Case Study: Improving Knee Extension with Floor-Reaction Ankle-Foot Orthoses in a Patient with Myelomeningocele and 20° Knee Flexion Contractures
Donald Freeman, CP
Michael Orendurff, MS
Michael Moor, CPO
ABSTRACT
Floor-reaction ankle-foot orthoses (FRAFOs) were fit to a patient with an L-5 level myelomeningocele to show their effect on increasing knee extension and the knee extension moment in the presence of 20° bilateral knee flexion contractures. It was hypothesized that FRAFOs would prevent the crouched-type gait pattern commonly seen in those with myelomeningoceles. Because of the rigid nature of the FRAFO, it was thought this would increase the external knee-extension moment and extend the knees to their maximum range. A patient with myelomeningocele underwent gait analysis testing while barefoot and while wearing FRAFOs set in 10° dorsiflexion. Joint kinetic and kinematic, along with electromyographic data on the vastus lateralis and rectus femoris were determined. Results showed a peak plantarflexor moment in late stance of 0.70 N·m/kg body weight while the patient was barefoot and 1.32 N·m/kg body weight while the patient was wearing the FRAFO (P < .0001). Knee extension during the barefoot trails was 20.5°, and was 12.3° during the FRAFO trials (P < .0001). Electromyographic activity of the rectus femoris in terminal stance decreased significantly during FRAFO trials compared to the barefoot trials (307 mV versus 53 mV; P < .0001) consistent with the improved knee extension. FRAFOs set in 10° dorsiflexion provided a significant increase in knee extension and knee-extension moment during gait for this patient with myelomeningocele, despite 20° bilateral knee-flexion contractures.
Key Words: spina bifida, knee-flexion contracture, floor-reaction ankle-foot orthosis
Introduction
During the past two decades, computerized clinical gait analysis has become widely used for the assessment of orthotic devices. The ability to analyze a patient's gait objectively and accurately provides the practitioner with another tool to optimize selection of an orthosis. A comparison of a patient's gait while barefoot and while wearing an orthosis can yield valuable information such as joint range of motion, kinetics, and muscle-firing patterns. In the future, such testing may be a requirement to document the improvement of gait patterns with an orthosis for reimbursement purposes.
Spina bifida, with an incidence of one per 1,000 births in the United States and occurring in the first month of pregnancy, is a neural tube defect occurring when the central nervous system of a developing fetus fails to form normally.1 The location of the defect can be anywhere from the brain to the distal end of the spinal cord. In myelomeningocele, the most common type of spina bifida, a portion of the spinal cord is undeveloped, vertebral bone formation is disrupted in the affected area, and an absence of skin covering the bones and spinal cord occurs. The most commonly affected location is the upper lumbar to the upper sacral vertebrae. Due to this dysfunction of the spinal cord, abnormal function of the brain, spinal cord, kidney, bladder, bones, and muscles may occur.2
Patients with myelomeningocele tend to stand in a crouched position (flexed hips, knees, and ankles) due to lower-extremity weakness. Compound this problem with knee-flexion contractures, and the patient's ability to achieve an efficient gait pattern is severely decreased. The loss of knee extension due to the contractures result in a shortening of step length seen at terminal swing. The inability to appropriately extend the knee in mid and terminal stance increases the force on the quadriceps.3 In this crouched position, the ground-reaction forces generally act posterior to the knee center, encouraging further knee flexion. A floor-reaction ankle-foot orthosis (FRAFO) may be prescribed with the goal of shifting the ground-reaction force more anterior to the knee center, providing a knee-extension moment and increasing knee extension in stance.
FRAFO Design and Biomechanics
The design of a FRAFO for this patient included a full toe plate, rigid ankle, and an anterior tibial shell section. The combination of these three components allow the plantarflexion-knee extension couple (PF/KE) to occur, causing a knee-extension moment.4 This knee-extension couple helps to support weak quadriceps and plantarflexor muscles. Lindseth et al.5 stated that pressure against the innervated area of skin just anterior and distal to the knee joint will provide proprioceptive feedback. Ounpuu et al6 recently reported that the benefits of a FRAFO in patients with myelomeningocele included improved knee and ankle function in the sagittal plane. An increased knee extension in terminal stance and an increased knee range of motion in patients with L-4 and L-5 myelomeningoceles were also reported.
Electromyographic (EMG) analysis of specific muscles of the lower extremity in conjunction with gait evaluation is a useful tool in evaluating pathologic gait. Because various muscles fire throughout phases of the gait cycle, EMG tests isolate minimum or peak muscular activity. Park et al7 examined the EMG activity of the tibialis anterior, medial hamstrings, gluteus maximus, gastrocnemius, and rectus femoris in patients with myelomeningocele. It was found that with the use of ankle-foot orthoses the timing of the knee-extensor stance-phase activity was improved. It was hypothesized that this reduction in knee-extensor activity would reduce energy consumption.
The purpose of this case study was to use computerized gait analysis on a patient with an L-5 myelomeningocele and 20° bilateral knee-flexion contractures to determine whether a FRAFO set in 10° dorsiflexion would produce a knee-extension moment and increase knee extension.
Methods
An active 15-year-old boy with an L-5 level myelomeningocele and 20° bilateral knee flexion-contractures was evaluated by using computerized gait analysis. Range of motion at the hip and ankle were normal; however, 20° flexion contractures were present at the knees.8 Manual muscle tests showed normal muscle strength at the hip and knee, and trace plantar and dorsiflexors at the ankle. The thigh-foot angles and transmalleolar axes were normal. The patient has been an active community ambulator in FRAFOs for the past five years (Figure 1
).
The FRAFO consisted of a posterior entry design with a solid toe plate that extended to the distal end of the phalanges. It was fabricated from 3/16 inch copolyester with carbon reinforcements extending from mid tibia to the distal phalanges to ensure maximum rigidity at the ankle. Ankle positions on both sides were set at 10° dorsiflexion, determined by the patient during a test socket fitting, which enable him to function 16 hours per day in the orthosis. The patient's activities include basketball, softball, and hiking.
Gait analysis was performed by using a 6-camera Vicon 370 system (Oxford Metrics, Oxford, England) with two AMTI force plates (Advanced Mechanical Testing, Bedford, MA). Markers were placed on the lower extremity in accordance with Vicon Clinical Manager (VCM, Oxford Metrics, Oxford, England). Data were processed with VCM, and representative trials were chosen. The average of these trials was used for statistical analysis. One-way analysis of variance (ANOVA) was performed on each variable by using repeated measures ANOVA comparing barefoot to braced conditions. Range of motion, joint kinematics (motion) and kinetics (moments and powers) were determined for the hip, knee, and ankle during barefoot and orthosis walking. EMG activity of five lower limb muscles were recorded using surface electrodes. These were medial gastrocnemius, tibialis anterior, medial hamstrings, rectus femoris, and vastus lateralis. Comparison of the joint motion and joint kinetics for the barefoot and orthosis walking was completed by using repeated measures ANOVA (Statview, SAS Institute, North Carolina). All joint moments are internal unless stated otherwise. For comparison purposes gait data was collected on 24 normal adults by identical methods as subject. (Unpublished) This data was in aggreement with previous research.9
It was hypothesized that an increase in knee extension moment and knee range of motion can occur while using FRAFOs for a patient with myelomeningocele and 20° bilateral knee-flexion contractures. A comparison of the knee and ankle range of motion, moments, stride length, and EMG activity of the quadriceps throughout the gait cycle barefoot and in the orthosis was used to determine if there was any improvement with the FRAFO.
Results
Ankle motion in the sagittal plane showed excessive dorsiflexion while the patient was barefoot and improved in late stance while the patient was wearing the orthosis (Figure 2
) (P < .000423). Decreased ankle plantarflexor moments occurred throughout the stance during the barefoot trials. While the patient was wearing the orthosis, the pattern was very close to normal, increasing gradually as stance progressed (Figure 3
) (P < .0001).
The sagittal motion of the knee showed flexion throughout stance while the patient was barefoot, which was significantly reduced toward normal while the patient was wearing the orthosis (P < .0001) (Figure 4
). The barefoot trials showed the lack of an internal knee flexor moment during the stance (Figure 5
). With the orthosis, the internal knee flexor moment occurred during midstance and tended to follow the normal curve. In late stance, the knee extension moment produced while the patient was wearing the orthosis was significantly greater (P < .0001) than that produced while the patient was barefoot. EMG activity of the vastus lateralis and rectus femoris muscles peaked at midstance during the barefoot trial, and diminished to near zero during the FRAFO trial (Figure 6
) (P < .0001), which was similar to normal.
Gait speed was not significantly different in the barefoot trials compared to the FRAFO trials (P = .6465), however, stride length was significantly increased with the FRAFO (P < .0001). The results are summarized in Table 1
.
Discussion
The results of the gait analysis clearly show an improved gait pattern in this patient with myelomeningocele and 20° knee flexion contracture when using FRAFOs set in 10° of dorsiflexion. The knee range of motion, as well as ankle and knee moment plots, normalized with the FRAFO.
The barefoot trials show an increase in dorsiflexion of the ankle, consistent with the subject's weak plantarflexors, that resulted in excessive anterior tibial translation over the talus during stance. During the FRAFO trials, the ankle range of motion curve tended to dorsiflex slightly from early to midstance, likely due to slight bending of the orthosis and also some movement of the markers placed on the shoe. Ideally, the orthosis should restrict ankle motion to near zero.
The reduced ankle plantarflexor moment produced in the barefoot trial is a result of weak plantarflexors not acting to retard anterior tibial advancement. The decreased ankle plantarflexion moment is caused by a reduced toe lever arm. With the FRAFO set at 10° dorsiflexion at the ankle, the ankle plantarflexor moment curve increases and closely follows the normal curve due to the rigid lever arm of the toe plate transmitting the ground-reaction force across the ankle joint to the anterior tibia.
In Normal gait the ground reaction force would pass anterior to the knee center in mid-stance (Figure 7a
) The subject's knee is in 20° of flexion at initial contact. While the patient is barefoot, an external flexion moment allows the knee to progress into further flexion, possibly due to weak plantar flexors and the knee flexion contracture (Figure 7b
). The restored PF/KE couple due to the FRAFO is likely the cause of the observed increase in knee extension. The rigidity of the FRAFO allows the transfer of the ground reaction force to the tibia, improving the external extensor moment at the knee. Because the plantarflexor moment is normalized with the FRAFO, and only small amounts of dorsiflexion at the ankle occur, the majority of the torque generated at the ankle by the FRAFO is transferred to the knee. This leads to a normalized sagittal moment at the knee that results in increased knee extension.
There is evidence to suggest that the weak plantarflexors and knee-flexion contracture are the driving forces behind the absence of an internal knee-flexor moment in the barefoot trial. This was concluded because the patient has no hip-flexion contractures, has strong quadriceps, and does not have tight hamstrings. As a result, the quadriceps must be active to prevent severe knee flexion or crouch. The improved internal knee-flexion moment in late stance with the FRAFO appears to be caused by the external knee-extension moment produced by the orthosis (Figure 7c
). This hypothesis is supported by the EMG results of the vastus lateralis and rectus femoris muscle activity that decreased significantly during the FRAFO trials. Therefore, it is likely that a decrease in quadriceps activity will result in a decrease in energy consumption.10
Conclusion
The improvement of sagittal-plane knee and ankle kinematics and kinetics was clearly seen with the use of FRAFOs on a patient with an L-5 level myelomeningocele (0/5 dorsi- and plantarflexors) with 20° bilateral knee-flexion contractions. The patient, a 15-year-old boy, is a community ambulator involved in high-activity sports. It was hypothesized that the external knee-extension moment and knee-extension range of motion would improve significantly with the FRAFOs.
While the patient was barefoot, the ankle plantar flexor moment was small due to a lack of plantarflexor muscle activity and an anteriorly translating tibia during stance, but this increased toward normal while the patient was wearing the FRAFO. Knee extension was improved significantly with the FRAFO, along with an increased external knee extension moment; both due to the increased plantarflexion moment at the ankle and a reestablished PF/KE couple from the rigid FRAFO. EMG data show that the quadriceps activity decreases with the FRAFO, supporting the conclusion that the FRAFO is producing the external knee-extension moment, which may lead to a possible reduction in energy consumption.11
Gait analysis was used as clinical tool for comparing orthosis and barefoot walking. Patients with myelomeningocele, depending on the spinal level, tend to have decreased lower-extremity muscle strength that results in a crouched-type gait pattern. Adding to this pattern, a knee-flexion contracture and an efficient gait is difficult to achieve. The FRAFO-even set in 10° dorsiflexion-as used in this case study, improved the patients gait by extending the knees to the maximum and increasing the external knee-extension moment, despite the 20° knee-flexion contractions present. It is unlikely the FRAFO will function effectively for every patient with knee-flexion contractures. Therefore, it is essential to evaluate each case individually. The use of a FRAFO proved successful in this case study and enabled the patient to lead a highly active lifestyle.
References:
- Questions about Spina Bifida, A Guide from the Spina Bifida Program Department of General Pediatrics. Washington, DC: Children's Natural Medicine Center; 1995.
- See note 1 above.
- Perry J. Gait Analysis Normal and Pathological Function. Thorofare, NJ: SLACK; 1992:239-240.
- See note 3 above.
- Lindseth RE, Glancy J. Polypropylene lower-extremity braces for paraplegia due to myelomeningocele. J Bone Jt Surg. 1974: 56A(3):556–553.
- Ounpuu S, Thomson JD, Davis RB, Deluca PA. Barefoot vs. AFO's in the patient with myelomeningocele. In: Clinical Gait Analysis: A Focus on Interpretation. Hartford, CT: Gait Laboratory, Connecticut Children's Medical Canter; Feb 1998 X1 part 3.
- Park BK, Song HR, Vankoski SJ, Moore CA, Dias L. Gait electromyography in children with myelomeningocele at the sacral level. Arch Phys Med Rehabil. In press.
- Winter DA. The Biomechanics and Motor Control of Human Gait. Waterloo, Ontario, Canada: University of Waterloo Press; 1988:1-55.
- See note 8 above.
- Cuddeford TJ, Thomas SS, Aiona MD, Freeling RP. Effect of flexed knee posture on energy consumption. Gait and Posture. 1995:3(2):105.
- See note 8 above.
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