Cerebral vascular accidents (CVA) with resulting hemiparesis frequently impair a person's ability to ambulate.1–4 Typically, a person with acute hemiparesis secondary to CVA will exhibit flaccidity or hypotonicity of the ankle dorsiflexor muscles, whereas a person with a chronic CVA will exhibit spasticity of ankle plantarflexor muscles.5 The hemiparesis often results in impaired dorsiflexion of the ankle with resulting sustained plantarflexion and inversion of the ankle during the swing phase of gait, a lack of eccentric control of ankle dorsiflexion during weight acceptance, and a decrease in gait velocity.1–4
Use of an ankle-foot orthosis (AFO) has been shown to improve ankle kinematics and increase the velocity of gait for persons with CVA.1,6–13 Therefore, AFOs are frequently prescribed to patients with chronic stroke who have difficulty advancing a hemiparetic lower limb during gait. Currently, commonly prescribed custom AFOs include the bi-channel adjustable ankle locking AFO and custom-molded polypropylene AFOs. These traditional AFOs have been shown to provide many benefits during gait including increased gait velocity,1,6–10,12–14 a more symmetrical gait pattern,9,11–14 and decreased energy expenditure.7,10 Increased step length, improved toe clearance, improved swing symmetry, and decreased equinus at the ankle during the swing phase of gait have also been demonstrated.9,11–14 During the stance phase of gait, heelstrike duration is increased, duration of stance is increased, double support time is reduced, equinus of the ankle and recurvatum of the knee are controlled, and hip extension is increased.1,7,9,11–14
The aforementioned custom AFOs should be prescribed at 4 to 6 months post-CVA15 and are primarily used once spasticity has emerged. These patients with chronic CVA tend to require a more rigid orthosis that will provide ankle stability and adequate dorsiflexion during swing.16 Patients during the subacute period post-CVA are less frequently prescribed custom orthoses secondary to being in the process of recovery, less force being required to lift a foot with hypotonia, and custom orthoses being difficult to obtain if a patient is being treated in a hospital or rehabilitation facility secondary to insurance limitations.17 Therefore, therapists are typically limited to types of orthoses available “off the shelf” or that can be manufactured quickly and cheaply.
A common off-the-shelf AFO is a posterior leaf AFO. A posterior leaf AFO consists of a footplate and a long narrow posterior cuff that is designed to keep the ankle joint in neutral (Figure 1).16 Another type of AFO that can be easily fabricated and used before obtaining a custom orthosis is the dynamic ankle orthosis (DAO) also known as the Utley's foot orthosis (Figure 2).18 The DAO design consists of a footplate and a short medial cuff fabricated from Polyflex II (Smith and Nephew Roylan, Menomonee Falls, WI). A DAO theoretically provides medial ankle stability by reducing subtalar joint inversion and providing the proper base of support for weight acceptance. This positioning allows for normal tibial advancement during stance phase of gait and potentially assists in foot clearance during the swing phase of gait.18 However, no published research exists that investigates the effects of the DAO on ankle kinematics.
Currently, it is common practice to prescribe posterior leaf AFOs for patients with decreased strength in the tibialis anterior muscle. 18–20 However, there are limited guidelines for prescription of a DAO. The purpose of this study was to determine guidelines for prescribing a posterior leaf AFO when compared with a DAO or no orthosis, based on ankle dorsiflexion manual muscle test (MMT) scores and ankle kinematics during gait in subjects post-CVA.
Fifteen subjects participated in this study. All participants were recruited during their stay at an inpatient rehabilitation hospital and had a diagnosis of CVA-acquired hemiparesis. The mean time of post-CVA was 86.3 days with a range of 16 to 208 days. Only one subject was within 6-month post-CVA. Inclusion criteria consisted of being 1 year or less post-CVA, the ability to actively extend the knee against gravity through at least one half of the knee range of motion while sitting, and the ability to walk a minimum of 20 m without assistance. All subjects exhibited normal to minimal spasticity of the triceps surae muscles as measured by the modified Ashworth Scale (Table 1).
A VICON 460 Motion Analysis System (Vicon – Lake Forest, Lake Forest, CA) was used to acquire a 3D motion images modeled as a segmented chain for the lower limb. Embedded force plates (Advanced Mechanical Technology Inc., Watertown, MA) were used for determining gait events. Video recording from a JVC (Victor Company of Japan Ltd, Yokosuka, Kanagawa) color video camera and video capture software (Broadway Pro 5.1, Data Translation Inc. Marlboro, MA) were acquired to allow an observational comparison of movements. Data from the video camera, force plates, and motion analysis cameras were simultaneously collected, synchronized, and saved using the VICON 460 Datastation.
Posterior leaf AFOs were acquired from a nationwide medical supply company and are representative of orthoses readily available in hospitals and rehabilitation facilities. Before testing, a posterior leaf AFO was sized for each participant according to manufacturer instructions. DAOs were also fabricated for the hemiparetic lower limb for each participant following guidelines outlined in the course materials “Orthotics used with the Neurodevelopmental Treatment Approach to Neurologic Patients.”21
To assure human rights protection, the study was approved by the institutional review board at a local university. Participants also signed an informed consent before participating in the study. During testing, participants wore a comfortable pair of walking shoes that could accommodate the orthosis and short athletic socks. For acquisition of data from the VICON 460, reflective markers were placed bilaterally at standardized anatomical positions including the anterior and posterior sacroiliac spines, thighs, knees, tibia, ankles, heels, and toes.
All trials were randomized via a Latin square.22 All trials were conducted on the same day, and different orthoses were donned and doffed without altering the reflective markers. Participants were allowed a minimum of 5 minutes to become comfortable wearing the reflective markers and orthosis between each condition. A repeated measure design was used, so the participants served as their own controls. Participants walked 10 m at a self-selected speed. Data were collected as the subjects walked across the force plates and were in view of the motion analysis cameras and video cameras. Participants were asked to walk during three different conditions: 1) shoes only, 2) posterior leaf AFO, and 3) DAO. Participants were allowed to use a cane during ambulation if necessary but were required to use the same cane for all trials. Participants were asked to walk for a minimum of 10 trials for each condition.
Sagittal plane ankle joint angles were acquired from the VICON 460 motion analysis system. Ground reaction forces acquired from the force plates and visual confirmation were used to mark gait events including toe-off and initial contact of bilateral lower limbs. From theses gait events, the swing phase of gait (toe-off to initial contact of the same foot) was determined for the hemiparetic lower limb. The ankle angle was investigated at the point of initial contact for the hemiparetic lower limb. Also, the average ankle angle from the middle one third of the swing phase of gait was used for data analysis. These portions of the gait cycle were selected based on normal gait kinematics. The ankle is normally dorsiflexed to a neutral (90°) position during initial contact and the middle one third of the swing phase of gait.23
Data were analyzed using a repeated measure analysis of variance. A p value of ≤0.05 was used to determine significance for statistical tests. Participants were divided into two groups based on MMT scores of the tibialis anterior muscle.24 Manual muscle testing was performed with all subjects in a seated position. Subjects were asked to move their ankle into dorsiflexion, and manual resistance was applied to the dorsum of the foot. The first group consisted of nine participants with dorsiflexion MMT of ≥3+. The second group consisted of six participants with a dorsiflexion MMT of ≤3.
When the orthoses were compared across groups, there was no significant difference in velocity of gait (p = 0.22), ankle angle during initial contact (p = 0.72), or swing (p = 0.86), demonstrating that the different orthoses alone did not make a significant difference in velocity or ankle angle. However, when comparisons were made between groups based on MMT scores, there was a difference based on an interaction between MMT scores and orthotic intervention. A significant interaction between ankle angle and brace was observed during initial contact (p = 0.001) and during midswing (p = 0.005) as demonstrated in Table 2. Participants with a MMT of ≥3+ exhibited ankle dorsiflexion angles approaching neutral (90° of dorsiflexion) when no brace was used or when the DAO was used compared with use of the posterior leaf AFO. Although participants with a MMT of ≤3 exhibited normalized ankle dorsiflexion angles approaching 90° with use of the posterior leaf AFO compared with using no brace or the DAO (Figures 3 and 4).
Previous studies have demonstrated individuals poststroke are able to walk with improved toe clearance during swing secondary to increased dorsiflexion when using an AFO.8,9,11,12 The current research helps to clarify a subset of individuals with stroke who may benefit from use of a posterior leaf AFO and a subset of individuals who may be hindered by use of a posterior leaf AFO. Participants with a tibialis anterior muscle MMT score of 3 or less showed an improvement in ankle dorsiflexion during swing and initial contact phases of gait when ambulating with a posterior leaf AFO. Participants with a tibialis anterior muscle MMT score of 3+ or greater exhibited a decrease in toe clearance during gait when using a posterior leaf AFO compared with ambulating without an orthosis. These results indicate that a tibialis anterior muscle MMT score can be used to identify individuals who may benefit from use of a posterior leaf AFO.
The posterior leaf AFO is designed to limit passive plantarflexion secondary to weakness but can have the unintended consequence of limiting active dorsiflexion in participants with a MMT of ≥3+. In contrast to the AFO, the DAO design is more flexible and allows greater freedom of movement in the sagittal plane. These results indicate that the DAO may be a better choice than the posterior leaf AFO in individuals with hemiparesis who also have an ankle dorsiflexion MMT score of 3+ or greater.
Use of dorsiflexion manual muscle testing can help to assist clinicians when determining which orthosis to use for patients post-CVA being treated in a hospital or rehabilitation facility. Individuals with a MMT of 3 or less will likely improve toe clearance during gait with use of a posterior leaf AFO. In contrast, individuals with a dorsiflexion MMT of 3+ or greater may be hindered by use of a posterior leaf AFO. If bracing is required for ankle stability, use of DAO may be more appropriate for individuals with a MMT of 3+ or greater.
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