The application of ultrasound for musculoskeletal injection is becoming a popular technique. As pain originating from the musculoskeletal system is one of the most common causes for patients to visit primary and tertiary care practitioners, pain physicians quite often encounter patients who can benefit from hip, knee, and shoulder injection. This chapter discusses the anatomy, sonoanatomy, and the interventional techniques of the shoulder, hip, and knee injections. Ultrasound-guided injection in these areas increases the accuracy and the efficacy of the injection, as well as potentially decreases the discomfort of these injections.
Keywordsglenohumeral joint, hip, joint injection, knee, rotator cuff, shoulder, sonoanatomy
Pain originating from the musculoskeletal (MSK) system is among the major global causes of disability and one of the most common reasons for patients to visit primary and tertiary care practitioners. The application of ultrasound for MSK examination and injection is increasingly popular and well established. The anatomy and sonoanatomy relevant to the injection of shoulder, hip, and knee joints is described in this chapter.
The shoulder is more prone to injuries or attrition and therefore it is the most common region where ultrasound-guided MSK injections are performed. Common sites of intervention in the shoulder include the acromioclavicular joint (ACJ), long head of the biceps (LHB), subacromial subdeltoid bursa (SASDB), and glenohumeral joint (GHJ).
The shoulder girdle is composed of the scapula, clavicle, and proximal humerus, all functioning as a single biomechanical unit. There are three joints (glenohumeral, acromioclavicular, and sternoclavicular) and two gliding planes (subacromial and scapulothoracic), providing the greatest range of movement of any joint in the body.
Osteoarthritis of the ACJ is a common source of shoulder pain; it is often ignored by clinicians due to the higher prevalence of rotator cuff pathology. The proper diagnosis of ACJ osteoarthritis requires a thorough physical examination, plain-film radiograph, and diagnostic local anaesthetic injection. The main indication for ACJ injection is osteoarthritis of this joint.
The ACJ is a small synovial joint with the articular surfaces separated either partly or completely by a wedge-shaped fibrocartilaginous disk ( Fig. 81.1 ). The capsule of the ACJ is reinforced by the acromioclavicular ligaments in its superior, inferior, anterior, and posterior aspects. Caudally it is also reinforced by fibers from the coracoacromial ligament, which blends with the undersurface of the ACJ. The coracoclavicular ligament, composed of the conoid and trapezoid ligaments, anchors the lateral aspect of the clavicle to the coracoid process and plays a crucial role in maintaining the vertical stability of the ACJ ( Fig. 81.2 ). The inferior surface of the joint is in direct contact with the subacromial bursa and rotator cuff and may play a role in the development of the impingement syndrome (see Fig. 81.1 ).
Sonoanatomy of the Acromioclavicular Joint
The joint can be simply reviewed with a high-frequency linear probe over the joint in the coronal plane (long-axis of joint) or sagittal plane (short-axis of joint). In a young healthy patient, a fibrocartilaginous disk is usually seen as a slightly hyperechoic wedge-shaped structure attached to the superior joint capsule ( Fig. 81.3 ). The hyperechoic ends of the acromion and the distal clavicle may not appear at the same level in 16% of patients because of the variable obliquity of the joint.
Injection Technique for the Acromioclavicular Joint
The main indication for ACJ injection is osteoarthritis of this joint. The patient’s position can be either sitting or supine. The arm should be in the neutral position, as the deep joint space is the widest in this position. A linear probe with high frequency is used because the structures are superficial. The probe is placed over the medial side of the acromion in line with the clavicle. The ACJ can thus be visualized with the capsule covering the two hyperechoic structures, acromion and clavicle ( Fig. 81.4 ). In young patients, the fibrocartilage can be seen interposing the ACJ.
Both out-of-plane and in-plane techniques have been described, but out-of-plane is preferred as the joint space is very superficial. The needle should be directed almost parallel to the probe. The depth of the joint is small and overzealous insertion of the needle can result in puncturing the deep capsule and entering the subacromial space. The volume of injectate is usually 2 mL, and a successful injection is indicated by elevation of the capsule and widening of the joint space under real-time scanning. With the use of ultrasound, the accuracy was high (95%–100%) in cadaver studies.
Long Head of the Biceps Tendon and Rotator Cuff Interval
The LHB tendon arises from the supraglenoid tubercle and the superior labrum. The proximal part of this tendon is intraarticular but extrasynovial. The tendon travels obliquely over the anterosuperior aspect of the humeral head and exits the joint within the bicipital groove formed by the greater and lesser tuberosities on the lateral and medial sides, respectively ( Figs. 81.5 and 81.6 ). In the bicipital groove, an extension of the synovial lining of the GHJ invests the LHB tendon down to approximately 3–4 cm beyond the distal end of the groove ( Fig. 81.7 ). Thus fluid distension within the sheath usually reflects an underlying GHJ disease. In the bicipital groove, the LHB tendon is accompanied by the ascending branch of the anterior circumflex artery and is covered by the transverse humeral ligament, a weak ligament formed by the superficial fibers of the subscapularis (SSC) tendon.
The rotator cuff interval is a triangular space that occupies the area between the tendons of SSC and supraspinatus (SS) and the base of the coracoid process. It is roofed by the rotator cuff interval capsule, which is principally made up of the CHL ( Fig. 81.8 ) and contains the tendon of the LHB and the superior glenohumeral ligament (SGHL). The combination of the CHL and SGHL has a complex relationship to the LHB tendon, which act together to prevent the tendon from subluxing in the anterior direction. The rotator cuff interval is a space where the GHJ synovial lining extends around the biceps tendon and the arthroscope enters the GHJ to avoid damaging the cuff tendons. Thus this is an entry site in which the interventionalist can access the GHJ.
Sonoanatomy of the Long Head of the Biceps Tendon and Rotator Cuff Interval
To examine the LHB tendon, the patient is placed in the sitting position with the arm placed in a neutral or slight internal rotation position, the elbow bent, and the palm facing up. A high-frequency linear probe is placed approximately at the level of coracoid process ( Fig. 81.9A ). A short-axis view of the humerus reveals the greater and lesser tuberosities and the bicipital groove, where the LHB tendon is found. The greater tuberosity has a rounder look, whereas the lesser tuberosity assumes a pointed shape (see Fig. 81.9B ). Because of the anisotropic nature of the biceps tendon in this short-axis view, the tilting of the probe is important (see Fig. 81.9B ). Doppler imaging of the area reveals the ascending branch of the anterior circumflex artery, which is usually on the lateral side of the tendon. In the bicipital groove, the tendon is invested by its synovial sheath and the effusion at this level should be noted.
Moving the ultrasound probe more proximally along the orientation of the LHB tendon reveals the rotator cuff interval (see Fig. 81.9C ). The LHB tendon appears as a hyperechoic elliptical structure at this level and is sandwiched between the SS tendon laterally and SSC tendon medially. The coracohumeral ligament (CHL) forms the roof of the interval.
Injection Technique for the Long Head of the Bicep Tendon
The main indication for injection around the LHB tendon is biceps tendinopathy, which involves a spectrum of pathology ranging from inflammatory tendinitis to degenerative tendinosis. Ultrasound is a useful tool that can reliably diagnose complete rupture, subluxation, or dislocation of the LHB tendon. To perform the injection, the patient is placed in a sitting position. A high-frequency linear probe is placed over the bicipital groove (approximately midway between the clavicle and anterior axillary fold) to reveal the short-axis view of the LHB tendon. A color Doppler scan is used to locate the anterior circumflex artery. An out-of-plane approach is used with a 25-gauge needle inserted from the medial side through the transverse humeral ligament ( Fig. 81.10 ). Methylprednisolone 10–20 mg diluted in local anesthetic with a total volume of 4 mL is used as an injectate. A well-directed injection will show the local anesthetic surrounding the LHB tendons at the bicipital groove (see Fig. 81.10 ).