Knee Reflex

KNEE REFLEX (patellar), described simultaneously by Westphal and Erb in 1875, i.e., earlier than all other tendon reflexes; it has acquired particularly great clinical significance. It is caused by irritation of the tendon of the quadriceps femoris muscle; it manifests as contraction of this muscle, i.e., extension of the lower leg at the knee joint. Often extension of the thigh at the hip joint is also added to this. The arc of the knee reflex passes through the L_II-L_IV segments of the spinal cord. -Methods of eliciting the K. r. The most common method: the patient sits on a chair, the knee of the leg being tested is thrown over the knee of the other, and a percussion hammer is struck in the area of the patellar tendon (see figure). Other suitable positions for eliciting the reflex: 1) the patient sits on a chair, his feet rest on the floor and are bent at an obtuse angle at the knee joints (Buccard's method); 2) the patient sits on a high stool or table with legs freely hanging down—an excellent method that gives particularly good results and allows, like the previous method, direct comparison of the strength of both K. r.; 3) the patient sits on a chair, the examiner rests the palm of his hand on the patient's knee, throwing the other leg over his forearm; the patient's leg should hang freely downward in this position; 4) the patient lies on his back, the examiner bends his leg at the knee joint at an obtuse angle, supporting his knee from below with his hand; 5) the patient lies on his back, the knee of one leg is thrown over the knee of the other. In all the methods described for eliciting the K. r., irritation is applied by striking the patellar tendon. A different principle is the basis of the Valbaum method. Here irritation is applied by rapid stretching of the quadriceps muscle. The patient sits on a chair with legs bent at an obtuse angle at the knee joints and resting on the ground with heels. The examiner places the palm of one hand on the patient's patella, pulling it slightly downward, and strikes the back of his hand with the edge of the other hand, directing the blow upward and thus forcefully stretching the patient's m. quadriceps. If the reflex is sufficiently intense and not inhibited, it manifests with a visible motor effect: the lower leg extends and shifts forward. Otherwise, the presence of the reflex is manifested by tension and thickening of the quadriceps muscle, easily felt by the examiner's hand. -In cases where the reflex is weakened or voluntarily or involuntarily inhibited by the subject, the Jendrassik method helps to reveal it. The patient clasps his hands fingers interlocked and then pulls them forcefully apart on command. At this moment, the tendon is struck. This helps to distract the patient's attention and thus reduce voluntary or involuntary inhibition; partly, however, it is also about a certain physiological phenomenon that facilitates the elicitation of the reflex by its facilitation (Banning). For the same purpose, other methods based on the same principle are also used: ordering the patient to take deep breaths and exhalations during the elicitation of the reflex, application of pricks, faradization, strong illumination of the eyes, etc. Of all these methods, the Jendrassik method undoubtedly has the greatest clinical significance. A number of devices have been proposed for the precise registration of knee reflexes. On the one hand, this aims to accurately dose the force of the blow (spring hammers, falling hammers, etc.), on the other hand—to measure the strength or amplitude of the reflex (the angle of extension of the lower leg, measured in Bechterev's apparatus with a simple protractor, especially accurately measured in Weiler's apparatus, which records it on a kymograph tape). Schaffer's apparatus is adapted for measuring the latent time of the reflex and marks the moment of irritation and the moment of occurrence of action currents in the quadriceps muscle. -K. r. are absent in healthy individuals only in very rare cases of congenital, usually general areflexia. The actual absence of them (so-called Westphal's symptom) can therefore almost always be considered a sign of organic damage to the nervous system. This symptom is found in all cases where the corresponding reflex arc is interrupted (L_II-L_IV): in fractures, in polyneuritis, in femoralis neuritis, in poliomyelitis and myelitis of lumbar localization, in damage to the corresponding muscles (myopathies). However, the absence of K. r. can also be observed in febrile conditions, in the flaccid stage of hemiplegia (see Dischez), in some cases of brain tumors (perhaps the influence of toxic factors, but mainly the influence of increased intracranial pressure, which injures the posterior roots of the spinal cord). Increased knee reflexes can also occur in neuroses; a sharp increase, especially accompanied by clonus (see), is a symptom of damage to the pyramidal tract.

I. Filimonov.