In an earlier post we explained what consisted of osteotendinous reflexes and why the doctor gave us a hammer to take these. If you have not read it I recommend going to the link before continuing reading. Next I will tell how and where we take the reflexes in the legs and the meaning they have in the context of the lumbar injury.
If we go with back pain, especially in cases of sciatica, it is likely that the doctor will take the reflexes of the leg during physical examination. Basically we take two, the patellar reflex and the aquile reflex. I will explain both reflexes and then we will see the meaning of what can happen when exploring.
Where do reflexes in the legs take us to evaluate lumbar lesions?
The patellar reflex is taken in the knee, just in the tendon that is underneath the kneecap (as we see in the photo). It is the final tendon of the quadriceps muscle that is responsible for extending the knee. We hit with the hammer here and the sensitive signal travels through the root L3 and L4 (especially L4). The signal reaches the medulla (already in the lumbar region of the back) and the reflex arc is sent that sends the signal to the quadriceps through the motor roots L2, L3 and L4. When the signal reaches the quadriceps, the muscle contracts and the knee is stretched. The nerve fibers from these roots that we mentioned, travel through the thigh forming part of the femoral nerve (also called the crural). In summary we are evaluating this reflex pathway involving the femoral nerve and the roots of L2 to L4. Then we will see the interpretation.
The achilles reflex is taken on the back of the heel (Achilles tendon). The signal will travel primarily through the root S1 contained in its leg journey within the sciatic nerve. Reflexes can also be taken in the medial hamstrings to evaluate the L5 root but is less common.
How do we interpret the result of the reflexes that we obtained with the hammer?
In principle, four things can happen.
– The reflex is normal. In this case we understand that the roots we are exploring are working. This means that there is no injury that interrupts the reflex arc or circumstances that have worked erratically.
– No reflex. The reflex arc is a closed circuit that if it is damaged or interrupted in any of its tracks, does not come out. We are not going to tell you the severity of the injury. For example, we may lose the achilles reflex by a disc hernia that affects the sensitive part of the root S1 and then leaves no sequelae. On the contrary there may be a serious injury affecting the motor root S1. Also keep in mind that sometimes we are not able to take the reflex even if there is no injury. This can occur due to lack of patient relaxation or other technical reasons. The doctor takes this into account and contrasts it with the rest of the scan.
– The reflection is weakened. In these cases there may be small or incomplete damage. The reflex arc is not interrupted but does not function completely. The doctor will consider other possibilities that may depress the reflex response such as the medication being taken by the patient, for example.
– The reflex is increased. Here we are talking about another type of injury that is not in the reflex arc that we have described but is on higher routes. There are nerve pathways in the medulla that are responsible for modulating the response. If these roads are damaged, the inhibitory signals do not arrive and the motor response is exacerbated. This can sometimes mean injury to the spinal cord or to the brain. Just as in previous cases it needs interpretation, by itself cannot draw this conclusion.
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