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Apex of patella

The apex of the patella is the pointed inferior tip of the patella, opposite its broad base. It serves as the attachment point for the patellar ligament (tendon) and transmits the force of the quadriceps femoris muscle to the tibia via the tibial tuberosity. Structurally, it is composed of cancellous bone with a thin cortical covering, surrounded by articular and periarticular structures of the knee joint.

It is clinically important as a common site of injury in patellar tendinopathy, Osgood–Schlatter disease (traction at the tibial insertion), and fracture assessment.

Synonyms

  • Inferior pole of the patella

  • Apex patellae

  • Patellar tip

Muscular Attachments

  • The apex does not directly attach to muscles but serves as the proximal attachment site of the patellar ligament, which continues from the quadriceps tendon.

  • Indirectly transmits the pull of the quadriceps femoris muscle group (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius) through the patellar ligament to the tibial tuberosity.

Relations

  • Anteriorly: Subcutaneous tissue and skin of the knee

  • Posteriorly: Fat pad (infrapatellar/Hoffa’s fat pad) and synovial lining of knee joint

  • Superiorly: Body of the patella and quadriceps tendon

  • Inferiorly: Patellar ligament extending to tibial tuberosity

  • Laterally/Medially: Retinacular fibers of quadriceps expansion

Function

  • Serves as a leverage point for transmission of quadriceps force to the tibia

  • Stabilizes the anterior aspect of the knee joint

  • Contributes to patellofemoral joint mechanics and knee extension

  • Acts as a bony landmark in clinical and imaging assessment of knee injuries

Clinical Significance

  • Site of patellar tendinopathy (jumper’s knee)

  • Vulnerable to avulsion fractures of the inferior pole

  • May show marrow edema in trauma, stress injuries, or inflammation

  • Key landmark in orthopedic surgery and knee arthroscopy

MRI Appearance (Marrow Signal)

T1-weighted images:

  • Marrow signal is intermediate to bright

  • Cortical bone is uniformly dark

T2-weighted images:

  • Marrow signal is intermediate to bright

  • Cortical bone remains dark

Proton Density (PD):

  • Marrow signal is intermediate to bright

  • Useful for detecting subtle marrow abnormalities

STIR (Short Tau Inversion Recovery):

  • Normal marrow signal is low

  • Pathological changes (edema, contusion, stress reaction) appear bright

Proton Density Fat-Saturated (PD FS):

  • Normal marrow signal is low after fat suppression

  • Abnormal marrow (edema, inflammation, tumor) becomes bright

T1 Fat-Sat Post-Contrast:

  • Normal marrow shows mild homogeneous enhancement

  • Pathological marrow lesions show focal, diffuse, or rim enhancement depending on etiology

CT Appearance

Non-Contrast CT:

  • Apex appears as dense cortical bone with underlying cancellous bone

  • Fractures, avulsions, or cortical irregularities are well seen

  • Fat within marrow cavity shows low attenuation

Post-Contrast CT:

  • Bone itself does not enhance

  • Adjacent soft tissue (patellar ligament, fat pad, synovium) may enhance in inflammation or injury

  • Pathologic lesions (tumors, infection) show surrounding enhancement

MRI image

Apex of patella sagittal cross sectional anatomy 3T MRI AI enhanced radiology anatomy image-img-00000-00000

MRI image

apex of patella coronal cross sectional anatomy 3T MRI AI enhanced radiology anatomy image-img-00000-00000

CT image

Apex of patella ct sag image

CT VRT image

Apex of patella