CHAPTER 55 • UPPER EXTREMITY NERVE ENTRAPMENT 325bands around the axillary nerve and posterior humeral
circumflex vessels (Cahill and Palmer, 1983).SUPRASCAPULAR NERVE
- Anatomy and origin:The C5–C6 nerve roots. Fibers
travel through the upper trunk of the brachial plexus,
pass through the supraclavicular fossa, and then
through the scapular notch (incisura scapulae), cov-
ered by the transverse scapular ligament (the 1st site
of possible entrapment). After innervating, and pass-
ing through the supraspinatus muscle, the suprascapu-
lar nerve bends around the spine of the scapula to
innervate the infraspinatus (the 2nd site of potential
entrapment, if enclosed by the spinoglenoid ligament,
which is present in about 50% of people) (Pecina,
2001). - Risk factors:Traumatic risk factorsfor compression
of the suprascapular nerve include fracture of the
scapula, rotator cuff tear, and shoulder arthrodesis.
Nontraumatic risk factors include repetitive overhead
loading activities, such as experienced in volleyball,
tennis, weightlifting, boxing, basketball, baseball, and
painting. Other sources of compression are backpack
straps or ganglion cysts at the scapular notch. - Symptoms and signs:Vague shoulder or acromio-
clavicular(AC) joint pain. Weakness and atrophy may
be apparent in the supra- and infraspinatus muscles.
Pain or a Tinel sign may be present upon palpation of
the scapular notch. Overhead activities may worsen
the symptoms. The crossed arm abduction test should
exacerbate symptoms on the effected side. The differ-
ential diagnosis is cervical radiculopathy, diskogenic
pain, shoulder or AC joint pathology, rotator cuff tear,
or musculoskeletal pain syndromes. - Treatment:Avoidance of exacerbating activities, e.g.,
overhead. Physical therapy should focus on maintain-
ing ROM of the scapula, and on improving muscle
strength. Dysfunction of scapulohumeral rhythm
should be corrected as possible. Injection of local
anesthetic into the scapular notch may assist in the
diagnosis and the treatment. Most patients will
respond to conservative measures; however, in some,
surgical release may be necessary (release of the
transverse scapular ligament with or without widen-
ing of the scapular foramen).
MUSCULOCUTANEOUS NERVE
- Anatomy and origin: The musculocutaneous nerve
is the terminal nerve of the lateral cord of the brachial
plexus (fibers from the C5–C7). It innervates the
coracobrachialis, brachialis, and biceps brachii mus-
cles. Its sensory terminal branch, the lateral ante-
brachial cutaneous nerve, innervates the volar and
dorsal forearm along its radial aspect, but not the
hand.- Risk factors:Compression of the musculocutaneus
nerve is uncommon. Shoulder dislocation is a risk
factor. Nontraumatic lesions may occur during exer-
cises, especially excessive resistive elbow extension,
as in push-ups or arm presses (weightlifters) a hyper-
trophic coracobrachialis muscle may entrap the mus-
culocutaneous nerve where it pierces the muscle.
Entrapment of the sensory branch distal to the biceps
aponeurosis, as the nerve enters the forearm is noted
to occur in association with strongly resisted exten-
sion and pronation of the elbow. - Symptoms and signs:Entrapment at the proximal
site presents with elbow flexor weakness, lateral arm
pain, and/or loss of sensation. A positive Tinel’s sign
and decreased biceps reflex may be observed.
Entrapment at the distal location presents with lateral
arm pain and numbness only. A positive Tinel’s sign
may also be elicited. - Treatment:Rest, ROM exercises and gentle stretch-
ing, and anti-inflammatory medication and modali-
ties. Entrapment of the lateral antebrachial cutaneous
nerve near the cubital fossa mostly needs surgical
decompression. Good long term outcome has been
reported (Davidson, Nunley, and Bassett, 1998).
RADIAL NERVE- Anatomy and origin:C5–C8 nerve roots. Fibers run
between the medial and long heads of the triceps,
through the spiral groove. There are four sites of poten-
tial entrapment. There is entrapment site 1 where the
nerve gives off motor branches to the extensor carpi
radialis longus muscle prior to and to the extensor carpi
radialis brevis muscle after entering the cubital fossa.
Just proximal to entering the supinator muscle, the
radial nerve gives off the superficial radial nerve (sen-
sory, which supplies sensation to the dorsum of the
wrist, hand, and dorsum of the first three and one half
digits). It then pierces the supinator at the Arcade of
Frohse (entrapment site 3) and becomes the posterior
interosseous nerve that is purely motor. It supplies the
extensor forearm muscles. Cutaneous (sensory) nerve
supply to the arm is by two branches to the posterior
skin of the arm and one for the dorsal forearm, the pos-
terior antebrachial cutaneous, which branches off the
radial nerve in the proximal arm and runs with the main
radial nerve through the spiral groove. It supplies a strip
of skin over the dorsum of the forearm and wrist.