Lower Subscapular Muscle Denervation
Updated: Mar 12, 2021
Right Shoulder Pain in Throwing Athlete • Xray of the Week 2016 • Week #47
This 21 year old college baseball catcher had decreased velocity when throwing and right shoulder pain for 2 months. What is the diagnosis?
Figure 1. Coronal and sagittal images shows mild atrophy in the inferior subscapularis muscle (yellow arrows) and teres major muscle (red arrows). Neuropraxia changes include atrophy and fatty replacement.
Figure 2. Left image. Coronal image showing the neuropraxia changes with mild atrophy in the inferior subscapularis muscle (yellow arrow) and teres major muscle (red arrow). Neuropraxia changes include atrophy and fatty replacement.
Figure 2. Right image. Axial image showing a “Kim’s” lesion with posterior bone buildup. This is often seen with Glenohumeral Internal Rotation Deficit (GIRD).
Figure 3. Axial MRI image shows a posterior peelback SLAP lesion seen in throwing athletes (yellow arrow).
The lower subscapular nerve innervates the lower (inferior) aspect of the subscapularis muscle as well as the teres major muscle. Denervation can occur with trauma to the nerve such as stretching (a.k.a.stretch neuropraxia), blunt trauma, laceration or transection of the nerve with penetrating trauma. The nerve can also be involved with inflammatory or inflammatory like conditions such as Parsonage Turner syndrome, denervation changes, and non specific brachial plexitis. Mass compression of the nerve may also cause denervation. Either adjacent neoplasia or scar entrapment from prior trauma can exert mass effect on the nerve, potentially causing ischemia and malfunction of the nerve. Lower subscapular nerve stretch neuropraxia is potentially reversible with the cessation of activities that lead to the neuropraxia or resolution of the swelling associated with a single traumatic event. MRI findings of lower subscapular nerve denervation involve the 2 muscles innervated by the nerve. Early findings are of muscle belly swelling (bright on T2 and fat sat PD or T2 images - see figure 1). Late findings are of atrophy, and the presence of atrophy indicates irreversibility.
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Phillip Tirman, MD is the Medical Director of Musculoskeletal Imaging at the Renaissance Imaging Center in Westlake Village, California. A nationally recognized expert in the applications of MRI for evaluating MSK and spine disorders, Dr. Tirman is the co-author of three textbooks, including MRI of the Shoulder and Diagnostic Imaging: Orthopedics. He is also the author or co-author on over sixty original scientific articles published in the radiology and orthopedic literature.