The Anatomy of the Patella (2024)

The patella, most commonly referred to as the kneecap, is the bone at the front of the knee. It's the largest sesamoid bone in the body. A sesamoid bone is one that is embedded in a tendon.

In the patella’s case, it exists within the quadriceps tendon. This tendon helps hold the patella in place along with other muscles found in and near the quadriceps so it can do its most important job: protect the knee joint.

This article will discuss the anatomy and function of the patella. It also covers the three main types of patella injuries and how to treat them.

Anatomy

The patella bone goes through the process of ossifying (turning into bone) between the ages of 3 and 6 years old. Normally, the patella is formed from one ossification center—a place that forms bone in fetal development and early childhood.

In some people, a secondary ossification center forms, and this may not fuse with the primary ossification center.For these people, the patella forms as two separate bones. This is called a bipartite patella.

The apex, or point, of the patella, points downward toward the shin. The base of the bone sits upward toward the thigh. The base is also what attaches to the quadriceps tendon.

The back of the patella forms a joint with the femur, otherwise known as the thighbone. This makes the femur become a joint facet, as it also connects with a medial and lateral condyle of the femur. The patella is also attached by the vastus lateralis and medialis, which are muscles in the thigh.

From the apex of the patella comes the patellar ligament, which connects to the front of the tibia (shin bone). The middle of the patella consists of openings for arteries to supply blood to the kneecap.

Different structures in the knee work together to keep the patella stabilized. These include the muscles in the thigh, parts of the femur bone, and a tendon in the knee referred to as medial patellar retinaculum, which crosses the knee joint in the middle of the patella.

Location

The patella sits between the femur and the tibia. It not only protects the knee joint but connects muscles in the front of the femur to the tibia.

Under the patella and at the end of the femur is articular cartilage, which makes it possible for the patella and femur bones to move alongside each other. This cartilage offers protection on top of added mobility with any knee movements.

Anatomical Variations

Most of the anatomical variations of the patella have to deal with the shape of the bone itself. There are three types of anatomical variations in a healthy patella based on the size and symmetry of the patella itself. These include:

• Hypoplasia of the patella (often referred to as patella parva), where the patella is smaller than it should be or, in rare cases, completely absent.
• Hyperplastic properties, where the patella grows larger than it should be for the space it lives in (known as patella magna).
• Hunter’s cap patella, where the lateral side of the patella takes up the anterior surface of the bone.

Function

The main job of the patella is to help with knee extension and movement while offering protection for the knee joint.

Knee extension happens as the patella offers leverage that the quadriceps tendons it's attached to can put on the femur. In terms of protection, the patella gives the front of the knee joint support during activities like exercise or daily wear and tear from walking and stepping.

Associated Conditions

Patella injuries can be relatively common, particularly in those who are extremely active and put a lot of extra stress or pressure on the bone through running, exercising, and competitive sports. Two of the most common conditions related to the patella are patellar tendonitis and patella dislocations. Patella fractures can also occur.

Patellar Tendonitis

Patellar tendonitis is also commonly referred to as jumper’s knee, as it is more likely to occur in sports or activities that require a lot of jumping, such as basketball.

People with patellar tendonitis will experience pain in their patella that starts when doing selected activities and may increase to interfere with daily movements, such as walking and going up and down stairs. This pain is caused by tiny tears in the patellar tendon, which cause inflammation and weakening.

Patella Dislocations

In a patella dislocation, the patella slips outside its grooved position inside the leg. This causes pain and swelling, as well as possibly tearing the ligaments that hold the patella in place.

Some people may not have a complete patella dislocation, but they can experience a patellar subluxation. This occurs when the patella doesn't dislocate from its groove entirely but does have difficulty moving within its groove tracking which causes pain and swelling.

Patella Fracture

A blow to the knee, such as from a fall or accident, can cause a patella fracture—a break in the bone. Symptoms of a patella fracture include:

• Pain around the patella
• Bruising
• Swelling
• Misshapen knee
• Visible bone piercing through the skin of the knee—this is known as an open fracture

Additionally, you may be unable to do the following with a patella fracture:

• Stand
• Walk
• Bear weight on the knee
• Hold the leg out straight or straighten the knee
• Bend the knee

Rehabilitation

Patellar Tendonitis

There are a number of ways to treat and rehabilitate the patella affected by patellar tendonitis. Treatment depends on the severity of the pain and tendonitis. Options range from over-the-counter pain relievers like ibuprofen to physical therapy to help stretch and strengthen the muscles and tendons surrounding the patella.

For more serious cases, your doctor may opt for a corticosteroid injection to help relieve pain—or even surgery if repairs to the tendons surrounding the patella are necessary.

Patella Dislocations

The only way to remedy patella dislocations is to relocate the patella back into its groove. This may happen on its own shortly after dislocation or with the assistance of a healthcare provider.

With dislocation, the tendon may tear and fragments of bone may come loose. While tendon tears usually repair on their own, bone fragments will likely need to be removed surgically.

If there are no fragments resulting from dislocation, the usual treatment consists of immobilizing the knee until the swelling decreases (roughly for three to six weeks), along with taking non-steroidal anti-inflammatory medications (NSAIDs) to help with any pain or discomfort.

For those who are experiencing patellar subluxation, treatment ranges from physical therapy to braces and tape to help guide the patella. Surgery may also be required depending on how severe the misalignment is—or if it leads to frequent patellar dislocations.

Patella Fracture

It can take about three to six months to fully recover from a patella fracture—and even longer if your injury is severe.

In severe cases, surgery may be necessary. A surgeon will typically reattach the bone using screws, pins, and wires. In very severe cases, they may remove all or part of the patella. The healthcare provider can also help treat any damage to the surrounding ligaments and skin.

In less severe cases, you may be able to avoid surgery. Instead, the healthcare provider may give you a cast or splint to stabilize the leg for healing. Pain relievers, physical therapy, walking aids, and reducing weight-bearing on the knee may also be recommended.

Summary

The patella, also known as the kneecap, protects the knee joint and helps with knee movement and extension. An injury to the patella can result in patellar tendonitis (also known as jumper's knee), dislocation, or fracture. Rehabilitation depends on the type and severity of the injury and can include pain relievers, physical therapy, using a cast, and, in some cases, surgery.