The use of ultrasound as an imaging modality in medicine was pioneered by the Glasgow obstetrician Ian Donald, but although it has been applied to the musculoskeletal system since the 1970s, more recent developments in real-time sonography and the use of high frequency, high resolution transducers have enabled high quality images of soft tissues to be achieved. Touch with cursor
There is already enough information in the literature to safely assert that high frequency ultrasound provides accurate diagnosis of most common musculoskeletal diseases. In addition no other modality can match the capacity of ultrasound to provide relatively comfortable, technically simple, dynamic evaluation of the soft tissue structures.
In the UK, ultrasound imaging of the musculoskeletal system has been widely used in veterinary practice for the diagnosis of soft-tissue injuries in race horses and has only recently begun to be used by radiologists as an imaging tool.
There are of course limitations in the use of musculoskeletal ultrasound. In particular bone cannot be readily imaged because of the sound wave scattering which occurs at the soft tissue/bone interface. The quality and interpretation of the images are also greatly dependent on the expertise and experience of the operator. A good working knowledge of joint and soft tissue anatomy, as well as an understanding of the clinical context of the problem to be investigated, is necessary if a sensible ultrasound report is to be obtained.
Musculoskeletal ultrasound provides a cost effective, noninvasive, method of obtaining diagnostic information from dynamic studies, tendon evaluations and bilateral comparisons. Examinations are quick, easy, with less patient discomfort than more invasive procedures and less expensive than other imaging modalities. Interest in this growing application is resulting in new areas of investigation.
Clinical Applications for Musculoskeletal Ultrasound
- Foot and Ankle
- Comparison with MRI
- Carpal Tunnel Syndrome
- Hip and groin
- Triangular fibrocartilage (TFC)
Ultrasound of the Shoulder
- fluid collections
- shoulder trauma
- soft tissue
- soft tissue
- glass and metal fragments
- splinters, thorns
- tears and ruptures
- fluid collections
- soft tissue masses
- muscle pain
- joint pain
- rotator cuff tears
- subdeltoid bursitis
- biceps tendonitis
- gleno-humeral effusion
Patients present with chronic shoulder pain. The affected side may be tender to touch and have some immobility.
The following anatomy is carefully studied:
- the biceps tendon
- the subscapularis tendon
The arm is examined in both neutral and externally rotated positions.
- The supraspinatus/infraspinatus tendon
Evaluation of the attachments to the humerus.
Any tendonitis or fluid collection, ruling out subluxation or dislocation, any changes in contour or echogenicity of the tendon is noted.
Documentation is taken in both transverse and longitudinal planes.
The ability of ultrasound to detect rotator cuff tears is well established, but also assessed is other ultrasound features of shoulder impingement or capsulitis.
Middleton W. Ultrasonography of the shoulder. Rad Clin No Amer Vol 30 No 5: 927-940, 1992.
Mack L, Matsen III F, et al: US evaluation of the rotator cuff. Radiology Vol 157 No 1: 205-209, 1985.
Tendons represent a portion of a muscle and consist of collagen fibres that transmit muscle tension to a mobile part of the body. The fibers are bound together in a three dimensional network of endothelium septa named the peritendinae. They originate from a fine connective sheath called epitenon which surrounds the whole tendon. In large tendons, blood and lymphatic vessels together with nerves run within these septa, while small tendons are almost avascular.
Tendon sheaths completely or partially cover a portion of the tendon where it passes through fascial slings or osseo-fibrous tunnels. They promote gliding and contribute to the nutrition of the tendon tissue. A tendon sheath consists of an outer layer and an inner layer which is intimately attached to the tendon. Both layers may be connected by a mesotenon. Long tendons such as the patellar or the Achilles are not covered by a synovial tendon sheath but lie within highly vascularised loose areolar and adipose tissue, the paretenon.
Structural abnormalities within a tendon are generally not visible radiographically unless calcifications occur.
Sonographically, tendons appear as fibrillar structures with hypoechoic collagen fibres and hyperechoic endotendineal septa intermingled between them. The number of fibrils visible with sonography closely correlates with the frequency of the ultrasound probe used.
Tendon imaging is mainly performed with ultrasonography and has been improved in recent years because of technical advancements and a better understanding of tendon pathology. Tendon rupture seems to be in many cases to be the final stage of tendinitis. Therefore, imaging may be used to predict the risk of tendon rupture.
The excellent near-field clarity of Diasus facilitates evaluation of even very superficial tendons such as those in the hand.
Changes that can be seen in overuse injuries depend on the localization and the clinical stage of damage. Radiographic examination is rarely of value in establishing the diagnosis of tendinitis. It should be used as an auxiliary modality to detect bony spurs or other types of abnormal calcification, or to quantify causative factors such as anatomic malalignment.
On sonograms the distinctive signs of tendinitis are hypoechoic foci with or without tendon thickening. In the Achilles tendon Fornage described them as nodular tendinitis. With high resolution imaging, the lesions appear oval with blurred borders and seem to be orientated parallel to the course of the tendon fibers. In later stages, generalized thickening with widening of the distance between fascicles is present. Abnormalities of the tendon sheath are in most cases clearly visible in the form of hypoechoic thickening of the sheath due to fluid accumulation.
Carpal Tunnel Syndrome
The carpal tunnel is the fibro-osseous space between the carpal bones and the flexor retinaculum. It contains the eight flexor digitorum tendons, the flexor pollicus longus, the median nerve and occasionally a persistent median artery.
The etiology of carpal tunnel syndrome is primarily the encroachment on the median nerve. This can be due to either a decrease in size of the tunnel (mainly osseous causes), or increase in the volume within the confined space of the tunnel. The most recently described common cause is repetitive strain injury (RSI), as in computer keyboard operators. It is the fastest growing occupational disease in the US and the world.
Anatomic landmarks and imaging technique
In the transverse imaging plane, the ulnar artery is the medial landmark of the carpal tunnel. The tunnel contains the flexor digitorum tendons which are hyperechoic. Anterior to the tendon is the median nerve. The median nerve has a characteristic appearance which differentiates it from the fibrillar hyperechoic tendons. The nerve is hypoechoic with a hyperechoic border and shows multiple bright reflectors in the transverse imaging plane. The median nerve is rounded or oval in the proximal wrist and flattens progressively as it courses through the carpal tunnel. Within the tunnel the nerve is in intimate contact with the flexor retinaculum; its size remains constant but its shape is quite variable.
In the longitudinal imaging plane the nerve is demonstrated coursing parallel and superficial to the flexor digitorum tendons. The sonographic appearance of the nerve in this plane demonstrates hyperechoic continuous anterior and posterior borders (the nerve sheath) and is easily distinguished from the characteristic fibrillar appearing tendons that lie posteriorly.
Sonographic findings in carpal tunnel syndrome
- flattening of the nerve, especially at the level of the hamate bone
- enlargement of the median nerve as it enters the carpal tunnel
- large fluid or fat layer surrounding the tendons
- decreased mobility of the median nerve on flexion and extension of the fingers, hand and wrist
Ultrasound provides a painless and convenient method of following the progress of disease in these patients.
Additional advantages include lower cost and fast examination time.
Artifact due to fiber anisotropy should not be mistaken for nodular tendinitis. They can be ruled out with proper investigation techniques including dynamic real time imaging in more than one direction. Tendon sheaths contain a small amount of fluid which is normally seen as a hypoechoic rim on ultrasound images gained with high frequency probes.
Signs of fresh tendon rupture as visible with sonography or MRI are principally similar.
When using ultrasound, characteristic findings like thinning or disruption of fibers may be masked by an overlying hypoechoic hematoma or artifacts. To avoid false-negative diagnoses, it is mandatory to perform a dynamic investigation under dorsal and plantar flexion of the foot. Partial tears present as focal regions of increased signal, thickening of the tendon and in some cases altered continuity of a portion of tendon fibers.
With sonography, partial tears principally are visible in the form of circumscribed hypoechoic lesions. They have been demonstrated by van Holsbeeck within the rotator cuff. In the Achilles tendon, differentiation between partial ruptures and tendinitis may not be possible with sonography.
The role of high-resolution imaging seems to be of increasing importance to analyze adaptive and degenerative mechanisms. Sonography and MRI should be used jointly in the case of diagnosing tendon diseases.
Hip and Groin
Ultrasound could revolutionize the management of chronic groin pain which is a common problem in sports that is often difficult to diagnose and potentially career ending for the athlete.
Ultrasound is an intriguing alternative to contrast herniography for the diagnosis of impalpable inguinal and femoral hernias, providing comparable results, while avoiding the need for injection and allowing other structures to be assessed at the same time.
Ultrasound is extremely good at characterizing tendinitis and diagnosing various lumps and bumps, such as synovial or meniscal cysts, assessment of meniscal tears, cruciate lesions and osteochondral lesions.
Foot and Ankle
Ultrasound is most often used to assess tendinitis. However, two recent developments that have relevance to sports concern Morton's neuroma and posterior ankle impingement.
The wrist presents an ideal anatomic region of evaluation by high frequency ultrasound. Highly detailed anatomy can be demonstrated while patients remain comfortable with out being subject to radiation and prolonged immobilization as with MRI.
Ultrasound is readily available and inexpensive; its greatest strength however lies in its dynamic capability to elucidate both normal and pathological anatomy.
Wrist ultrasound is technically simple. Transverse and longitudinal planes are examined. A high frequency linear array transducer is used allowing adequate penetration through the shallow wrist anatomy while providing excellent resolution.
Triangular fibrocartilage (TFC)
- carpal tunnel syndrome
- ganglion and synovial cysts
- tears of the triangular fibrocartilage
The TFC lies between the ulnar styloid, triquetrum and lunate and distal radius deep to the pronator quadratus muscle. The TFC maintains the stability of the distal radioulnar and ulnocarpal joints. Disruption and degeneration of the TFC are common causes of ulnar and wrist pain.
Conditions diagnosed in the hand
- tendon rupture
- ganglion cysts - well defined
- synovial cysts - lobulated, arising from joints or tendons
Buchberger W, Schon G, Strasser K, et al: High Resolution ultrasonography of the carpal tunnel. J Ultrasound Med 10:531-537, 1991.
Buchberger W, Judmaier W, Birbamer G, et al: Carpal tunnel syndrome: diagnosis with high resolution sonography. Aamer J Roentgen 159:793-798, 1992.
Fornage BD, Schernberg FL, Rifkin MD: Ultrasound examination of the hand. Radiology 155:785-789, 1985.
Hoglund M, Tordai P, Engkvist O: Ultrasonography fro the diagnosis of soft tissue conditions in the hand. Scand J Plast Reconstr Surg Hand Surg 25:225-231, 1991.
Journal of Ultrasound in Medicine.
Vol 15. Number 3. March 1996. Pages 213 (fingers) and 221 (shoulder)
Vol 15. Number 4. April 1996. Page 277 (ankle)
Comparison with MRI
Ultrasound and MRI have greatly expanded our capacity for accurate diagnosis in the musculoskeletal system. Although MRI has for some years been the main focus of attention, ultrasound is also a powerful tool that is growing in importance as radiologists and other physicians become more familiar with its potential. Several applications of ultrasound rival or exceed the present capabilities of MRI.
Musculoskeletal ultrasound is still an emerging subspecialty, made possible by recent advances in technology. State-of-the-art ultrasound systems can resolve exquisite superficial soft tissue detail. Equipment that can effectively suppress image noise while operating at a wide dynamic range and ultra high transmit frequencies is also important as it allows the demonstration of subtle variations in tissue texture and the differentiation of anechoic fluid from markedly hypoechoic tissue.
Ultrasound is cheaper, faster and better tolerated than MRI.
Even more importantly ultrasound is interactive. Unlike MRI, the ultrasound examiner is in the room with the patient probing the affected part with the transducer and directly correlating the site of reported pain or tenderness with its scan appearances.
Although ultrasound is a particularly operator dependent modality, its accuracy and reproducibility in both shoulder and hip scanning are supported by a large volume of published work. Poor results generally indicate poor technique rather than a poor test, and it is the limited availability of good training that limits ultrasound growth Remarkable technological developments are ongoing and many frontiers remain to be explored.
In imaging of the hand and wrist, ultrasound is often more convincing than MRI because routine comparison views of the normal side provide compelling objectivity. Carpal ligament injuries can be readily appreciated by ultrasound but are typically missed on MRI because of obstruction by the signal of adjacent joint space fluid.
High resolution ultrasound is obviously more sensitive than radiography in demonstrating soft tissue changes in superficial joints and these are the ones most commonly involved in early rheumatoid arthritis (RA).
The imaging requirements for an ultrasound screening assessment of patients with rheumatologic diseases are the simultaneous availability of high quality equipment, appropriately trained personnel and a correctly appointed scanning site.
The system resolution required for the diagnosis of changes in small superficial joints such as those of the hands and feet is much greater than that needed for most sports medicine/soft tissue injury applications. A small transducer footprint is helpful and a very high frequency (L10-22MHz is available on Diasus) will improve resolution of joint surfaces within 5mm of the skin. The near field resolution is not solely related to transducer frequency. It is important that the whole system is optimized for rheumatologic ultrasound.
The person operating the machine is equally important to diagnostic accuracy. The examiner must fully understand the clinical features of rheumatologic diseases as well as the relevant normal sonographic anatomy and pathological appearances. The examiner should be specifically and highly trained for the role.
At early stage metacarpal head erosions as small as 1mm in diameter may be demonstrated Sonographically if appropriate equipment and technique are employed. These erosions should only be confidently diagnosed if they are demonstrable in two planes.
Ultrasound is more cost effective than MRI as a screening tool in the rheumatology clinic. With experience, ultrasound is also substantially faster, it is possible to examine hands, feet and knees in 30-35 minutes, the time it takes for one knee joint to be adequately examined with MRI.
MRI is probably more appropriate for defining pathology highlighted by ultrasound and for assessment of cases that are equivocal on ultrasound.
Swen WAA, Bruyn GA, Dijkmans AC. Why Rheumatologists should be interested in sonography. Rheumatol Eur 1995;2;98-9.