I am almost sure that most of you, when you hear the word “trapezius muscle”, or “trap”, think about “bodybuilders”, or “a stress ball”. Many bodybuilders develop very large “traps”, which provide a distinct visual cue associated with strength. On the other hand, stress, or siting at a desk for too long, can lead to “painful knots” in the trapezius, very familiar to many. What you may not know is that the trapezius is one of the most important muscles for shoulder function; individuals who suffer from a trapezius paralysis know how disabling this condition is…
The trapezius
The right and left trapezius are flat, triangular muscles with their base along the midline and the tip pointing to the shoulder blade. The name of these muscles derives from the fact that the two of them together have the shape of a diamond-shape kite (referred to in the field of geometry as trapezoid or trapezium). The origin of the trapezius includes the back of the base of the skull, the neck, and all thoracic vertebrae. From there, the trapezius attaches to part of the collarbone (clavicle) as well as a thick beam of bone on the back of the shoulder blade called scapular spine and acromion.
Since the trapezius comes out of the head and back, it can aid in arching the back or rotating the head and neck to the opposite side. More important are the effects of the trapezius on the shoulder blade. As you may know, the shoulder blade is a “floating bone” on the back of the chest. The trapezius is the largest muscle responsible for the shoulder blade to be anchored to the body, “suspended” in space. Additionally, the trapezius is essential to rotate and straighten the shoulder blade when we raise the arm. Finally, the upper portion of the trapezius “shrugs” the shoulders, whereas the middle and lower trapezius bring the shoulder blades together.
The spinal accessory nerve
What an interesting nerve! The spinal (accessory) nerve (SAN) is one of the so-called “cranial nerves”. This nerve exists the spinal cord, but instead of coursing directly to the shoulder, it enters the skull to exit again. Old thinking was that this nerve helped another important nerve (the vagal nerve, hence the name “accessory”). The spinal nerve courses very close to the skin on the side of the neck before reaching the trapezius.
How does trapezius paralysis occur?
Trapezius paralysis may occur because of tumors or injuries to the skull, spinal cord, or the bundle of nerves called brachial plexus. However, the most common reason is a direct injury to the SAN due to surgery, radiation or wounds on the side of the neck. Another relatively common reason for trapezius paralysis is spontaneous chronic inflammation, known medically as Parsonage-Turner syndrome.
Several surgeries performed on the side of the neck can result in accidental injury to the SAN, since it courses so close to the skin, and its location varies from individual to individual. Procedures commonly associated with injury to the SAN include lymph node biopsy, surgery for cancer at the side of the neck, and procedures involving the neck blood vessels. The risk of injury to the SAN with lymph node biopsy approaches 1 in 10 patients!
Evaluation
This diagnosis is missed all the time…
For whatever reason, injury to the SAN is misdiagnosed or diagnosed late in many cases. This can lead to substantial frustration for individuals suffering with this condition. Over 50% of patients with an injury to the SAN are initially misdiagnosed of “frozen shoulder” or “rotator cuff tendonitis”, and the average delay to diagnosis can range between a few months and several years. This means that patients may spend months with wasted treatment efforts before anyone realizes that the SAN was injured. Delay in diagnosis translates into another unfortunate scenario: procedures to repair or graft the nerve are time-sensitive, and may not be successful at all after 6 months.
Pain, loss of motion abnormal shoulder blade position
Patients with trapezius palsy complain of pain, difficulty raising their arm, and abnormal position of the shoulder blade. The abnormal position and motion of the shoulder blade in this and other conditions has been called multiple ways over time: scapular winging, dyskinesis (from Greek dys- (δυσ-) “bad” + kinesis (κίνησις) “movement), or scapulothoracic abnormal motion (STAM).
What the doctor can do to confirm…
Since the trapezius is in the back, to properly identify trapezius paralysis patients need to be examined with the back uncovered by cloths. Typically, the shoulder blade on the affected side drifts away from the midline. It is more difficult to raise the arm to the side than to the front, and there is weakness with shoulder shrugs and scapular retraction. When these patients are requested to rotate their arm at the side outwards against resistance, the shoulder blade becomes more prominent, like the fin of a shark! (“scapular flip sign”).
Electromyography with nerve conduction studies can confirm poor function of the SAN and determine whether there is any evidence of at least partial recovery (reinnervation). MRI of the shoulder is not very helpful, because the trapezius is not captured in the typical field of view of shoulder MRI; on the contrary, an MRI of the chest will allow comparison of the bulk and possible degeneration of the affected trap compared to the contralateral normal trap. Ultrasound has tremendous value to assess the course of the SAN, identify the zone of injury, and other features such as neuromas or gaps between the two ends of a severed SAN.
Treatment options
Spontaneous recovery of some or all the trapezius strength may happen when this condition is the result of inflammation (Parsonage-Turner syndrome) or the nerve has been stretched but not severed. Unfortunately, these are uncommon situations.
Surgery is needed to help most patients with trapezius palsy. If injury to the SAN is diagnosed right away, nerve repair or grafting is recommended. However, if the nerve is not sutured or grafted in the first 6 months after the injury, the chances of success decrease dramatically. Nerve transfers can be attempted between 6 and 12 months after the injury.
For patients who do not undergo surgery during the first year, certain muscles and tendons can be relocated (transferred) to compensate for the lost trapezius. The most common tendon transfers are decried below. Rarely, when tendon transfers do not work or patients present with associated paralysis of other muscles around the shoulder, fusing the scapula to the chest wall (scapulothoracic arthrodesis) can be very beneficial.
Muscle/tendon transfers for trapezius paralysis
There are three muscles deep to the trapezius that can be transferred to compensate for its function: the levator scapulae, the rhomboid minor and the rhomboid major. This is not a new idea… Dr. Eden suggested this procedure in 1924, further refined by Dr. Lange in the 1950s. However, Eden and Lange recommended moving the rhomboids from the inner border of the shoulder blade to the scapular body, which does not truly replicate the line of action of the trapezius.
The way we currently transfer the levator scapulae and the two rhomboids was first reported at Mayo Clinic in 2015: the levator and rhomboids are transferred to the acromion and spine of the shoulder blade. After surgery, patients need to wear a so-called external rotation brace for 2 months. Physical therapy is needed for several months, and it takes about a year for the levator and rhomboids to grow (hypertrophy) and provide the patient with optimal recovery.
Further reading…
If you want to learn more, we have published articles on examination of the shoulder blade (scapula) in general, as well as a review on trapezius paralysis.