Shoulder Arthrogram

Excerpt

Within musculoskeletal radiology, arthrography has served as an essential technique for close to 100 years. Glenohumeral arthrography was described in 1933 when Oberholzer was studying capsular distortion secondary to shoulder dislocation. During this time, he injected air into the shoulder joint to evaluate the structures, including the axillary recess, on a conventional radiograph. In 1934, Codman had suggested that injecting contrast material into the shoulder joint could demonstrate rupture within the rotator cuff. In 1939 Lindbolm and Palmer determined that arthrography was accurate in diagnosing lesions in the rotator cuff in a substantial number of patients.

The use of iodinated contrast, computed tomography, and magnetic resonance imaging naturally came after this time. At this time, magnetic resonance imaging (MRI) is the first-line imaging modality for assessing joints as it has a superior soft-tissue contrast capability. In a patient who is claustrophobic or has any contraindications to undergo an MRI, a computed tomography (CT) arthrogram is a suitable option. Postoperative joints can lead to artifacts for which CT is a good option. Arthrography remains a useful imaging modality with computed tomography, CT scan, and magnetic resonance imaging, MRI, to allow a detailed assessment of articular structures of interest.

Glenohumeral arthrography, shoulder arthrography, is an imaging technique used in evaluating the glenohumeral joint and associated components. During an arthrogram, a joint injection is done typically under fluoroscopic guidance, but ultrasound or CT can be utilized. The process of a direct arthrogram leads to joint distention and separation of the intra-articular structures. This capsular distention allows for the enhancement and visualization of small joint bodies, the labrum, glenohumeral ligaments, rotator cuff undersurface, the structures of the rotator interval, and the long head of the biceps. Direct arthrography in which contrast is injected into the joint has an alternative procedure termed an indirect arthrogram. An indirect arthrogram is a technique that produces arthrographic images without utilizing direct joint injection.

Historically, arthrography was performed with fluoroscopy and plain radiographs only, but today all patients undergo cross-sectional imaging of the shoulder after the injection of contrast. Typically, this is an MRI, but CT can be performed if contraindications to undergo an MRI are present, or there is a high clinical suspicion of a bony abnormality.

Generally, radiographic examinations demonstrate soft tissues like cartilage, muscle, joint fluid, and menisci to be of the same density. Therefore, these structures are not distinguishable from one another. The term arthrography refers to an imaging modality following the injection of contrast into a specific joint, typically performed with fluoroscopic guidance. Utilizing injected contrast outlines the intraarticular structures and differentiates them from other adjacent soft tissues. The injection also allows for distention of the joint, providing better visualizations and separation of structures. During an arthrogram, a sterile technique and local anesthetic are utilized. A needle is introduced into the joint space where synovial fluid can be aspirated if needed for any diagnostic purpose. Contrast like iodinated contrast is injected into the joint.

Additional medication like an anesthetic or a glucocorticoid can also be injected into the joint space for therapeutic purposes during the arthrogram. The arthrogram can aid in facilitating the identification of ligamentous or tendon injuries, intraarticular "loose" bodies, cartilage or synovial abnormalities, loosening of the joint prosthesis, and sinus tracts. The implementation of fluoroscopy allows for real-time tracking of contrast, which will pass into and fill the joint. The contrast pattern can highlight abnormalities like abnormal contrast leakage or synovitis. The arthrogram can be followed with computed tomography or magnetic resonance imaging. Rotator cuff tears and the labrum are more appreciated when there is delineation by contrast.

Glenohumeral instability is common and can be a perplexing clinical issue where both an accurate and a non-operative method of diagnosis is desirable. Shoulder arthrograms can serve as a useful aid in diagnosis. The glenohumeral joint is susceptible to instability and dislocation due to a combination of the bony discrepancy between the humeral head and the glenoid. This discrepancy allows for a larger range of motion. The biomechanics within the shoulder joint is based upon the interaction of both static and dynamic stabilizing systems. The static structures of the joint include the glenoid, glenoid labrum, humeral head, and capsule. The capsule includes the glenohumeral ligaments. The dynamic stabilizing structures include the rotator cuff and muscular structures surrounding the joint. When evaluating for shoulder pathology, it is crucial to remember the relevance of radiographs to assess osseous and joint structure abnormalities. Typically, an MRI study after conventional radiographs have been evaluated is performed.

The glenohumeral joint has both complex anatomy and physiology. It is the most mobile yet unstable joint in the body and requires appropriate imaging exams for varying clinical scenarios. A thorough history and physical examination are necessary to develop a differential diagnosis before selecting which imaging examination. Plain film radiography evaluation typically includes internal rotation, external rotation, axillary and transscapular views, with other specialty views as needed. The plain film is the first-line imaging modality for nearly all shoulder pathology. They are also often the only imaging examination necessary for evaluating calcific tendinitis, arthritis, acute shoulder trauma, and osteolysis of the distal clavicle in athletes.

Computed tomography of the glenohumeral joint is reserved for evaluating a fracture or fracture-dislocation and a prosthetic joint. The CT scan can demonstrate fractures displacement, angulation, and complexity. On CT, the visualized images in the coronal, axial, sagittal planes, and three-dimensional format, can aid in the interpretation and any preoperative planning. Magnetic resonance imaging is the primary imaging modality used to evaluate soft tissues of the shoulder. Soft tissues include the rotator cuff, tendons, biceps muscle, subacromial and subdeltoid bursae. It also has a high level of sensitivity in detecting subtle fractures, acromioclavicular joint changes, erosive changes to the distal clavicle, early avascular necrosis, bone marrow edema, muscular atrophy, and morphology of the acromion.

The MRI is the second-line imaging modality to evaluate shoulder instability and labral tears when MR arthrography is not performed. Radionuclide bone scans, technetium-99m bone scans, are typically used for evaluating an infection post arthroplasty or suspected metastases and whole-body imaging.

Arthrography involves the percutaneous puncturing into the shoulder joint and then instilling a contrast agent. Iodinated contrast is used for conventional arthrography and CT arthrography, whereas gadolinium contrast is used for MR arthrography. With conventional arthrography, radiographs are obtained after injecting the iodinated contrast, which is still the procedure of choice in diagnosing adhesive capsulitis, frozen shoulder. With the injection, there is distention of the shoulder capsule that can be used therapeutically. MR arthrography involves an injection in the intra-articular space, but a gadolinium-based contrast agent is injected with an MRI following. MR arthrography, or MRA, is the gold standard in evaluating a suspected labral tear or shoulder instability.

MRA is also indicated when there is a high suspicion of a rotator cuff tear in a patient with a normal or inconclusive MRI and the evaluation for intra-articular small bodies. The systemic administration of the gadolinium-containing contrast agent in a patient with moderate to severe impaired renal function with a GFR of less than 15 to 30 mL per minute does have an associated increased risk of developing nephrogenic systemic fibrosis. Given that the MR arthrography involves a small dosage of gadolinium and the administration is via intra-articular, nephrogenic systemic fibrosis has never been reported in this procedure. The risk of nephrogenic systemic fibrosis has been reduced further by using Group II gadolinium-based contrast agents, which have proven safe for use even in patients with severe renal impairment.

Computed tomography arthrography is used when there is a contraindication for MR arthrography, like a patient with incompatible vascular clips, claustrophobia, a pacemaker, or when MRA is unavailable. CT arthrography can be used for evaluating a prosthetic joint which would ultimately result in an artifact on MRI. Ultrasonography of the glenohumeral joint is useful when assessing the rotator cuff, calcific deposits, and biceps tendon. It can also measure the subacromial space and detect the presence of muscular atrophy. It serves as a tool in the dynamic evaluation for the shoulder and shoulder impingement.

The American College of Radiology, ACR, has criteria for selecting the imaging modalities of choice for patients with traumatic or atraumatic shoulder pain. Imaging examination choices are based upon the etiology of the shoulder pain, whether traumatic or atraumatic, the duration of symptoms, the age of presentation, and any clinical or radiographic suspicions for a particular condition. Again, the initial imaging modality of choice for traumatic or atraumatic shoulder pain should be radiography. Indications for conventional radiographs include evaluation for dislocation or fracture following trauma, evaluation of calcific tendinitis, crystal deposition disease, osteoarthritis, suspicion of a bony neoplasm, particularly with a patient with a non-diagnosis of cancer, suspicion for septic arthritis, or suspected humeral head avascular necrosis. The next imaging choice should be guided by the clinical scenario and findings from the plain films.

For example, a patient who is less than 30 years old and suffers an anterior glenohumeral dislocation may have a suspected labral injury. MR arthrography is indicated in these cases. An anterior shoulder dislocation can also have an associated rotator cuff injury in approximately 50% of patients under 40 years old and about 80% of patients over 60 years old. With these patients, ultrasound may be of value as a screening modality.

MR arthrography is indicated in a younger patient with shoulder instability, suspicion of a labral tear, and within the setting of a shoulder dislocation. MRA allows for distinguishing between a partial versus a full-thickness rotator cuff tear and can identify suspected cartilage or labral tear.

When MR arthrography is contraindicated, then CT arthrography should be used. CT arthrography can detect occult fractures, tendinitis, or labral tears when MRI is contraindicated. In a patient with a suspected rotator cuff tear or impingement, MR arthrography has a higher sensitivity and specificity than MRI or ultrasound for diagnosing both partial as well as full-thickness rotator cuff tears. MRA has a specificity and sensitivity greater than 95% for detecting full-thickness rotator cuff tears. In partial-thickness tears, MRA has a specificity and sensitivity are 96 and 86%, respectively. MRA can differentiate between small partial versus small full-thickness tears and tendinosis.

CT arthrography is indicated if a patient cannot undergo MRI or ultrasound expertise is unavailable. Both the sensitivity and specificity are over 90% for CTA in detecting supraspinatus and infraspinatus tears, but low sensitivity for detecting subscapularis tears.

CTA can also aid in preoperative evaluations by demonstrating the extent of fatty degeneration and tendonous retraction of the corresponding muscle. MRA is also the imaging of choice for labrocapsular structures. It is the most accurate imaging modality for evaluating sports injuries to the shoulder. MRA can evaluate the dynamic stabilizers of the glenohumeral joint that are extra-articular, the static stabilizers that are intra-articular, and the morphology of the capsule. The sensitivity and specificity of MRA in detecting labral tears range from 88 to 100% and 88 to 96%, respectively.

Using the abduction external rotation technique increases MRA sensitivity for labral tear diagnosis to close to 100%; hence this modality is indicated for suspected lesions to the rotator cuff and glenoid labrum in athletes. CTA is accurate in delineating anatomic derangement, including the glenoid labrum, but soft tissue evaluation is limited. The sensitivity for CTA for labral tears is between 73 to 76% and a specificity of 92%.

In a patient with atraumatic shoulder pain with suspected adhesive capsulitis, the diagnosis is mainly based on clinical findings. Adhesive capsulitis, also known as frozen shoulder, is due to the contraction and thickening of the glenohumeral joint capsule and synovium. This process results in a progressive limitation in the joint's mobility with associated significant pain. Conventional arthrography is the imaging modality of choice for both diagnosis and treatment. There is a decreased capacity for injecting contrast into the joint, which is diagnostic for adhesive capsulitis in these cases. The distention of the capsule during the arthrogram can serve as a therapeutic tool.