The shoulder joint is an incongruous ball and socket joint without any fixed axis of rotation, which has a wide range of motion in multiple planes; hence stability is compromised for mobility. Shoulder joint is used for movement of the hand in all directions, for powerful throwing activities and less commonly for climbing and crawling. This much range is unique to humans and primates. To compensate for the unstable bony anatomy the shoulder is protected anteriorly, posteriorly and superiorly by a capsule and the tendons that form the rotator cuff.
The understanding of shoulder disorders has changed considerably as a result of improved diagnostic tools, such as arthroscopy and multiplanar imaging modalities. 1
Shoulder pain is one of the most common complaints encountered in routine practice and often leads to considerable disability. Common causes of a painful shoulder are lesions involving muscle, tendons, bursa, labrum and bones.
The diagnosis of various shoulder pathologies can be difficult because of spectrum of disorders, including cervical spine disease, acromio-clavicular arthritis, and shoulder instability. Impingement and denervation syndromes can present with similar clinical findings. 1
The tendon is subject to wear and tear during the day to day activities. Accurate depiction of anatomic abnormalities is important for treatment planning.
USG has its own limitations such as high operator dependency, long learning curve and problems of anisotropy. It has limited utility in evaluation of labral, rotator cuff interval, and in demonstrating subtle bony lesions.
MRI has become the ?gold standard for detecting both subtle and obvious internal derangement and assessing overall joint structure. MRI is an excellent modality because of its multi-planar capability in painful shoulder.
IMAGING MODALITIES OF THE SHOULDER JOINT:
The shoulder joint is quite unstable owing to its anatomical structure and its wide range of movements. The multidirectional stability of the joint is a function of multiple structures including the glenoid labrum and the overlying cartilage, the capsule, the rotator cuff tendons and other muscles surrounding the joint. Painful shoulder can present with or without limitation of either passive or active movements and the choice of appropriate imaging modality will depend on the suspected cause of the pain.
It is primary imaging modality necessary in evaluating acute shoulder trauma, calcific tendinitis, arthritis and osteolysis. It is quite useful in trauma. It has a poor pick up rate of etiology of shoulder pain especially in soft tissue injuries.
Contrast arthrograghy involves injecting iodinated contrast media. Radiographs are taken at different positions. In complete tears, contrast floods the joint and into the subacromial-subdeltoid bursa. In partial tears, the contrast is seen as a line or small filled cavities within the tendon but not into the subacromial-subdeltoid bursa. These findings are more difficult to demonstrate than when there is a complete tear. Intra tendon tears and tears on the superior aspect of the tendon are not demonstrated by this technique.
Mainly for diagnosis of rotator and non rotator cuff soft tissue lesions. It has a very high sensitivity in diagnosis of complete tears. However the pick-up rate depends on the operator. Ultrasonography has limitation in sonographically inaccessible areas like bone, labral cartilage, deep parts of ligament and posterior surgical shoulder thus need other imaging modalities such as magnetic resonance imaging. USG is operator dependent.
Computer tomography (CT):
Computer tomography has a role in imaging of a painful shoulder. Its ability to depict bony structures makes it important especially in evaluating suspected fractures and fracture dislocations. CT arthrography sensitivity is very low in tendinosis and partial tears.
Magnetic Resonance imaging (MRI):
MR is currently considered as the reference standard for imaging of shoulder disorders. It is a reliable non invasive imaging modality for evaluating shoulder disorder especially those related to rotator cuff and glenohumeral instability. MR is better than either ultrasound or CT in identifying partial thickness tears of the rotator cuff. Studies have shown that MRI can depict soft tissues without the need for intraarticular contrast media and can detect early ischemic necrosis, primary and secondary tumor deposits and infections of the shoulder joint. MRI has very high sensitivity and specificity in diagnosis of complete rotator cuff tears, in differentiating tendinosis from degenerative changes.
MR arthrography increases the sensitivity and enhances the accuracy offered by conventional MR imaging. MR imaging of the shoulder gives confidence to the orthopedic surgeons in decision making. It has a major effect on diagnostic thinking and therapeutic decisions by orthopedic surgeons.
Thus MRI is an excellent reliable imaging tool for shoulder pathology. Its accuracy leads to improvement in management of the shoulder pathology. It is the imaging modality of choice in characterizing the various disorders and evaluating the extent of osseous, chondral and soft tissue involvement.