The technique below demonstrates how to identify normal anatomy. Remember to assess all musculoskeletal anatomy dynamically and thoroughly.
Divide the knee into 4 compartments.
Transverse scan plane for the quadriceps
Transverse suprapatella region:
•RF: Rectus Femoris •VI: Vastus intermedius
•VL: Vastus Lateralis •VM: Vastus Medialis
Suprapatella scan plane.
Longitudinal suprapatella region showing the suprapatella bursa and quadriceps tendon.
Prepatella scan plane
To avoid loss of contact, use plenty of thick gel or a standoff.
Infrapatella scan plane.
The infrapatella tendon.
Also called the patella ligament.
The insertion of the infrapatella tendon onto the tibial tuberosity. Note: The normal physiological amount of fluid along the underside of the tendon.
Transverse Infrapatella tendon. Note how wide it is, to then have an understanding of the area you need to examine in longitudinal.
Medial collateral ligament (MCL) – Joint space/meniscus – Pes Anserinus.
Medial knee joint scan plane.
The medial collateral ligament (green) directly overlying the medial meniscus (purple).
Pes anserinus scan plane.
The Pes Anserine bursa and tendon insertion are medial to the Infrapatella tendon on the tibia, adjacent to the MCL insertion.
Remember the Pes Anserine tendons as (sargent) SGT:
Sartorius, Gracilis and semi-tendinosis.
Lateral knee joint scan plane.
Assess the Lateral collateral ligament, Ilio-Tibial band insertion and peripheral margins of the lateral meniscus. Unlike the medial side, the LCL is separated from the meniscus by a thin tissue plane.
Rotate the probe off the LCL, with the toe of the probe angled slightly posteriorly.
Popliteal fossa scan plane
Medial aspect of the popliteal fossa showing the semimembranosus/gastrocnemius plane.
Ultrasound of the Popliteal vein and artery in transverse.
Without and with compression to exclude DVT.
Confirm both arterial and venous flow and exclude a popliteal artery aneurysm. If a Popliteal aneurysm is discovered, always extend the examination to the other leg and the abdomen. There is a risk of bilateral and high association with aortic aneurysm.
Role of Ultrasound
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 bony 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.
- None required.
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.
- Joint effusion
- Bakers cyst
- Collateral ligament injury
- Patella tendinopathy
- Meniscal bulging/cysts
- Quadriceps injury
- Pes anserine bursitis/tendinopathy
- Patella retinaculum pathology
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.
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) Suprapatella bursa (bursitis-simple/complex, synovial thickening, loose bodies) Patella (gross changes eg erosion, bipartite, fracture) Patella tendon (tears, tendonitis, insertion enthesopathy) Infrapatella bursa (tendonosis, tears, bursitis, fat pad changes) Infero-Medial – Pes anserine bursa
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)
Basic Hardcopy Imaging
A knee series should include the following minimum images;
- Quadriceps tendon – long, trans +/- MT junction
- Suprapatella bursa
- Pre patella – long
- Patella tendon – long, trans, insertion onto tibial tuberosity
- Medial meniscus and MCL
- Lateral Meniscus and LCL
- Popliteal artery and vein to demonstrate patency
- Medial popliteal fossa
- Document the normal anatomy and any pathology found, including measurements and vascularity if indicated.