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The patella, or kneecap, is the largest sesamoid bone in the human body. It is embedded within the tendon of the quadriceps femoris muscle, which contracts to extend or straighten the knee. Patellar stability is governed by unique anatomy and biomechanics, including lower extremity alignment, articular geometry, dynamic muscular stabilizers, and passive ligamentous stabilizers. The vastus medialis obliquus (VMO) is the patella's primary dynamic stabilizer, inserting onto the superomedial patella at an oblique angle to stabilize the patella with medial and posterior forces. The medial patellofemoral ligament is the primary ligamentous stabilizer, while the quadriceps muscles and their associated tendons also play a role in patellar stability.
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What You'll Learn
- The Vastus Medialis Obliquus (VMO) is the patella's primary dynamic stabiliser
- The patella is attached to the quadriceps femoris muscle
- The patella is a sesamoid bone
- The patella's secondary ligamentous stabiliser is the medial patellofemoral ligament
- The patella's stability is influenced by lower extremity alignment
The Vastus Medialis Obliquus (VMO) is the patella's primary dynamic stabiliser
The patella, or kneecap, is stabilized by a combination of lower extremity alignment, articular geometry, dynamic muscular stabilizers, and passive ligamentous stabilizers. The Vastus Medialis Obliquus (VMO) is the patella's primary dynamic stabiliser. It originates from the medial intermuscular septum, adductor longus, and adductor magnus tendon, and it inserts onto the superomedial patella at an oblique angle. The VMO's nerve supply comes from the branches of the femoral nerve, and its blood supply is provided by the femoral artery.
The VMO's primary function is to pull the patella medially, helping to align it within the trochlear groove during knee flexion and extension. This medial translation of the patella by the VMO reduces the load on the patellofemoral joint. The VMO also participates in the last phase of knee extension.
Weakness or alterations in the VMO's muscle activity can result in maltracking of the patella, leading to instability and potential damage to surrounding structures. This can cause pain in the area, known as patellofemoral pain syndrome (PFPS). Atrophy of the VMO has been implicated in the instability of the patellofemoral joint, and VMO strengthening exercises are often recommended for individuals with PFPS.
The role of the VMO in patellar stability is complex, and its effectiveness under clinical conditions is still being studied. In cadaveric knee studies, simulating VMO weakness resulted in increased lateral patellar shift and reduced the force required to displace the patella laterally. However, the extended knee, where the patella is least stable, showed a lesser loss of stability when the VMO was relaxed.
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The patella is attached to the quadriceps femoris muscle
The patella, or kneecap, is a small bone located in front of the knee joint. It plays a crucial role in protecting the knee and facilitating movement. The patella is attached to several muscles, including the quadriceps femoris muscle, which is essential for maintaining patellar stability and overall knee health.
The quadriceps femoris muscle is a large muscle group located at the front of the thigh. It is composed of four main muscle heads: the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. These muscles converge to form the quadriceps tendon, which attaches to the base of the patella. The rectus femoris muscle, in particular, contributes to the central part of the quadriceps tendon and plays a key role in knee extension and thigh flexion.
The quadriceps femoris muscle is responsible for extending or straightening the knee, enabling movements such as kicking, running, jumping, and walking. It is the most powerful extensor of the knee and allows for independent walking, stair climbing, and standing. The muscle also helps to stabilize the patella and maintain proper knee alignment.
The patella moves within the patellofemoral joint, which is formed by the articulation of the patella and the femur (thigh bone). This joint transmits the forces of the quadriceps muscles, allowing for the extension of the knee and the reduction of friction during movement. The stability of the patellofemoral joint depends on factors such as lower extremity alignment, articular geometry, dynamic muscular stabilizers, and passive ligamentous stabilizers.
The vastus medialis obliquus (VMO) is particularly important for patellar stability. It originates from structures such as the medial intermuscular septum and inserts onto the superomedial patella at an oblique angle. The VMO produces medial and posterior forces that counterbalance the lateral forces exerted by the other components of the quadriceps muscles.
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The patella is a sesamoid bone
The patella, or kneecap, is a sesamoid bone. It is the most easily found sesamoid bone in the body, located at the front of the knee joint, within the patellofemoral groove of the femur. The patella is the largest sesamoid bone in the body. It is embedded within the patellar tendon that attaches the quadriceps to the tibia. The patella provides an extra mechanical advantage to the thigh, helping to extend the knee during the last 30 degrees of movement.
The patella is prone to injury due to its exposed position. It is also the primary cause of knee pain and discomfort. Patellar dislocation is common, accounting for around 3% of knee injuries. This occurs when the patella is displaced out of the patellofemoral groove, usually caused by high-force impact or a forceful, sudden twist of the knee. The kneecap will generally dislocate in one of two ways: traumatic dislocation, which involves a significant force, often during sports; and atraumatic dislocation, which occurs with much less force due to an underlying abnormality in the shape of the joint. Patellar fractures are usually the result of direct trauma to the bone or a sudden contraction of the quadriceps muscle.
Sesamoid bones are also found in the hands and feet. In the hand, there are usually five sesamoids, with two small bones at the base of the thumb. In the foot, sesamoid bones are located in the big toe: the tibial sesamoid on the medial plane and the fibular sesamoid on the lateral plane. These bones help to transfer force while standing, walking, running, etc.
The patella is stabilized by four factors: lower extremity alignment, articular geometry, dynamic muscular stabilizers, and passive ligamentous stabilizers. The vastus medialis obliquus (VMO) is the patella's primary dynamic stabilizer. The VMO originates from the medial intermuscular septum, adductor longus, and adductor magnus tendon and inserts onto the superomedial patella at an angle of 47 degrees from the anatomical axis.
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The patella's secondary ligamentous stabiliser is the medial patellofemoral ligament
The patella is a sesamoid bone with a triangular configuration, also known as the kneecap. It is part of the patellofemoral joint, which is a unique and complex structure consisting of static elements (bones and ligaments) and dynamic elements (the neuromuscular system). The patella is stabilized by lower extremity alignment, articular geometry, dynamic muscular stabilizers, and passive ligamentous stabilizers. The primary muscular stabilizer of the patella is the vastus medialis obliquus (VMO), which acts as a dynamic stabilizer.
The patella's primary ligamentous stabilizer is the medial patellofemoral ligament (MPFL). The MPFL is a complex network of soft tissues that stabilize the knee. It is an hourglass-shaped ligament made of bands of retinacular tissue. The MPFL attaches the inside part of the patella (kneecap) to the femur (thigh bone). The patella and femur compose the patellofemoral joint. The MPFL is critical for patellar tracking and stability within the trochlear groove, especially during early knee flexion. It provides restraint to the patella and prevents lateral displacement.
Injury to the MPFL can occur when the patella dislocates or becomes subluxated, often due to sports injuries or twisting movements. These incidents are more common in patients with anatomical predispositions such as patella alta (high kneecap) or loose joints. Left untreated, an injured MPFL may heal in a loosened position, increasing the risk of future patellar dislocations and subsequent cartilage damage. Therefore, treatment is important to prevent further dislocations and potential joint damage.
MPFL reconstruction surgery is a common treatment option, where a new medial patellofemoral ligament is created to stabilize the knee and protect the joint. The surgery has excellent outcomes and a low complication rate. Patients undergoing MPFL reconstruction receive regional anesthesia and sedation, and the procedure is performed through small incisions with the aid of an arthroscope. The orthopedic surgeon replaces the injured ligament with a portion of a tendon, taken either from the patient's hamstring or from donor tissue.
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The patella's stability is influenced by lower extremity alignment
The patella is stabilized by four factors: lower extremity alignment, articular geometry, dynamic muscular stabilizers, and passive ligamentous stabilizers. Lower extremity alignment is a critical component of patellofemoral stability. The patellofemoral joint is the articulation of the kneecap (patella) over the thigh bone (femur). The patella is tethered proximally by the quadriceps tendon and distally by the patellar tendon. The patella moves 5 mm medially due to the static restraint of the MPFL and muscle forces. The MPFL is the primary static stabilizer of the patellofemoral joint. The VMO is the patella's primary dynamic stabilizer. It originates from the medial intermuscular septum, adductor longus, and adductor magnus tendon and inserts onto the superomedial patella.
Lower extremity malalignment results in increased lateral forces on the patella, contributing to instability. Lower extremity malalignment can also result from poor neuromuscular control. The lateral trochlear geometry resists lateral translation, and when hypoplastic, it contributes to instability. The primary muscular stabilizer of the patella is the vastus medialis obliquus. It inserts on the patella at an oblique angle relative to the anatomic axis of the femur, stabilizing the patella with medial and posterior forces. The medial patellofemoral ligament is the primary ligamentous stabilizer of the patella and guides it into the trochlear groove during early knee flexion.
Patellar malalignment is a translational or rotational deviation of the patella to any axis, associated with several soft-tissue and osteochondral abnormalities. It is mostly characterized by a tilted and laterally displaced patella. Osseous abnormalities associated with patellar malalignment include patella alta and baja, a high tibial tuberosity, and trochlear dysplasia. A weakened vastus medialis obliquus is also associated with patellar malalignment. This may result in the loss of effectiveness of the VMO as a dynamic stabilizer. Other soft tissue abnormalities related to patellar malalignment include a lesion of the medial retinaculum, tightness of the lateral retinaculum, and an increased Q-angle.
The Q-angle, or quadriceps angle, is a measure of lower extremity alignment in the coronal plane. A larger Q-angle is associated with an increased lateral quadriceps vector that promotes lateral patellar maltracking and is a risk factor for lateral patellar dislocation and patellofemoral osteoarthritis. Physical examination of a patient with patellar malalignment can be challenging as there is no specific sign accepted as proof of malalignment. However, symptoms such as giving-way, stiffness, crepitation, and tenderness may indicate patellar malalignment. Lower extremity alignment, foot abnormalities such as pronation and gait, and the apprehension sign may also be inspected during a physical examination.
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Frequently asked questions
The patella is the knee cap. It is the largest sesamoid bone in the body, connecting the muscles to the knee joint.
The vastus medialis obliquus (VMO) is the patella's primary dynamic stabiliser. It originates from the medial intermuscular septum, adductor longus, and adductor magnus tendon.
The VMO stabilises the patella with medial and posterior forces, preventing it from dislocating during flexion.
Patellar stability is governed by unique anatomy and biomechanics. Lower extremity alignment, articular geometry, dynamic muscular stabilisers, and passive ligamentous stabilisers all play a role in maintaining patellar stability.
Patellar dislocations are common, especially in young female athletes. Patellar tendinitis, ruptured quadriceps tendon, and quadriceps strain are also prevalent issues.
