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Shoulder: Anatomy and Techniques
Overview
The important bony landmarks in the evaluation of the supraspinatus tendon are the humeral head, the coracoid, the clavicle and acromium, joined at the acromioclavicular joint. The glenohumeral joint is an inherently unstable joint and depends on the surrounding soft tissues for stabilization. Soft tissue stabilizers are divided into intrinsic and extrinsic. The most important extrinsic soft tissues are the supraspinatus tendon superiorly, infraspinatus posteriorly and subscapularis anteriorly ( Fig. 1.1 ). The important intrinsic soft tissue stabilizers are the glenohumeral joint and capsule.
The supraspinatus and infraspinatus are difficult to separate close to their insertions and share what is almost a conjoined tendon. Some of the fibres crisscross each other, making the two tendons difficult to separate. Anteriorly the subscapularis tendon is separated from the supraspinatus tendon by a gap, the rotator interval, which allows passage of the long head of biceps out of the joint and into its groove in the upper arm. The long head of biceps originates from the superior glenoid margin. The coracohumeral ligament helps keep the long head of biceps in position within the upper groove, by forming a sling mechanism in conjunction with the superior glenohumeral ligament. These ligaments pass from the coracoid and glenoid respectively, and insert into the humeral head on either side of the biceps tendon, securing it in place. Another important ligament, the coracoacromial ligament (CAL). Links the coracoid to the acromium and forms the coracoacromial arch along with the bony acromium.
Shoulder pain is a common complaint in the general population and impingement is a common underlying cause. Impingement is a clinical diagnosis, whereby pain occurs during arm abduction, as the supraspinatus tendon and subacromial subdeltoid bursa are compressed between the humeral head and the coracoacromial arch. This clinical scenario is also called painful arc syndrome, as pain is maximal in an arc of abduction between 30° and 60°. Interestingly, patients frequently complain of pain on the lateral deltoid rather than in the region of the acromion.
A complete ultrasound examination involves evaluating the four major tendons of the rotator cuff (biceps, subscapularis, supraspinatus and infraspinatus), the subacromial subdeltoid bursa and the acromioclavicular joint.
Patient Position
The easiest position in which to examine the shoulder is with the patient seated. A stool with either no back or a low back and arms is ideal. This will allow for full access and permit the shoulder to be moved into a range of positions. It is a matter of personal preference whether the examiner carries out the examination standing or sitting, behind or in front of the patient. There are minor advantages and disadvantages to each of these, but none is particularly important and the choice is a matter of personal preference. Some variations in position are required for patients in wheelchairs and for patients who must remain recumbent whether because of illness, surgery or fear of fainting. Many wheelchairs allow the sidearm to be removed, facilitating arm movement. If the patient is also able to sit a little forward in the chair then generally all of the important positions can be achieved without too much difficulty.
It is important to take a history directly from the patient before the examination begins as this can often provide useful diagnostic information. The examination itself begins with a brief inspection of the shoulder, useful to detect muscle wasting. As with most ultrasound examinations the probe should be held lightly with sufficient, but not excessive, contact with the skin. Holding the probe between the thumb and adjacent fingers while resting the little finger on the patient's skin is an ideal way of obtaining excellent contact with minimal pressure.
The cuff is examined from biceps anteriorly to teres minor posteriorly and from the acromioclavicular joint superiorly to deltoid insertion inferiorly. The examination is concentrated on the four major tendons, but it is important to have a routine to ensure that none of the other important structures is overlooked. My preference is to begin with the biceps tendon and rotator interval anteriorly, then move sequentially through subscapularis, supraspinatus and infraspinatus and teres in that order ( Fig. 1.2 ). The examination concludes with an assessment of the posterior glenohumeral joint, infraglenoid notch, supraspinatus muscle and the acromioclavicular joint, before sweeping down to the deltoid insertion.
The cuff tendons, particularly supraspinatus, should be examined both statically and dynamically. The static examination is divided into six standard positions with specific imaging goals in each position. The dynamic examination has many components, but primarily seeks to evaluate the behaviour of the subacromial subdeltoid bursa as it abuts the coracoacromial arch on arm abduction.
Standard Position 1: Biceps Tendon
Imaging Goals
- 1.
Confirm that biceps tendon lies within groove.
- 2.
Identify abnormal fluid in the sheath and bursa.
- 3.
Identify normal internal tendon structure.
Technique
The patient sits and places their hand on their knee palm upwards. This induces a little external rotation sufficient to bring the bicipital groove to an anterior position ( Fig. 1.3 ). The groove is easily located by placing the probe in an axial plane on the anterior aspect of the humeral head. The probe is then moved superiorly and inferiorly, tracing the biceps tendon from the upper part of the groove to below its upper musculotendinous junction. The normal tendon has a bright speckled appearance in the axial plane, made up of the poorly reflective tendon fibre bundles and the hyperechoic connective tissue matrix. Care must be taken to ensure that the probe is always held at 90° to the tendon to remove the effects of anisotropy. Anisotropy is an artefact whereby areas of reduced reflectivity simulating tendinopathy occur as a result of incident echoes arriving at angles other than perpendicular and being reflected away from the tendon, rather than bouncing back to the probe to help form an image.
At its upper part, the biceps tendon sheath surrounds the tendon. As is well known, this is an extension of the glenohumeral joint and a small quantity of fluid is often identified within it. Also in its upper part, the anterior portion of the subacromial subdeltoid bursa can be seen deep to the deltoid muscle and anterior to the biceps sheath. The anterior limb of the circumflex humeral artery is frequently visible around the tendon. Distally, the relationship of the musculotendinous junction with the traversing pectoralis tendon should be noted. A number of tendon variations may be identified. There are often a number of slips that pass from the upper humerus to the tendon. Occasionally a duplex tendon is encountered.
The probe is then rotated 90° so that the tendon can be examined in its long axis ( Fig. 1.4 ). Maintaining the tendon in view during this manoeuvre takes a little practice; however, if the probe falls off the tendon it is very easy to move a little medial or lateral to find it again, noting where the reflective humeral shaft drops away as the probe crosses the groove. In most individuals, the tendon travels deeper as it passes distally. This introduces an element of anisotropy, which can be easily corrected by some gentle pressure at the distal end of the probe. This manoeuvre is called ‘heel toeing’ and is used in several locations in musculoskeletal ultrasound. The long-axis image of the tendon is very useful for confirming integrity; however, as with most tendons, the internal structure is best evaluated in the axial plane.
When assessment of the long head of biceps is complete, the probe is moved medially to locate the short head of biceps. The bony margin of the coracoid process provides a very useful landmark. The short head arises from its inferior margin superficial to the insertion of the pectoralis minor and coracobrachialis tendons. The tendon of pectoralis major can be identified as a long, thin slip passing over the biceps tendon around the level of the proximal musculotendinous junction. The more detailed anatomy of the arm will be covered in a later section. The probe is then returned to the upper biceps to review the rotator interval.
Standard Position 2: Rotator Interval
Imaging Goals
- 1.
Identify ligamentous sling around biceps.
- 2.
Confirm ligaments are intact.
- 3.
Evaluate Doppler signal.
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