Knee - Posterior View
How to perform the examination
Patient Positioning
Primary position (recommended): the patient is positioned prone with the knee in full extension or slight flexion (5–10 degrees). A pillow can be placed under the ankle to maintain comfort and facilitate muscle relaxation. It is important to ensure that the patient is completely relaxed to optimize visualization of the deep structures of the popliteal fossa.
Alternative position: the patient can be positioned supine with the knee flexed at 90–120 degrees, allowing posterior access through the intercondylar approach. This position is useful for patients who cannot tolerate the prone position and facilitates the dynamic assessment of posterior structures.
Anatomy to Identify
- Popliteal vessels (popliteal artery and vein, vascular alterations)
- Sciatic nerve and its branches (compressions, morphological alterations)
- Cruciate ligaments (partial visualization, structural changes)
- Posterior horns of the menisci (lesions, extrusions)
- Baker’s cyst (size, joint communication, complications)
- Posterior synovial bursae (inflammation, effusions)
Probe
High-frequency linear transducer (5–12 MHz) with deep penetration capability to reach the intra-articular posterior structures. Compound imaging techniques are essential to improve resolution in deep structures. Doppler is fundamental for vascular assessment of the popliteal fossa and for identifying lesion vascularization. Frequency modulation allows optimization of imaging from superficial to deep structures.
Anatomical Zones
Popliteal fossa
The popliteal fossa is a rhomboid-shaped anatomical space bounded superiorly by the biceps femoris, semitendinosus, and semimembranosus muscles, and inferiorly by the medial and lateral heads of the gastrocnemius. In hemophilic arthropathy, this space may contain hematomas, synovial thickening, and cystic formations that can compromise neurovascular structures.
Characteristic: Rhomboid shape; contains popliteal vessels, sciatic nerve, and adipose tissue
Findings:
- Popliteal effusions: Anechoic or hypoechoic fluid collections extending within the popliteal fossa.
- Synovial thickening: Hyperplastic synovial proliferation with possible increased vascular component.
- Organized hematomas: Blood collections in the organization phase with internal echoes and possible calcifications.
- Neurovascular compressions: Displacement or compression of the popliteal vessels and sciatic nerve by expansive masses.
Probe Positioning
Place the probe transversely over the popliteal fossa, starting proximally at the musculotendinous junction of the posterior thigh muscles. The probe marker should be oriented laterally. Proceed distally with sequential scans to visualize all compartments of the popliteal fossa.
Baker’s cyst
Baker’s cysts (or popliteal cysts) are dilatations of the gastrocnemius–semimembranosus bursa that communicate with the knee joint cavity. In hemophilic arthropathy, these cystic formations are particularly frequent and may reach considerable sizes, representing a significant complication of chronic joint disease.
Characteristic: Location: between the medial head of the gastrocnemius and the semimembranosus; communicates with the joint cavity
Findings:
- Multilocular cysts: Complex cystic formations with multiple internal septations.
- Heterogeneous content: Presence of internal echoes due to blood products at different stages of evolution.
- Thickened walls: Cyst wall thickening with possible active inflammatory component.
- Compressive complications: Compression of the popliteal neurovascular structures with associated clinical symptoms.
- Cyst rupture: Extravasation of cystic content into the posterior compartments of the leg, producing a pseudothrombophlebitic presentation.
Probe Positioning
Perform transverse and longitudinal scans in the medial portion of the popliteal fossa, between the tendons of the semimembranosus and the medial gastrocnemius, where Baker’s cysts most frequently develop.
Clinical Cases by Severity grade
The clinical cases are organized according to four levels of severity of hemophilic arthropathy. Click on each level to explore the available cases for that specific joint–projection combination.