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 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.
Shin splints are pain and inflammation of the tendons, muscles and bone tissue along the tibia or shinbone (lower leg). It occurs because of vigorous physical activities such as exercise or sports. The condition is also referred to as medial tibial stress syndrome (MTSS).
Knee infection is a serious medical condition that needs immediate treatment. Infection may occur followed by a knee replacement surgery or trauma and is usually caused by bacteria. Infection may spread to the space of the knee joint or deep layers of your knee causing serious complications.
Meniscal tears are among the commonest injuries to the knee joint. It can occur at any age but are more common in athletes involved in contact sports. The meniscus has no direct blood supply and for that reason, when there is an injury to the meniscus, healing is difficult.
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 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.
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).
The articular or hyaline cartilage is the tissue lining the surface of the two bones in the knee joint. Cartilage helps the bones move smoothly against each other and can withstand the weight of your body during activities such as running and jumping.
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. The undersurface of the kneecap and the lower end of the femur are coated with articular cartilage, which helps in smooth movement of the knee joint
Knee replacement, also called knee arthroplasty, is a surgical procedure in which the worn-out or damaged surfaces of the knee joint are removed and replaced with artificial implants. Any resulting fractures or breaks in the bone around the implant are called periprosthetic knee fractures.
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.
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.
The knee joint is stabilized by four strong ligaments. The anterior cruciate ligament (ACL) passes diagonally in the middle of the knee, ensuring that the thigh and shin bone do not slide out of alignment during movement.
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.
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.
Periprosthetic knee fracture fixation is a procedure performed to stabilize a fracture that occurs in the bone present around a knee prosthesis. The fracture may involve the lower part of the thighbone (femur), the kneecap (patella) or the upper part of the shinbone (tibia).
An osteotomy is a surgical procedure that involves cutting of bone. The distal femur is part of the femur (thighbone) just above the knee joint. Distal femoral osteotomy is performed to correct knee alignment which can lead to excessive loading and degeneration of one side of the knee joint.
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.
Viscosupplementation refers to the injection of a hyaluronan preparation into the joint. Hyaluronan is a natural substance present in the joint fluid that assists in lubrication. It allows the smooth movement of the cartilage-covered articulating surfaces of the joint.
Physical therapy is an exercise program that helps you to improve movement, relieve pain, encourage blood flow for faster healing, and restore your physical function and fitness level. It can be prescribed as an individual treatment program or combined with other treatments
Traditionally, arthritis in only one compartment of the knee is treated by partial knee replacement surgery. Patellofemoral knee replacement is a minimally invasive surgical option performed in the patellofemoral compartment only, preserving the knee parts not damaged by arthritis as well as the stabilizing anterior and posterior cruciate ligaments (ACL and PCL).
Revision knee replacement surgery involves replacing a part or all your previous knee prosthesis with a new prosthesis. Although total knee replacement surgery is successful, sometimes the procedure can fail due to various reasons and may require a second revision surgery.
Robotic-assisted knee replacement surgery is an alternative to the conventional knee replacement procedure. It is performed using robotic-arm technology that allows your surgeon to precisely perform the surgery through a smaller incision as compared to traditional surgery.
Robotic-assisted partial knee surgery is an innovative alternative to the conventional surgical procedure to treat degenerative knee diseases such as osteoarthritis. It is performed using robotic-arm technology that allows your surgeon to precisely perform the surgery through small incisions.
The medial patellofemoral ligament can rupture or get damaged when there is patellar lateral dislocation. Dislocation can be caused by a direct blow to the knee, twisting injury to the lower leg, strong muscle contraction, or because of a congenital abnormality such as shallow or malformed joint surfaces.
Knee ligament injuries are common in athletes involved in contact sports such as soccer, football, and basketball. Knee ligament injuries are graded based on the severity of the injury.
PCL injuries are very rare and are more difficult to detect than other knee ligament injuries. Cartilage injuries, bone bruises, and ligament injuries often occur in combination with PCL injuries. Injuries to the PCL can be graded as I, II or III depending on the severity of injury.
Anterior cruciate ligament (ACL) reconstruction patellar tendon is a surgical procedure that replaces the injured ACL with a patellar tendon. The goal of ACL reconstruction surgery is to tighten your knee and to restore its stability.
The goal of ACL reconstruction surgery is to tighten your knee and restore its stability.
Anterior cruciate ligament reconstruction hamstring method is a surgical procedure to replace the torn ACL with part of the hamstring tendon taken from your leg.
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.
Subchondroplasty is a minimally invasive procedure that is performed to specifically repair chronic BMLs by filling them with a bone substitute material. The bone substitute is then slowly resorbed and replaced with healthy bone, repairing the bone defect.
The ACL (anterior cruciate ligament) is one of the four major ligaments located within the knee joint. It connects the femur (thighbone) to the tibia (shinbone). It plays a key role in holding the two bones within the knee and keeping the joint stable while your knee moves back and forth.