Absent knee jerk signifies the lesion at the level of L4 spinal segment.
- Absence of the knee jerk signify an abnormality anywhere within the reflex arc, including the muscle spindle, the Ia afferent nerve fibers, or the motor neurons to the quadriceps muscle.
- In general the afferent loop is much more critical for reflex function than the efferent loop, hence that unless the muscle is almost paralysed, loss of reflexes suggests a sensory nerve or root lesion rather than a motor nerve lesion.
- The most common cause is a peripheral neuropathy from such things as diabetes, alcoholism, and toxins.
- Non-cooperative patient or faulty technique.
- Acute anterior poliomyelitis.
- Peripheral neuropathy.
- Myelopathy in shock stage.
- Progressive musclar atrophy (MND).
- Subacute combined degeneral ion.
- Friedreich's ataxia
- Tabes dorsalis
- Sometimes in diseases of myoneural Junction (myasthenic crisis, hypokalaemia etc).
- Muscular dystrophy in late stages.
- Acute anterior poliomyelitis,
- Entrapment neuropathy,
- Leprosy
- Diabetic mononeuropathy.