Application of ultrasound to assess large joints seems still challenging because of the inherent inability of ultrasound to pass through bony structures and scan deeper portions of the joint.[41,42] Thus, US visualization of the articular cartilage is limited by the width of the acoustic windows that depends on the anatomy of the joint. Even with advances in the resolution of the transducers, deeper structures are difficult to visualize as the higher-frequency transducers have lower tissue penetration.
In patients with arthritis, however, assessment of the cartilage of the weight-bearing areas can be difficult in patients with advanced OA and/or painful knee resulting from limited maximal active flexion. In addition, the cartilages of the patella and the tibia are always inaccessible to US. Although US can be used to detect bone erosions, it is not applicable for estimation of bone erosion depth, because it visualizes only the bone surface and not the subchondral bone.
Moreover, US has been regarded as a highly operator-dependent imaging method with poor reproducibility, partly due to the intrinsic real-time nature of US image acquisition. However, its usage is reassured by recent studies that have established moderate to good interobserver reliability.[43–45]
Acquisition of US skills takes time depending on the trainee's hand-eye coordination skills. A long learning curve may be an important limiting factor in widespread use of US. In addition, examination of multiple scanning planes in the clinical setting can be time consuming. Focused examination is proposed with concentration on a small number of scanning planes to reduce examination time.
J Clin Rheumatol. 2016;22(6):324-329. © 2016 Lippincott Williams & Wilkins