• The commonest pathology causing shoulder pain is rotator cuff pathology, like partial or full thickness tears and the next common labral pathology.
• Subacromial – subdeltoid bursal fluid is the commonest associated finding.
• Ultrasound has a high sensitivity and specificity for full thickness tears of the rotator cuff tendons. However comparatively less sensitivity and specific in cases of partial tear , intrasubstance tear and tendinosis
• USG provides dynamic assessment of shoulder with comparison with contralateral shoulder.
• USG is not sensitive in evaluating labral and capsular pathologies as MRI
• MRI can be used in problematic cases, where the diagnosis is doubtful on USG.
• USG imaging can be considered almost equally effective as compared to MRI, in the evaluation of rotator cuff injuries, especially full thickness tears.
• Though operator dependent, a well performed USG can effectively serve as a primary diagnostic method and screening of all painful shoulder joints because it is economic and fast and MRI should be used secondary because it provides more information about the extent of tendons, labral pathology and has lower risk of artifacts.
• MRI is very helpful in providing detailed information such as tendon retraction and muscle atrophy required for surgical management.
• MRI has good sensitivity for non rotator cuff pathologies such as labral lesion which are not appreciated on USG.
In our study of ultrasound and MRI correlation, 49 patients referred from orthopaedic department were included. These patients’ underwent USG and were correlated with MRI of the shoulder in question.
Since clinical examination does not provide adequate diagnosis to the underlying pathology, radiological diagnosis is more sort after.
Pitfalls of USG:
1. Anisotropy: The rotator cuff appears echogenic when the ultrasounds beam insonates at 90° to the long axis of the tendon fibers because the beam is then reflected maximally. The more the angle deviates from this angle, the fewer reflected sound waves will be detected by the transducer. The tendon becomes isoechoic to muscle at angles of 2°– 7° and hypoechoic at greater angles. Tendon insertions, where most rotator cuff tears occur, are most vulnerable to the anisotropic artifact due to their curved course. If unaware of this artifact, less experienced scanners could erroneously take this for tendinosis or a partial thickness rotator cuff tear.
2. Humeral head anomalies like fractures, distorts the anatomy of the rotator cuff.
3. Muscle bulk is not appreciated in USG examinations; hence denervation injuries are not picked up.
4. USG is operator dependant and has a high inter-observer variation and a high learning curve for radiologists.
MRI has both limitations and pitfalls:
Limitations: are claustrophobia, obese patients, and post-surgical metallic implant fixations.
The magic angle artifact is routinely encountered in MRI examinations of the shoulder. It mostly occurs in T1 weighted images on the coronal plane. The appearance of intermediate signal intensity is seen within the normal supraspinatus tendon on T1 weighted images.
This phenomenon occurs due to the orientation of the tendon fibers with that external magnetic field. The normal supraspinatus tendon is oriented 55-60 degrees to the external magnetic field. However, the signal intensity will not increase on T2 weighted images.
Hence USG can be used as a first line of investigating a case of shoulder joint to rule out rotator cuff pathologies and for confirmatory and other pathologies MRI examination can be used Magnetic resonance imaging (MRI) of the shoulder joint has achieved wide acceptance as an imaging technique and more definitive in diagnosis.