The extensor digitorum reflex is also known as the Braunecker-Effenberg reflex, BER, or finger stretch reflex. It is one of the intrinsic reflexes and is used to test the spinal nerves from segments C6 and C7.
What is the extensor digitorum reflex?
The extensor digitorum reflex is also called the finger stretch reflex. It belongs to the intrinsic reflexes. Just like the finger flexor reflex, the biceps femoris reflex, or the biceps tendon reflex, for example, the extensor digitorum reflex also belongs to the intrinsic reflexes. In the intrinsic reflex, the organ that receives the stimulus and the organ that performs the reaction are located in the same muscle. In the extensor digitorum reflex, this is the extensor digitorum muscle. The extensor digitorum muscle is also called the finger extensor. It is a skeletal muscle and belongs to the superficial extensors of the forearm. Its four insertion tendons pass through the fourth tendon sheath to the dorsum of the hand. There, the tendons are connected by bridges. These bridges prevent the extension of individual fingers, especially the isolated extension of the ring finger. The task of the extensor digitorum muscle is to stretch the hand and fingers two to five. In addition to this muscle, the C6, C7 and the radial ramus profundus nerves are also involved in the extensor digitorum reflex.
Function and task
The extensor digitorum reflex is one of the deep tendon reflexes. When the extensor digitum muscle is struck with the fingers slightly to moderately flexed, extension of the index, middle, and ring fingers occurs physiologically. Reflex testing is performed in side-to-side comparison and the overall reflex level is assessed. Normal would be a medium to lively response. Failed and weak responses to the stimulus indicate a disorder, as do increased or even clonic, i.e., jerky and violent, responses. There are also clinical scale systems for the precise classification of reflex reactions. For example, reflex intensity can be classified using the nine-point MayoClinicScale (MCS) or the National Institute of Neurological Disorders and Stroke scale (NINDS scale). However, the reliability, i.e., the dependability, of these scales is limited because the assignment can vary considerably between different examiners. Therefore, the scales are rarely used in everyday practice and clinical practice. To facilitate reflex testing, the patient can clench his teeth firmly and clench his fist vigorously before the test. This serves the purpose of what is known as reflex facilitation. By pre-tensioning the muscle fibers of the muscle spindles, sensitivity to stretching is increased. This serves to increase sensitivity. As a result, the reflex can be triggered more easily. Alternatively, the patient can also perform the so-called Jendrassik grip. To do this, the patient angles his arms in front of his upper body and clasps his hands. He then tries to pull the hands apart forcefully. The extensor digitorum reflex and reflex testing in general are an integral part of the physical examination and especially of the neurological examination. The aim is, on the one hand, to check physiologically present reflexes and, on the other hand, to find pathological reflexes. The result of reflex testing is also called reflex status. The examination is usually performed with a reflex hammer. A light blow is applied to the muscle with the hammer. The reflex that now results is an involuntary response to the rapid stretching of the muscle spindles. The muscle contraction occurs via a monosynaptic spinal reflex arc. Monosynaptic means that only one nerve connection (synapse) is involved. In the extensor digitorum reflex, the C6 and C7 nerve pathways are tested. The nerve roots for these nerves arise from the spinal cord in pairs and then extend out of the spinal canal toward the arms, hands, and fingers. These are spinal nerves. These are part of the peripheral nervous system. In addition, the extensor digitorum reflex also captures the function of the radial nerve and, in particular, the ramus profundus. The ramus profundus is the motor portion of the radial nerve.
Diseases and complaints
Failure of the expected response in the extensor digitorum reflex is indicative of damage to the C6 and C7 nerves. Such damage can result, for example, from a herniated disc in the cervical spine.In the case of a herniated disc, tissue emerges suddenly or slowly from the nucleus pulposus of an intervertebral disc. The tissue can escape both posteriorly into the spinal canal and posteriorly-laterally in the direction of the nerve roots. The pressure on the nerve roots causes pain, paralysis or sensory disturbances in the affected segment. Herniated discs in the cervical spine are mainly found between the ages of forty and sixty. A bulging disc can occur much earlier. This can also trigger similar symptoms and lead to an attenuated extensor digitorum reflex. However, the extensor digitorum reflex can also be affected by damage to the radial nerve. Damage to the radial nerve is also known as radial nerve palsy. In particular, upper and middle radialis palsies result in a failure of the extensor muscles of the hand and thus also in a weakened or abolished extensor digitorum reflex. Upper radialis paralysis is mainly caused by forearm crutches. It is therefore also referred to as crutch paralysis. The nerve can also be damaged by trauma or by a cast. Middle radial nerve palsy is usually caused by prolonged exposure to pressure. It is called park bench paralysis because the nerve can be damaged by lying on a hard park bench, for example. A cast that is too tight can also be the cause of the lesion.
