The knee is a complex joint made up of different structures - bones, tendons, ligaments, and muscles. They all work together to maintain the knee’s normal function and provide stability to the knee during movement.
Having a well-functioning healthy knee is essential for our mobility and ability to participate in various activities. Understanding the anatomy of the knee enhances your ability to discuss and choose the right treatment procedure for knee problems with your doctor.
Bones of the Knee
The knee is a hinge joint made up of two bones, the thighbone (femur) and shinbone (tibia). There are two round knobs at the end of the femur called femoral condyles that articulate with the flat surface of the tibia called the tibial plateau. The tibial plateau on the inside of the leg is called the medial tibial plateau and on the outside of the leg, the lateral tibial plateau.
The two femoral condyles form a groove on the front (anterior) side of the knee called the patellofemoral groove. A small bone called the patella sits in this groove and forms the kneecap. It acts as a shield and protects the knee joint from direct trauma.
A fourth bone called the fibula is the other bone of the lower leg. This forms a small joint with the tibia. This joint has very little movement and is not considered a part of the main joint of the knee.
Articular Cartilage and Menisci of the Knee
Movement of the bones causes friction between the articulating surfaces. To reduce this friction, all articulating surfaces involved in the movement are covered with a white, shiny, slippery layer called articular cartilage. The articulating surface of the femoral condyles, tibial plateaus and the back of the patella are covered with this cartilage. The cartilage provides a smooth surface that facilitates easy movement.
To further reduce friction between the articulating surfaces of the bones, the knee joint is lined by a synovial membrane that produces a thick clear fluid called synovial fluid. This fluid lubricates and nourishes the cartilage and bones inside the joint capsule.
Within the knee joint, between the femur and tibia, are two C-shaped cartilaginous structures called menisci. Menisci function to provide stability to the knee by spreading the weight of the upper body across the whole surface of the tibial plateau. The menisci help in load-bearing i.e. it prevents the weight from concentrating onto a small area, which could damage the articular cartilage. The menisci also act as a cushion between the femur and tibia by absorbing the shock produced by activities such as walking, running and jumping.
Ligaments of the Knee
Ligaments are tough bands of tissue that connect one bone to another bone. The ligaments of the knee stabilize the knee joint. There are two important groups of ligaments that hold the bones of the knee joint together, collateral and cruciate ligaments.
Collateral ligaments are present on either side of the knee. They prevent the knee from moving too far during side to side motion. The collateral ligament on the inside is called the medial collateral ligament (MCL) and the collateral ligament on the outside is called the lateral collateral ligament (LCL).
Cruciate ligaments, present inside the knee joint, control the back-and-forth motion of the knee. The cruciate ligament in the front of the knee is called anterior cruciate ligament (ACL) and the cruciate ligament in the back of the knee is called posterior cruciate ligament (PCL).
Muscles of the Knee
There are two major muscles in the knee - the quadriceps and the hamstrings, which enable movement of the knee joint. The quadriceps muscles are located in front of the thigh. When the quadriceps muscles contract, the knee straightens. The hamstrings are located at the back of the thigh. When the hamstring muscles contract, the knee bends.
Tendons of the Knee
A tendon is a tissue that attaches a muscle to a bone. The quadriceps muscles of the knee meet just above the patella and attach to it through a tendon called the quadriceps tendon. The patella further attaches to the tibia through a tendon called the patella tendon. The quadriceps muscle, quadriceps tendon, and patellar tendon all work together to straighten the knee. Similarly, the hamstring muscles at the back of the leg are attached to the knee joint with the hamstring tendon.
The joint surface is covered by a smooth articular surface that allows pain-free movement in the joint. Arthritis is a general term covering numerous conditions where the joint surface or cartilage wears out. This surface can wear out for several reasons; often the definite cause is not known.
A meniscal tear is a common knee injury in athletes, especially those involved in contact sports. A sudden bend or twist in your knee causes the meniscus to tear. Elderly people are more prone to degenerative meniscal tears as the cartilage wears out and weakens with age.
The knee is a hinge joint made up of two bones, the thighbone (femur) and shinbone (tibia). Ligaments are tough bands of tissue that connect one bone to another bone. The ligaments of the knee stabilize the knee joint. Knee problems may arise if any of these structures get injured by overuse or suddenly during sports activities. Pain, swelling, and stiffness are the common symptoms of any damage or injury to the knee.
A multiligament injury is a tear in one or more ligaments of the knee, which affects the knee stability. Multiligament instability occurs because of a direct blow to the knee, fall from a height or motor vehicle trauma. Multiple ligament knee injuries are common in athletes involved in contact sports such as soccer, football, and basketball.
Patellar dislocation occurs when the patella moves out of the patellofemoral groove, (trochlea) onto the bony head of the femur. If the kneecap partially comes out of the groove, it is called subluxation; if the kneecap completely comes out, it is called dislocation (luxation).
Patellofemoral pain syndrome also called runner’s knee refers to pain under and around your kneecap. Patellofemoral pain is associated with a number of medical conditions such as anterior knee pain syndrome, patellofemoral malalignment, and chondromalacia patella.
The kneecap or patella forms a part of the knee joint. It is present at the front of the knee, protecting the knee and providing attachment to various muscle groups of the thigh and leg. A fracture in the kneecap is rare but common in adult males. The most common cause of fracture is a direct blow to the kneecap such as a fall or a motor vehicle accident. The patella can also be fractured indirectly, due to a sudden contraction of the thigh muscles.
An unstable knee can be caused by the sudden twisting of the knee, tears of the meniscus, ligament or capsule, osteoarthritis of the knee (wear and tear of the cushioning cartilage tissue between the bones) and sports injuries. When these tissues get injured, the patella or kneecap can move out of its groove in the knee joint and lead to instability.
The medial collateral ligament (MCL) is the ligament located on the inner part of the knee joint. An MCL tear can be associated with pain, swelling, and locking or catching sensation in the knee during movement. You may also feel as though your knee may buckle or give way suddenly.
Posterior cruciate ligament (PCL), one of the four major ligaments of the knee, is situated at the back of the knee. PCL injuries are very rare and more difficult to detect than other knee ligament injuries. Cartilage injuries, bone bruises, and ligament injuries often occur in combination with PCL injuries.
The anterior cruciate ligament (ACL) is a ligament that provides stability, reduces stress and prevents the knee from rotating or slipping out of position while jumping, running and landing. This ligament can tear during sports activities and exercise, as a result of a non-contact twisting injury, and is becoming a common injury in children.
The articular or hyaline cartilage is the tissue lining the surface of the two bones in the knee joint. The damage of the articular cartilage can affect you regardless of your age. It can be damaged by trauma such as accidents, mechanical injury such as a fall or from degenerative joint disease (osteoarthritis) occurring in older people.
Patellar dislocation occurs when the kneecap slides out of the trochlea. When dislocation of the patella occurs on more than one occasion, it is referred to as recurrent patellar dislocation. The risk of further dislocation increases to almost 70% to 80% after two episodes of dislocation.
Articular or hyaline cartilage is the tissue lining the surface of the two bones in the knee joint. The damage in articular cartilage can affect people of all ages. It can be damaged by trauma such as accidents, mechanical injury such as a fall, or from degenerative joint disease (osteoarthritis) occurring in older people.
The anterior cruciate ligament is one of the four major ligaments of the knee that connects the femur (thigh bone) to the tibia (shin bone) and helps stabilize the knee joint. Anterior cruciate ligament (ACL) injury is one of the common injuries of the knee. ACL injuries are more common in women than men due to anatomical differences.
Of the menisci within the knee, it is the medial that is more easily injured. Differences in the anatomical attachments of the medial meniscus compared to the lateral, mean that the medial meniscus becomes distorted during combined flexion and rotation movements in a manner not experienced on the lateral side. Medial meniscal injuries are usually considered as either traumatic or degenerative.
Osgood-Schlatter disease refers to a condition in older children and teenagers caused by excessive stress to the patellar tendon (located below the kneecap). Participants in sports such as soccer, gymnastics, basketball, and distance running are at higher risk for this disease.
Anterior knee pain is characterized by chronic pain over the front and center of the knee joint. It is common in athletes, active adolescents (especially girls) and overweight individuals. Anterior knee pain refers to various conditions, which include runner's knee or patellar tendinitis, and chondromalacia of the patella.
The anterior cruciate ligament (ACL) is one of the major stabilizing ligaments in the knee. When this ligament tears, unfortunately, it does not heal on its own, and often leads to the feeling of instability in the knee. ACL reconstruction is a commonly performed surgical procedure. With recent advances in arthroscopic surgery, it can now be performed with minimal incision and low complication rates
The posterior cruciate ligament (PCL), one of four major ligaments of the knee, is situated at the back of the knee. PCL injuries are usually characterized by knee pain and swelling immediately after the injury. There may also be instability in the knee joint, and knee stiffness that causes limping and difficulty in walking. Generally, surgery is considered for a dislocated knee and multiple ligament injuries, including the PCL. Surgery involves reconstruction of the torn ligament using a tissue graft taken from another part of the body, or from a donor.
Total knee replacement is the surgical treatment for knee arthritis, where the damaged knee is removed and replaced with an artificial knee implant. Traditionally performed as an inpatient procedure, total knee replacement surgery is now being conducted on an outpatient basis, allowing you to go home on the same day of the surgery.
The treatment of a meniscal tear depends on the type, size, and location of the tear, as well as your age and activity level. If the tear is small, with damage limited to the outer edge of the meniscus, non-surgical treatment may be sufficient. However, if the symptoms do not resolve with non-surgical treatment, surgical treatment may be recommended.
The medial patellofemoral ligament is a band of tissue that extends from the femoral medial epicondyle to the superior aspect of the patella. It is a major ligament that stabilizes the patella and helps in preventing patellar subluxation (partial dislocation) or dislocation. Medial patellofemoral ligament reconstruction is a surgical procedure indicated for severe patellar instability.
The surgical repair of the completely torn ligament involves reconstruction of the torn ligament using a tissue graft taken from another part of the body or from a donor. The damaged ligament is replaced by the graft and fixed to the femur and tibia using metallic screws.
Articular or hyaline cartilage is the tissue that covers bone surface of the knee which helps in smooth interaction between the two bones in the knee joint. It has less capacity to repair by itself because there is no direct blood supply to cartilage. Cartilage replacement is a surgical procedure performed to replace the worn-out cartilage with new cartilage.
Quadriceps tendon is a thick tissue located at the top of the kneecap. The quadriceps tendon works together with the quadriceps muscles to allow us to straighten our leg. Quadriceps tendon rupture most commonly occurs in middle-aged people who participate in sports which involve jumping and running.
Medial collateral ligament reconstruction is indicated for chronic MCL instability despite appropriate non-surgical treatment. Medial collateral ligament reconstruction is contraindicated for degenerative changes in the medial or lateral compartment, active infection, ligament instability, or presence of chronic diseases that can hamper surgical management or compliance to postoperative rehabilitation instructions.
Matrix-Induced autologous chondrocyte implantation is an innovative, FDA-approved cartilage restoration procedure that uses your own cells to repair cartilage defects in your knee. It can alleviate knee pain, help you regain function and may even delay or prevent arthritis.
Arthroscopic debridement or a clean-up is a surgical procedure performed using an arthroscope. In this procedure, the cartilage or the bone that is damaged is removed using surgical instruments and the edges of the articular cartilage that are rough will be smoothened.
Anterior cruciate ligament reconstruction failure may be due to the following problems which include technical, biological, traumatic and arthrofibrosis.
Meniscal repair may be performed either by open surgery under direct vision or minimally invasively using an arthroscope, which is a thin tube fitted with a camera that can be inserted into the knee through a very small incision to locate and repair the damaged meniscus. Three months following meniscal repair if pain and disability persist, a failed meniscal repair may be suspected and can be confirmed by performing a repeat arthroscopy.
Meniscectomy is a surgical procedure indicated in individuals with torn meniscus where the conservative treatments are a failure to relieve the pain and other symptoms. Meniscectomy is recommended based on the ability of meniscus to heal, patient’s age, health status, and activity level.
An autograft refers to using organ or tissue (bone, cartilage, tendon or skin) from the same person to transplant elsewhere on their body. ACL reconstruction with BPTP autograft is a surgical procedure that replaces the injured ACL with an autograft containing patellar tendon and bony attachments.
An allograft is an organ or tissue such as bone, cartilage, tendon or skin, taken from one person (donor) and surgically placed in another person to repair damaged tissue. ACL reconstruction with BPTP allograft is a surgical procedure that replaces the injured ACL with an allograft containing patellar tendon and bony attachments.
An autograft refers to using organ or tissue (bone, cartilage, tendon or skin) from the same person to transplant elsewhere on their body. ACL reconstruction with BPTP allograft is a surgical procedure that replaces the injured ACL with an allograft containing patellar tendon and bony attachments.
Physeal sparing reconstruction of the anterior cruciate ligament is a surgery to replace a torn anterior cruciate ligament or ACL, a major ligament of the knee, while minimizing damage to the growth plate (physis) present near the end of the bone.
The knee is a complex joint which consists of bone, cartilage, ligaments, and tendons that make joint movements easy and at the same time it is more susceptible to various kinds of injuries. Knee problems may arise if any of these structures get injured by overuse or suddenly during sports activities.