Rate Coding & Motor Unit Recruitment

Interactive Hip:

Patella

By Primal Pictures

EDITOR'S NOTE: The following is a small sample of the Interactive Hip CD in the ground breaking Primal Pictures 3-D Anatomy CD ROM series.

Patella

The patella, the largest sesamoid bone in the body, is embedded in the tendon of quadriceps femoris, and is located anterior to the tibio-femoral articulation. Its outline is somewhat in the shape of an inverted triangle with the apex of the bone directed inferiorly. Thus it possesses a base, lateral and medial borders and an apex. The base is a relatively expansive surface and receives the lower end of the quadriceps tendon. The patella is part of the knee joint extensor mechanism.

The patella has an anterior surface, which is gently convexed forwards. It often shows a number of small perforations (for nutrient vessels) and a few ridges, but is otherwise featureless.

The posterior surface of the patella carries a large, smooth, undulant and quadrangular articular area. This facet occupies the upper four-fifths or so of the posterior surface of the patella, and is covered by a continuous plate of articular hyaline cartilage. A vertical ridge on this articular surface divides the area into lateral and medial facets, the lateral facet usually being larger and significantly more concave. These two facets of the patellar articular surface are apposed to the corresponding femoral condyles, while the vertical ridge separating them faces the groove on the anterior aspect of the lower end of femur between the two femoral condyles. The medial patellar articular facet is further subdivided into two narrow vertical regions by means of a faint ridge, the medial of the two regions coming into contact with the medial femoral condyle in extreme flexion of the knee.

Attached to the apex of the patella and the adjoining part of the posterior patellar surface is the patellar ligament, the inferior continuation of the quadriceps tendon. Attached to the medial and lateral borders of the patella are, respectively, the medial and lateral patellar retinacula. Superficial to these retinacula, the medial and lateral patellar borders receive the attachments of the lowest fibers of vastus medialis and vastus lateralis respectively.

Ossification

The patella is cartilaginous at birth. Multiple ossification centers appear around the age of three years in girls, and at around the fourth or fifth year in boys. These centers fuse with each other; ossification usually being complete by the time of puberty.

Patellar Ligament

The patellar ligament (ligamentum patellae) may be regarded as the distal continuation of the quadriceps tendon. It extends from the apex of the patella (the inferior pole of the patella) to the upper half of the anterior surface of the tibial tuberosity. The tibial attachment of the patellar ligament is indicated on the dry bone by a smooth facet on the upper half of the tibial tuberosity. The patellar ligament is a strong, flat band to whose medial and lateral edges are attached, respectively to the medial and lateral patellar retinacula. Respectively superficial and deep to the patellar ligament are the superficial and deep infrapatellar bursae. The patellar ligament is approximately 6 to 8cms long.

Patellar Plexus

The patellar plexus is a plexus of cutaneous (sensory) nerves located in the superficial fascia in front of, and around the patella. The patellar plexus receives contributions from the following nerves:

1. Medial cutaneous nerve of thigh (branch of femoral nerve).

2. Intermediate cutaneous nerve of thigh (branch of femoral nerve).

3. Lateral cutaneous nerve of thigh (branch of lumbar plexus).

Infrapatellar branch of saphenous nerve.

Patella - Surface Anatomy

The patella is part of the knee joint extensor mechanism and is readily palpable. It is the largest sesamoid bone in the body and is embedded in the tendon of quadriceps femoris, anterior to the tibio-femoral articulation. Its outline is somewhat in the shape of an inverted triangle with the apex of the bone directed inferiorly. Thus it possesses a base, lateral and medial borders and an apex. The base is a relatively expansive surface and receives the lower end of the quadriceps tendon .

Ossification

The patella is cartilaginous at birth. Multiple ossification centers appear around the age of three years in girls, and at around the fourth or fifth year in boys. These centers fuse with each other, ossification usually being complete by the time of puberty.

Patella: Apex

The apex of the patella is the narrow and somewhat pointed lower pole of the patella. Attached to the apex of the patella and to the adjacent posterior surface of the patella just below the articular facet is the patellar ligament. The patellar apex is at the level of the tibial plateau.

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