Overview
This lecture covers the MRI anatomy of the knee in the coronal, sagittal, and axial planes, focusing on identifying clinically important structures systematically.
MRI Knee Planes and Orientation
- Coronal, sagittal, and axial planes provide different views to assess knee anatomy.
- Orientation clues: fibula is lateral, convex tibial plateau is medial, patella facets distinguish sides on axial images.
Bones of the Knee
- Femur: medial and lateral condyles articulate with the tibia.
- Tibia: medial and lateral tibial plateaus with corresponding tibial spines.
- Fibula: lies laterally, with identifiable styloid process, head, and neck.
- Patella: anterior bone, may be bipartite or multipartite (normal variant).
Ligaments and Tendons
- Medial Collateral Ligament (MCL): thick band on medial side.
- Lateral Collateral Ligament Complex: includes IT band, biceps femoris tendon, fibular collateral ligament, and popliteus tendon.
- Anterior Cruciate Ligament (ACL): runs from anterior tibia to lateral femoral condyle, has anteromedial and posterolateral bands.
- Posterior Cruciate Ligament (PCL): attaches posterior tibia to medial femoral condyle, thicker than ACL.
- Quadriceps tendon and patellar tendon form the extensor mechanism.
Menisci
- Medial and lateral menisci: C-shaped cartilage with anterior and posterior roots, horns, and body.
- Tears involve disruption of the articular surface.
- Medial meniscus is broader; lateral meniscus is tight and C-shaped.
Articular Cartilage and Subchondral Bone
- Cartilage lines femoral condyles and tibial plateaus; should be smooth and uniform.
- Subchondral bone plate is a black line beneath cartilage, not to be confused with cortex.
Fat Pads
- Infrapatellar (Hoffa’s) fat pad: beneath the patella.
- Suprapatellar fat pads: anterior and posterior, separated by joint effusion.
- Fluid between medial head of gastrocnemius and semimembranosus forms a Baker's cyst.
Key Muscles
- Quadriceps attach to the patella; patellar tendon continues to tibial tuberosity.
- Biceps femoris attaches laterally; semimembranosus, semitendinosus, gracilis, and sartorius attach medially at pes anserinus.
Key Terms & Definitions
- MCL (Medial Collateral Ligament) — medial knee ligament for stability.
- LCL (Lateral Collateral Ligament) — lateral stabilizing ligament; part of a complex.
- ACL (Anterior Cruciate Ligament) — prevents anterior displacement of tibia.
- PCL (Posterior Cruciate Ligament) — prevents posterior displacement of tibia.
- Meniscus — C-shaped cartilage for load distribution and joint stability.
- Articular Cartilage — smooth tissue covering bone ends for joint movement.
- Hoffa’s Fat Pad — infrapatellar fatty tissue.
- Baker’s Cyst — fluid collection between gastrocnemius and semimembranosus.
- Pes Anserinus — insertion area for sartorius, gracilis, and semitendinosus.
Action Items / Next Steps
- Review linked MRI case and practice identifying knee structures.
- When reviewing scans, always assess if structures appear normal, not just their presence.