Musculoskeletal ultrasonography basics
ABSTRACT
Utrasonography is emerging as a core method to evaluate musculoskeletal problems. It is best used for imaging superficial structures limited to 1 quadrant of a joint. It has several advantages over other imaging methods: lower cost, ability to perform dynamic examinations, higher spatial resolution of superficial structures, better patient comfort, and essentially no contraindications.
KEY POINTS
- Ultrasonography can be used to evaluate small fluid collections in soft tissue; joint effusions and synovitis; soft tissue masses (≤ 5 cm in diameter); tendon, ligament and muscle injuries; and peripheral nerve entrapment and lesions.
- Ultrasonography is not appropriate for survey examinations of vague or diffuse symptoms or for evaluating soft-tissue areas more than a few centimeters in diameter or more than a few centimeters deep.
- Musculoskeletal ultrasonography requires specially trained sonographers and interpreting physicians.
Tendons
Musculoskeletal ultrasonography can be effective for evaluating tendons around joints, especially 1 or a small number of nearby superficial tendons. Tendons particularly well suited for ultrasonographic examination include:
- Upper-extremity tendons located in the rotator cuff or around the elbow, and flexor and extensor tendons of the hands; ultrasonographic evaluation of the rotator cuff is highly accurate, equivalent to that of MRI for partial-thickness and full-thickness tearing40–43
- Lower-extremity tendons of the extensor mechanism of the knee, distal hamstring tendons, tendons around the ankle,44–46 and flexor and extensor tendons of the foot.
Ultrasonography can help diagnose a variety of tendon abnormalities (Table 1),48,49 including tearing, for which a dynamic examination can be performed.
Many tendons have a tendon sheath containing tenosynovium, while others have surrounding peritenon only; either can become thickened and inflamed. Tenosynovitis is a nonspecific finding and may be inflammatory, infectious, or posttraumatic. The presence of tendon sheath fluid alone on ultrasonography can be a normal finding, and some tendon sheaths that communicate with adjacent joints (eg, the long head biceps tendon, the flexor hallucis longus tendon) commonly contain simple fluid.6 A dynamic examination with ultrasonography can help diagnose snapping related to abnormal tendon movement, for example, in the case of intra-sheath and extra-sheath subluxation of the peroneal tendons.45,50,51
Ligaments
Ultrasonography can detect abnormalities in many superficial ligaments (Table 1).
Ankle. Ankle ligaments are superficial and can be clearly visualized. The diagnostic accuracy of ultrasonography for tearing of the anterior talofibular ligament may be as high as 100%.50,52,53
Elbow and thumb. The larger of the collateral ligaments of the elbow, especially the ulnar collateral ligament, and the ulnar collateral ligament of the thumb can be effectively evaluated with ultrasonography.54,55
Knee. The collateral ligaments of the knee can be seen with ultrasonography, but injuries of the external ligaments of the knee are often associated with intrinsic derangements that cannot be evaluated with ultrasonography.56,57 Intra-articular ligaments such as the anterior cruciate ligament are also not amenable to ultrasonography.
Dynamic examination of a ligament with ultrasonography can help determine the grade of the injury.
Deeply located ligaments (eg, around the hip) and ligaments surrounded by bone, such as the Lisfranc ligament, cannot be completely seen on ultrasonography.
Muscle
Musculoskeletal ultrasonography is useful for small areas of concern within a muscle (Table 1). It can detect muscle strains and tears, intramuscular collections or lesions, and fascial scarring or fascial injuries such as superficial muscle herniation. Although ultrasonography may yield a definitive diagnosis for a muscle problem, further imaging may be needed.
Nerves
Ultrasonography is useful for peripheral nerve investigation but requires a steep learning curve for sonographers and interpreting physicians.58,59 It is best suited for directed questions regarding focal abnormal nerve findings on physical examination.
Ultrasonography can help identify areas of nerve entrapment caused by a mass or dynamic compression. It can detect neuritis (Table 1), lesions of peripheral nerves (eg, nerve-sheath tumors), and neuromas (eg, Morton neuroma of the intermetatarsal space). In a large meta-analysis, ultrasonography and MRI were found to be equally accurate for detecting Morton neuroma.60 Even for nerve-sheath tumors located deep to the muscular fascia, ultrasonography can confirm the diagnosis because of the characteristic appearance of the nerves. Ultrasonography can also demonstrate a large extent of the course of superficial peripheral nerves while keeping the imaging plane appropriately oriented to the nerves.
Acknowledgment: We would like to sincerely thank Megan Griffiths, MA, for her help in the preparation and submission of this manuscript.
