Dominic Stone
The patella, or kneecap, is a thick, flat, triangular bone situated at the front of the knee joint. It is the largest sesamoid bone in the human body and is located within the tendon of the quadriceps femoris muscle. The patella acts as a pulley for the quadriceps muscle, with the quadriceps tendon attaching to it proximally and the patellar tendon attaching to it distally. The patella is subject to various forces and can be prone to dislocation or fracture, particularly during sports or after prolonged bed rest. The vastus medialis, lateralis, and intermedius muscles attach to the patella and influence its movement and stability.
| Characteristics | Values |
|---|---|
| Muscles attached to the patella | Quadriceps femoris, Vastus lateralis, Vastus medialis, Vastus intermedius, Rectus femoris, Patellar ligament |
| Patella's role at the knee joint | Acts as an anatomic pulley for the quadriceps muscle |
| Patella's function | Protects the quadriceps tendon from frictional forces, Acts as a bony shield for deeper structures in the knee joint, Adjusts the length, direction and force of the quadriceps tendon and patella tendon |
| Patella's shape | Thick, flat, triangular bone with apex pointing downwards |
| Patella's composition | Dense trabecular or cancellous tissue, covered by a thin compact lamina |
| Patella's ossification | Usually ossified from a single centre, appearing between the ages of 3-6, with ossification completed at puberty |
| Patellar dislocation | Occurs when the patella is pulled laterally by the vastus lateralis and vastus intermedius, against the medial pull of the vastus medialis |
| Patellar fractures | Usually caused by direct trauma or sudden contraction of the quadriceps muscle, common in males aged 20-50 |
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What You'll Learn
Quadriceps femoris muscle
The quadriceps femoris muscle, commonly known as the quad muscle, is the strongest muscle in the human body. Located in the anterior compartment of the thigh, the quadriceps femoris muscle translates to "four-headed muscle" from Latin. This name is derived from the fact that it consists of four individual muscles: the rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius. Of these four muscles, only the rectus femoris crosses both the hip and knee joints. The other muscles cross only the knee joint.
The rectus femoris is a fusiform muscle that consists of two heads. It originates from two sites on the ilium: the anterior inferior iliac spine (straight head) and the supraacetabular groove (reflected head). The two heads unite into a common muscle belly that courses down the thigh, covering the anterior aspect of this region. The muscle fibres converge towards a thick tendon that inserts into the base of the patella. Occasionally, the rectus femoris can have a third head that originates from the iliofemoral ligament.
The vastus medialis originates from several landmarks of the proximal femur, including the inferior part of the intertrochanteric line, pectineal line of the femur, medial lip of the linea aspera, and proximal half of the medial supracondylar line. The lowermost fibres of the vastus medialis lie in an almost horizontal plane, forming a noticeable bulge superior to the medial side of the patella. This particular part of the vastus medialis is often referred to as the vastus obliquus. The muscle inserts into the base of the patella via the quadriceps femoris tendon.
The quadriceps femoris muscle functions to extend the leg at the knee joint and flex the thigh at the hip joint. It is involved in everyday movements such as getting up from a chair, walking, climbing stairs, and squatting. The quadriceps femoris muscle is also essential for activities such as kicking, jumping, cycling, and running.
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Patellar ligament
The patella, derived from the Latin for 'small plate', is a flat, inverted triangular bone situated on the front of the knee joint. It is the largest sesamoid bone in the human body and is located within the tendon of the quadriceps femoris muscle. The patella is attached to the quadriceps muscles by the quadriceps tendon. The quadriceps tendon and the patella tendon work together to enable knee straightening.
The patellar tendon, also known as the patellar ligament, is a strong, flat ligament that attaches the bottom of the kneecap (patella) to the top of the shinbone (tibia). The patellar ligament envelopes the inferior third of the patella. The patellar tendon is the distal portion of the common tendon of the quadriceps femoris. It originates on the apex of the patella distally and adjoining margins of the patella and the rough depression on its posterior surface. Below, it inserts on the tuberosity of the tibia. Its superficial fibres are continuous over the front of the patella with those of the tendon of the quadriceps femoris.
The patellar tendon can be injured in a patellar tendon rupture. Tendon does not regenerate fully in humans, so there is a significant clinical need for research into therapies for patellar tendon rupture. The patellar tendon can be used as a tissue source in the repair of other ligaments. For example, in the event of a torn anterior cruciate ligament, the patellar tendon can be used in the rehabilitation process.
Patellar tendinitis, also known as jumper's knee, is an injury to the tendon connecting the kneecap to the shinbone. It is a common overuse injury caused by repeated stress on the patellar tendon. The stress results in tiny tears in the tendon, which the body attempts to repair. As the tears in the tendon multiply, they cause pain from inflammation and weakening of the tendon. When this tendon damage persists for more than a few weeks, it is called tendinopathy.
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Patellar tendon
The patella is a flat, inverted triangular bone, situated at the front of the knee joint. It is the largest sesamoid bone in the human body. The patella is attached to the quadriceps muscles by the quadriceps tendon. Working together, the quadriceps muscles, quadriceps tendon, and patellar tendon enable you to straighten your knee. The patellar tendon is also sometimes called the patellar ligament as it forms a bone-to-bone connection when the patella is fully ossified. The patellar tendon is a strong, flat ligament, which originates on the apex of the patella distally and adjoining margins of the patella and the rough depression on its posterior surface. Below, it inserts itself on the tuberosity of the tibia. Its superficial fibres are continuous over the front of the patella with those of the tendon of the quadriceps femoris.
The patellar tendon is the distal portion of the common tendon of the quadriceps femoris. It is continued from the patella to the tibial tuberosity. The patellar tendon is about 4.5 cm long in adults, with a range of 3 to 6 cm. The medial and lateral portions of the quadriceps tendon pass down on either side of the patella to be inserted into the upper extremity of the tibia on either side of the tuberosity. These portions merge into the capsule, forming the medial and lateral patellar retinacula. The patellar tendon can be injured in a patellar tendon rupture. As tendons do not regenerate fully in humans, there is a significant clinical need for research into therapies for patellar tendon rupture.
The patellar tendon works with the muscles in the front of the thigh to straighten the leg. Patellar tendinitis, also known as jumper's knee, is an injury to the tendon connecting the kneecap to the shinbone. It is a common overuse injury caused by repeated stress on the patellar tendon. The stress results in tiny tears in the tendon, which the body attempts to repair. As the tears in the tendon multiply, they cause pain from inflammation and weakening of the tendon. When this tendon damage persists for more than a few weeks, it is called tendinopathy. Patellar tendon tears can be either partial or complete. When the patellar tendon is completely torn, the tendon separates from the kneecap, and a piece of bone can break off along with the tendon.
Patellar dislocations are more common in sports such as football, rugby, and ice hockey. They occur when the patella is displaced out of the patellofemoral groove. Patellar fractures are more common in males in the 20-50 age range and usually occur from a sudden contraction of the quadriceps muscle or direct trauma to the bone. 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. Conversely, an inferior glide occurs during knee flexion.
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Vastus medialis and lateralis
The patella is a flat, inverted triangular bone, situated on the front of the knee joint. It is the largest sesamoid bone in the human body. The patella is developed in the tendon of the quadriceps femoris muscle, which includes the vastus lateralis, vastus intermedius, and vastus medialis.
The vastus medialis and lateralis insert on the medial and lateral borders of the patella, respectively. The quadriceps tendons coalesce at their distal attachment points, passing superficially over the patella's anterior surface to form the deep fascia lata, which attaches to the lateral condyle of the tibia. The vastus medialis and lateralis provide both functional mobility and stability of the knee joint. They maintain balance between the two muscles, so the degree of activation and temporal coordination of these two muscles are key to providing safe movement of the knee joint. An imbalance between the vastus medialis and lateralis of the quadriceps leads to pain, as the patella glides abnormally.
The vastus medialis longus (VML) attaches at 15 to 18 degrees medial to the quadriceps tendon, and the vastus medialis oblique (VMO) attaches at 50 to 55 degrees. The VMO has a more oblique pull on the patella, stabilising it against excessive lateral pull. Lateral tracking is guided by both the vastus lateralis and the iliotibial band. The vastus medialis, together with the other muscles that make up the quadriceps femoris, extends the knee joint and contributes to the correct tracking of the patella.
The vastus lateralis is located on the lateral side of the thigh and is the largest of the quadriceps. It is part of the quadriceps muscle group, which acts on the knee and hip to promote movement, strength, and stability. The quadriceps muscle group allows a person to stand up from a sitting position, walk up or down stairs, and perform basic walking and running.
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Patellofemoral joint
The patellofemoral joint is a diarthrodial plane joint that consists of the posterior surface of the patella and the trochlear surface of the distal anterior femur. The patella is the largest sesamoid bone in the body and is located anterior to the knee joint. The patella is a flat, inverted triangular bone, perforated by small apertures for the passage of nutrient vessels. The patella acts as a bony shield for deeper structures in the knee joint.
The patellofemoral joint is supported and stabilized by a complex network of ligaments, tendons and other soft tissues. The patellar retinaculum is an important stabilizer of the joint, with its medial and lateral components playing a key role. The medial patellofemoral ligament (MPFL) is another important stabilizer, originating on the medial femur and attaching to the patella and quadriceps tendon. The lateral patellofemoral ligament (LPFL) is a lateral stabilizer of the patella, preventing medial subluxation or dislocation.
The patella acts as a pulley with the quadriceps tendon attaching proximally and the patellar tendon attaching distally, transmitting the forces of the knee extensor mechanism. The quadriceps muscle is the largest and strongest extensor muscle, consisting of the rectus femoris and the vastus group. When the quadriceps muscle contracts, it pulls the patella laterally and posteriorly. The patella's tracking is guided by the vastus lateralis and the iliotibial band.
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Frequently asked questions
The patella is attached to the quadriceps muscle. The superior third of the patella acts as the attachment point for the rectus femoris and vastus intermedius. The vastus medialis and lateralis insert on the medial and lateral borders of the patella, respectively.
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.
The patella functions as an anatomic pulley for the quadriceps muscle. It also acts as a bony shield for deeper structures in the knee joint, protecting the quadriceps tendon from frictional forces.
