Sunday, September 18, 2011

Expectations, Perceptions, and a Shoulder Fracture

Our expectations can certainly influence our perceptions. For example, in the figure below, the image "13" is perceived readily as a number when it is surrounded by other numbers (lower line). In the upper line, it is surrounded by letters, and it is perceived differently, recognized more slowly and less readily by the brain.
 


Expectations influence perception over and over in our lives, and this phenomenon extends to radiology. The clinical setting creates a certain set of expectations in the mind of the radiologist. This situation cuts both ways, enhancing the ability of the radiologist to detect subtle findings (when he is explicitly looking for them), but also detracting from his ability to see these same subtle findings (when the expectation is that they will not be present).

In this case, an 80 year old grandmother tripped over her grandchild's toy and hit a wall 8 weeks ago. She had arthritis in both shoulders, and went to her orthopedic surgeon, since her right shoulder was hurting more than usual. X-rays were negative, and she was sent for an MRI for further evaluation.

A coronal T2 fatsat image reveals an unexpected, easily missed fracture of the spine of the scapula:




An axial gradient echo weighted image of the patient confirms the scapular spine fracture:


Fractures of the scapula are typically associated with major trauma, such as high-speed motor vehicle accidents or other crashes. 




In the absence of such trauma, one typically does not think of a scapular fracture as a cause of shoulder pain, but this was indeed the case in this example.

The scapula is also called the "shoulder blade" and helps stabilize the upper extremity against the chest. Here is a posterior view of the chest, showing the scapula:


Scapula, anterior view:


Scapula, posterior view:


The scapula is a flat, triangular bone that lies over the posterior surface of the rib cage. At its upper lateral corner is a cuplike depression called the glenoid fossa (red arrows) which forms the socket for the head of the humerus. The posterior surface of the scapula is divided by a nearly horizontal ridge of bone, the scapular spine (blue arrows). The spine extends laterally to form the acromion (black arrows) which overhangs the glenoid fossa. The anterior surface of the scapula, just medial to the glenoid fossa, has a beaklike projection called the coracoid process (green arrows) that acts as an attachment for muscles and ligaments. (chionline)

Most scapular fractures can be treated nonoperatively. In general, the results are satisfactory with conservative treatment. A sling support for 3-4 weeks and early rehabilitation is the key to successful non operative treatment. Treatment emphasizes symptom relief and early motion to prevent long-term stiffness. After motion is restored in the first four to 6 weeks, therapy is directed at rehabilitating the rotator cuff and strengthening parascapular musculature. (shoulderdoc.co.uk)

This case illustrates that although scapular fractures are traditionally associated with high-energy trauma, they can also occur in elderly osteoporotic patients with a history of a minor trauma.

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