Entrapment Neuropathies of the Shoulder

Does the Suprascapular Nerve Move within the Suprascapular Notch? Biomechanical Perspective Using the Finite Element Method

PURPOSE

We aimed to analyze changes in suprascapular nerve (SSN) position within the suprascapular notch during in vivo shoulder abduction.

MATERIALS AND METHODS

Three-dimensional models of the shoulder complex were constructed based on magnetic resonance imaging of the brachial plexus (BP-MR) in a patient diagnosed with SSN dysfunction but normal scapular movement. Using BP-MR in neutral position and computed tomography data on shoulder abduction, shoulder abduction was simulated as the transition between two positions of the shoulder complex with overlapping of a neutral and abducted scapula. SSN movement during abduction was evaluated using the finite element method. Contact stress on the SSN was measured in the presence and absence of the transverse scapular ligament (TSL).

RESULTS

In the neutral position, the SSN ran almost parallel to the front of the TSL until entering the suprascapular notch and slightly contacted the anterior-inferior border of the TSL. As shoulder abduction progressed, contact stress decreased due to gradual loss of contact with the TSL. In the TSL-free scapula, there was no contact stress on the SSN in the neutral position. Towards the end of shoulder abduction, contact stress increased again as the SSN began to contact the base of the suprascapular notch in both TSL conditions.

CONCLUSION

We identified changes in the position of the SSN path within the suprascapular notch during shoulder abduction. The SSN starts in contact with the TSL and moves toward the base of the suprascapular notch with secondary contact. These findings may provide rationale for TSL release in SSN entrapment.

Denervation pseudohypertrophy of calf muscles associated with diabetic neuropathy

Denervation of muscle usually leads to muscle atrophy with fatty replacement but, uncommonly, also results in muscle hypertrophy or pseudohypertrophy with fatty replacement. We report the ultrasonographic and magnetic resonance imaging (MRI) findings of a patient with diffuse fatty infiltration of calf muscles as a result of denervation pseudohypertrophy. The elevated fasting glucose, neurogenic electromyographic changes, and muscle atrophy with adipose tissue infiltration are consistent with diabetic neuropathy as the cause of denervation pseudohypertrophy. Lumbosacral radiculopathy and plexopathy were excluded by MRI. The imaging features reported in the literature are reviewed. The important differential diagnosis of infiltrating lipoma and denervation hypertrophy, as well as other causes of monomelic hypertrophy or swelling, is discussed. This case report demonstrates the importance of MRI, with clinical, biochemical, electrophysiological, and histologic correlation in the diagnosis of denervation pseudohypertrophy. Correct diagnosis of denervation pseudohypertrophy has an important role in guiding further investigations and treatment of the disease and the underlying cause.

Posterior labral tear with a paralabral cyst causing suprascapular nerve compression

The patient was a 21-year-old man who was currently enrolled in a military academy. He was seen by a physical therapist in a direct-access capacity for a chief complaint of right shoulder fatigue and discomfort that was present for the past week. Due to marked atrophy and weakness with no history of injury, an orthopaedic surgeon was consulted and diagnostic imaging was requested. Magnetic resonance imaging revealed a posterior labral tear with a large paralabral cyst, likely resulting in significant compression of the suprascapular nerve.