There are several solid advantages of ultrasound. It is relatively cheap, does not emit any radiation, is accessible, is capable of visualizing tissue function in real time and allows to the performing of provocative maneuvers in order to replicate the patient’s pain.
Those apparent benefits have helped ultrasound become a common initial choice for assessing tendons and soft tissues. Limitations include, for example, the high degree of operator dependence and the inability to define pathologies in bones. One also has to have an extensive anatomical knowledge of the examined region and keep an open mind to normal variations and artifacts created during the scan.
Although musculoskeletal ultrasound training, like medical training in general, is a lifelong process, Kissin et al. suggest that rheumatologists who taught themselves how to manipulate ultrasound can use it just as well as international musculo-skeletal ultrasound experts to diagnose common rheumatic conditions.
After the introduction of high-frequency transducers in the mid-eighties, ultrasound has become a conventional tool for taking accurate and precise images of the shoulder to support diagnosis.
Adequate for the examination are high-resolution, high-frequency transducers with a transmission frequency of 5, 7.5 and 10 MHz. To improve the focus on structures close to the skin an additional „water start-up length“ is advisable. During the examination the patient is asked to be seated, the affected arm is then adducted and the elbow is bent to 90 degrees. Slow and cautious passive lateral and/or medial rotations have the effect of being able to visualize different sections of the shoulder. In order to also demonstrate those parts which are hidden under the acromion in the neutral position, a maximum medial rotation with hyperextension behind the back is required.
To avoid the different tendon echogenicities caused by different instrument settings, Middleton compared the tendon’s echogenicity with that of the deltoid muscle, which is still lege artis.
Usually the echogenicity compared to the deltoid muscle is homogeneous intensified without dorsal echo extinction. Variability with reduced or intensified echo has also been found in healthy tendons. Bilateral comparison is very helpful when distinguishing and setting boundaries between physiological variants and a possible pathological finding. Degenerative changes at the rotator cuff often are found on both sides of the body.
Consequently unilateral differences rather point to a pathological source and bilateral changes rather to a physiological variation.
In addition, a dynamic examination can help to differentiate between an ultrasound artifact and a real pathology.
To accurately evaluate the echogenicity of an ultrasound, one has to take into account the physical laws of reflection, absorption and dispersion. It is at all times important to acknowledge that the structures in the joint of the shoulder are not aligned in the transversal, coronal or sagittal plane, and that therefore during imaging of the shoulder the transducer head has to be hold perpendicularly or parallel to the structures of interest. Otherwise the appearing echogenicity may not be evaluated.
Orientation-aid for the longitudinal plane: As an aid to orientation, it is advisable to begin the examination with the delineation of the acromion, as it is easy to palpate and it has an identifiable echo extinction. To adjust the longitudinal plane image the way it is known in the x-rays and the physical examination, the acromion has to be visible at the image border.
Orientation-aid for the transversal plane: Again it is advantageous to start above the acromion and then move the transducer to the humerus. The acromion echo extinction disappears and the wheel-like figure with almost concentric projection of the deltoid muscle, supraspinatus muscle tendon and humeral head-outline turns up as soon as the transducer is directed perpendicularly and parallel to the acromion edge. Using the anterior transversal plane one can depict the intraarticular part of the long head of the biceps brachii muscle. Additionally one can use the posterior transversal plane to depict the intersection of the infraspinatus muscle tendon and the posterior edge of the fossa.
Extracted from Wiki: http://en.wikipedia.org/wiki/Shoulder under the Creative Commons Attribution-ShareAlike License