Is it normal to not have a knee jerk reflex?

The knee-jerk reflex is a very natural conditioned reflex. Generally speaking, the knee-jerk reflex requires the cooperation of different nerves and organs such as afferent nerves, efferent nerves, and effectors. Some people find that they don't have a knee-jerk reflex but don't know why. It is best to go to the hospital for an X-ray to avoid neurological diseases. So, is it normal to not have a knee jerk reflex?

1 Causes

Weakened or absent knee reflex is most commonly seen in spinal cord or peripheral neurological diseases. It is one of the signs of lower motor neuron paralysis and is more common in myopathy, cerebellar and extrapyramidal diseases. Weakened and disappeared reflexes are mostly caused by organic diseases. For example, when there are central damages such as peripheral neuritis, radiculitis, and anterior horn myelitis, the knee reflexes will be hyperactive.

2 Diagnosis

In patients with lumbar disc herniation, positive knee tendon reaction is often manifested as weakened or even disappeared knee tendon reflex. This is more common in patients with L3 and L4 disc herniation resulting in invasion of L4 nerve root.

The patient lies supine, and the examiner holds the patient's head with his left hand or forearm, with the hip and knee joints bent at an obtuse angle, and the heels do not leave the bed.

, so as not to affect the reflex movement and make it difficult to obtain the correct result. The examiner taps the quadriceps tendon with a percussion hammer held in the right hand, and the calf straightens. When sitting, the calf is completely relaxed and hanging down at a right angle to the thigh. Tapping the quadriceps tendon below the knee will result in the calf stretching. Enhanced leg reflexes are often seen in pyramidal tract damage, and hyperactive knee reflexes are often accompanied by patellar clonus. [1]

3. Identification

The entire reflex process of the knee jerk reflex can be carried out only through the control of the spinal cord. Normal people have a knee jerk reflex when they relax. However, these muscles can still be controlled by the higher centers of the brain. This is the state of preparation you mentioned. The muscles that antagonize the knee jerk reflex become tense consciously, and the knee jerk reflex cannot occur.

Peripheral neuritis: Symmetrical sensory and motor disorders in the distal end of the limbs, developing from distal to proximal, accompanied by burning pain and tenderness in the affected area. Symmetrical lower motor neuron paralysis of the distal limbs, decreased muscle tone, muscle atrophy, autonomic dysfunction, hyperhidrosis or anhidrosis, etc., decreased or absent tendon reflexes in the limbs, and decreased ankle reflexes earlier than knee reflexes.

(ii) Guillain-Barre's syndrome

syndrome) is often accompanied by a history of upper respiratory tract infection, symmetrical ascending flaccid paralysis, with the distal end being more severe than the proximal end. In severe cases, respiratory paralysis may occur due to involvement of the intercostal muscles and diaphragm. It is often accompanied by cranial nerve involvement, transient paresthesia or hyperalgesia, obvious muscle tenderness in the distal limbs, weakened or absent tendon reflexes, and negative pathological reflexes. After 2 weeks, the cerebrospinal fluid showed protein-cell separation.

(III) Progressive myodystrophy is a sex-linked recessive trait that occurs almost exclusively in males and rarely in females. Symptoms usually become apparent between the ages of 3 and 6 and gradually worsen, with weakness beginning in the trunk and proximal limbs, with the lower limbs being more severe than the upper limbs. Difficulty walking and climbing stairs, pelvic instability when walking, Gowers sign when standing up from supine position, and about 90% of cases begin to show pseudohypertrophy of the gastrocnemius muscles, that is, the volume increases without increasing muscle strength. After the age of 6, muscle atrophy and contracture gradually occur. The tendon reflex decreases first, and finally the knee tendon reflex disappears when the muscle atrophy reaches a severe level. However, in the early stages of pseudohypertrophy and at the site of muscle hypertrophy, the tendon reflex can be active.