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Patella

The patella is the largest sesamoid bone in the human body, embedded within the quadriceps femoris tendon. It lies anterior to the knee joint, improving the leverage of the quadriceps during knee extension and protecting the femoral condyles. Its triangular shape with an apex inferiorly and base superiorly makes it a key component of the extensor mechanism of the knee.

The posterior surface of the patella is covered with thick articular cartilage, which articulates with the femoral trochlea. This joint surface is crucial for smooth patellofemoral motion.

Synonyms

  • Kneecap

  • Rotula

  • Patellar bone

Muscular Attachments

  • Quadriceps femoris tendon: Attaches to the superior base of the patella (rectus femoris, vastus medialis, vastus lateralis, vastus intermedius)

  • Patellar ligament: Extends from the apex of the patella to the tibial tuberosity

  • Medial and lateral patellar retinacula: Reinforce medial and lateral borders of patella, connecting to vastus medialis and vastus lateralis

Relations

  • Anteriorly: Skin, subcutaneous tissue, prepatellar bursa

  • Posteriorly: Femoral condyles, patellofemoral joint, thick articular cartilage

  • Superiorly: Quadriceps femoris tendon

  • Inferiorly: Patellar ligament leading to tibial tuberosity

  • Laterally: Lateral retinaculum, vastus lateralis

  • Medially: Medial retinaculum, vastus medialis

Nerve Supply

  • No direct nerve supply; periosteum and surrounding soft tissues innervated by femoral nerve branches and saphenous nerve

Arterial Supply

  • Genicular branches of the popliteal artery (superior, inferior, and descending genicular arteries)

  • Contribution from anterior tibial recurrent artery

Venous Drainage

  • Drains via genicular veins into the popliteal vein

Function

  • Increases leverage of the quadriceps tendon, improving efficiency of knee extension

  • Protects anterior surface of the femur and knee joint

  • Guides quadriceps tendon alignment during movement

  • Acts as a sesamoid bone reducing tendon wear

MRI Appearance

T1-weighted images:

  • Patellar bone marrow shows intermediate to bright signal intensity

  • Cortical bone appears dark

T2-weighted images:

  • Bone marrow shows intermediate to bright signal intensity

  • Cortical bone remains dark

  • Articular cartilage appears bright

STIR (Short Tau Inversion Recovery):

  • Normal marrow shows low signal

  • Pathological changes (edema, contusion, fracture) appear bright hyperintense

Proton Density Fat-Saturated (PD FS):

  • Normal marrow signal is low

  • Marrow edema, osteochondral injury, or contusion show bright hyperintensity

T1 Fat-Sat Post-Contrast:

  • Normal marrow shows mild uniform enhancement

  • Pathology (osteomyelitis, tumor, synovitis) shows focal or heterogeneous enhancement

CT Appearance

Non-Contrast CT:

  • Patella appears as a dense bony structure with well-defined cortex and cancellous trabeculae

  • Detects fractures, bipartite patella, sclerosis, or lytic lesions

  • Shows relationship with femoral trochlea

Post-Contrast CT:

  • Bone itself does not enhance

  • Surrounding soft tissue inflammation, synovitis, or tumor infiltration show enhancement

  • Useful for assessing adjacent joint pathology and soft tissue extension

CT VRT 3D image

Patella 3d image

MRI image

Patella coronal cross sectional anatomy 3T MRI AI enhanced radiology anatomy image-img-00000-00000

MRI image

Patella sagittal cross sectional anatomy 3T MRI AI enhanced radiology anatomy image-img-00000-00000

MRI image

Patella bone anatomy image 3t MRI

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Patella bone anatomy image coronal 3t MRI

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Patella bone anatomy image

CT image

Patella ct axial

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Patella ct coronal