1/20/2024 0 Comments Define briskThe initial brisk dorsiflexion and sustained pressure are sometimes done with slight eversion of the foot.Īt the knee, the process is somewhat similar, but the positioning is different. The initial beat is the longest, with decreasing duration of beats until the fourth beat, after which the beat frequency becomes equivalent from one to the next. Each beat will be felt as a plantarflexion followed by a relaxation. ![]() It is against this pressure that the clonus beats will be felt, and the rhythm and number of beats can be appreciated. Next, at the ankle, the examiner places their hand on the dorsum of the patient’s forefoot and briskly dorsiflexes it, after which the examiner continues to maintain dorsiflexion pressure. In these cases, the examiner maintains sustained pressure on the joint which allows the clonus to be appreciated through tactile feedback and helps elicit this response.įor the ankle this involves allowing the patient to relax with a passively flexed ankle to about ninety degrees and a passively flexed knee if possible this usually involves the examiner supporting the leg with the hand not performing clonus. This article will focus on the clonus specific reflex maneuvers at the knee and ankle. Some other commonly tested clonus reflexes include the :Įliciting the clonus reaction can be done in the same manner as eliciting a muscle stretch reflex, which involves tapping the tendon of the joint when it is in a relaxed position often at ninety degrees of flexion (see MSR Statpearls article for a more detailed description of these techniques). The most common site to test for clonus is in the ankle/Achilles reflex (S1/S2 nerve routes). For example, the wrist or fingers will oscillate at a higher frequency (shorter interval between beats) than the ankle which is significantly further from the spine. The longer the nerves involved, the longer it takes for a signal to be conducted to the spine and back out to the periphery, and therefore the longer the time between beats. The rhythm of a given joint's clonus is defined by the nervous anatomy involved in that joint's stretch reflex. Therefore, clonus is considered a manifestation of upper motor neuron pathology and this explains why other signs of hyperreflexia generally accompany it. The inhibitory dampening effect of these descending nerves on alpha and gamma motor neurons is removed, leading to a hyper excitatory state in the muscle stretch reflex circuit. Hyperexcitability in muscle stretch circuits is produced when there is less tonic inhibition of motor neurons involved in the monosynaptic stretch reflex. This can occur when there is a lesion to descending motor nerves, predominantly the dorsal reticulospinal pathway, which can occur anywhere from the cortex to the spinal cord. On the other, there is an initial appropriate external stimulus that leads to activation of the stretch reflex circuit followed by a central signal which commands the muscles to continue to produce that motor response in the absence of an appropriate stimulation of the stretch reflex. A complete explanation may be a combination of the 2 theories. In one, clonus is caused by a self-perpetuating reactivation of peripheral muscle stretch circuits, with each beat producing the next. The precise pathophysiology behind clonus is not known, but there are 2 leading theories. ![]() It has other roles, for instance, it is prognostic of seizures in certain drug overdoses and therefore can be used to decide when to treat this condition prophylactically. Like other signs of upper motor neuron syndrome clonus indicates some insult to the central rather than peripheral nervous system, so part of its utility as a clinical examination skill is in differentiating the two. The test is free of cost, generally requires no equipment and can be performed rapidly and easily in a hospitalized patient. An illustrative example of what clonus might look like is a clinician tapping the patellar tendon once lightly and a subsequent series of obvious repeated knee extensions and relaxations going on for a dozen beats. It can be evaluated in many joints but is most commonly seen in the ankle joint by briskly dorsiflexing the foot. Therefore, clonus is used as part of the neurological physical exam to evaluate the status of a patient’s nervous system. ![]() Clonus is a rhythmic, oscillating, stretch reflex, the cause of which is not totally known however, it relates to lesions in upper motor neurons and therefore is generally accompanied by hyperreflexia.
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