Knee Ultrasound

Ultrasound is sound having a frequency above the audible range (> 20 kHz)
Frequencies range millions of cycles per second
Ultrasound is used in medicine for diagnostic purposes
Diagnostic ultrasound uses the principle that ultrasound is reflected by an interface between media of different acoustic impedances
The image is produced by the display of the echoes returning to the transducer. The image is composed of pixels varying in light intensity, which depends on the intensity of the reflected echo
The reflection depends on the density of the media and subsequently, various structures produce specific images depending on the acoustic mismatching of the reflected sound waves
In musculoskeletal imaging, a linear probe is used to assess structures

Knee Anatomy: Muscles around the Knee

Posterior

Anterior surface anatomy

Posterior surface anatomy

Probe held longitudinally over Hamstring muscle

Longitudinal ultrasound of normal hamstring muscle

Probe held transversely over Hamstring muscle

Transverse view of normal Hamstring muscle

FIGURE Hamstring muscle strain

L Hamstring muscle strain: Longitudinal ultrasound.
A – Acute L Hamstring muscle injury. Anechoic area (Asterix) surrounded by torn muscle tissue.
B – Longitudinal R Hamstring muscle normal.

Normal anatomy of proximal Quadriceps

Transverse view of Quadriceps tendon

Right quadriceps complete tear.

A – Longitudinal sonogram of R quadriceps demonstrating complete tear (thick arrows).
Retracted muscle (thin arrow).
B – Surgical exploration: complete tear of ® quadriceps. Free edges of tendon demonstrated by thin arrows.

Patient ultrasound positioning to assess infrapatellar tendon

With seated position, it is easier to assess dynamic real-time ultrasound imaging with knee extension

Longitudinal ultrasound – infrapatellar tendon at patellar insertion, normal.

Longitudinal ultrasound – infrapatellar tendon, at tibial insertion, normal.

Chronic infrapatellar tendon rupture

Avulsion bone retracted

Pre-operation: Previous scar from failed infrapatellar tendon repair

Intra-operative: Area marked from the pre-operative ultrasound that required excision
& then followed by infrapatellar tendon repair

Intra-operative: After bone avulsion segment excision, tendon repaired with augmentation of the infrapatellar tendon

FIGURE Patellar tendinopathy.

A – Longitudinal sonogram of the fast bowler with infrapatellar tendinopathy. Thickening of an infrapatellar tendon (white arrow), calcification (arrowhead) demonstrating overuse injury.
B – Transverse view of the same athlete, showing calcification ‘ossicle’.

FIGURE Osgood – Schlatter Disease:

A – Longitudinal sonogram through the distal patella tendon. Sonography shows small avulsions from the apophyseal cartilage (asterix). The avulsions calcify and may grow as separate ossification centres.
B – Normal contralateral distal patella tendon. No avulsion injury present at the insertion site (white arrow).

Bipartite patella:

A – Longitudinal sonogram of patella showing separate patella fragment (b) with joint (J). Inferior bipartite patella represents 5% of bipartite type.
B – AP & Lateral X-Ray of the same athlete.