Patella reflex

[MudPhud20XX]

So I get that when testing patella reflex, you are basically testing a patient's L2, L3, L4 sensory and afferent reflex. But unlike other reflex such as Moro reflex (infant response to sudden loss of support when the infant feels as if it is falling), which I think is linked to an evolutionary process of human, I feel like there is no point of having patella reflex.

Also, is patella reflex really useful in clinic? Let's say the patient does not show any reflex or less reflex, it just means that the patient's sensory or LMN (or both) not working well, right?

Wiki says that abnormal patella reflex may indicate cerebellum damage, how come?

Lastly, this is probably not important for the board exam, but I just seem to have a problem accepting that a blow to the patella tendon stimulates muscle spindle in the leg extensor muscles such as quadriceps. I mean why can't you do the same by stimulating the other parts or let's say the leg extensor muscle itself?

I would really appreciate any help.

Many thanks in advance.

---

Members don't see this ad.

 

[ChessMaster3000]

So I get that when testing patella reflex, you are basically testing a patient's L2, L3, L4 sensory and afferent reflex. But unlike other reflex such as Moro reflex (infant response to sudden loss of support when the infant feels as if it is falling), which I think is linked to an evolutionary process of human, I feel like there is no point of having patella reflex.

Also, is patella reflex really useful in clinic? Let's say the patient does not show any reflex or less reflex, it just means that the patient's sensory or LMN (or both) not working well, right?

Wiki says that abnormal patella reflex may indicate cerebellum damage, how come?

Lastly, this is probably not important for the board exam, but I just seem to have a problem accepting that a blow to the patella tendon stimulates muscle spindle in the leg extensor muscles such as quadriceps. I mean why can't you do the same by stimulating the other parts or let's say the leg extensor muscle itself?

I would really appreciate any help.

Many thanks in advance.

For patellar, I'd stick with L3/L4. You may have read L2, and that might be true in some people, but patellar is definitely considered to be a L3/L4 reflex. As to your question, it is absolutely useful in clinic. You answered your own question (LMN lesion, less likely sensory).

Not sure about cerebellum damage, havent ever heard that one. I would tend to disagree with it, at the very least for the purposes of boards

 

[sanj238]

So I get that when testing patella reflex, you are basically testing a patient's L2, L3, L4 sensory and afferent reflex. But unlike other reflex such as Moro reflex (infant response to sudden loss of support when the infant feels as if it is falling), which I think is linked to an evolutionary process of human, I feel like there is no point of having patella reflex.

Also, is patella reflex really useful in clinic? Let's say the patient does not show any reflex or less reflex, it just means that the patient's sensory or LMN (or both) not working well, right?

Wiki says that abnormal patella reflex may indicate cerebellum damage, how come?

Lastly, this is probably not important for the board exam, but I just seem to have a problem accepting that a blow to the patella tendon stimulates muscle spindle in the leg extensor muscles such as quadriceps. I mean why can't you do the same by stimulating the other parts or let's say the leg extensor muscle itself?

I would really appreciate any help.

Many thanks in advance.

What Wiki poorly describes is the concept of the "pendular knee jerk."

This is the loss or inability to control overflexion or overextension of muscles. Remember, the UMN (which includes cerebellum) are involved primarily in inhibitory signals to the LMN. the loss of these in the cerebellum leads to the inability to coordinate involuntary inhibitions of motor movements. In this case- the repeated swinging of the leg is the result of hypotonia- decreased stimulation of inhibition to the quads/hamstrings leads to decreased myotatic reflex. This reflex as you know is the result of the activation of intrafusal fibers known as the muscle spindles which deal with muscle tone. Anyway the decrease in muscle spindle action (which can be modulated by the UMN) leads to decreased control of the extension or flexion of the knee- so the knee will just swing on its own back and forth.
Boy maybe i will write wiki pages after med school.

Anyway, its beyond the scope of usmle. But I thought you'd like to know.

Finally, you ask why you hit the patella? This is because of two things. One is because the gogi tendon organ is located in the...tendon. And what does the tendon connect- bone to muscle!. the gogi tendon organ is also used to modulate and enhance musclep sindle activity. In fact, when coupled together their activity can be enhanced. Thus hitting the patella- to the golgi to the muscle spindle can lead to a noticable response. Also hitting hard surfaces is more convenient to the doctor 🙂

Finally- why does hitting the patella work? Because the tendon is located there there will be a stretch in the tendon- this stretching is sensed by the spindle itself- the passive stretching will cause activation of the spindle fiber.