Instrumented gait analysis can help characterize abnormal gait patterns in patients with cerebral palsy, which improves clinical decision making. Early interventions based on gait analysis can help minimize the long-term adverse effects of poor biomechanics.
By Frank M. Chang, MD, Jason T. Rhodes, MD, MS, Katherine M. Davies, BA, and James J. Carollo, PhD, PE
Walking is an almost effortless activity for most people, usually done without a second thought. For people with cerebral palsy (CP), however, this is not the case.
CP is the most common pediatric neurologic disorder, defined as “a group of permanent disorders of the development of movement and posture, causing activity limitations that are attributed to non-progressive disturbances that occurred in the developing fetal or infant brain. The motor disorders of cerebral palsy are often accompanied by disturbances of sensation, perception, cognition, communication, and behavior, by epilepsy, and by secondary musculoskeletal deformities.”1
Children with CP frequently experience problems with muscle tone, motor control, spasticity, and balance that lead to gait abnormalities. If left untreated, these musculoskeletal deformities will increase in severity as the child grows. Although assessment and treatment of impairments associated with CP are especially critical during the growing years, CP is a lifelong disability that confers an increased incidence of secondary medical conditions as children mature. Therefore, it is essential to address gait abnormalities early to prevent the long-term effects of poor biomechanics, which can result in pain and deteriorating ambulatory function.
No two individuals with CP have the same levels of overall function and societal participation, and this necessitates an individualized assessment of each patient by a qualified practitioner. This assessment should ideally be part of a multidisciplinary approach that includes assessing the patient’s functional level and anatomic deformities, as well as determining how far the patient has progressed in the natural history of their particular CP gait pattern. Understanding the patient’s level of progression of skeletal deformities and contractures is important for practitioners tasked with making treatment decisions, as the main goal of any treatment is to optimize the patient’s function.
Instrumented gait analysis
Treatment for children with CP varies across the world; however, use of instrumented 3-D gait analysis to define gait deviations and facilitate appropriate treatment options is the current standard of care in many centers. Typically, a clinician will perform a static physical examination and use visual analysis to assess the patient. Instrumented gait analysis adds biplanar video recording of the patient’s gait pattern; 3-D motion capture to describe joint angles, velocities, and accelerations; ground reaction forces; plantar pressures; and recording of the timing of muscle activity using dynamic electromyography (EMG).2
In practice, instrumented gait analysis allows one to understand joint angular displacements, joint moments and forces, and actual alignment of all the skeletal elements dynamically, as the child is ambulating. All of these data are collected, processed, and analyzed and then presented to a team of clinicians, therapists, and engineers with experience in gait abnormalities and treatment. Final therapeutic recommendations are determined from this team assessment. This technology based multidisciplinary approach has evolved over the last 40 years into a systematic method for analyzing gait abnormalities. Both the Commission for Motion Laboratory Accreditation,3 an independent nonprofit organization responsible for accrediting U.S. gait and motion laboratories, and a position statement from the Gait and Clinical Movement Analysis Society4 have endorsed the approach. Instrumented gait analysis is not a replacement for clinical experience, but is a tool that can be utilized to enhance clinical decision making, while also supplying evidence in support of a specific treatment plan.
Children with CP will have varied walking abilities, as the extent of injury to the developing brain is different in every child. Functional ability in children with CP can range from highly functional community ambulators to assisted-mobility household ambulators to nonambulatory individuals who rely on wheeled mobility for much of their independent locomotion. The interaction of multiple deformities produces complex gait deviations in individuals with CP. A validated and widely used classification scheme known as the Gross Motor Function Classification System (GMFCS) is used to describe the functional ability of children with CP.5 The GMFCS is broken down into five levels of motor function connected to the level of ambulation independence, from Level I children, who are able to walk without assistance in all environments, to Level V children, who are nonambulatory and require assistance for most activities.
Although the GMFCS system helps clinicians determine the functional ability of a child with CP, it does not describe the specific gait pattern a child may have. Differences in severity of impairment, compensatory mechanisms for biomechanical hindrances, and functional ability mean that every child with CP has unique gait pathologies. Practitioners can identify certain distinct gait patterns within this patient population that can help them make comparisons to determine the mechanisms of an individual’s unique gait characteristics. Gait analysis provides more in-depth information to inform appropriate treatment options.
Stiff knee gait
Instrumented gait analysis is required to detect stiff knee gait (SKG), an example of an abnormal gait pattern that can affect gait efficiency. SKG is defined by Sutherland as a decrease in the magnitude of peak knee flexion (<45°), a decrease in dynamic range of knee flexion, and delayed peak knee flexion, all of which occur during swing phase of the normal gait cycle.6 These deviations are easily recognized and quantified with instrumented gait analysis. SKG is one of the most common gait patterns that affects gait performance in children with CP, and a recent study shows that as many as 80% of the gait abnormalities in children with CP involved a SKG.7
The etiology is thought to arise from an abnormally firing rectus femoris muscle, which restricts knee flexion throughout the swing period of the gait cycle.8,9 The rectus femoris muscle firing pattern as seen with EMG either has prolonged activity throughout the entire gait cycle or an increase in activity during swing phase.10 The patient in Figure 1 was identified as having SKG based on visual analysis, joint angle measurements at the knee (Figure 3), and muscle activity of the rectus femoris as seen with EMG (Figure 4). As seen in the kinematic graphs in the sagittal plane in Figure 3, the knee is continually in extension throughout the entire gait cycle with very little flexion. A SKG pattern leads to problems with hip flexion, knee flexion during swing, energy-inefficient compensatory walking mechanisms such as forward trunk lean to keep the center of gravity over the weight-accepting foot,11 vaulting or hip hiking, and problems with foot clearance that increase the risk of tripping and falling.12,13
Surgical treatment for SKG includes a rectus femoris (RF) release or transfer; an RF transfer, however, is believed to preserve hip flexion more effectively than RF release and increase knee flexion during the swing phase of gait (Figure 2).8 The diagnosis of SKG and the subsequent treatment protocol are based almost purely on gait analysis. In addition, one-year postoperative repeat gait analysis is used consistently to monitor and evaluate results.
In our center at Children’s Hospital Colorado in Denver, Muthusamy et al investigated the effects of different RF transfer sites on kinematic measurements in children with SKG.14 When all transfer sites were analyzed together, we found an improvement in three out of five sagittal plane kinematic measurements, including knee range of motion during swing, peak knee flexion in swing (improved an average of 9°), and peak knee extension at terminal swing. We found no statistically significant effect on knee range of motion, peak knee flexion at loading response, peak knee flexion in swing, or peak knee extension at terminal swing when the distal RF transfer sites were compared; however, there was a significant improvement in postoperative knee range of motion in patients who had less than 80% of normal knee range of motion before surgery.
There are two similar gait patterns that, if not distinguished correctly, can lead to interventions with undesirable effects later in a patient’s life. An equinus gait pattern is generally characterized by the foot being in excessive plantar flexion due to spasticity and inadequate motor control. The plantar-flexed foot position leads to forefoot initial contact and premature heel rise.
Two variations of the equinus gait pattern have been described by Rodda and Graham15: true equinus and apparent equinus. A true equinus gait pattern is caused by gastrocnemius and/or soleus spasticity or contracture, and subsequent excess plantar flexion at the ankle. Hip and knee extension are near normal; however, knee recurvatum may be present if the posterior knee capsule is stretched beyond normal. On the other hand, apparent equinus is due to pathologic flexion of the knee during weight acceptance that alters the shank position and produces forefoot initial contact.16
Both patterns have an equinus appearance and a toe-toe gait pattern, but the differing etiologies call for different surgical interventions. Surgical treatment for the patient with a true equinus gait pattern involves lengthening the gastrocnemius and/or soleus muscles, lessening the degree of foot and ankle plantar flexion. However, lengthening the gastrocnemius and/or soleus muscles in an apparent equinus gait pattern causes relative calf weakness, leading to earlier tibial advancement after initial contact and, ultimately, to a crouch gait pattern,16 which is characterized by increased hip flexion, knee flexion, and ankle dorsiflexion throughout the gait cycle.
Appropriate treatment of an apparent equinus gait pattern addresses the proximal deformities, including increased hip and knee flexion. Ultimately, treatment will depend on the cause of these proximal deformities and can include multiple soft tissue and bony procedures. The use of instrumented gait analysis can allow the treating physician to determine clearly whether a patient has an apparent or true equinus gait pattern, preventing inappropriate surgical procedures.
In 2006, we completed a study at the Children’s Hospital Colorado Center for Gait and Movement Analysis comparing outcomes of patients with CP who underwent gait analysis and then followed the resulting surgical recommendations or who elected to use nonsurgical treatments instead.18 Patients received an initial gait analysis and a group of physicians, physical therapists, and bioengineers familiar with gait abnormalities made surgical recommendations.
Patients underwent follow-up gait analysis an average of one year after their surgical intervention or initial gait analysis. Kinematic measurements between the two time points in each group were compared and categorized as having a positive outcome, negative outcome, or no change. A positive outcome was an improvement in hip, knee, and/or ankle joint angles in a direction toward normal by >5° relative to the first analysis. A negative outcome was alteration of joint angles in a direction away from normal by >5° relative to the first analysis. Individuals with ≤5° of difference in either direction between the joint angles were categorized as having no change.
We found that children who followed surgical recommendations were more likely to have a positive change than children whose treatment used nonsurgical treatments. Multiple studies have shown that instrumented gait analysis can alter physician decision making about surgical treatments in children with CP compared with clinical evaluation of the patient alone.19-22 Studies have also shown that after a gait analysis, surgical correction improved function in ambulatory children and adults with CP.23-25
Many types of gait patterns are seen in patients with CP. Instrumented gait analysis makes it easier for clinicians to analyze many gait patterns by critically reviewing the kinematics, kinetics, and EMG curves of the pelvis and hip, knee, and ankle joints. Clinicians can then use quantitative measures to precisely describe and compare each patient’s information to typically developing age-matched normal individuals, which helps practitioners determine the etiology of gait abnormalities and recommend interventions that can best help this challenging group of patients.
Frank Chang, MD, is medical director of the Center for Gait and Movement Analysis (CGMA) at Children’s Hospital Colorado and professor of orthopedic surgery and rehabilitation medicine at the University of Colorado, both in Denver. Jason Rhodes, MD, MS, is an orthopedic surgeon with the CGMA and the Department of Orthopaedics at Children’s Hospital Colorado and assistant professor at the University of Colorado Denver. Katherine Davies, BA, is a senior research assistant in the CGMA at Children’s Hospital Colorado. James Carollo, PhD, PE, is director of the CGMA at Children’s Hospital Colorado and associate professor with the departments of physical medicine and rehabilitation and orthopedics at the University of Colorado Denver.
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