ORTHOPAEDIC OR NEUROLOGIC? A PRACTICAL APPROACH TO GAIT PROBLEMS Gualtiero Gandini, DVM, Dipl. ECVN; Dipartimento di Scienze Mediche Veterinarie - Università di Bologna Via Tolara di Sopra, 50 – 40064 – Ozzano Emilia (BO) Email: [email protected] Gait examination is of crucial importance and is a relevant part of the neurological examination. The correct evaluation of gait requires experience and, especially during the first steps of the veterinary profession, may be necessary to observe carefully and for long time the gait of a patient in order to “decode” adequately what is appreciated during the examination. Re-evaluation of video recording and the use of slow motion video can be very helpful. During gait evaluation, the first aim should be the pure description of what was noticed. The interpretation of the observed signs should be done only in a second time, matching them with the categories of gait abnormalities. FUNCTIONAL ANATOMY: the normal gait –Normal gait in the dog and cat depends on the functional integrity of the cerebral cortex, the brainstem, cerebellum, spinal cord (including ascending and descending pathways), peripheral nerves (sensory and motor), neuromuscular junctions and muscles. A voluntary movement is initiated by nerve impulses generated in the cerebral cortex or brainstem. The cerebellum coordinates these voluntary movements and the vestibular system maintains balance during the performance of the movement. The nerve impulses from the brain to the peripheral nerves and, subsequently, to the muscles, travel along the descending tracts of the spinal cord. Information on the position of the limbs during movements reach the cerebellum and the forebrain from the periphery through the ascending tracts of the spinal cord and brainstem. For didactical purposes, it can be said that voluntary movement is the result of synergism between motor function (descending pathways) and sensory function (ascending pathways). Motor function – grossly, it can be said that two types of motor neurons form the descending motor tracts. The upper motor neurons, whose cell bodies are located in the encephalon, are the neurons that initiate a voluntary movement: the axons leaving these cells run down the central nervous system forming the descending tracts of the spinal cord and synapse with the lower motor neurons, bulky cells in the ventral horn of the spinal cord. The axons of the lower motor neurons exit from the spinal cord and, joining other motor fibres, form the spinal roots of the nerves, then the spinal nerves and, when appropriately grouped, the peripheral nerves. These axons connect to the striated muscle through the neuromuscular junction. Traditionally, the descending motor pathways are divided into the pyramidal and extrapyramidal tracts. These latter are formed of a series of interconnected and functionally related structures that run from the neurons of the forebrain to the lower motor neurons in the ventral horn of the spinal cord (in the brainstem for the cranial nerves). In the dog and the cat, the direct contribution of the forebrain (pyramidal pathways) to the control of gait is much less important than in anthropomorphic primates. In the dog and cat, lesions to the forebrain often cause modest or barely perceptible changes in gait, while lesions to the brainstem or spinal cord provoke fairly obvious abnormalities. Animals with lesions in the frontal or prefrontal cortex can have normal or almost normal gait as far as concerns coordination and strength of movements (sometimes there can be a mild hemiparesis on the opposite side of the lesion). In presence of a forebrain lesion, the gait can be compulsive: in severe cases the animal tends to walk continuously and aimlessly until it encounters an obstacle, where he can push its head against it. This particular compulsive behaviour is described as “head pressing”. Sensory function - proprioception – Kinaesthesia is the awareness of the position and movement of one’s own body and, in particular, the limbs. Kinaesthetic information is detected and conveyed by general proprioceptive neurons. The general proprioception system is, for teaching purposes, traditionally divided into the conscious proprioception system, which projects into the somatosensory cortex, and the unconscious proprioception system, which projects into the cerebellum. The general proprioceptive system is schematically formed of a peripheral receptor, part of the sensory component of the peripheral nerve, the ascending tracts carrying information to the cerebellum or, through the medial lemniscus, to the cerebral cortex. General proprioception, by providing continuous information on the position of the limbs during movement, is essential for the coordination of the movement itself. Other information inputs necessary for the coordination of movement derive from the vestibular system (special proprioception) and the visual system, with integration from the cerebellum. GAIT EVALUATION - The gait of a dog must be evaluated by observing the animal from the side, from the front and from behind while it walks on a non-slippery surface in a straight line and turning, while it goes up and down stairs or while it walks on a slope. For dogs, it is advisable to carry out the examination in the open air and, if necessary, in a room in which the animal can move freely. Evaluating the gait of a cat can be much more difficult: a useful strategy can be to release the animal in the centre of the consulting room and observe its movements as it tries to reach the transport container, deliberately placed at a certain distance, or any other shelter. Video recordings from the owners may be very helpful in evaluating the gait of cats. It is important to be familiar with the normal gait of different species, breeds and age groups of animals. Subjects that have difficulty in remaining in a standing position and walking should be supported if necessary. Obviously, it is essential to ensure immediate and adequate immobilisation of the spine in patients suspected to have an unstable lesion of the vertebral column and gait evaluation should be performed only when after vertebral luxation/fractures have been excluded. GAIT ABNORMALITIES - From the neurological point of view, the pathological gait can be the consequence of changes in coordination (ataxia), decrease in the strength of voluntary movements (paresis) or both. ATAXIA- Ataxia can be classified into proprioceptive (or spinal or sensory), cerebellar and vestibular. Proprioceptive ataxia derives from lesions to nervous structures involved in the control of general proprioception (sensory fibres of the peripheral nerves, dorsal nerve roots, spinal cord, brainstem, forebrain). In clinical practice, proprioceptive ataxia is often associated with disorders of the spinal cord. This type of ataxia is characterized by a loss of the awareness of the spatial position of the body and, in particular, of the limbs (kinaesthesia). The severity of the ataxia depends on the extent of the lesion and can range from just perceptible changes to obvious deficits. In the latter cases the limbs are excessively abducted and/or adducted during walking, they cross and, sometimes, there is a tendency to stand on the dorsum of the foot (“knuckling”). It is important to remember that, neuroanatomically, the proprioceptive and motor pathways are intimately related throughout the spinal cord and caudal brainstem and proprioceptive ataxia is, therefore, often associated with paresis. Ataxia can affect the hindlimbs (for spinal lesions caudal to the T2 vertebra) or all four limbs (for spinal lesions cranial to the T2 vertebra). Cerebellar ataxia is caused by disorders of the cerebellum or, more rarely, lesions that selectively affect the spino-cerebellar tracts. This type of ataxia is characterized by inability to regulate the force and range of movements with consequent dysmetria, often detected as hypermetria (an exaggerated elevation and protraction of the step). This type of ataxia is often associated with other cerebellar symptoms such as a broad- based stance and intention tremors. Cerebellar ataxia, unlike proprioceptive ataxia, is not associated with paresis. Vestibular ataxia associated with unilateral vestibular lesions is characterized by a tendency to sheer, fall or roll to one side (usually ipsilateral to that of the lesion). This type of ataxia is associated with vestibular signs such as head tilt, resting nystagmus, positional strabismus and the tendency to circle. In case of peripheral bilateral vestibular disorder, the animal develops symmetrical ataxia with loss of balance on both sides and movements of the head from one side to the other. In order to show defects in coordination it can be useful to make the animal walk up and down a flight of stairs. Animals with ataxia usually have more pronounced difficulties descending the stairs, where the imperfect control of the movements can cause the animal to fall. PARESIS/PARALYSIS - Paresis is the partial loss of voluntary motor function. Paralysis (or -plegia) is the complete loss of this function. Paresis and paralysis are, therefore, two terms that define the same type of defect (motor deficit or defect of the descending function), differing only in quantitative terms. Paralysis is a more severe condition than paresis, although not necessarily irreversible. Paresis can show different degrees of severity and can be distinguished into ambulatory (when the animal, despite the motor deficit, is able to stand on its four