Atlas of Shoulder MRI Anatomy

Radiologists primarily perform shoulder imaging to assess injuries within the shoulder joint. Experts analyze the different imaging techniques to identify better diseases associated with the shoulder, including AC joint osteoarthritis and RC tendinosis(1).

How Does Shoulder MRI Work?

Magnetic resonance imaging (MRI) tests involve large machines that use radio wave energy pulses and a magnetic field to produce images of the shoulder(2).

Compared to X-ray, ultrasound, or CT scan, MRI tests allow doctors to see joint structures, including muscles and ligaments, more clearly.

During an MRI test, the patient places their shoulder inside the magnet machine. This process allows the magnetic field to find changes in the organ and tissue structures, identifying any tissue disease or damage, including infections or tumors.

MRI images are digital, allowing other doctors to remotely review the pictures from an MRI scan for further study.

For physical copies of the MRI images, technicians may use a contrast material during the MRI scan to highlight specific structures. Contrast material is a substance that makes structures appear more clearly, which helps show areas of infection or inflammation and find some types of tumors.

Bone Structures

Shoulder MRI includes assessments of the joint’s bone structures, including the proximal humerus (upper limb’s long bone; shoulder to elbow), scapula (shoulder blade) and glenoid (end of the scapula), coracoid process (bone structure located below the lateral fourth of the clavicle), acromion (the shoulder’s highest point), and the distal clavicle (collarbone).

Assessing these parts help doctors identify the following diseases:

  • Osteonecrosis of the humeral head: Also known as Hass disease, this disease is less common than osteonecrosis of the hip. Similar risk factors remain, including those that lead to loss of circulation and eventual bone death(3).
  • Bone tumors: When cells within a bone uncontrollably divide, a lump of abnormal tissue develops forms and develops into bone tumors. Primary bone tumors associated with the shoulder include osteosarcoma and chondrosarcoma(4).
  • Fractures: a fracture is a break in the bone that may occur after vehicular accidents, falls, or sports injuries.
  • Hill-Sachs lesion: The Hill-Sachs lesion is a bone defect of the humeral head, typically associated with anterior shoulder instability(5).
  • Bony Bankart lesion: Patients with a bony Bankart lesion usually have anterior shoulder dislocation. Experts define this condition as a detachment of the anteroinferior labrum associated with a glenoid rim fracture(6).

Acromioclavicular Joint

The acromioclavicular joint (ACJ) is the planar diarthrodial synovial joint of the pectoral girdle, which connects the upper limb to the axial skeleton.

The planar diarthrodial synovial joint is a type of joint that features an articular capsule, synovial fluid, and articular cartilage.

Some related conditions that an MRI test can identify may include:

  • Acromioclavicular injury: Common among athletes, this injury is a significant source of morbidity in athletes who engage in overhead sports.

This injury may disguise as other shoulder conditions. Thus, examiners must understand the shoulder’s anatomy and biomechanics to perform a systematic clinical evaluation correctly and accurately identify the injury(7).

  • Arthritis: Shoulder osteoarthritis (OA) may be a significant cause of pain and disability. In the USA, 32.8% of patients over 60 years old have this condition(8).
  • Hooked acromion: Hooked acromions are the third type of acromion, the others being flat and smoothly curved types(9). Individuals with hooked acromion may experience increased incidences of rotator cuff tears(10).
  • Lateral downslope: A study investigating the lateral downsloping of the acromion assessed whether its appearance is a good MR sign in impingement syndrome(11). Although the authors suggested that lateral downslope is not predictive of impingement syndrome, standardized measurements partially validated the condition.

Impingement syndrome is a condition where the rotator cuff tendons get pinched as they pass between the upper arm and tip of the shoulder.

Rotator Cuff

Surrounding the shoulder joint is the rotator cuff, which is a group of muscles and tendons(12). Shoulder MRI assesses the following tendon and muscle structures:

  • Supraspinatus tendon and supraspinatus muscle
  • Infraspinatus tendon and infraspinatus muscle
  • Teres minor tendon and teres minor muscle
  • Subscapularis tendon and subscapularis muscle

Assessing these muscles and tendons allow doctors to diagnose conditions concerning rotator cuff tears, including:

  • Atrophy: Muscle atrophy is the muscle tissue’s gradual shrinking as a result of disease or inactivity. Chronic rotator cuff tears are the most common reasons for rotator cuff atrophy. Other causes may include cuff aging, diabetes, and disuse(13).
  • Fatty degeneration: massive rotator cuff tears may lead to fatty degeneration(14). Fatty degeneration is a rotator cuff degenerative condition characterized by fatty accumulation within and around the muscles. Atrophy of muscle fibers and fibrosis may also manifest(15).
  • Edema: MRI commonly finds bone marrow edema (BME), which may occur in all bones(16). Excessive water signals characterize BMEs in the marrow on MRI tests(17).

  1. Kvalvaag, E., Anvar, M., Karlberg, A. C., Brox, J. I., Engebretsen, K. B., Soberg, H. L., Juel, N. G., Bautz-Holter, E., Sandvik, L., & Roe, C. (2017). Shoulder MRI features with clinical correlations in subacromial pain syndrome: a cross-sectional and prognostic study. BMC musculoskeletal disorders, 18(1), 469. https://doi.org/10.1186/s12891-017-1827-3
  2. Magnetic Resonance Imaging (MRI) of the Shoulder. Michigan Medicine – University of Michigan. 2019 December 8. Retrieved from https://www.uofmhealth.org/health-library/tu6374
  3. Harreld, K. L., Marker, D. R., Wiesler, E. R., Shafiq, B., & Mont, M. A. (2009). Osteonecrosis of the humeral head. The Journal of the American Academy of Orthopaedic Surgeons, 17(6), 345–355. https://doi.org/10.5435/00124635-200906000-00003
  4. Bone Tumor. OrthoInfo. Retrieved from https://orthoinfo.aaos.org/en/diseases—conditions/bone-tumor
  5. Provencher, M. T., Frank, R. M., Leclere, L. E., Metzger, P. D., Ryu, J. J., Bernhardson, A., & Romeo, A. A. (2012). The Hill-Sachs lesion: diagnosis, classification, and management. The Journal of the American Academy of Orthopaedic Surgeons, 20(4), 242–252. https://doi.org/10.5435/JAAOS-20-04-242
  6. Skupiński, J., Piechota, M. Z., Wawrzynek, W., Maczuch, J., & Babińska, A. (2017). The Bony Bankart Lesion: How to Measure the Glenoid Bone Loss. Polish journal of radiology, 82, 58–63. https://doi.org/10.12659/PJR.898566
  7. Beim G. M. (2000). Acromioclavicular joint injuries. Journal of athletic training, 35(3), 261–267.
  8. Chillemi, C., & Franceschini, V. (2013). Shoulder osteoarthritis. Arthritis, 2013, 370231. https://doi.org/10.1155/2013/370231
  9. Epstein, R. E., Schweitzer, M. E., Frieman, B. G., Fenlin, J. M., Jr, & Mitchell, D. G. (1993). Hooked acromion: prevalence on MR images of painful shoulders. Radiology, 187(2), 479–481. https://doi.org/10.1148/radiology.187.2.8475294
  10. Yadav, Sachin Kumar; Zhu, Wen Hui. A systematic review: Of acromion types and its effect on degenerative rotator cuff tear. International Journal of Orthopaedics Sciences. 2017. Retrieved from https://journals.indexcopernicus.com/search/article?articleId=1998795
  11. Yao, L., Lee, H. Y., Gentili, A., & Shapiro, M. M. (1996). Lateral down-sloping of the acromion: a useful MR sign?. Clinical radiology, 51(12), 869–872. https://doi.org/10.1016/s0009-9260(96)80085-7
  12. Rotator cuff injury. Mayo Clinic. Retrieved from https://www.mayoclinic.org/diseases-conditions/rotator-cuff-injury/symptoms-causes/syc-20350225
  13. Chung, S. W., Kim, S. H., Tae, S. K., Yoon, J. P., Choi, J. A., & Oh, J. H. (2013). Is the supraspinatus muscle atrophy truly irreversible after surgical repair of rotator cuff tears?. Clinics in orthopedic surgery, 5(1), 55–65. https://doi.org/10.4055/cios.2013.5.1.55
  14. Kang, J. R., & Gupta, R. (2012). Mechanisms of fatty degeneration in massive rotator cuff tears. Journal of shoulder and elbow surgery, 21(2), 175–180. https://doi.org/10.1016/j.jse.2011.11.017
  15. Osti, L., Buda, M., & Del Buono, A. (2014). Fatty infiltration of the shoulder: diagnosis and reversibility. Muscles, ligaments and tendons journal, 3(4), 351–354.
  16. Baumbach, S. F., Pfahler, V., Bechtold-Dalla Pozza, S., Feist-Pagenstert, I., Fürmetz, J., Baur-Melnyk, A., Stumpf, U. C., Saller, M. M., Straube, A., Schmidmaier, R., & Leipe, J. (2020). How We Manage Bone Marrow Edema-An Interdisciplinary Approach. Journal of clinical medicine, 9(2), 551. https://doi.org/10.3390/jcm9020551
  17. Eriksen E. F. (2015). Treatment of bone marrow lesions (bone marrow edema). BoneKEy reports, 4, 755. https://doi.org/10.1038/bonekey.2015.124

References

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