USG and MRI Findings on Shoulder Joint Pathology - An Overview

Introduction:

The shoulder joint is a ball and socket joint made of three bones which include the clavicle, the humerus, and the scapula. It is a combination of the glenohumeral joint, acromioclavicular joint, sternoclavicular joint, and scapulothoracic joint. As the shoulder joint is a very mobile joint in the body, it relies on muscles, ligaments, and tendons to hold them stable and allows a wide range of movement. Shoulder pain is the most common orthopedic complaint after spine and knee pain. Due to the spheroidal shape of the glenohumeral joint, it allows a wide range of motion and is also prone to injuries and dislocation. A rotator cuff is a group of tendons and muscles (supraspinatus, subscapularis, teres minor, and infraspinatus) that attach the bones of the arm to the shoulder. Rotator cuff injury is the most common shoulder injury.

What Are the Causes of Rotator Cuff Injury?

• Repeated arm weaving or throwing while performing activities such as playing tennis, volleyball, baseball, or swimming in young people.

• Impingement syndrome - When the space between the acromion and humeral head is reduced, the bursa becomes constricted, and results in painful inflammation and edema of the bursa and tendon.

• Trauma (fall onto an arm).

• In elderly people, due to the decreased blood flow, there might be degeneration of tendons of the rotator cuff.

What Are the Clinical Signs of Rotator Cuff Injury?

The signs of rotator cuff injuries are as follows:

• Pain in the anterior or lateral aspect of the superior part of the arm becomes intense when the patient lies on the affected side.

• Decreased arm strength.

• Limited arm movement.

• Cracking noises are heard while moving the arm.

How Is the Rotator Cuff Tear Classified?

Rotator cuff tear is classified as follows:

1. No visible tears.

2. Partial-thickness tear-

• Articular side tear.

• Bursal side tear.

3. Full-thickness tear-

• With retraction.

• Without retraction.

What Are the USG and MRI Protocols Used in the Diagnosis of Shoulder Joint Injury?

• Ultrasonography (USG) Protocols - For imaging the shoulder joint pathology, an ultrasound is performed using a linear transducer at the frequency of about 10 MHz.

• The Long Head of the Biceps Tendon - For imaging, the long heads of the biceps tendon patient’s forearm are slightly rotated internally with the palm facing upwards and the elbow rotated at 90 degrees. The biceps tendon is identified between greater and lesser tuberosities. Imagine is done in both short and long axes starting from the intra-articular course to the muscle belly.

• Subscapularis Tendon (SSC) - For imaging the subscapularis tendon, the patient’s elbow is placed at the same side iliac crest with the palm facing upwards. The arm is rotated externally, and the probe is placed at the bicipital groove. The subscapularis tendon is imagined in two planes which include transverse and sagittal planes with internal and external rotation. SCC appears as a convex, elongated tendon entering the groove medially.

• Supraspinatus Tendon - For imaging, the supraspinatus tendon, the dorsal surface of the hand, is placed on the opposite side pocket with the elbow placed opposite to the lateral wall of the chest in which the supraspinatus tendon projects anteriorly. Imaging of the supraspinatus tendon is done in the transverse and longitudinal axis. The subacromial-subdeltoid bursa appears as a hypoechoic structure found between the deltoid and supraspinatus tendon.

• Infraspinatus Tendon - For infraspinatus tendon imaging, the transducer is placed over the posterior aspect of the glenohumeral joint, with the palmar surface placed on the opposite shoulder. The infraspinatus and supraspinatus fossae are viewed by moving the transducer upward and downward, with the scapula as a landmark. The infraspinatus muscle and the teres minor muscle are seen separately inside the infraspinous fossa.

• Magnetic Resonance Imaging (MRI) Scan Protocols - MRI is performed at a 1.5 Tesla unit following the imaging protocols such as PD SPAIR coronal, T2W SPAIR coronal, PD SPAIR sagittal, STIR coronal sequences, axial T1W coronal, T2W FFE sagittal sequences.

What Are the USG and MRI Findings of Shoulder Joint Injury?

Ultrasonography:

• In ultrasound, full-thickness tears appear as they are extended from the bursae to the articular surface.

• They appear as hypoechoic or mixed echogenic areas of the entire thickness of the tendon with irregular tear margins. The direct sign of a complete tear is that the supraspinatus tendon is not visible.

• Focal thinning or loss of normal convex structure on the bursal surface of the tendon.

• Double cortex sign - As the fluid replaces the tendon, the presence of a hyperechoic line between the hypoechoic hyaline cartilage of the humeral head and the hypoechoic injured supraspinatus tendon. Ultrasound shows 100 percent specificity in diagnosing supraspinatus tears.

• Peribursal fat - Due to supraspinatus tear, the peribursal fat over the tendon dips into the gap between the tendon and creates a sagging peribursal fat sign.

• The partial thickness tear appears as focal hypoechoic or mixed echogenic areas of the partial thickness of the tendon, which might be within the tendon, articular surface, or bursal side.

• Focal thinning or loss of normal convex structure on the bursal surface of the tendon.

Magnetic Resonance Imaging (MRI) Scan:

• MRI findings are classified on the basis of the presence or absence of retraction in full thickness tear and the involvement of the articular or bursal side in partial thickness tear.

• Full-thickness tears are more easily diagnosed in MRI than partial thickness tear.

• Rotator cuff injury appears as a high signal intensity area on T2-weighted images and PD TSE-weighted images, along with irregular tear margins.

• Full thickness tear appears as a continuous tear between the articular surface bursae space.

• Partial thickness tear appears as high signal intensity on T2-weighted and fat-suppressed PD-weighted images inside the tendon without tendon retraction.

• In the transverse plane, the long biceps tendon shows increased signal intensity on T2-weighted images.

Conclusion:

Ultrasound is an effective imaging tool in the diagnosis of shoulder joint injuries such as rotator cuff tears and is also effective in differentiating partial and complete tears. It is a non-invasive, highly specific economic imaging tool used to detect shoulder joint injuries. MRI provides detailed information on the soft tissues of the shoulder joint. MRI shows 75 to 94 percent sensitivity and 88 percent sensitivity in detecting the complete thickness tear in rotatory cuff injury.