Triceps Tendon Reflex: Function, Tasks, Role & Diseases

The triceps tendon reflex is one of the intrinsic reflexes. When the tendon of the triceps muscle is struck, a contraction of the muscle is triggered. An attenuated reflex may indicate dysfunction in the C6 and C7 segments or impairment of the radial nerve.

What is the triceps tendon reflex?

Striking the tendon of the triceps muscle (see figure) causes the muscle to contract. The triceps tendon reflex is also known as the TSR or pocket knife reflex. Like the biceps tendon reflex or the patellar tendon reflex, it belongs to the intrinsic reflexes. In intrinsic reflexes, both the receiving organ and the organ of success are located in the same muscle. In the case of the triceps tendon reflex, this is the triceps muscle. The triceps muscle is also called the three-headed upper arm muscle, arm extensor or triceps. It belongs to the group of upper arm muscles and originates on the humerus and scapula. Together with the anconeus muscle, the triceps is responsible for extending the forearm at the elbow joint. Consequently, the triceps tendon reflex triggers extension in the elbow joint.

Function and task

Reflex testing and, therefore, the triceps tendon reflex are an integral part of the clinical examination and, in particular, the neurologic examination. Testing of the triceps tendon reflex can be performed with the patient sitting or lying down. With the patient lying down, the arm is placed bent on the chest. If the patient is sitting, the examiner must hold the arm up so that it is angled at the shoulder joint and bent at the elbow joint. The reflex is triggered by a short and not too forceful blow to the tendon of the triceps brachii muscle. This lies just above the so-called olecranon. The olecranon is the end of the ulna that lies towards the elbow. A reflex hammer is suitable for the blow. Most hammers have two rubber inserts of different sizes on the head. For the triceps tendon reflex, the thicker rubber pole is used. Reflex testing is always done on both sides so that the reflex response can be compared afterwards. As a rule, the reflex response is divided into categories. Thus, a reflex may be normal, attenuated, diminished, increased or absent. For a more precise classification, there are two clinical scale systems: The nine-level MayoClinicScale (MCS) and the National Institute of Neurological Disorders and Stroke scale, however, are rarely used in everyday practice and clinical practice because the assignment to the individual scale values varies from examiner to examiner, so comparability is not guaranteed. If the reflex response initially appears to be very weak, a reflex tapering can be performed. To do this, the patient clenches his teeth tightly or clenches his hands in a fist. Alternatively, the Jendrassik grip can be used. To do this, the patient bends his arms in front of his upper body and clasps his hands. The examiner now asks the patient to pull the hands apart very forcefully. This creates a preload that sensitizes the muscle fibers of the muscle spindles to stretching. The reflex then results from an involuntary reaction to the sudden stretching of the muscle spindles caused by the blow with the reflex hammer. A contraction of the muscle is then initiated via a monosynaptic reflex arc. The triceps tendon reflex is mediated by motoneurons from segments C6 and C7 and by the radial nerve.

Diseases and complaints

Accordingly, if the triceps tendon reflex is weakened or abolished, a disorder in segments C6 and C7 or a lesion of the radial nerve is suspected. The most common cause of damage to the nerve roots in this area is a herniated disc in the cervical spine (C-spine). In the case of a herniated disc, the gelatinous core of the disc protrudes and presses on the nerves leading from the spinal cord. These are also called spinal nerves. The nerves can also be affected by a bulging disc. A bulging disc (protrusion) is the precursor to the actual herniated disc (prolapse). A herniated disc manifests itself primarily through acute pain. The pain has a stabbing character and can radiate. In the case of a herniated disc in the C6 and C7 region, the pain typically radiates into the arm. Often there are additional sensory disturbances such as numbness or tingling.Muscle weakening is also possible. Symptoms are aggravated by coughing and sneezing. A lesion of the radial nerve also affects the triceps tendon reflex. The radial nerve is one of the nerves of the brachial plexus. Among other things, it innervates the triceps brachii muscle. A weakened or abolished triceps tendon reflex occurs primarily in the case of upper radialis paralysis. This is defined as damage to the radial nerve in the axillary region. This is often caused by forearm crutches. It is therefore also referred to as crutch paralysis. However, a cast or trauma, such as a fracture of the humeral head, can also cause upper radial nerve palsy. The paralysis of the triceps muscle prevents the forearm from being extended. The triceps tendon reflex is thus absent or weakened. A drop hand and drop fingers can also be seen. This means that finger joints and wrists can also no longer be stretched. With the help of the triceps tendon reflex, crutch paralysis can be distinguished from park bench paralysis. In so-called park bench paralysis, a middle radialis paralysis is present. This is caused by prolonged exposure to pressure. For example, the radial nerve can be damaged if the arm rests on a hard surface for a long period of time or if a cast does not fit properly. Damage can also occur after fractures of the humerus. Unlike crutch paralysis, parker’s bench paralysis does not affect the triceps tendon reflex because the nerve fibers for the triceps muscle come off above the lesion site.