Pathological Gait: Parkinson's Disease
The ability to walk efficiently, by producing smooth and coordinated movements, is compromised in Parkinson’s disease patients. This reduced ability to walk efficiently due to diseases is termed pathological gait. A number of studies have observed many alterations in pathological gait, and such alterations are discussed in depth in this article. Also, are described in details the interventions, implemented by clinicians and physiotherapists, aiming at helping Parkinson’s disease patients improve the ability to walk efficiently.
For proper execution of locomotor movements, functional integration of neural structure involved in locomotor and postural control is essential. Both locomotor and postural control systems share common neural structure of motor centres i.e. brain stem and spinal cord. However, for smooth movements during locomotion the afferent information from visual, vestibular (balance), and proprioceptive systems are also very important, as they may influence the central pattern generator. Thus, pathological alteration of the pattern generator or of the afferents is conducive to abnormities in the muscle activity (kinetics) and consequently to kinematics parameter such as joint movements, as well as floor reaction forces.
Parkinson disease (PD) is caused by a dramatic reduction in the neurotransmitter striatal dopamine (DA) levels, as a consequence of the degeneration of the DA neurons in the substantia nigra, located in the region of the basal ganglia of the brain. Parkinson disease is a chronic and progressive disease of the brain, and the clinical symptoms consist of variable manifestation of tremor, rigidity, bradykinesia (slowness), hypokinesia, (reduced movement), and postural dysfunction combined in some cases with such disorders as psychiatric disturbance, and dementia. Slowness in initiating and performing movements, as well as reduced excursion of movement are typical features of PD. A reduction in the variety and amount of physical activity follows as result of a tendency to these changes in PD persons.
Alteration of gait cycle associated with Parkinson Disease
In parkinsonian patients (PP), monosynptic and polysynaptic reflexes are diminished in the leg extensor muscles, and preprogrammed responses of the flexor muscles are impaired. It also appears that PP have difficulties in both preparation and execution the phases of ambulation. Neurophysiological studies indicate that the control of posture and locomotion are interdependent at many different levels of the central nervous system, from the motor cortex to the basal ganglia, the brain stem, and the spinal cord. Parkinsonian patients ambulation is often characterized by marked shuffling, which is probably due to the deterioration of balance control. In fact, impairment of postural control, and balance are cardinal symptoms of PD, which often result in falls. In addition, impaired balance can be related to the increased gait variability, particularly the double support duration.
The hypokinesia in parkinsonian patients is associated with a reduction of stride length, cadence and an increase of stride-stance, and double support duration. Furthermore, PP have difficulties combining the single step to an accurate sequential motion. The lack of basal ganglia may be the cause of such inability to coordinate sub-movements. These factors often result in a slower ambulation, and reduced ability to maintain stable walking patterns. In terms of cadence often there is not significant difference compared with normal gait suggesting that hypokinesia during ambulation in PP may be attributable predominantly to decreased stride length.
In PP ambulation normally exhibits abnormities in both kinetics and kinematics. In normal gait when the foot strikes the ground, the initial contact occurs with the heel, and progressively the body weight (BW) is shifted to midfoot and then to forefoot (heel to toe motion). In PP this ability appears to be impaired, in fact they tend to produce a footflat strike, and sometimes even the forefoot strikes first (toe heel walking). Footflat striking results in a reduced ability to cushioning the body’s centre of gravity (COG) and thereby increasing the shock. In toe striking there is a comparatively increase in energy expenditure, as triceps surae (calf muscles) has to contract, and this is associated with a lesser effective propulsion during heel strike (HR) and toe off (TO), since the ankle is already plantar flexed. The higher forefoot loading typical in PP and decreased heel contact can be related to dynamic balance impairment, as the forefoot structure allows much more muscular control to compensate for imbalances. Thus, PP may use this strategy of forefoot balance control to compensate for the neuromuscular deficiency. There is some evidence to suggest that less heel loading normally augments as the severity of the disease increases.
Furthermore, PP exhibit the tendency to tilt excessively the trunk forward in order to facilitate the forward motion of the COG. Such excessive leaning can also occur as a result of diminished stride length and augmented cadence. The reduced propulsive capability of PP due to inefficient kinematics is associated with diminished strength (kinetics), resulting in a reduced foot lifting during the swing phase, and in turn this produces a smaller clearance between toe and ground. The reduced foot clearance and stride length, impaired coordination, stooped posture, decreased arm swing, and increased instability may predispose PP to fall. Some studies have shown that 51% of PP with moderately advances disease fell at least once, whereas only 15% of the age matched control subject fell. Falls in patients with PD are commonly related to sudden turning movements, and are particularly likely to occur when turns are made while performing a secondary task, such as talking or carrying an object. Despite detailed testing of gait and balance in fallers and non-fallers, the specific factors that are critical to falls, as well as falls prediction in PP remain elusive.
In addition to all the previously mentioned factors associated with falls in PP, some more may also be conductive to such events. This may include, stride time variability, the magnitude of the fluctuations of the gait duration associated with diminished functional status. Furthermore, the increased variability of gait may be a manifestation of a decline in motor control and dynamic balance deficits that apparently heighten the risk of falling. In PD, the gait initiation disorder becomes obvious when the patient start suffering from postural instability, which progressively appears in the later stage of the disease. On physical examination, the gait initiation impairment, also called “slipping clutch phenomenon”, can be aggravated to such an extent that the patient becomes “frozen” to the spot, or “suddenly blocked”. These freezing episodes suggest that the impairment of postural phase could reach a stage beyond which step triggering would become no longer possible. To explain these observations, two complementary hypotheses can be put forward. In the first one, the deficit of propulsive force would be restricted to the postural preparation preceding and accompanying the first step. In the second hypothesis, the main deficit would concern the coordination between postural preparation and the triggering of the first step. However, it is well established that in PD that the freezing episodes become more obvious when a direction change occur during gait. It can be expected that the postural preparation becomes more complex when it comprises not only the body’s inclination forward and onto the supporting leg, but also the whole body re-orientation in the step direction. Such re-orientation corresponds to an axial rotation of different body segments; namely the head and the trunk (shoulders and pelvis). Because of their difficulty to coordinate two tasks simultaneously, or sequentially, any directional change during gait should stress the step initiation in PP.
Interventions
The following section will discuss the possible interventions in order to reduce and possibly correct the disabilities presents in parkinsonian gait. A sound intervention programme usually comprises various stages, and these may include: a) Distinguish between “normal” and “abnormal”. During this stage of treatment the therapists analyse the kinetics and kinematics of normal gait, and compare to parkinsonian gait. Thus, after a sound analysis and comparison the therapists identify, those individual components of parkinsonian gait that are aberrant or missing, b) Classify the severity of disability; in this stage the therapists evaluate the extent of the gait patterns deviation, c) Identify the underlying mechanisms that cause such deviation e.g. lack of balance, coordination, or strength, and d) Design an appropriate program of interventions in order to reduce, and possibly restore the equilibrium of kinetics and kinematics of parkinsonian gait.
Furthermore, the space in which the training occurs should have some relevance to the space in which the patient will function ultimately. If there is an interaction between environments and performer then the way the environment is structured will directly affect the movement that emerges as well as the learning process. Thus, since the goal is to function successfully, then the environments should be as much as similar to the real environment where the patient ultimately will spend much of his/her time; where people and obstacles are moving and where timing is critical. Additionally, physical education and motor learning literature has identified that as a general rule the skill in performance increase as a direct function of the amount of practice. However, it has to be noted that the training should aim to correct aberrant gait patterns, and depending on the severity of the disease some piece of equipment are useful, and at time may be necessary during rehabilitation.
Other factors to be considered include patient’s anthropometric characteristic, and the ability to handle one or more of the requirements of gait (balance, limb advancement and limb support). For instance, if the patients balance is very weak walking, the aid of parallel bars may help the patient during the initial stage of rehabilitation. However, the parallel bars tend to promote the use of the upper extremity in a pulling fashion for postural support and forward progression. There is some evidence suggesting that compensatory strategies, i.e. pulling or pushing by the upper limb, may become efficient and be difficult for the patient to discard later. Thus, therapist should gradually remove such support as the patient progresses.
Another important feature present in PP, are weakened coordination associated with rigidity. The patient has to relearn the efficient gait coordination, and the training for this purpose may include: while sitting the patient alternates flexion and extension of the toes, ankles, and knees. Thus, by breaking down the different aspects will facilitate learning. However, since gait is a dynamic activity requiring control over perturbations occurring during both double support and single support phases, perhaps the only way to improve locomotor balance and coordination is to practice locomotor type activities. The activities must have both double support and single support phases linked together. They must not be discrete, but cyclical and rhythmic. Hence, the training should always include the associative phase, which involves the linking of the various components of the skill into a smooth action during ambulation.
Other exercise may include: while laying in a crok position the patient rolls his knees from side to side. Then, while in the supine position the patient alternates hip and knee flexion and extension. Finally, while standing the patient practices high stepping, ankle dorsiflexion with straight knees, cross-over stepping focusing on heel-strike, and walking sideways. These exercises attempt to correct the decrease in heel-strike, weight transfer, and the range of motion of hips and knees seen in Parkinson's disease. They also help to decrease stiffness and weakness in the lower extremity muscles.
Other important aspects of gait in PP that should be improved are stride length, and foot clearance. Some studies have shown that the electromyography (EMG) activity, especially the gastrocnemius muscles, was smaller in amplitude and less well modulated under various conditions in PP compared to healthy subjects. In addition, the amount of co-activation of antagonistic leg muscle is normally grater in PP, and this tends to accentuate with the severity of the disease. This has an important functional significance, as the leg extensor activity determines the force of pushing-off, thereby determining the shortened stride length. This may be related to impaired function of extensor load receptors leading to an inappropriate activation of the gastrocnemius muscles. In fact, the effectiveness of synergy is dependent on the timing and magnitude of the muscle’s activation patterns, and the strength of the muscle. Furthermore, the ability of the muscular system to generate tensile force also depends upon the ability of the nervous system to appropriately activate the various muscles. Thus, some training aim to improve the strength on the extensor muscle may help to augment the propulsive force during push-off, thereby increasing the stride length. Additionally, strength training also improves the nervous system ability of muscle recruitment patterns, and firing frequency.
The training programme may include exercises of ankle plantar flexion, for strengthening the triceps surae. Standing calf raise would involve more the gatracnemius, whereas seated calf raise would activates more the soleus. Such exercises should be combined with locomotor practice, in order to incorporate the strength gain into the gait movement pattern. Encouraging the patient to increase his/her step length, by placing a series of obstacles at distance appropriate for the individual’s step length, and ask to patient to step over the obstacles, this may help to improve both stride length and foot clearance. However, since such training would require a certain degree of balance and coordination, care has to be exercised during such training in order to prevent the patient from falling.
The location and the surface where the training takes place appear to be particularly important. Treadmills have been used in different in locomotor training; there are both advantages and disadvantages to use of the treadmill in gait training in PP. The use of treadmill could assist PP by forcing them to speed up their gait. Additionally, it may help to gain aerobic endurance without having to handle the requirements of overground motion, i.e., person or obstacle avoidance, or reduction in ankle propulsion for push-off phase of stance. There are however, a number of arguments against training on the treadmill, and these may include: i) the speed of walking is driven by the treadmill rather than the patient, ii) the patient is not required to push-off as there is not forward motion, c) the stance limb is pulled backward under the trunk instead of the trunk gliding ever the stance limb. Essentially, in overground ambulation there is a forward progression of the COG (sagittal plane). In contrast in treadmill locomotion such forward progression does not take place, since the “ground” is moving under the patient feet. This will change considerably, coordination, technique, kinetics, and kinematics compared to overground gait, hence, the use of training on treadmill should be limited.
Ultimately, any locomotor skill gained on clinics, gymnasiums, and other venues where the training takes place, should then be transferred gradually in environment where the patients would spend much of his/her time. Some studies have found that walking in hilly terrain with expected as well as unexpected obstacles acting as environmental cues as well as intentional strategies, may contribute to the beneficial decrease in PD symptoms. Furthermore, spending time, and walking in natural environment, such as parks, mountains can initiate a process where the patients can get new insight, better self-confidence, and start using their own resources, and this may help to restore the ability of efficient locomotion in PP. Additionally, the training approach should also provide strategies to overcome freezing spells often seen in the third phase of Parkinson's. The patient should try to rock from toes to heels in order to improve posture and reposition his centre of gravity. If this does not allow the patient to proceed he should try to step in place or step backwards. Environmental changes can also affect the frequency and severity of freezing spells. For example, if the patient is given a cordless phone to carry with him, his stress level decreases and as a result freezing may decrease. Accurate assessment of turning strategies might assist clinicians in evaluating the risk of falls, and could be used to evaluate the outcome of intervention studies, such as physiotherapy.
In conclusion, Parkinsonian patient’s exhibits variable motor manifestation such as gait dysfunction e.g. shortened stride length, and hypokinesia. Parkinsonian’s patients are likely to restrict their physical activity because of their adaptation to their reduced physical performance, and possibly fear of falling. The training should aim to help the patients to regain the physical performance, locomotor capacity, and self-confidence. In addition, the venues training where the training takes places e.g. clinics, or gymnasiums, and the use of equipment e.g. treadmills, should be particularly used at the beginning of the intervention. As the patient progresses any equipment should be gradually removed, and the training environmental condition should mimic the environment in which the patient will function ultimately. This may help Parkinsonia’s patients to improve their physical performance, and possibly to infuse the feeling of being able to produce efficient, smooth, and harmonious locomotor movements.