed additional types of orthoses. Patients with spastic hemiplegia were fitted with either a solid or articulated AFO for select motion control about the foot, ankle and knee when ambulation was achieved. Patients with spastic diplegia used the greatest variety of devices.

In addition to the solid and articulated AFOs, a small number of the spastic diplegic patients were prescribed floor-reaction and articulated floor-reaction devices, the latter intended to control excessive ankle dorsiflexion and crouch during ambulation. The articulated floor-reaction AFO introduced in the 1980s concurrently by Beverly Cusick, MS, PT (described as a hinged crouch-control ankle-foot splint) and Algis Maciunas, CPO, in conjunction with James Gage, MD, (described as a rear-entry hinged floor-reaction AFO) recently was introduced at SIUO/P and used during the last 10 months of this study (5,6).

This distribution of orthosis type by patient diagnosis also relates the spina bifida patient's functional status to type of orthosis prescribed. Because spina bifida typically presents with paralysis at and below the level of neural tube defect, those patients with high levels of pathology (superior to the lumbar level) were prescribed solid or floor-reaction devices while patients retaining greater distributions of muscular function through lower levels of spinal cord involvement used the articulated floor-reaction device. The entire spina bifida group with the exception of one dorsiflexion-assist AFO prescribed for a patient with a low-level myelomeningocele displayed the importance of crouch control offered by the two variations of floor-reaction devices.

In effect, the spina bifida group was treated for foot and ankle control in addition to control of knee buckling secondary to weak-knee extensors associated with the level of their pathology. The cerebral palsy group was treated for foot, ankle and knee control depending on each person's level of upper motor neuron pathology. This distribution comparison supported the principle that the orthosis prescription was related to the patient's functional needs based on the level of his or her neuromusculoskeletal involvement.

Replacements

The dwindling size of the patient populations when treated with subsequent replacement orthoses was due to several factors. Fewer older patients required replacements due to discontinuance of the orthosis or reduced rate of growth. The patient's moving from the area, surgical intervention performed for contracture (tendon and/or muscle transfer or lengthening), spasticity (dorsal rhizotomy), joint instability (arthrodesis), nutritional status or change of referring physician and/or the orthotist also may have contributed to this effect.

Distribution of Adjustments

Overall, adjustments to orthoses were performed for multiple reasons, including limb growth, biomechanical changes secondary to surgical procedures and progression of deformities such as joint contractures or other neuromusculoskeletal change. By corresponding anatomical site, heat flaring modifications in the proximal calf region of floor-reaction AFOs were performed to allow adequate malleoli clearance for donning and doffing. This procedure modified the existing orthosis design so the foot and ankle could pass through the proximal posterior section. Fewer adjustments were performed in the proximal leg region of solid and articulated AFOs than other sites since the gastrocnemius and soleus tissues in this region are more accommodating for donning and doffing.

The similarity of adjustments within the foot section points to the importance of providing adequate relief of bony prominences, particularly at the medial posterior region where the navicular tuberosity resides. This condition may be related to the great range of motion through which the medial longitudinal arch of the foot moves during weightbearing in conjunction with positional changes during musculoskeletal growth and development. In the ankle region, adjustments were performed to provide adequate clearance of the malleoli with varying distributions for each of the three devices.

Conclusion

Through a 10-year retrospective to determine how long a thermoplastic AFO will last and when it requires adjustment and replacement, this study exhibited a host of factors involved. The main variable determining type of orthosis prescribed appears to relate to the patient's neuromusculoskeletal functional status. Replacement of AFOs was related to the patient's neuromusculoskeletal functional status and possibly the gender, but the latter could not be determined in this study. The anatomical site of adjustments involving heat flaring depends largely on the type of orthosis and the patient's anatomy. Adjustments were made to provide sufficient space for donning and doffing in addition to providing relief of the patient's bony prominences and skin pressure tolerance.

A typical scenario of orthotic intervention as gleaned from this study may be that a patient with spastic cerebral palsy usually required a solid or articulated AFO, necessitated adjustment mostly at the medial rearfoot section at the navicular followed by adjustments at the ankle and anterior leg sections within the proximal third, with average replacement in 10.8 months. A patient with spina bifida and a neural tube defect in the lumbar region may be prescribed a floor-reaction or solid AFO.

The floor-reaction device required most adjustment in the posterior calf section at the proximal third followed by the medial rearfoot section at the navicular and least adjustment in the ankle section. The solid ankle device required adjustment mostly in the medial rearfoot section at the navicular followed by the ankle and anterior leg section at the proximal third. Both the solid ankle and floor-reaction AFOs worn by patients with spina bifida average replacement in 1.51 years.

Since this retrospective study considered only some of the many factors involved in lower-limb thermoplastic AFO treatment patterns for a neuromusculoskeletally maturing patient population, further research would be needed to evaluate the results obtained.

A copy of the AFO adjustments and replacements spreadsheet format is available upon request by contacting Christopher F. Hovorka, CO, Newington Orthotic and Prosthetic Systems, Children's Hospital Center, 181 E. Cedar St., Newington, CT 06111.

Acknowledgements

The authors thank Stephen Hill for his review of the manuscript.


TERRY J. SUPAN, CPO, is director of Orthotic/Prosthetic Services and associate professor of the Division of Orthopaedics and Rehabilitation, Department of Surgery, Southern Illinois University School of Medicine, P.O. Box 19230, Springfield, IL 62794-9230.

CHRISTOPHER F. HOVORKA, CO, was an orthotic resident at Orthotic/Prosthetic Services Southern Illinois University School of Medicine during the time this study was conducted and is a staff orthotist/prosthetist at Newington Orthotic and Prosthetic Systems, Children's Hospital Center, 181 E. Cedar St., Newington, CT 06111.

References:

  1. von Lanz T, Wachsmuth W. Praktische Anatomie. In: Tachdjian MO [edi. The child's foot. Philadelphia: W.B. Saunders Co., 1985:42-3.
  2. Zerin JM, Hernandez RJ. Approach to skeletal maturation. Hand Clinics 1991; 7:1:53-62.
  3. American Orthotic and Prosthetic Association/Health Care Financing Administration Common Procedure Coding System. 1981:12-3.
  4. Sutton RS. Thermoplastic elastomer (TPE)-the TPE ankle-foot orthosis and the TPE biomechanical-foot orthosis. JPO 1990; 2:2:164-72.
  5. Cusick BD. Progressive casting and splinting for lower-extremity deformities in children with neuromotor dysfunction. Tucson: Therapy Skill Builders, 1990: 251-5.
  6. Gage J. Gait in cerebral palsy. London: MacKeith Press, 1991:179-80.