A mechanically effective and metabolically efficient bipedal gait pattern is the result of the intricate integration of numerous physiological systems. "Normal" gait allows for the displacement of the body as a whole, in a specified direction, using momentum and streamlined movement patterns to decrease metabolic costs. As a result, the vertical and horizontal deviations of the center of mass are minimized.
For many patient populations, even minor disruptions to any physiological system can produce devastating limitations to upright stability and functional mobility. This is most often recognized by excessive displacement of the body segments accompanied by an observable decrease in velocity in an attempt to conserve energy.
This article reviews the characteristic gait patterns of six specific patient populations: muscular dystrophy, polio and flaccid paralysis, cerebrovascular accident and hemiplegia, cerebral palsy and diplegia, spina bifida, and spinal cord injury. Overviews of the epidemiology, natural history, characteristic gait patterns, gait impedance factors and orthopedic management are presented.
Key Words: Gait; Muscular Dystrophy; Polio; CVA; Hemiplegia; Cerebral Palsy; Diplegia; Spina Bifida; Spinal Cord Injury; Pathology.
According to Inman (1), "The human body, if not influenced markedly by internal or external factors, will integrate the motion of the various segments of the body and control the activity of the muscles so the energy required for each step is minimal" (1). Normal gait patterns are developed as the neurological and musculoskeletal systems adapt movement patterns over time to produce an efficient mode of ambulation.
Inman's hypothesis may be restated for many rehabilitation populations in the following manner: The human body, when influenced by internal or external factors, will acquire a pattern of motion of the various segments of the body and attempt to control the activity of the muscles and/or alignment of the skeletal levers so the energy required for each step is minimized. Application of this basic premise to six patient groups can help identify many primary factors leading to the development of compensatory movement patterns to maintain upright ambulatory abilities.
Muscular dystrophy is comprised of a group of genetically determined disorders of muscle presenting with diffuse weakness of many muscle groups. The degeneration of muscle cells and replacement by fat and fibrous tissue creates distorted and dysfunctional muscles that disrupt static and dynamic balance capabilities. Duchenne's muscular dystrophy is reported in one of 5,000 live male births. The disorder usually is identified in a child when he or she is between the ages of 1 and 5-when the child experiences difficulties with hopping, running, climbing stairs or rising up off of the ground (Gower's sign) (2) (see Figure 1) .
With the onset prior to age 5, a progressive weakness of the hip extensors, knee extensors and ankle dorsiflexors predisposes the child to contracture formation. Over time, most muscle groups of the lower extremity are significantly involved, followed by upper-extremity weakness in later years. The primary cause of decreased ambulatory abilities is directly related to measurable weakness.
Characteristic walking features of the Duchenne's patient include a wide-based, waddling gait, toe-walking, increased lumbar lordosis, significant pelvic instability with bilateral Trendelenburg signs and noticeable knee instability with a tendency for anterior collapse. Static and dynamic balance is severely challenged, and many children rely on bilateral knee-ankle-foot orthoses (KAFOs) by the age of 9. Ambulation difficulties increase and are compounded by the weakness of the upper limbs, which precludes the use of external support by canes or crutches. By 12 years of age, the child most often progresses to wheelchair independence and finally is resigned to bed care.
Orthopedic management of Duchenne's muscular dystrophy varies considerably. In general, three treatment protocols can be followed (3):
The primary gait impedance factors are related to progressive weakness, contracture formation and balance difficulties. Contracture management and orthoses have been successful in enhancing and sustaining upright ambulatory abilities in Duchenne's patients. Unfortunately, Duchenne's is a universally fatal disease secondary to pulmonary and cardiac complications, usually occurring in late adolescence or early adulthood.
Polio is a viral infection that affects the motor cells of the spinal cord and produces permanent paralysis of varying degrees. Fortunately, the polio virus is preventable with immunization but remains a major threat in many Third-World countries. There are approximately 1.6 million polio survivors worldwide, and more than 500,000 Americans contracted the virus during the 1940s and 1950s (4). More men than women were affected, with a greater percentage of lower-limb than upper-limb involvement (see Figure 2) . The infection attacks and destroys the anterior horn cells of the spinal cord, causing paralysis, flaccidity and atrophy. Recovery varies considerably among patients, from permanent disability to nearly full recovery.
In recent years, postpolio syndrome has become the primary focus of treatment for this aging population. Postpolio syndrome affects approximately 80 percent of all polio survivors with an onset from 10 to 50 years post-infection (5). The most common complaint is fatigue. Additionally, many patients report new weakness in both affected and unaffected muscle groups, pain, decrease in function, increased atrophy and muscle spasms. Postpolio syndrome was once thought to be caused by a reactivation of the polio virus but now appears to be a result of muscle fibers becoming detached from the adopted axons after many years of overuse (5).
A typical polio gait pattern is difficult to describe since polio patients are unique and creative with compensations to maintain their walking function. Common observations include lower-limb flaccidity, contracture, genu recurvatum, dropfoot, hip flexor weakness and abdominal weakness leading to lordosis. Surgical interventions such as fusions, osteotomies and tendon transfers create altered skeletal mechanics that must be further investigated and related to the overall movement pattern. A variety of static and dynamic postural compensations are noted, and excessive trunk deviations in the sagittal and coronal planes serve to increase knee stability (i.e., anterior trunk lean) and compensate for hip weakness (i.e., lateral trunk lean).
The orthopedic management of polio patients may consist of the return to functional orthoses, often after many years of nonuse. For patients with existing orthoses, new designs incorporating increased function and stability with decreased weight are desirable. Also, certain lifestyle changes as well as external walking aids may be in order. Part-time wheelchair use for community outings may help to prolong ambulatory status.
Cerebrovascular accident (CVA) or stroke is the result of a nontraumatic brain injury, specifically from the occlusion or rupture of cerebral blood vessels. Patients present with neurologic deficits, loss of motor control, altered sensation, cognitive and language impairments, and disequilibrium. Ultimately, the residual effects of the CVA relates to the size and location of the damage and the premorbid health condition of the patient.
There are approximately 500,000 new stroke patients each year; CVA is identified as the third leading cause of death in this country. CVA afflicts more men than women and is more prevalent in people over the age of 65 (6). It is the most common of all neurological deficits and the leading cause of gait impairment in rehabilitation facilities.
With loss of selective muscle control, patterned movements emerge that allow upright abilities but disrupt efficient movement patterns. It is reported that 90 percent of neurological recovery occurs within three to six months following the stroke. Therefore, long-term treatment programs are required to maximize and maintain functional status (see Figure 3) .
Observational gait assessment identifies poor coordination and dysfunctional movement patterns. Dropfoot, ankle and knee instability, loss of forward progression, and significant asymmetry lead to decreased walking velocities, often 30 percent to 40 percent of normal speeds (7). Limited load transfer through the affected limb places increased demands on the sound side. An extensor synergy emerges with hypertonicity and presents with 1) hip extension, adduction and internal rotation; 2) knee extension; and 3) ankle plantarflexion and inversion. The equinovarus posturing is usually present throughout swing and stance phases on the involved limb. With hypotonicity, a flexor synergy emerges with 1) hip flexion, abduction and external rotation and 2) knee flexion and ankle dorsiflexion and eversion. Both profiles present gait impedance factors such as altered posture, decreased functional mobility, joint pain and predisposition to contracture formation.
Orthopedic management consists of early and aggressive physical therapy and orthotic treatment programs during the initial phases of in- and outpatient rehabilitation. Occasionally, surgical interventions may be required for the release of long-standing contractures or muscle-tendon transfer procedures for improved joint dynamics. Generally, most CVA patients are managed effectively without surgical procedures.
Cerebral palsy is a nonprogressive insult to the brain occurring prenatally, perinatally or postnatally. Approximately 750,000 people are diagnosed with cerebral palsy, and 86 percent of these cases are congenital in nature (8). The most common causes associated with cerebral palsy remain low birth weight and prematurity (birth at less than 32 weeks) (9) (see Figure 4) .
While the neurological damage is nonprogressive, the orthopedic problems resulting from the insult are very progressive. Ninety-one percent of children who have cerebral palsy present with spasticity (8), predisposing these children to an ongoing battle with contracture formation. Asymmetric muscle involvement compounds movement patterns although ambulation is achieved by 70 percent of the entire cerebral palsy population (10). Indicators for ambulatory potential include the achievement of head balance by 9 months, independent sitting by 24 months and crawling by 30 months (11).
Spastic diplegia accounts for approximately 40 percent to 50 percent of children affected by this disorder. Of this group, it is estimated almost 90 percent achieve ambulatory status (9). The gait pattern often is precarious and may be observed as a "controlled fall" from one limb to the next. These children often are unable to stand and balance well statically, using momentum and velocity to maintain their upright posture and forward advancement. Delayed walking abilities often predispose these children to the development of an anteverted femoral alignment. Hip adduction, internal rotation and flexion contractures further deviate the hip joint alignment and often result in dislocation.
Dynamically, the limbs are oriented internally with various disruptions to base levers. With hypertonicity, the foot-ankle complex may present as sustained equinus with a toe-walking pattern punctuated by knee hyperextension moments. Hypotonicity predisposes the child to a more crouched gait with foot and ankle pronation, excessive dorsiflexion and sustained knee flexion. Both profiles increase metabolic costs; it has been estimated spastic diplegic children ambulate at 31-percent efficiency when compared to noninvolved children (12).
Orthopedic management is diverse with this group. Early hip procedures include derotation osteotomies and musculotendinous releases. Hamstring lengthening and rectus femoris transfers are performed at the knee to decrease contractures and increase swing-phase function, respectively. Derotation osteotomies may be performed at the distal limb segment as well as gastrocnemius-soleus lengthenings at the ankle and subtalar fusions. Pharmacological intervention may help to address the hypertonicity but also may produce undesirable side effects. Early intervention with physical therapy and orthotic treatment programs have produced positive long-term effects for patients with cerebral palsy.
Spina bifida occulta results from incomplete closure of the neural tube around the 20th day of embryonic development and may affect up to 40 percent of Americans although the deviation remains asymptomatic (13). Meningocele presents as a protruding sac containing the meninges; however, the spinal cord remains intact and can be surgically repaired with little or no damage. Myelomeningocele accounts for 96 percent of the spina bifida population and is the most severe form. In this case, a portion of the spinal cord protrudes through the back and presents as a complex multisystem involvement with both upper and lower motor neuron syndromes. Hydrocephalus is commonly associated with both meningocele and myelomeningocele (see Figure 5) .
Myelomeningocele is the most common birth defect in live-born infants with an incidence of 1 in 1,000 births or approximately 12 babies born per day with this pathology (14). Girls have a slightly higher incidence than boys, and limb deformities often are present at birth secondary to intrauterine positioning and muscle imbalance. Approximately 90 percent of these lesions occur in the midlumbar, lumbosacral and sacral regions, making most of these children ambulatory candidates (15). It is important to note the neurologic lesion is not stable throughout growth, and continual reevaluation of function is necessary.
General gait features include overall limb hypotonicity, flexed posturing of the lower limbs, decreased velocity in an attempt to conserve energy and significant foot deformities. Lesions at the 12th thoracic level allow for limited ambulation abilities while lesions at lumbar levels 1 through 4 promote limited household ambulation. Moving distally, lesions found at lumbar level 5 and below most often obtain community walker status. Gait impedance factors relate to the level of paralysis, obesity, age, motivation, energy costs, degree of deformities and decreased sensation, which can lead to pressure sores. As the child ages and gains weight, energy costs promote decreased velocity and activity levels, often leading to early wheelchair use.
Correction of lower-limb deformities by surgical management usually occurs within the first two years. Fifty percent of these children require corrective procedures for hip joint deformities, and orthoses are used to enhance ambulation and maintain plantigrade foot and ankle alignment (15). Associated medical problems include osteopenic fractures, pressure sores and neuropathic joints.
Injury to the spinal cord may be the result of trauma, vascular disorders, tumors, infectious conditions and developmental disorders. The neurologic level of injury identified refers to the most caudal segment of the spinal cord with intact motor and sensory function. There are approximately 30 to 50 spinal cord injury cases per million (approximately 200,000 individuals in the United States each year) with mild to severe injuries. The average age of injury is 26 years, with men more often injured than women (16). Eighty percent of the spinal cord injured population is under the age of 45, and approximately 25 percent of all spinal cord injuries result from violence (17) (see Figure 6) .
Sixty percent of these individuals retain a strong desire to walk after their initial injury. With combined upper and lower motor neuron deficits, patients with incomplete lesions are more likely to ambulate than those with complete lesions. Children tend to be more adaptable and often surpass adults with similar lesion levels in terms of function and ambulatory abilities. Key lower-limb muscles and muscle grade strengths required for a reciprocal gait pattern are fair hip flexors bilaterally and fair knee extensor strength unilaterally. Generally, the ambulatory potential after injury relates to the level and completeness of the lesion as well as residual strength and function of lower-limb muscles.
A majority of low thoracic level lesions are complete, resulting in a loss of both motor and sensory functions. In the lumbar and sacral regions, most injury levels retain some degree of sensation and functional motor control. Energy costs are up to 20 times greater than for nonparalyzed individuals, and these individuals present with decreased velocity with greater O2 costs (18). A large percentage of this group experiences pain as well as spastic flexor and extensor patterns, weakness, and dysfunctional coactivation of agonist and antagonist muscle groups.
Orthopedic management may be needed to address central cord, Brown-Sequard, anterior cord, conus medullaris or cauda equina syndromes. Early and aggressive physical therapy is aimed at restoring and maintaining functional range of motion and strengthening available muscle groups for recruitment and ambulation. Orthotic management ranges from ankle-foot to knee-ankle-foot orthoses with higher-level lesions requiring hip-knee-ankle-foot control or reciprocating gait orthoses to maximize functional abilities.
In the study of "normal" gait, it can be stated that each ambulatory individual acquires a unique pattern of movement that represents an efficient integration of all sensory and mechanical systems. In pathological gait patterns, patients also develop or acquire a unique pattern of movement that best assimilates the required movement patterns from both functional and dysfunctional physiological systems. The task of walking is accomplished, however precarious, and the resulting demand to the mechanical and metabolic systems often increases beyond anatomical design. Many structural and functional compensations are developed to maintain advancement of the body mass. The most observable compromise in many of these movement patterns is the reduction of velocity in an attempt to minimize the metabolic costs.
This article has identified six patient populations commonly seen in orthotic practices: muscular dystrophy, postpolio and flaccid paralysis, hemiplegia (i.e., cerebrovascular accident), cerebral palsy and diplegia, spina bifida, and spinal cord injury. The epidemiology, natural history, characteristic gait patterns and orthopedic management of the disorders have been outlined for each group.
The most important factor in determining appropriate treatment methods for any patient remains the evaluation and identification of individual characteristics to preserve ambulatory status. As such, each treatment program must remain unique to the individual to maximize both structural and functional outcomes as well as enhance overall quality of life.
Rusk (19) summarized the rehabilitation process of the individual with the following analogy: "You don't get fine china by putting clay in the sun. You have to put the clay through the white heat of the kiln if you want to make porcelain. Heat breaks some pieces. Disability breaks some people. But once the clay goes through the white-hot fire and comes out whole, it can never be clay again; once a person overcomes a disability through his own courage, deteination and hard work, he has a depth of spirit you and I know little about." (5)