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Ultrasound allows for a detailed visualization of a wide range of joint cartilage abnormalities in several rheumatic diseases.
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The present chapter reviews the available evidence for using ultrasound in the assessment of joint cartilage in patients with osteoarthritis, calcium pyrophosphate dihydrate disease, gout, and rheumatoid arthritis.
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Proper scanning of the hyaline cartilage requires the ultrasound beam direction to be maintained perpendicular to the cartilage surface.
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The main ultrasound-related limitation is the acoustic barriers, which restrict its use to only some anatomic areas.
Ultrasound hardware and software are rapidly evolving, and these technologic developments are expanding the range of clinical applications in rheumatology. Although ultrasound has been used for assessing synovitis and bone erosions in patients with rheumatoid arthritis, a wide range of joint cartilage lesions can be detected in patients with other rheumatic diseases.
This chapter reviews the available evidence for joint cartilage ultrasound in healthy subjects and in patients with osteoarthritis, calcium pyrophosphate dihydrate (CPPD) disease, gout, or rheumatoid arthritis. Table 10-1 presents the main acoustic windows for ultrasound visualization of joint cartilage.
| Anatomic Site | Ultrasound Views | Assessable Cartilage |
|---|---|---|
| Shoulder | Posterior longitudinal and transverse scans with shoulder in intrarotation | Wide posterior portion of the hyaline cartilage of the humeral head and glenoid fibrocartilage |
| Elbow | Anterior longitudinal and transverse scans with elbow in neutral position | Anterior portion of the hyaline cartilage of the humeral distal epiphysis and of the radial head |
| Wrist | Ulnar longitudinal and transverse scans with wrist in neutral position | External portion of the triangular fibrocartilage complex |
| Metacarpophalangeal joint | Dorsal longitudinal and transverse scans with the joint in maximal flexion | Dorsal portion of the hyaline cartilage of the metacarpal head |
| Volar longitudinal and transverse scans with the joint in neutral position | Volar portion of the hyaline cartilage of the metacarpal head | |
| Radial longitudinal and transverse scans with the metacarpophalangeal joint of the second finger in neutral position | Radial portion of the hyaline cartilage of the metacarpal head of the second finger | |
| Proximal interphalangeal joint | Dorsal longitudinal and transverse scans with the joint in maximal flexion | Dorsal portion of the hyaline cartilage of the proximal phalanx head |
| Hip | Anterior longitudinal scan with hip in neutral position | Limited external portion of the hyaline cartilage of femoral head and acetabular fibrocartilage |
| Knee | Anterior suprapatellar transverse and longitudinal scans with the knee in maximal flexion | Anterior portion of the hyaline cartilage of the femoral condyles |
| Anterior infrapatellar transverse and longitudinal scans with the knee in neutral position | Anterior portion of the hyaline cartilage of the femoral condyles | |
| Anterior medial parapatellar transverse and longitudinal scans with the knee in maximal flexion | Anterior portion of the hyaline cartilage of the medial femoral condyle | |
| Posterior transverse and longitudinal scans with the knee in neutral position | Posterior portion of the hyaline cartilage of the femoral condyles | |
| Lateral and medial longitudinal scans with the knee in neutral position | External portion of the lateral and medial meniscal fibrocartilage | |
| Ankle | Anterior transverse and longitudinal scans with the ankle in maximal plantar flexion | Anterior portion of the hyaline cartilage of the talus |
| Metatarsophalangeal joint | Dorsal longitudinal and transverse scans with the joint in maximal flexion | Dorsal portion of the hyaline cartilage of the metatarsal head |
Normal Cartilage
Normal hyaline cartilage appears as a homogeneously anechoic band delimited by two well-defined, sharp, hyperechoic margins. These features are basically the same at the anatomic sites that can be explored by ultrasound ( Fig. 10-1 ). Correct scanning depends on the operator’s ability to correctly place the probe to obtain a direction of the ultrasound beam perpendicular to the margins to avoid missing the superficial margin and improper visualization of the deeper one.
Homogeneity is the hallmark of normal cartilage echotexture. Its reflectivity depends on the setting of the gain; it is anechoic at low levels of gain and shows various degrees of echogenicity according to the increment of the gain value ( Fig. 10-2 ). While scanning the cartilage, settings of the ultrasound equipment must be changed to check the persistence of the cartilage layer homogeneity at different levels of gain value.
Visualization of the superficial margin is fundamental for the accurate measurement of the cartilage thickness. The hyaline cartilage thickness ranges from 0.1 mm at the head of the proximal phalanx to 2.8 mm at the lateral femoral condyle of the knee ( Fig. 10-3 ). The thickness of the hyaline cartilage at the metacarpal head ranges from 0.2 to 0.5 mm.
Normal fibrocartilage appears as a structure with a punctate, homogeneous echogenicity. Because of the acoustic barrier, only the outer portion of the menisci can be visualized by ultrasound. The presence of a lesion cannot be excluded by ultrasound.
Abnormal Cartilage
Osteoarthritis
Several ultrasound abnormalities can be detected in patients with osteoarthritis involving the cartilage layer and margins. Both margins can show some degree of irregularity or discontinuity, or both. The margins’ integrity must be carefully assessed with the ultrasound beam’s direction maintained perpendicular to the area of interest, and all pathologic findings must be depicted on at least two perpendicular scans. Echotexture inhomogeneity due to a patchy increment of echogenicity can be regarded as an early sign of a cartilage lesion and may correspond to fibrillation or cleft formation. Particular attention must be paid to the machine settings to differentiate this pathologic finding from an artifact generated by relatively high levels of gain.
Various degrees of cartilage layer thinning can be observed in patients with osteoarthritis. Cartilage narrowing may be focal or diffuse ( Figs. 10-4 to 10-6 ). In patients with advanced disease, accurate assessment of the cartilage thickness can be impaired by poor visualization of the superficial margin.
