patellar tendon

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The patellar tendon, also - less correctly - referred to as the patellar ligament, attaches the patella to the tibia and is part of the extensor mechanism of the knee.

Summary

origin: patellar apex
insertion: tibial tuberosity
action: aids in knee extension, as the distal part of the extensor mechanism of the knee

Gross anatomy

The patellar tendon is biconvex and, similarly to the calcaneal tendon, does not have a tendon sheath but only a paratenon composed of loose areolar tissue. It measures approximately 5 cm in length (i.e. height of the patella) and 20-30 mm in width, being wider proximally and narrower distally, and is 4-6 mm thick .

Origin

The patellar tendon begins at the patellar apex, but is actually considered the distal part of the quadriceps tendon - or, more accurately, a continuation of the rectus femoris tendon over the patella - while the patella itself is a sesamoid bone embedded in the quadriceps tendon .

Insertion

Tibial tuberosity (tubercle).

Relations

It is bounded posteriorly by the infrapatellar (Hoffa) fat pad.

Blood supply

The patellar tendon is supplied by the following arteries and their anastomoses :

descending genicular artery, a branch of the deep femoral artery
inferior medial genicular artery, a branch 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

Action

Assists in proper patellar alignment and knee extension.

Variant anatomy

Variation of >20% between the patellar tendon length and patellar height will result in either

patella alta: tendon longer than patella
patella baja: tendon shorter than patella

Radiographic features

Ultrasound

Identified between the caudal tip of the patella and the tibial tuberosity, the tendon appears as an ovoid structure just deep to the subcutis; characteristic echotexture of striated alternating hyperechoic and hypoechoic bands representing fasicles and connective tissue, respectively. The body of the tendon maintains a constant dimensions throughout the majority of its course, expanding to insert on the tibial tuberosity.

Deep to it, the infrapatellar (Hoffa) fat pad is homogeneously hyperechoic . Common pathologic abnormalities which should be specifically sought include the presence of heterogenous echotexture, discontinuities, thickening, neovascularization (presence of flow with power Doppler insonation), and stability with dynamic range of motion and/or longitudinal tension.

MRI

Shows low homogeneous signal on all sequences .