Patellar Tendon

Description

The cortical reflection of the patella is to the left and is the proximal hyperechoic arc with shadowing deep to it. The hyperechoic, fibrous echotexture of the patellar tendon demonstrates a sharp “beak-like” origin from the patella, and the tendon thickens to display a uniform band of fibers. Deep to the tendon are mixed/marbled echoes of Hoffa’s Fat Pad.

The patella tendon is seen in cross section as well-defined, wide/broad, bristle-like structure superficial to Hoffa’s Fat Pad. The tibia is deep to the fat pad, but is a variable landmark based on probe location along the 5 cm length of the patella tendon.

Drawing of lateral view of knee showing that the patellar tendon has a sharp and smooth margin and a normal infrapatellar fat pad.

Name

• Patellar Tendon
• Patellar Ligament

General

• Originates on the inferior pole of the patella and inserts on the tibial tuberosity
• Contributes to the knee extensor mechanism and extension of the knee

Gross Anatomy

• Runs inferiorly from the patella bone to the tibial tuberosity
• The patella is the largest sesamoid bone in the body
• Origin: patellar apex
• Insertion: tibial tuberosity, a bony protrusion on the anterior proximal tibia
• Length is approximately 5 cm, increases from full extension to 30 degrees of knee flexion
• Patellar retinacula
  • Medial and lateral parts of quadriceps femoris descend on either side of the patella
  • Insert on the anterior surface of the tibia
  • Merge into a continuous capsule, forming medial/lateral patella retinacula
• Posterior aspect
  • Separated from the knee joint by the infrapatellar fat pad and synovial membrane
  • Deep infrapatellar bursa separates the patellar tendon from the tibia

Function

• Increase the length of the lever arm of the patellar tendon
• This allows the quadriceps to exert a higher moment around the axis of rotation of the knee
• Makes knee extension more efficient, transmitting forces clearly from the quadriceps to the tibia

Vascular Supply

• The patellar tendon is supplied by the following arteries and their anastomoses
  • Descending genicular artery, branch of the deep femoral artery
  • Inferior medial genicular artery, ranch of the popliteal artery
  • Superior and inferior lateral genicular arteries, branches of the popliteal artery
  • Anterior tibial recurrent artery, a branch of the anterior tibial artery

Patellar Ligament

• The tendon has been called both a tendon and a ligament
• Technically, because the patella is a sesamoid bone, tendon is the correct nomenclature
• Embryologically the quadriceps tendon attaches to the tibia
• Mesenchymal condensation develops and becomes the patella
• However, because the patellar tendon connects the patella to the tibia, it is often called a ligament
• The names can be used interchangeably, although tendon is the correct vernacular

Variant Anatomy

• Approximately 20% variation between patellar tendon and height can result in pathology
• Patella alta: tendon longer than patella
• Patella baja: tendon shorter than patella

Ultrasound Features

• Easily identified sonographically between its proximal and distal attachments
• Appears as an ovoid structure just deep to subcutaneous tissue
• Characteristic echotexture is striated alternating hyper/hypoechoic bands/fascicles of connective tissue
• Dimensions are relatively constant, expanding slightly as it inserts on the tibial tuberosity

MRI Features

• Shows low homogenous signal on all sequences

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Clinical Significance

• Patellar Tendonitis
• Extensor Mechanism Injury
• Patellar Tendon Rupture
• Infrapatellar Bursitis

Pediatric

• Patellar Apophysitis (Sinding-Larsen-Johnansson Disease)
• Patellar Pole Avulsion Fracture
• Tibial Tubercle Avulsion Fracture
• Tibial Tuberosity Apophysitis (Osgood Schalatters Disease)

Procedural

• Patellar Tendon Needle Tenotomy

Physical Exam

• Patellar Tendon Reflex

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See Also

• Knee Pain Main
• Physical Exam Knee
• Knee Anatomy Main

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