Why does a medical doctor often tests the knee for reflexes? What is it really testing for ? Surely not that single area for a single purpose (reflex). What am I missing?
In: Biology
If mommy has a baby in her tummy, they tap on her knee to see if it jumps faster than normal. If it jumps faster, she may be sick and need to have the baby soon so she doesn’t get all shaky and hurt.
Neurological lesions.
In simplest terms, the intensity of a reflex can identify where along the neuron path (i.e. brain, spinal cord, muscle) a lesions could be.
For example. An Upper motor neuron (UMN) lesion will increase the intensity of the knee jerk. UMN lesions are those located anywhere between the brain to the spinal cord.
Lower Motor Neuron (LMN) Lesions demonstrate the opposite, it actually decreases the intensity of of the knee jerk. These lesions are located anywhere from the spinal cord to the Muscle itself.
However, the knee reflex is only one part of a physical exam – to reach a firm diagnoses you will need to perform other tests a well as obtain a good history from the patient.
I have zero reflex based on that test, but that can’t be true, right? I mean I guess my reflexes are generally garbage when trying to catch stuff, but they’ve also saved me from injury many times
Hitting the knee with the little hammer is one of the quick tests for a nerve in the leg. A really big kick, or no kick at all, means the doctor will do a few more tests to check you are ok!
They are really just checking DTRs. Deep Tendon Reflexes. As mentioned above, any inability for these joints to react to nerve stimulation could indicate other neurological or muscular/skeletal problems.
It’s a little out dated in terms of assessments but it is a super common procedure. The default reaction is striking the tendon there causes the nerve to spasm the muscle as a result of wanting to protect you from the “attack”.
No kick could mean a neurological issue as well as would an exaggerated or inappropriate response. However, it isn’t a super accurate thing. Even if you dont kick, it doesnt mean anything. Theyd have to do much more specific assessments and use actual machines to see if there is an issue and odds are you would be presenting with an issue already.
Testing the reflex can give you an idea of if there is any damage to the spinal cord or nervous system. Overactive or under active reflexes can also be a sign of other medical conditions
Hyperreflexia, or overactive reflexes can be a sign of hyperthyroidism, electrolyte imbalance, severe brain trauma, multiple sclerosis and preeclampsia
Hyporeflexia, or absent reflexes, can be a sign of ALS, Guillain-Barré syndrome, hypothyroidism, stroke
We don’t just check knee reflexes. We can check ankles, soles of your feet, biceps, triceps, jaw jerk, pupils, gag reflex, and several others too.
Each reflex gives us information about what might be going on. The ones at the joints, like the knee one that everybody knows, can give information about conditions affecting the entire body like electrolyte disturbances, but also by testing at different sites it can give information about where in the brain, spinal cord, peripheral nerves or muscles the problem is, and which side of the body is affected.
This information, coupled with assessment of muscle power, muscle tone, abnormal movements, gait, speech, cognition, vision, hearing, temperature sensation, vibration sensation, pain sensation, soft touch, pin prick sensation, joint position sense (with your eyes closed) can lead to the diagnosis.
To do a full neurological assessment takes a long time – by far the longest examination to perform on a patient if you are doing it properly and completely.
They check your reflexes because it part of a neurological test. A lack of reflex could indicate spinal injury, muscle degredation, and neuromuscular disease.
Reflexes are often diminished or hyper-excitable if other medical conditions, such as magnesium imbalances.
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