Ultrasound is essentially used for the external structures of the knee. Ultrasound is a valuable diagnostic tool in assessing the following indications; Muscular, tendinous and ligamentous damage (chronic and acute) Bursitis Joint effusion Popliteal vascular pathology Haematomas Masses such as Baker’s cysts, lipomas Classification of a mass eg solid, cystic, mixed Post surgical complications eg abscess, oedema Guidance of injection, aspiration or biopsy Relationship of normal anatomy and pathology to each other Some boney pathology.
It is recognised that ultrasound offers little or no diagnostic information for internal structures such as the cruciate ligaments. Ultrasound is complementary with other modalities, including plain X-ray, CT, MRI and arthroscopy.
Med meniscus tear.
Use of a high resolution probe (7-15MHZ) is essential when assessing the superficial structures of the knee. Careful scanning technique to avoid anisotropy (and possible misdiagnosis) Beam steering or compounding can help to overcome anisotropy in linear structures such as tendons. Good colour / power / Doppler capabilities when assessing vessels or vascularity of a structure. Be prepared to change frequency output of probe (or probes) to adequately assess both superficial and deeper structures.
SCANNING TECHNIQUE
POSTERIOR FOSSA
Patient prone on bed, knee flexed slightly with a pad under the ankle for support. Survey the entire fossa to identify the normal anatomy, including; Popliteal artery and vein (patency. aneurysm, thrombosis) Posterior joint (joint effusion) Medial popliteal fossa [ bursa between semi-membranosus tendon and medial gastrocnemius muscle] (Baker’s cyst) Document the normal anatomy and any pathology found, including measurements and vascularity if indicated.
Baker’s cyst. Medial gastrocnemius.
ANTERIOR KNEE
Patient lies supine on bed with knee flexed 20 – 30 degrees. Alternatively patient may sit on the side of a raised bed with foot resting on Sonographer’s knee for support. Identify the normal anatomy, including: Quadriceps tendon (tears, M/T junction, tendonitis) Suprapatellar bursa (bursitis-simple/complex, synovial thickening, loose bodies) Patella (gross changes eg erosion, bipartite, fracture) Patella tendon (tears, tendonitis, insertion enthesopathy) Infrapatellar bursa , (tendinosus ,tears, bursitis, fat pad changes) Infero-Medial – Pes anserine bursa
BAKER’S CYST.
LATERAL AND MEDIAL KNEE
May be scanned as above. Assess the medial and Lateral Collateral ligaments and meniscal margins. Joint lines (ligament tears or thickening, meniscal bulging/cysts, joint effusion, gross bony changes).
LCL Tear.
Lateral Meniscus tear , anterior horn.
Mcl thickening and hyperemia.
BASIC IMAGING
A knee series should include the following minimum images;
- Quadriceps tendon – long, trans +/- MT junction
- Suprapatellar bursa
Transverse scan plane for the quadriceps
TRV Suprapatellar , RF =rectus femoris, VI vastus intermedius, VL= Vastus lateralis, VM=Vastus medialis
Suprapatellar scan plane sag.
Prepatellar scan plane
- Prepatellar – long
- Patella tendon – long, trans, insertion onto tibial tuberosity
- Medial meniscus and MCL
bursa fluid at the tibial insert. sag.
Pes anserinus scan plane. Remember the Pes Anserine tendons as (sargent) SGT: Sartorius, Gracilis and semiTendinosus.The Pes Anserine bursa and tendon insertion are medial to the Infrapatellar tendon on the tibia, adjacent to the MCL insertion.
- Lateral Meniscus and LCL
- Popliteal artery and vein to demonstrate patency
- Medial popliteal fossa
Medial aspect of the popliteal fossa showing the semimembranosus/gastrocnemius plane.
- Document the normal anatomy and any pathology found, including measurements and vascularity if indicated.
SPT Bursa. 
lipoma or other masses.
infrapatellar proximal insert hyperemia/ infilmation .
Meniscus tear with laparoscopy.
Take good care of your knees.
Have a good day And thank you for reading.
Steve Ramsey, PhD. Public Health. MSc- Medical Ultrasound.
Calgary, Alberta- Canada.