Musculoskeletal ultrasound, used to visualize musculoskeletal abnormalities

Musculoskeletal UltrasoundCommon Errors in Ultrasound Examination of Arthritis

Musculoskeletal ultrasound is an emerging ultrasound technique that is increasingly being used to visualize musculoskeletal abnormalities. High-resolution ultrasound has been proven to be a very accurate and reliable technique in the diagnosis of various musculoskeletal diseases. Using musculoskeletal ultrasound to diagnose diseases of the musculoskeletal system can clearly show the superficial soft tissue structures such as muscles, tendons, ligaments, and peripheral nerves, and the lesions that occur, such as inflammation, tumors, injuries, and structural abnormalities caused by malformations.

Musculoskeletal ultrasound, used to visualize musculoskeletal abnormalities

Joint effusion and synovitis are hallmarks of chronic arthritis, and ultrasound and MRI are widely used for the detection, grading, and monitoring of this disease.

On musculoskeletal ultrasound, synovial effusion manifests as a mobile and compressible anechoic or hypoechoic abnormality within the joint, while synovial hypertrophy manifests as a non-mobile and incompressible hypoechoic abnormality within the joint, sometimes with detectable blood flow signals within it.

Intra-articular effusion and/or synovial hypertrophy may be missed during ultrasound examination. In some small joints, excessive pressure from the ultrasound probe can squeeze the fluid within the joint to the other side, making it impossible to detect the effusion. In addition, probe pressure can also compress the blood vessels within the synovium, causing the blood flow signal originally visible in the congested synovium to disappear. Therefore, during ultrasound examination, the ultrasound probe must "float" on the coupling agent to minimize pressure.

Whether it is a small joint or a large joint, the proper position of the joint is also a necessary condition for detecting joint effusion. If the position of the joint causes excessive tension in the joint capsule on the side where the probe is placed, it will cause the effusion fluid to flow to the other side, making it impossible to detect the effusion. Therefore, during the examination, the joint should be in a flexed position toward the side of the probe to reduce the tension on that side of the joint capsule.

Some normal anatomical structures may resemble pathological changes, which can also lead to examination errors.

During hip joint ultrasound examination, a normal hyperechoic layer about 7 mm thick formed by the iliofemoral ligament and joint capsule can be seen. If the probe is not perpendicular to it, the iliofemoral ligament may appear hypoechoic due to anisotropy, similar to joint effusion. In addition, if the hip joint is internally rotated during the examination, the anterior joint capsule will protrude forward, and the measured value will exceed 7 mm.

During musculoskeletal ultrasound examination, the appearance of normal fat structures can also be similar to synovial hypertrophy, such as the pre-femoral fat located anterior to the distal femoral cortex and between the suprapatellar recess above the knee. If the suprapatellar recess is expanded, it can cause the posterior wall of the recess anterior to the femur to be displaced, similar to synovial thickening (Figure 3). Understanding the location of the fat pad, the echo characteristics of the adipose tissue, and the lack of blood flow signals within the adipose tissue helps to correctly identify this structure.

The examiner should understand the distribution of normal blood vessels to avoid confusing normal and synovitis-produced blood flow signals. For example, oblique deep vessels in the anterior and middle grooves of the humerus above the dorsal ligament of the wrist and ascending branches of the anterior interosseous artery in the bicipital groove can be displayed during energy Doppler ultrasound examination.

In addition, joint effusion can also be found in healthy people through ultrasound and MRI, most commonly in the metatarsophalangeal joints, and increases with age, so diagnosis should be cautious.

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