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The patella is the largest sesamoid bone in the human body, located at the front of the knee joint. It is also known as the kneecap and is embedded within the tendon of the quadriceps femoris muscle. The patella acts as a gliding joint and can move in multiple planes. It is prone to injuries such as fractures, dislocations, and tendinitis, commonly referred to as jumper's knee. The patella plays a crucial role in increasing the leverage of the quadriceps tendon, enhancing knee flexion, and protecting the knee joint.
| Characteristics | Values |
|---|---|
| Definition | The patella is the largest sesamoid bone in the human body, located anterior to the knee joint within the tendon of the quadriceps femoris muscle. |
| Other names | Kneecap |
| Shape | Oval, triangular |
| Size | On average, 1.75 inches long and 1.5 inches wide. The articular surface is about 12 cm2 (1.9 sq in) and covered by cartilage, which can reach a maximal thickness of 6-7 mm. |
| Function | The patella functions primarily as an anatomic pulley for the quadriceps muscle, increasing the lever arm of the extensor mechanism and thus increasing quadriceps strength by 33–50%. It also protects the knee joint and supports muscles, tendons, and ligaments. |
| Ossification | The patella ossifies from a single centre, which usually makes its appearance in the second, third, fourth, or sixth year. More rarely, the bone is developed by two centres, placed side by side. Ossification is completed at about the age of puberty. |
| Injuries | Patellar dislocations, fractures, subluxations, tendinitis (jumper's knee), and tendinopathy are common injuries. |
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What You'll Learn
The patella is the kneecap
The patella is shaped like an oval with a slight point at the bottom. The apex is the most inferior part of the patella and is pointed to give attachment to the patellar ligament. The patellar ligament connects the bottom of the patella to the tibia (shin bone). The patella's medial facet articulates with the femur's medial condyle. The patella's articulating surface changes as the knee completes its range of motion. When the knee flexes, the patellar contact point moves inferiorly and posteriorly along the femoral condyles and more proximally on the patella.
The patella functions primarily as an anatomic pulley for the quadriceps muscle. It increases the lever arm of the extensor mechanism, allowing for more effective knee flexion and increasing quadriceps strength by 33-50%. The patella also protects the quadriceps tendon from frictional forces by minimising tendon contact with the femur.
The patella is prone to injury because of its particularly exposed location. Patellar dislocations and fractures are common injuries. Patellar dislocations occur with significant regularity, especially in young female athletes. Patellar fractures are more common in males aged 20-50 and usually occur from a sudden contraction of the quadriceps muscle or direct trauma to the bone. Treatment for patellar fractures usually involves surgery, unless the damage is minimal and the extensor mechanism is intact.
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Patellar fractures
The patella, or kneecap, is the largest sesamoid bone in the human body, located at the front of the knee joint. It acts as a shield for the knee joint, protecting it and supporting the muscles, tendons, and ligaments. Patellar fractures are breaks in the patella and are usually caused by a direct blow to the kneecap, such as during a fall, vehicle collision, or contact with a ball, bat, or stick in sports. They can also occur due to a sudden contraction of the quadriceps muscle, which pulls the patella apart.
The treatment for patellar fractures depends on the severity and displacement of the fracture. Nonsurgical treatment is typically recommended for more stable fractures or less severe breaks and may include the use of a cast or splint to hold the leg in place while the bone heals. Pain medications and physical therapy may also be prescribed to help manage pain and regain strength and mobility.
However, if the bone pieces are displaced or out of place, surgery is usually required to restore and stabilize the kneecap. Surgical repairs may involve using screws, pins, and wires to hold larger pieces of the patella together or removing fragments of bone that are too small to reattach. In very severe cases, part or all of the kneecap may need to be removed. After treatment, individuals may still experience continued pain and reduced range of motion. Physical therapy can help minimize muscle loss and improve strength, flexibility, and range of motion.
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Patellar dislocations
The patella, or kneecap, is the largest sesamoid bone in the human body and is located at the front of the knee joint. It protects the knee joint and supports muscles, tendons, and ligaments. The patella also functions as an anatomic pulley for the quadriceps muscle, increasing its effective extension capacity.
Following a patellar dislocation, the kneecap must be relocated into the trochlear groove. This often happens spontaneously as the individual extends their knee. However, associated problems can occur with patellar dislocations, the most common being tearing of the ligaments that stabilize the kneecap. Small fragments of cartilage and bone may also break off during relocation, requiring removal through an arthroscopic procedure.
The treatment and management of patellar dislocations vary depending on the severity and recurrence of the injury. In general, conservative management includes rest, appropriate hip and thigh muscle strengthening, and the use of a patellar buttress brace. Alternative treatments may include glucosamine, hyaluronic acid, and non-steroidal anti-inflammatory medications (NSAIDs). In cases of recurrent dislocations or cartilage lesions, surgical stabilization procedures may be necessary.
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Patellar tendinitis
The first symptom of patellar tendinitis is usually pain between the kneecap and where the tendon attaches to the shinbone. Initially, the pain may only be noticeable during or after physical activity. Over time, the pain intensifies and starts to interfere with sports performance. Other symptoms may include muscle spasms and reduced knee function.
To diagnose patellar tendinitis, a doctor will typically apply pressure to different parts of the knee to identify the source of pain. They may also recommend imaging tests such as X-rays, ultrasounds, or magnetic resonance imaging (MRI) to confirm the diagnosis and assess the extent of tendon damage.
Treatment for patellar tendinitis typically begins with conservative approaches, including physical therapy, stretching exercises, and strengthening exercises to improve muscle strength and flexibility around the knee. Icing the affected area and temporarily reducing or avoiding activities that trigger symptoms are also recommended as part of self-care. In more severe cases, medical interventions such as corticosteroid injections, platelet-rich plasma injections, or surgical procedures may be considered.
To prevent patellar tendinitis, it is important to maintain a balance in muscle strength among the leg muscles. Tight thigh muscles (quadriceps) and hamstrings can increase strain on the patellar tendon. Additionally, gradual progression in training intensity and frequency can help reduce the risk of overuse injuries like patellar tendinitis.
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The patella's role in knee extension
The patella is the largest sesamoid bone in the human body and is located at the front of the knee joint. It is also known as the kneecap. The patella is a flat, rounded, triangular bone that articulates with the femur (thigh bone) and covers and protects the anterior articular surface of the knee joint.
The primary function of the patella is knee extension. It increases the leverage that the quadriceps tendon can exert on the femur by increasing the angle at which it acts. The patella is attached to the tendon of the quadriceps femoris muscle, which contracts to extend and straighten the knee. The patella acts as a fulcrum, increasing the moment arm of the extended knee. In physics, a moment refers to a force's rotational effect on an object with respect to a specific point or axis. The patella increases the moment arm during extension, allowing for more effective knee flexion and increasing quadriceps strength.
During tibiofemoral motion, the patella acts as a gliding joint and can move in multiple planes. A superior glide occurs during knee extension as the quadriceps muscle contracts and pulls the patella superiorly. This movement is important for normal patellar tracking, which helps to ensure the patella stays in its groove and does not become dislocated.
The patella also protects the knee joint and supports muscles, tendons, and ligaments. It acts as a bony shield for deeper structures in the knee joint and helps to protect the quadriceps tendon from frictional forces by minimising tendon contact with the femur.
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Frequently asked questions
The patella is the kneecap—a bone at the front of your knee joint.
The patella supports muscles, tendons, and ligaments, and protects the knee joint. It also functions as an anatomic pulley for the quadriceps muscle, increasing the lever arm of the extensor mechanism and thus increasing quadriceps strength.
The patellar ligament connects the bottom of the patella to the tibia (shinbone).
Patellar tendinitis, also known as jumper's knee, is a common overuse injury caused by repeated stress on the patellar tendon. It results in tiny tears in the tendon, causing pain from inflammation and weakening of the tendon.
Common patella injuries include dislocations, fractures, subluxations (partial dislocations), and tendinitis.
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