A Step in the Right Direction

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November 2001

By Edelle Field-Fote, PhD, PT

Edelle Field-Fote, PhD, PT, uses stimulation of a patient's legs to increase his walking ability.

A Step in the Right Direction

The effects of interventions for people with SCI can be objectively analyzed through the documentation of temporal-distance measures, assistive device use, and step and stance characteristics.

Who can forget the 2001 Super Bowl commercial featuring Christopher Reeve walking on stage to accept an award? While this commercial generated much discussion and controversy, no one can deny that it highlighted a predominant aspiration among those with spinal cord injury (SCI)-the desire to walk. The clinicians who work with these individuals in rehabilitation and those who investigate interventions to improve movement following SCI are also focused on this goal.

In recent years, the literature on rehabilitation research has seen many reports of interventions to improve walking function using treadmill training, body weight support, and electrical stimulation¹ as well as combinations of these interventions.² These interventions, as well as many more traditional treatments such as exercise, pharmacological management, and surgery, have the potential to affect quality of life by improving functional mobility. How can we measure the effectiveness of an intervention in improving walking function in patients with SCI? What are the key gait parameters to assess to determine whether the quality of gait has improved with training? What tools can be used to document functional change?

In individuals with SCI who retain or have regained some walking ability, there are three general categories of criteria that inform the physical therapist about a patient's walking ability: temporal-distance measures, assistive device use, and step and stance characteristics. These measures have recently been integrated into a gait assessment tool, the Spinal Cord Injury Functional Ambulation Inventory (SCI-FAI)³ designed for use in individuals with SCI who have some walking ability.

Temporal-distance Measures
Temporal-distance measures provide the therapist with information about the speed and distance of walking; speed is certainly a tremendously important variable in determining whether walking ability is functional. For example, if the individual can walk for long periods of time, but is unable to walk fast enough to cross the street before the traffic light changes, can this individual be characterized as a functional community walker? Conversely, what of the individual who can walk at satisfactory speeds, but is unable to walk far enough to get from the car to the house? For this reason, both the walking speed and walking distance must be standardized if meaningful comparisons are to be made between trials.

While it is a common practice to simply time the patient walking over a measured pathway and determine walking distance traversed per time, such measures may be misleading if the same walking distance is not measured each time. In addition, there is no consensus regarding how far the patient should be asked to walk in order to determine the average walking speed. For this reason, when assessing walking function in individuals with SCI, timed walks such as the 2-minute walk test may provide the best available temporal distance measure. It has been suggested that 2 minutes of walking is adequate for individuals with incomplete SCI to achieve metabolic steady state.³

In other patient populations, this time period has been shown to yield measures comparable to the 6- and 12-minute walk tests⁴; 2 minutes likely represents a more feasible time period for assessment in many individuals with SCI who have limited walking ability. While some authors have used temporal-distance measures as the primary means to define walking ability,^5,6 from the point of view of rehabilitation these measures may be of limited use in determining treatment goals and selection of interventions. Temporal-distance measures in isolation give the therapist little information regarding how the patient performs and coordinates the tasks of stepping and standing.

Assistive Device Use
As is the case with temporal-distance measures, the type of lower extremity orthotic device or upper extremity balance/weight-bearing device that the patient uses gives important information about walking ability.⁷ It conveys information regarding adequacy of balance, muscle strength, or, in the case of tone-inhibiting orthoses, the tone reduction needed for accomplishing the elements of walking. Documenting assistive device use allows the therapist to establish a record of progress as the patient advances to devices that require more control by the user. But as with temporal-distance measures, knowing what kind of assistive device the patient uses furnishes only limited information about their functional status.

Step and Stance Characteristics
If one is interested in assessing how the patient accomplishes the task of walking, it is necessary to examine the critical parameters that characterize the stepping (or swing) and standing (or stance) phases. The characteristics that define functional walking can be categorized into six parameters: weight shift, step width, step rhythm, step height, foot (orientation at) contact, and step length.

Weight shift refers to the ability to bear weight and to transfer weight from one lower extremity to the other as opposed to hopping on a single leg or transferring weight onto a walker, crutches, or cane. A component of this parameter is the ability to stand erect. An erect stance encourages decreased dependence on upper extremity assistive devices as it keeps the body in proper alignment with the weight over the legs. Perhaps more important, erect stance allows the hips to fully extend during walking, and there is good evidence to suggest that hip extension is important for activating the spinal neural circuitry (ie, the central pattern generator or CPG) thought to be important for the generation of locomotion.⁸

Step width has two components: the step should be wide enough so that as the swing limb is brought forward it does not strike the stance limb, and second, the final placement of the swing limb should be such that it does not pose an obstruction to the other limb when it steps. This parameter is frequently problematic for individuals with SCI in whom adductor spasticity can cause a scissoring gait.

Step rhythm is a characteristic of walking that contributes to the symmetry of the stepping pattern. The relative proportion of time spent in swing and stance (40%/60% of the cycle in the typical nondisabled [ND] individual⁹) for each limb determines the symmetry of the walking behavior. It is not uncommon for individuals with SCI to have asymmetric lower extremity strength and function. This symmetry can be defined in terms of the relative amount of time that is necessary to advance the swing limb following heel strike of the stance limb.

In individuals with good locomotor function, the swing limb begins to advance within 1 second of heel strike of the stance limb. In those with significantly impaired locomotor function, the swing limb may take 3 seconds or more to begin advancing following heel strike of the stance limb. Between these two extremes, individuals with moderate locomotor impairment may require between 1 and 3 seconds to begin advancing the swing limb. As the time to advance the swing limb increases, the symmetry of the gait pattern becomes progressively poorer. The symmetry of the pattern is further disrupted when one limb has significantly more spasticity or is significantly weaker than the other.

Step height is critical to walking as the foot must clear the floor for the step to be functional. In individuals with SCI, inadequate dorsiflexion during swing phase is the most common reason that step height is not adequate. This problem can remain even in individuals who are fitted with an ankle-foot orthosis, especially if the lack of dorsiflexion is accompanied by deficits in hip and/or knee flexion. If the patient demonstrates an inability to achieve adequate step height, this may be a problem throughout the swing phase or be a problem only at the initial part of the swing phase.

Foot contact describes the orientation of the foot as it meets the ground. In ND individuals, the body's center of mass progresses smoothly over the foot. This is due in no small part to the fact that the nervous system suppresses the soleus stretch reflex during swing phase and the early part of stance.¹⁰ Were it not for this, the stretch on the soleus that occurs as the body progresses over the base support could promote dorsiflexion and pose an impediment to forward progression. Evidence suggests that in individuals with SCI this ability to modulate the size of the stretch reflex during walking is defective.¹¹ This may contribute to the lack of heel strike in many of these individuals, resulting in the foot contact being made with the forefoot or with the foot flat.

Step length, like step rhythm, contributes greatly to the symmetry of the stepping pattern. Muscle strength and length contribute to the distance the patient is able to traverse in a single step. The foot of the swing limb can be placed in one of three possible points relative to the foot of the stance limb: 1) with the swing heel forward of the stand toe, 2) with the swing toe forward of the stand toe, or 3) with the swing toe placed rearward of the stance toe.

Change In Walking Function
The SCI-FAI has been tested and found to be a valid, reliable, and sensitive measure of walking function in individuals with SCI. It was designed to allow the therapist to record and rate each limb's step and stance characteristics independently of the other limb. In addition to providing a means to assess baseline function and record of progress, it allows the therapist to identify the areas on which the intervention may be focused. Because each of the three general categories of criteria addresses a different domain of walking function, measures within each category can be summed, but it is not meaningful to add together scores from different categories. In addition to using this form for on-site observational gait analysis, testing of the form indicated that it is equally reliable when used to assess walking on the basis of videotaped records.³

Locomotor training for individuals with SCI has functional benefits beyond walking. In addition to improvements in strength and endurance,² this training may also have a positive effect on balance and on the patient's perception of quality of life (unpublished observation). For this reason, when documenting the effects of training, it is important to consider using measurement instruments beyond those that are directly related to the type of training being utilized.

Exciting new treatments for individuals with SCI may be just on the horizon. When the time arrives that these become widely available, documenting the effects of the intervention on the full range of motor functions will be imperative. Physical therapists are the professionals who are best equipped to make the types of measurements and observations that are central to the objective evaluation of walking function. By documenting temporal-distance measures, assistive device use, and step and stance characteristics, the usefulness of rehabilitation and medical interventions for individuals with SCI can be objectively assessed.

Edelle "Edee" Field-Fote, PT, PhD, is assistant professor, Department of Orthopaedics and Rehabilitation, Division of Physical Therapy; and Department of Neurological Surgery, the Miami Project to Cure Paralysis, at the University of Miami School of Medicine.

REFERENCES
1. Barbeau H, Norman K, Fung J, Visintin M, Ladouceur M. Does neurorehabilitation play a role in the recovery of walking in neurological populations? Ann N Y Acad Sci. 1998;860:377-392.
2. Field-Fote EC. Combined use of body weight support, functional electric stimulation, and treadmill training to improve walking ability in individuals with chronic incomplete spinal cord injury. Arch Phys Med Rehabil. 2001;82:818-824.
3. Field-Fote EC, Fluet GG, Schafer SD, et al. The Spinal Cord Injury Functional Ambulation Inventory (SCI-FAI). Scand J Rehabil Med. 2001;33:177-181.
4. Butland RJ, Pang J, Gross ER, Woodcock AA, Geddes DM. Two-, 6-, and 12-minute walking tests in respiratory disease. Br Med J (Clin Res Ed). 1982; 284:1607-1608.
5. Holden MK, Gill KM, Magliozzi MR. Gait assessment for neurologically impaired patients. Standards for outcome assessment. Phys Ther. 1986;66:1530-1539.
6. Richards CL, Malouin F, Dean C. Gait in stroke: assessment and rehabilitation. Clin Geriatric Med. 1999;15:833-855.
7. Ditunno JF, Ditunno PL, Graziani V, et al. Walking index for spinal cord injury (WISCI): an international multicenter validity and reliability study. Spinal Cord. 2000; 38:234-243.
8. Pang MY, Yang JF. The initiation of the swing phase in human infant stepping: importance of hip position and leg loading. J Physiol. 2000;528:389-404.
9. Perry J. Gait Analysis: Normal and Pathological Function. Thorofare, NJ: Slack Inc; 1992.
10. Capaday C, Stein RB. Amplitude modulation of the soleus H-reflex in the human during walking and standing. J Neurosci. 1986;6:1308-1313.
11. Yang JF, Fung J, Edamura M, Blunt R, Stein RB, Barbeau H. H-reflex modulation during walking in spastic paretic subjects.

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November 2001