Sensory assessment: dermatome topography
Spinal nerve root lesions at the cervical level lead to clearly localized sensory alterations on the anterior (volar) surface of the arm. For accurate diagnosis, one must be familiar with the innervation zones:
- C4 root: The supraclavicular area overlying the clavicle.
- C5 root: The lateral (outer) surface of the shoulder.
- C6 root: The lateral surface of the forearm, including the first digit (thumb).
- C7 root: Strictly the third (middle) digit of the hand.
- C8 root: The medial (inner) surface of the hand including the fifth digit (little finger), as well as the lower medial part of the forearm.
- T1 (Th1) root: The inner surface of the forearm and the distal inner region of the arm.
Motor function: testing motor roots
Clinical examination of muscle strength helps determine the level of nerve compression. An important rule for hand tests: the indirect influence of finger muscles on wrist movements themselves must be excluded by fixing the fingers in a specific position.
- C5 (Shoulder abduction): The patient flexes the elbow and abducts the arm to a 90-degree angle. The physician presses downward on the elbow joint, evaluating the resistance of the m. deltoideus.
- C6 (Wrist extension): The forearm is pronated. The patient actively extends the wrist joint. The physician presses on the metacarpophalangeal joint of the index finger, testing the radial extensors.
- C7 (Wrist flexion): The patient's fingers must be fully extended. The physician attempts to forcefully move the flexed wrist into extension by applying pressure to the palm.
- C8 (Grip strength): Finger flexion is evaluated. The patient squeezes the examiner's index and middle fingers as hard as possible.
- T1 (Finger abduction): The patient spreads their fingers apart and holds them while the physician attempts to bring them together, overcoming the resistance of the hand muscles.
Transient brachial plexus plexopathy
This specific injury (known as "stinger" syndrome) often occurs in athletes during a forced, rapid lateral neck flexion. The pathogenesis is based on compression or traction of the brachial plexus elements (brachial plexus). The key feature of the syndrome is the temporary nature of the symptoms, which can regress anywhere from a couple of minutes to several days.
Injury severity is classified according to the degree of nerve fiber damage:
- Grade 1 (Neurapraxia): The axon remains intact, with only local myelin loss occurring. Function recovers quickly.
- Grade 2 (Axonotmesis): The connective tissue sheath of the nerve is preserved, but the axon itself is damaged. Deficit is more pronounced, and recovery takes weeks.
- Grade 3 (Neurotmesis): Complete anatomical transection of the nerve trunk occurs. Symptoms are persistent, and function may never recover.
Differential diagnosis and warning symptoms
In an initial uncomplicated episode of transient plexopathy, imaging is generally not required. However, in the presence of "red flags", differentiation from severe pathology is necessary, for which MRI, CT, or radiography is ordered.
- Cervical radiculopathy: The clinical picture is similar, but symptoms persist for more than 24 hours.
- Shoulder injuries (dislocation, acromioclavicular joint injury): Require mandatory exclusion of bone pathology using instrumental methods.
- Thoracic outlet syndrome: Pain and paresthesias are provoked by head rotation, and the hand may become pale and cold due to vascular compression.
- Spinal stenosis or fracture: Occurs during severe impacts. Accompanied by strict "red flags"—lower extremity involvement or bilateral symptoms, which requires immediate neck immobilization.
"Red flags" requiring further investigation:
- Symptoms do not resolve for more than 24 hours.
- Involvement of both arms simultaneously (indicates a fracture or pronounced stenosis).
- Presence of neurological deficit in the legs (a sign of spinal cord injury).
- Development of muscle atrophy (indicates a recurrent course of the syndrome or another disease).
Briefly: answers to topical questions
Which muscles are innervated by the C5 spinal nerve root?
The C5 spinal nerve root provides innervation to the deltoid muscle and participates in the innervation of the biceps brachii.
- Deltoid muscle (m. deltoideus) — shoulder abduction
- Biceps brachii (m. biceps brachii)
Which anatomical structures form the brachial plexus?
The brachial plexus is formed by five roots, C5–T1. Anatomically, it comprises roots, trunks, divisions, cords, and branches. Roots C5 and C6 form the upper trunk, root C7 forms the middle trunk, and roots C8 and T1 form the lower trunk.
- Upper trunk (superior trunk) — formed by roots C5 and C6
- Middle trunk (middle trunk) — formed by root C7
- Lower trunk (inferior trunk) — formed by roots C8 and T1
Which tendon reflexes are tested for topical diagnosis of cervical root lesions?
For topical diagnosis of cervical root lesions, tendon and periosteal reflexes of the biceps, triceps, and brachioradialis muscles of the arm are tested. A decrease or absence of a specific reflex indicates the level of the corresponding spinal nerve root lesion.
- Biceps reflex (biceps reflex) — for the C6 root
- Triceps reflex (triceps reflex) — for the C7 root
- Brachioradialis reflex (from the brachioradialis muscle) — for the C6 root
Which specific vessels and nerves are compressed in thoracic outlet syndrome?
In thoracic outlet syndrome, the trunks of the brachial plexus and subclavian vessels are compressed as they pass through narrow anatomical spaces from the base of the neck to the upper extremity. Specifically, the brachial plexus and the subclavian artery or subclavian vein are compressed.
- Brachial plexus (plexus brachialis) — neural structures
- Subclavian artery (a. subclavia) — blood vessel
- Subclavian vein — venous vessel in the venous form of the syndrome
For quick memorization of hand motor tests: C6 pulls the hand up (extension), C7 drops it down (flexion), C8 gathers the fingers into a tight fist (grip), and T1 spreads them out like a fan (abduction).
Class and exam questions
Why must the patient's fingers be extended when testing the motor function of the C7 nerve root?
This specific position allows you to exclude the muscles that move the fingers and isolate the activity of the target muscles that flex the wrist itself.
Is an MRI required for a first episode of transient plexopathy?
As a rule, imaging is not required for the first uncomplicated attack. Cervical MRI is indicated only when "red flags" are identified or if symptoms do not resolve.
Can "stinger" syndrome cause weakness in the legs?
No. The neurological status of the lower extremities in this syndrome should be completely normal. Any deficit in the legs indicates damage to spinal cord structures.
What else to study on this topic
- Pathogenesis and morphological differences of neuropraxia, axonotmesis, and neurotmesis
- The role of MRI in assessing the state of the spinal cord and ligamentous apparatus
- Biomechanics of traction injuries of the brachial plexus in athletes
- Thoracic outlet syndrome: vascular and neurological components
- Method for isolated assessment of radial wrist extensors
Master the entire topic in the "Traumatology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Diagnosis of Degenerative Spine Diseases" plus 812 more pages on the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 35 video lessons on the subject
Other Topics in "Orthopedics"
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.