Overview
This lecture covers the MRI anatomy of the knee, explaining how to systematically identify key bones, ligaments, menisci, cartilage, fat pads, muscles, and the extensor mechanism in coronal, sagittal, and axial imaging planes.
MRI Planes and Orientation
- MRI anatomy of the knee is viewed in coronal, sagittal, and axial planes.
- Medial and lateral sides are identified using anatomical landmarks (e.g., fibula is lateral, medial collateral ligament is medial).
Bones & Landmarks
- Main bones: femur, tibia, fibula, and patella.
- Femoral condyles (medial and lateral) articulate with tibial plateaus.
- Tibial spines and fibular head can be visualized in coronal images.
Ligaments
- Medial collateral ligament (MCL) is a thick band on the medial side.
- Lateral collateral ligament complex consists of: fibular collateral ligament, iliotibial (IT) band, biceps femoris tendon, and popliteus tendon.
- Cruciate ligaments:
- Anterior cruciate ligament (ACL) runs from anterior tibia to medial surface of lateral femoral condyle.
- Posterior cruciate ligament (PCL) runs from posterior tibia to femur, thicker and stronger than ACL.
- Both ACL and PCL are best seen in sagittal and axial planes.
Menisci
- Medial and lateral menisci are triangular, wedge-shaped cartilages between femur and tibia.
- Each meniscus has anterior and posterior roots, anterior horn, body, and posterior horn.
- Meniscal tears require disruption of the articular surface.
- Lateral meniscus is more C-shaped and tighter; medial is broader.
Articular Cartilage & Subchondral Bone
- Articular cartilage covers femoral condyles and tibial plateaus—should be smooth and intact.
- Subchondral bone plate appears as a black line under cartilage on MRI.
Muscles and Tendons
- Quadriceps tendon runs from quadriceps muscle to the patella.
- Patellar tendon extends from patella to tibial tuberosity.
- Biceps femoris, semimembranosus, sartorius, gracilis, and semitendinosus are major muscles around the knee.
- IT band attaches laterally to tibia.
Fat Pads
- Hoffa's (infrapatellar) fat pad lies below patella.
- Suprapatellar fat pad (anterior and posterior) located above patella.
- Joint effusion can separate fat pads, visible on MRI.
Clinical Tips & Variants
- Bipartite or multipartite patella is a normal variant, not a fracture.
- Baker’s cyst appears as fluid between semimembranosus tendon and medial gastrocnemius.
Key Terms & Definitions
- Meniscus — Crescent-shaped cartilage cushioning the knee joint.
- Cruciate Ligaments (ACL/PCL) — Stabilizing ligaments crossing within the knee.
- Collateral Ligaments (MCL/LCL) — Ligaments stabilizing the inner and outer knee.
- Articular Cartilage — Smooth tissue covering joint surfaces.
- Subchondral Bone Plate — Bone layer beneath cartilage.
- Hoffa’s Fat Pad — Infrapatellar fat pad beneath the patella.
Action Items / Next Steps
- Review and label knee structures on provided case MRI images.
- Always assess if anatomical structures look normal on scans.
- Prepare questions or topics for further anatomy tutorials.