Advancements and Applications of Musculoskeletal Ultrasound: A Comprehensive Overview - Dr Rajesh Botchu
Ultrasound(US) utilizes harmless non-ionising sound waves to produce detailed images of internal body structures. Similar technology is used in sonar to navigate submarines.
Musculoskeletal applications of US include diagnosing muscle tears, inflammation of muscle tendons, and joints, checking the vascularity of organs or tissue by the Doppler principle, and guiding diagnostic and therapeutic interventional procedures.
Musculoskeletal sonography, a rapidly advancing imaging technique, gained popularity for evaluating joint and soft-tissue diseases due to its easy accessibility, quick scan time, low cost, multi-planar imaging, dynamic real-time imaging, and contralateral comparison capability. Technology advances with higher frequency transducers, power Dopplers, and extended field-of-view function.
Limitations include operator dependency and, a steep learning curve. The primary benefits are US is a cost-effective alternative for musculoskeletal imaging, effective for assessing joint and soft-tissue diseases.
Optimal musculoskeletal sonography necessitates high-frequency linear array transducers (≥7-12 MHz) and meticulous patient positioning, enabling detailed visualising structures of interest.
A common indication for musculoskeletal sonography includes the evaluation of tendon abnormalities. Tendons in the body (wrist, shoulder, ankle, etc.) show uniform appearance, key sonographic features are fibrillar pattern (parallel hyperechoic lines) in the longitudinal plane, hyperechoic, round-to-ovoid shape in the transverse plane.
Ligaments are similar to tendons but have a more compact fibrillar pattern connecting bone to bone. Superficial ligaments are easily visualised, whereas deeper ones are difficult to visualise. Skeletal Muscle on US appear as low-to-mid echogenicity with echogenic fascial planes. US can detect partial/complete tears and retraction of muscle fibres.
Peripheral Nerves typically appear as echogenic fascicular structures with echogenicity less than tendons/ligaments, appearance is variable depending on the orientation of the nerve.
Only the superficial surface of bone can be evaluated, it appears as an echogenic surface with posterior shadowing, thus occult fractures can be detected as step-off defects.
Cartilage appears as a thin hypoechoic rim paralleling the echogenic articular cortex (hyaline cartilage). Calcifications are seen as echogenic structures with posterior acoustic shadowing (PAS), when calcifications are seen within tendons it represents calcific tendonitis.
Real-time compression of soft tissue using a linear probe reveals underlying structure composition and can detect abnormalities which otherwise may be hidden. Contralateral comparison distinguishes significant findings from normal variants and can reveal unsuspected abnormalities which are crucial for treatment plans.
Colour/Power Doppler assesses inflammation and solid masses. Power Doppler detects vascularity in cellulitis, abscesses, synovitis, myositis, bursitis etc.
Advancements
Recent 3D imaging advances and tissue harmonics advances enhance diagnostic effectiveness. Recent research on fibrocartilage assessment by US provided promising results, with improving technologies US may play a significant role in assessing labral, and meniscal tears in future.
Anisotropy artefacts are common and occur when the ultrasound beam is non-perpendicular to tendon fibrils, causing an artificial hypoechoic/anechoic appearance therefore proper transducer positioning, and adjusting probe angulation minimizes artefacts.
US has increased significance in interventional radiology, particularly for musculoskeletal procedures, due to its real-time imaging capabilities. Key benefits include Precise needle guidance by monitoring needle position, precise lesion localization, and Follow-up imaging by monitoring post-procedure outcomes.
Protocols include Evaluation of lesions in multiple (at least two) planes, determining depth, choosing the shortest needle path, avoiding neurovascular bundle, taking aseptic precautions and administering lidocaine or ethyl chloride spray.
A few common Interventional procedures include Aspiration of cysts, fluid collections, abscesses, Arthrocentesis (joint fluid aspiration), Biopsy, Steroid injections, Calcified tendinitis treatment (needle puncture, corticosteroid injection), Foreign body retrieval, intratendinous injections, nerve hydrodissection etc.
Needle Visualization by US can be observed as a bright echoic line (longitudinal orientation), as a bright echoic dot (non-parallel/transverse angle). Reverberation artefacts are seen behind the needle when the US beam is at a 90-degree angle.
The needle is easily visible within fluid collections, it may be challenging to observe in solid masses. Ultrasound guidance enhances accuracy and safety in interventional radiology.
Examples of use of ultrasound in musculoskeletal pathologies:
