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The Possible Effects of Solid Ankle-Foot Orthoses on Trunk Posture in the Nonambulatory Cerebral Palsy Population: A Preliminary Evaluation

Robin B. Beals, CO

children with cerebral palsy use ankle-foot orthoses for a variety of reasons. Some physicians and therapists prescribe them to control muscle tone, prevent deformity, and give a child stability during standing and ambulation. Some therapists use AFOs to affect a child's trunk posture in a seated position, such as on a therapy bench or in a wheelchair. For children with cerebral palsy, adaptive seating serves several purposes:

• It helps train the child in sitting.
• It corrects abnormal postures.
• It provides stimulation in the upright position to develop a child's social, visual, and hearing abilities.
• It helps develop hand function in the upright position of supported sitting.¹

Achieving an optimal sitting position when a child has hypertonia in his or her lower extremities can be quite difficult. Solid ankle-foot orthoses set at 90° of dorsiflexion and in subtalar neutral may help improve trunk posture by keeping the pelvis in a neutral position and by decreasing kyphosis.

A child with cerebral palsy who displays hypertonicity in the lower extremities often sits with his or her pelvis in a posterior tilt. This tilted pelvic position is caused when tight hamstrings pull on their point of origin, the ischia. A child's legs may adduct and rotate internally, with the knees in extension and the feet plantar flexed. Collectively, this movement pattern is known as extensor spasticity of the lower extremities.2 Extensor spasticity can lead to poor trunk posture.

An increased amount of evidence indicates that spasticity, which is a high resistance to stretch, may have more than one component. It has been suggested that the increased tonus of spastic muscles can originate from changes in both the reflex and the nonreflex components of the tissue. The reflex component of spasticity is demonstrated clinically by causing an increase in muscle tone with a rapid stretch. A slower stretch reflects the nonreflex component, the properties of connective and muscular tissue. A myometer can measure the forces of a fast or a slow stretch to test for these two components. Comparing the ratios between the two origins of spasticity may help determine the most effective treatment for a child.³

Pharmocologic treatment may be beneficial in treating the reflex component of spasticity. Baclofen, dantrolene sodium, diazepam, and tizanidine all affect the inhibition of reflex pathways.⁴ Although medication may eliminate or drastically reduce the reflex component of spasticity, a child is still affected by the disability.¹ The nonreflex component can also be addressed through surgical⁴ or orthotic intervention. However, it should be recognized that voluntary motion might be stronger, weaker, or even absent as compared with motion with spasticity.¹

Levitt¹ explains that "postural reactions" occur independently of spasticity. These reactions are neurological mechanisms related to development that help maintain posture and equilibrium. A child's level of independence depends on how developed his or her postural reactions are. Spasticity is only relevant to function when it leads to abnormal postures. Recent trends in physical therapy emphasize the improvement of motor development levels of posture rather than focus on the treatment of spasticity. Developmental levels begin with prone activities, building up to supine activities, sitting, standing, then walking. However, there can be "postural blocks" that can inhibit the progression of development. An example of a postural block is a plantar flexed ankle, the nonreflex component of spasticity. This condition prevents the use of a plantigrade foot, which is needed for the later developmental levels of sitting, standing and walking.1 With the ankle in an AFO at 90° of dorsiflexion and in subtalar neutral, this postural block can be eliminated and trunk posture can be improved. For sitting, a child can plant his or her feet on the floor or on a footrest, thereby limiting the distance that his or her pelvis slides forward in the seat. For a child with high muscle tone in the lower extremities, this AFO position also limits the amount of knee extension due to tightness of the gastrocnemii muscles. Additionally, it prevents a stretch on tight hamstrings that pulls the pelvis into a posterior tilt. If a posterior tilt is prevented, kyphosis should also be of smaller magnitude and head placement should be directed axially above the spine. There is little documentation to support the use of AFOs for improved trunk position in the seated cerebral palsy population.

Methods

The "Slump Test," which was designed by M. Anne White and Karen E. Pape, measures and quantifies changes in trunk control that affect upper extremity function.6 In their study, White and Pape primarily examined the trunk posture of subjects during cross-legged, long-legged, ring, and reverse-W sitting. The shadow of a subject, viewed sagittally, was projected onto paper. Sitting angles, pelvic tilt, and kyphosis measurements were analyzed. In the current study, the Slump Test was modified to focus upon trunk posture during sitting with hips, knees, and ankles at 90° of flexion.

Subjects

The subjects for this study are students at a local school for physically or otherwise health impaired children. Four children (three girls and one boy) were tested; each has cerebral palsy and uses a wheelchair and a seating system as their source of mobility. They all have adequate trunk control for closely supervised independent sitting. Each child has increased tone in their lower extremities and wears solid ankle AFOs set at 90° and in subtalar neutral. One of the subjects had bivalved serial casts set at 90° and in subtalar neutral at the time that she was tested. Consent forms explaining the purpose of the study and all of the testing procedures were sent home with each subject for parental or guardian signature.

Instrumentation

A KAYE adjustable therapy bench (Kaye Products, Inc., Hillsborough, NC) was used as the sitting surface for each subject. Parameters set forth by Myhr and von Wendt2 were used to determine the seat angle of 0° in the sagittal plane. The level of the seat was adjusted to the appropriate height as determined by the subject's heel-to-medial hamstring insertion measurement. The appropriate height was that which allowed the feet to contact the ground with the ankle dorsiflexed to 90° with level femurs. A low-profile adjustable backrest was fabricated that could be moved anteriorly or posteriorly, ensuring that the depth of the seat was such that the femurs were supported up to 1 inch proximal to the popliteal region. An abductor was fabricated to maintain the hips at 10 to 15° of abduction, a hip position that contributes to symmetrical weight distribution on the ischia.2 The therapy bench was oriented perpendicular to and 1 foot away from a wall in the sagittal plane. A 150-watt floodlight was positioned 3 feet away from the end of the therapy bench and facing the same wall. White paper was mounted on the wall opposite to the floodlight.

Procedures

ProceduresTesting took place at the subjects' school, with a physical therapist, the author, and an assistant present. Each trial was videotaped, as the subjects were tested both with and without their AFOs. The children were first tested with their AFOs and shoes on. Each child was placed on the sitting frame, with pelvis in neutral and feet planted on the ground. The physical therapist was located in front of the subject, encouraging a level eye gaze with toys and food. After a period of 1 minute, the sagittal image that was projected onto the white paper by the floodlight was traced by the author. The image of the horizontal surface of the bench was also traced. Both the intersection of where the pelvis met the bench and the level of C7 were indicated on the tracing (Figure 1 ).

The AFOs were removed, and the subject was allowed to lie on a mat for 10 minutes. The subject was tested again, following the same procedure used with the AFOs on. Three of the subjects were tested on one day. The fourth was in serial casts and could not be tested without the casts on. We returned to the school a second day to test the fourth subject once her casts were bivalved and to retest the third subject because of inadequate horizontal reference on the tracings from the first day.

Data Analysis

Three variables were analyzed on the tracings--the degree of posterior pelvic tilt (?), the sitting angle (T), and the displacement of the apex of the kyphotic curve (CD) (Figure 2 ). Using a one-tail, paired t test at a p value of .05, each variable was analyzed for the four subjects, both with and without the AFOs (Table 1 ).5 For variables &bgr; and CD, the difference between subjects with and without AFOs was expected to be a positive value. The hypotheses were as follows:

05For the variable T, we expected the difference between subjects with and without AFOs to be a negative number. The following hypotheses were used for T:

Results

CResultsIn this study, with the use of AFOs, the degree of posterior pelvic tilt and the displacement of the kyphotic curve apex were expected to decrease and the sitting angle was expected to increase. The amount of pelvic tilt decreased in two of the subjects, but the t test failed to prove the significance of this variable at a p value of .05 (Figure 3 ). The displacement of the apex of the kyphotic curve decreased in all subjects when they wore their AFOs; this decrease was significant at a p value of .05 (Figure 4 ). The sitting angle increased in one subject, but the t test failed to prove the significance of this variable at a p value of .05 (Figure 5 ).

Discussion

As predicted, the value of the posterior pelvic tilt angle, ?, was smaller in two of the subjects wearing the AFOs. However, this variable failed to be statistically significant in the study. Subjects 1 and 3 showed an increase in posterior pelvic tilt with the AFOs on, suggesting that these subjects may use their spasticity to improve posture. For such children, AFOs may be contraindicated for improving sitting posture.

The displacement of the apex of the kyphotic curve, CD, was consistently smaller for all four subjects when wearing the AFOs. This variable was significant at a p value of .05, indicating that wearing the AFOs may promote trunk elongation with decreased kyphotic curvature of the spine when sitting.

Without the AFOs, C7 was expected to be anterior to the pelvis, thereby creating a smaller sitting angle. The sitting angle, T, was expected to increase in all subjects with the AFOs on, demonstrating that C7 is more axially aligned above the pelvis. However, only one subject showed a sitting angle increase with the AFOs, a measure that proved to be statistically insignificant. The use of AFOs did not affect the sitting angle in the study.

The subject with the serial casts was not eliminated from the study because the bivalved casts met the AFO criteria, providing proper ankle positioning with an appropriate plantar surface. Because the casts were bivalved, it was possible to remove them for the testing without the orthoses.

The study's small sample size makes drawing definitive conclusions difficult. There were disparities between individual subjects for some of the variables that were measured. For instance, the value of the posterior pelvic tilt, which was expected to decrease, actually increased in two of the subjects. However, it did decrease in the other two subjects. We know that variance among the sample means decreases as the sample size increases, implying that the variable is more likely to be close to the population mean as the sample size increases. For example, the mean of the change in posterior pelvic tilt values will be closer to the actual mean for seated children with cerebral palsy as the number of children who are tested increases.

Although the tracings of the subjects provide an estimate of these variables, they are somewhat subjective. The person creating a tracing has to attempt to capture the trunk position from a moment in time. A motion analysis lab would provide a more accurate measurement of these variables, helping to improve reliability within the rater by eliminating flaws with the tracings. The test used in this study, which can be easily reproduced by therapists and orthotists, may help to determine if a seated child (who may otherwise not use AFOs) can benefit from wearing orthoses. Not only can AFOs improve certain aspects of sitting, the devices can also prevent certain postural blocks and deformities, potentially allowing a child to bear weight through their legs in the future.

Conclusions

For children with cerebral palsy who are mostly seated, solid AFOs set at 90° of dorsiflexion and in subtalar neutral may help to improve certain aspects of trunk posture when they are in a seated position. A kyphotic position of the spine during sitting may be reduced with the use of the orthoses, enabling a child to focus his or her attention on activities other than maintaining posture in the chair. In addition, proper bony alignment of the feet and ankles, paired with maintained stretch of the plantar flexors, will help prevent postural blocks for future developmental progression. AcknowledgmentThe author wishes to acknowledge the contributions of Jan Holda, PT, for subject recruitment and active participation in data collection.

ROBIN B. BEALS, CO, is a staff orthotist with Becker Orthopedic, Waterford, MI. Robin B. Beals, CO, Becker Orthopedic, 5210 Highland Road, Waterford, MI 48327. Phone: (248) 674-9600; Fax: (248) 674-9603.

References:

1. Levitt S. Treatment of Cerebral Palsy and Motor Delay. 3rd ed. Oxford: Blackwell Science; 1998.
2. Myhr U, von Wendt L. Influence of different sitting positions and abduction orthoses on leg muscle activity in children with cerebral palsy. Dev Med Child Neurol. 1993;35:870-880.
3. Boiteau M, Malouin F, Richards CL. Use of a hand-held dynamometer and a Kin-Com dynamometer for evaluating spastic hypertonia in children: a reliability study. Phys Ther. 1995;75:796-802.
4. Ko Ko C, Ward A. Management of spasticity. Br J Hosp Med. 1997;58:400-405.
5. Rothman E, Ericson W. Statistics Methods and Applications. 2nd ed. Dubuque, IA: Kendall Hunt Publishing; 1987.
6. White M, Pape KE. The Slump Test. Am J Occup Ther. 1992;46:271-275.