As children we often try to provoke the patellar reflex: hitting a hammer under the kneecap causes the lower leg to be pulled forward. It is not recommended to do this yourself: incorrect tapping can damage the kneecap. The doctor will perform this examination if necessary. The lack or absence of this reflex may mean that the central nervous system or the nerve itself is not working properly or is damaged. We sometimes see this occur with a hernia or Parkinson’s disease.
What is a reflex?
A patellar reflex falls under the reflexes. These are responses to certain stimuli. A reflex is often named after the reaction that the stimulus provokes. Just think of the sneeze reflex, where sneezing is a reflex to an irritating substance in the nose. Reflexes are innate and are present in everyone. When the nerve pathways are damaged or when there is a disorder in the nerve pathway, the reflex may be absent, weakened or increased. A reflex may also occur that would not occur under normal circumstances.
Patellar reflex
The patellar reflex is one of the many reflexes we know. It is also called the patellar reflex. It is the reflex that occurs when the tendon that connects the muscle to the kneecap is stimulated. Two muscles in the thigh ensure that the leg can be bent and straightened. We call these the extensor and the flexor. Muscle spindles are sensors that measure muscle tension. We find these sensors in the muscles. The muscle spindles continuously transmit information about the muscles to the spinal cord. This information runs through the nerve pathways.
The patellar reflex plays an important role in the balance of the body, especially the legs. When the body leans backwards, the patellar reflex comes into action. This stretches the knee joint, causing the thigh to move forward. This restores the balance of the body.
Research
The patellar reflex, or at least its elicitation, is often part of a physical examination. This can be used to demonstrate whether the nervous system is functioning optimally.
The examination often takes place in a sitting position. The legs hang freely over the edge of the table/chair without touching the ground. In a lying position, the knees are raised 20 to 30 centimeters from the bed. A reflex hammer is used. The doctor will tap the tendon just below the kneecap with this hammer.
If there are no abnormalities, the expected effect will be that the lower leg is stretched forward. This can be a short or somewhat larger movement. The four-headed thigh muscle can also show movement (contraction). In any case, the muscle will contract and the leg will be moved forward/up. The leg then falls back to the starting position. Children often use this investigation to elicit this reaction from each other. Irresponsible, because a wrong tap on the kneecap can cause damage.
Patellar tendon reflex is absent
The patellar reflex may be increased, which means that the reflex is also present when it should not normally occur. But this reflex can also be absent. During the examination with the hammer, the desired response is not elicited. This may be due, for example, to the patient being tense and concentrating too much on the knee movements. In this case, it is advisable to have the patient close their eyes and think about something else or have the patient do something else that will distract their attention. If the patellar reflex is still absent, this may mean that the nervous system is not functioning optimally.
Causes
There are several causes when there is no patellar reflex. For example, the fault or damage may be in the nerve that controls the muscle. A spinal hernia is a well-known example of this. This causes an intervertebral disc to bulge. This causes nerves to become pinched. A greater increase in pressure in the intervertebral disc is the cause of this. Heavy lifting could be a possible culprit. People with a spinal hernia often lack the patellar reflex, but also the Achilles tendon reflex.
Another cause may be Parkinson’s disease . For example, the patellar reflex can be reduced due to damage to the nerve cells, but can also be increased when the damage is higher up. Parkinson’s disease is a brain disease and cannot be cured. A group of cells in the brain slowly dies. As a result, dopamine is no longer produced. This substance works as a neurotransmitter and transmits signals between nerve cells.
The lumbosacral radicular syndrome also sometimes causes a reduced or absent patellar reflex, sometimes in one leg or both. With this syndrome, a nerve root in the back is compressed. This is accompanied by tingling, loss of strength or loss of feeling in one or both legs. A hernia is a common cause for this syndrome, but it can also have other causes.
Other causes of the absence of the patellar reflex include damage due to an accident or trauma, surgery, use or ingestion of harmful substances, congenital damage, etc.
