Musculoskeletal Interventional Radiology

1

What are some common image-guided musculoskeletal interventional procedures?

Musculoskeletal radiology is a subspecialty that encompasses many diagnostic and therapeutic procedures using image guidance. Some common ultrasonography-guided (US-guided) procedures in musculoskeletal radiology include: joint injections, tendon sheath injections, calcific tendinosis lavage, bursal injections, tendon fenestration, and soft tissue biopsy. Fluoroscopy is often used to guide joint injections as well as joint aspiration and arthrography. Computed tomography (CT) may be used to guide sacroiliac joint injections, bone biopsies, and radiofrequency (RF) ablation of osteoid osteoma. Magnetic resonance imaging (MRI) may be used to target bone marrow lesions for percutaneous biopsy that are occult on CT or radiography.

2

What is MR arthrography, and what are its indications?

Direct MR arthrography involves the injection of dilute gadolinium-based contrast material into a joint under fluoroscopic guidance followed by MR imaging. This technique is commonly employed in the shoulder and hip to evaluate the labrum and articular cartilage ( Figure 75-1 ). Wrist arthrography is used to evaluate the intrinsic carpal ligaments and the triangular fibrocartilage complex (TFCC). Intraarticular administration of contrast material allows for improved contrast resolution as well as distention of the joint capsule, both of which make it easier to visualize and evaluate small intraarticular structures (e.g., the labroligamentous complex of the shoulder joint).

3

What concentration of gadolinium-based contrast material is used when performing MR arthrography? What are the components of the MR arthrogram injectate?

For MR arthrography, the injectate is diluted to a concentration of 1 to 2.5 mM. The final gadolinium dilution ratio should be 1 : 100 to 1 : 250 to achieve maximal signal intensity on T1-weighted MR images. Although the final injectate solution slightly varies from institution to institution, a suggested injectate solution may consist of 10 ml of saline, 10 ml of iodinated contrast material, 0.2 ml of gadolinium-based contrast material, and 0.1 ml of epinephrine (although not used for hip injections).

4

What will occur if the concentration of gadolinium in the injectate is too high?

If the intraarticular concentration of gadolinium in the injectate for MR arthrography is too high, for example with a gadolinium dilution ratio of 1 : 5, this will result in a “black arthrogram” seen on MRI, where the injectate appears low in signal intensity. If this occurs, one option is to perform MRI after a waiting period of several hours.

5

What are the indications for a CT arthrography? What contrast material is used?

CT arthrography is most often used when patients have contraindications to undergoing MR arthrography including: implanted pacemaker/defibrillator devices, any internal metal objects that make MRI unsafe, or claustrophobia. CT arthrography is particularly useful for the demonstration of cartilage defects, evaluation of intraarticular bodies, fracture fragments, synovial disease, and assessment of ligamentous integrity. Additionally, CT arthrography is very helpful to evaluate postoperative patients with implanted metallic hardware, because beam hardening artifact can be mitigated. Some of the common indications for CT arthrography include: evaluation of labral pathology of the shoulder, evaluation of the postoperative rotator cuff, evaluation for meniscal tears in the postoperative knee, and evaluation for ligamentous pathology in the wrist. The injectate for CT arthrography varies by institution but can range from a 1 : 1 mix of 300 mg/ml nonionic iodinated contrast material and sterile saline, to full-strength contrast material ( Figure 75-2 ).

6

What are the commonly used approaches for injecting the glenohumeral joint? What are the pros and cons of each?

Several approaches are commonly used for accessing the shoulder joint for direct arthrography. The most common approach is straight anterior with insertion of the needle at the junction of the middle and lower thirds of the glenohumeral joint, targeting the medial lower third of the glenohumeral joint while aiming for the side of the humeral head to avoid contacting the labrum. Using this approach, the needle must traverse the subscapularis tendon, which results in a theoretic risk of damaging the tendon.

An alternative anterior approach is the rotator interval approach. With this method, the skin is marked superficial to the upper outer medial quadrant of the humeral head such that the rotator interval above the subscapularis tendon and lateral to the coracoid process is targeted. Advantages of the rotator interval approach are that a shorter needle (1.5 inch) can be used and that the operator can avoid traversing the subscapularis tendon, labrum, glenohumeral ligaments, and subcoracoid bursa. The drawback to this approach is the potential inadvertent injection of the subacromial-subdeltoid (SASD) bursa, which overlies the superior aspect of the rotator interval, which may result in difficulties with interpretation of the MR images if injected.

A final technique is the posterior approach, which has been employed by some operators for suspected anterior instability and for muscular patients. This approach offers the added benefit of traversing fewer important anterior stabilizing structures of the glenohumeral articulation. The patient is placed in the prone position with the arm in internal rotation, and the needle is advanced toward the inferomedial aspect of the humeral head. With the posterior approach, once the needle tip contacts bone, it is important to apply continuous downward pressure during contrast material test injection to find the potential space between the humerus and joint capsule. Failure to provide downward pressure during contrast material test injection will likely result in contrast infiltration into the posterior aspect of the rotator cuff.

7

What imaging modalities can be used to guide joint injections, aspirations, or arthrography?

US, CT, or fluoroscopy may be selected to perform joint injections, aspirations, or arthrography. The selection of the specific imaging modality to guide the procedure depends upon the joint to be accessed, operator preference, patient characteristics (such as body habitus, age, pregnancy status, and ability to comply with the examination, among others), and the clinical question to be answered. One should consider using US rather than fluoroscopy for patients who are young or pregnant, in order to avoid ionizing radiation.

8

What are some benefits of using US to guide musculoskeletal procedures?

There are multiple benefits of using US to guide musculoskeletal procedures. First, there is no ionizing radiation, which is especially attractive when imaging pediatric and pregnant patients. US allows for real-time dynamic evaluation, which enables the operator to directly visualize the needle as it is advanced, ensuring avoidance of neurovascular structures. US allows the operator to deploy the biopsy needle in real time, unequivocally confirming needle placement within the targeted lesion. US guidance for injections allows the operator to observe the injection of the corticosteroids or other medications in real time, confirming accurate targeting of the joint or tendon sheath.

9

What are some commonly used corticosteroids in musculoskeletal interventions?

There are a variety of commonly used synthetic corticosteroids for musculoskeletal interventions that are derivatives of prednisolone, which is an analogue of cortisol. The most commonly used preparations include: methylprednisone acetate, triamcinolone acetonide, betamethasone acetate, and dexamethasone sodium phosphate.

10

What are some important contraindications to corticosteroid joint injections?

Absolute contraindications to corticosteroid joint injections include local or intraarticular sepsis, bacteremia, intraarticular fracture, and joint instability. If a patient has an infection at the time of corticosteroid injection, the primary concern is introduction of infection into the joint or worsening of a preexisting joint infection. In the setting of fracture and joint instability, corticosteroids inhibit bone healing and lead to worsening of joint instability due to the potential for subchondral osteonecrosis, as well as weakening of the joint capsule and ligaments. Relative contraindications to corticosteroid joint injection include: severe juxtaarticular osteoporosis, coagulopathy, and injection of a joint three times within a year or an injection within the last six weeks.