symptomatic upper extremity: An algorithmic approach to diagnosis, Part 2, The

Journal of the American Chiropractic Association, May 1999 by Schimp, David J

Dorsal scapular nerve entrapment

Entrapment of the dorsal scapular nerve is easily over looked asa cause of upper-arm pain. Regraded as somewhat obscure, the dorsal scapular nerve receives notoriety as the first branch of the brachial-plexus-C5 ventral rami. Altough it has no specific cutaneous distribution afferents are carried from the spindles of the muscles it innervates, the rhomboids and levator scapuli. As such, there is minimal or sensory loss. But mild lower scapular winging accentuated by over head placement of the arm, may be present. Because the nerve is usually trapped as it exits from the lower two-thirds of the scalenus medius, neck rotation or extension may reproduce or exacerbate symptoms. Conservative treatment can effectively control symptoms14 when entrapment occurs from a hypertonic scalenus medius, abnormal insertion of the scalenus medius into the first rb, or mechanical friction or rub on the nerve. An abnormal EMG of the rhombodis when other C5 root innervated muscles are normal can help confirm the diagnosis.

Trigger points:

Trigger points popularized by travel and Simons, are widely recognized as a source of local and referred pain.When these hyperirriable areas occur within taut bands of a skeletal muscle or its fascia, patients may experience symptoms ata distant location Palpating muscles of the neck, girdles, and limbs may locate a sensitive band or nodule that, when pressed reproduces the patient's symptoms. This is a common phenomenon, which can be treated, conservatively. Improvement after an initial trial of care eliminates the need for expensive EMG/NCV testing. Consult "Myofascial Pain and Dyfunction: "The Trigger Point Manual." by Travel and Simons for more information.

Radiculopathy

Radiculopathy describes an event that occurs when a nerve root is compromised. The root of a spinal nerve is that portion found passing through the intervertebral foramen (IVF). Root lesions may follow degenerative or neoplastic processes that narrow the IVF, cause mechanical friction or rub on the nerve, or create traction on the nerve from fixed adhesions. If the lesion involves sensory fibers or compresses cell bodies within the dorsal root ganglion, patients may experience pain in the form of paresthesia, hyperesthesia, or hyperalgesia in a dermatomal pattern. Motor involvement is less common but elicits a greater degree of concern (see nerve root charts.) An upperextremity radiculopathy should prompt a careful evaluation of the long tracts (i.e., vibration, temperature, sharp vs. dull, Babinski, Hoffman, balance, and proprioception), which, if abnormal, suggests concomitant myelopathy. In older patients, spondylotic changes may compress both the nerve root and spinal cord, producing cervical spondylotic myelopathy. In younger patients, with both nerve root and spinal cord signs, a central disk lesion or neoplastic process may be found.

Although the region of the intervertebral foramen is a common site of entrapment, other sites exist. For example, the medial branch of the dorsal rami may be entrapped as it passes by the joint capsule of the apophyseal joint. Additionally, cutaneous nerve branches may be trapped as they pass through muscle and fascia en route-for example, the dorsal rami of C2 (the greater occipital nerve) can be entrapped as it pierces suboccipital muscles.

Differentiating radiculopathy from peripheral nerve entrapment is usually straightforward. Sensory disturbances are found within a dermatomal, rather than peripheral, nerve distribution. Patients with radiculopathy usually experience neck pain that may be accompanied by pain in the medial scapular and precordial areas. Valsalva exacerbates a root lesion because the root traverses the subarachnoid space. Cervical compression tests reproduce the radicular pattern of pain. Weakness is found in muscles innervated by the particular root, which may encompass muscles innervated by several different peripheral nerves. Electromyographic evaluation will be normal initially, but abnormal potentials may be seen in paraspinal muscles at two weeks. Limb muscles do not demonstrate EMG abnormalities until several weeks later and are confined to muscles of that particular root. Peripheral nerve conduction velocities are normal, but F-wave, H-reflex, and somatosensory evoked potentials may be helpful in identifying the specific root and degree of involvement.

Axillary nerve entrapment

Axillary nerve entrapment occurs infrequently, but may complicate humeral fracture or reduction following dislocation. Weakness of the deltoid and teres minor will affect the patient's strength in abduction beyond 30 degrees (initially performed by the supraspinatus) and external rotation. Atrophy of the deltoid produces a flattening of the shoulder. Sensory changes are confined to a small area on the lateral aspect of the shoulder. The usual site of entrapment is within the quadrangular space, which is a narrow arcade bordered by the teres major superiorly, teres minor inferiorly, surgical neck of the humerus laterally, and long head of the triceps medially.