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.
Chondromalacia patella is a common condition characterized by softening, weakening and damage of the cartilage. The condition is most often seen in young athletes and older adults who have arthritis of the knee.
Lateral Patellar Compression Syndrome
Lateral patellar compression syndrome refers to pain under and around your kneecap. It is a common complaint among runners, jumpers and other athletes such as skiers, cyclists, and soccer players.
Pain, swelling, and stiffness are the common symptoms of any damage or injury to the knee. If care is not taken during the initial phases of injury, it may lead to joint damage, which may end up destroying your knee.
The knee joint is one of the largest joints in the body. This highly complex joint has several tissues supporting and stabilizing its movement.
Knee sprain is a common injury that occurs from overstretching of the ligaments that support the knee joint. A knee sprain occurs when the knee ligaments are twisted or turned beyond its normal range, causing the ligaments to tear.
MCL sprains occur due to a sudden impact from the outside of your knee, most commonly while playing sports such as rugby and football. Rarely, the MCL can get injured when the knee gets twisted or following a quick change in direction.
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.
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.
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.
The knee is a complex joint of the body that is vital for movement. The four major ligaments of the knee are anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL) and lateral collateral ligament (LCL).
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.
Patellar Dislocation/Patellofemoral Dislocation
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).
Posterior cruciate ligament (PCL), one of the four major ligaments of the knee, is situated at the back of the knee. It connects the thighbone (femur) to the shinbone (tibia). The PCL limits the backward motion of the shinbone.
Chondral or Articular Cartilage Defects
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.
Any damage to the supporting ligaments may cause the patella to slip out of the groove either partially (subluxation) or completely (dislocation). This misalignment can damage the underlying soft structures such as muscles and ligaments that hold the kneecap in place.
Patellofemoral instability means that the patella (kneecap) moves out of its normal pattern of alignment. This malalignment can damage the underlying soft structures such as muscles and ligaments that hold the knee in place.
Recurrent Patella Dislocation
The patella (kneecap) is a small bone that shields your knee joint. It is present in front of your knee, on a groove called the trochlear groove that sits at the junction of the femur (thighbone) and tibia (shinbone).
Quadriceps Tendon Rupture
The quadriceps can rupture after a fall, direct blow to the leg and when you land on your leg awkwardly from a jump. Quadriceps tendon rupture most commonly occurs in middle-aged people who participate in sports that involve jumping and running.
Patellar Tendon Rupture
The patellar tendon works together with the quadriceps muscle and the quadriceps tendon to allow your knee to straighten out. Patella tendon rupture is the rupture of the tendon that connects the patella (kneecap) to the top portion of the tibia (shinbone).
Tibial Eminence Spine Avulsion Fracture
Tibial eminence spine avulsion fracture is the avulsion (tearing away) of the tibial eminence.
Knee Angular Deformities
Angular deformities of the knee are variations in the normal growth pattern during early childhood and are common during childhood.
Articular Cartilage Injury
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 the body during activities such as running and jumping.
Loose Bodies in the Knee
Loose bodies are fragments of detached cartilage or bone inside the knee joint. These fragments may be free floating (unstable) or may be trapped (stable) within the joint.
Knee Sports Injuries
Trauma is any injury caused during physical activity, motor vehicle accidents, electric shock, or other activities. Sports trauma or sports injuries refer to injuries caused while playing indoor or outdoor sports and exercising.
Pediatric Tibial Tubercle Fractures
Tibial tubercle fractures are quite rare occurrences that typically affect physically active adolescents between the age of 14 and 17. It is caused by violent tensile forces exerted over the tibial tuberosity (a bulge in the tibial bone) during activities involving sudden contraction of the knee extensors (springing and jumping).
Women and ACL Injuries
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.
Adolescent Knee Problems
Osgood-Schlatter disease refers to a condition in older children and teenagers caused by excessive stress to the patellar tendon (located below the kneecap).
Multiligament Knee Injuries
Injury to more than one knee ligament is called a multiligament knee injury and may occur during sports or other physical activities.
Anterior Knee Pain
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.
Physeal Sparing Surgery (Micheli-KocherTechnique)
Surgery may be necessary to reconstruct an irreparable anterior cruciate ligament (torn ACL). In adults, reconstruction of the ACL involves passing a soft tissue graft through tunnels drilled into the shinbone (tibia) and thighbone (femur).
Partial Arthroscopic Meniscectomy
Partial arthroscopic meniscectomy is a procedure to remove the damaged part of a meniscus in the knee joint with the help an arthroscope. The meniscus is a C-shaped disc of cartilage between your thighbone and shinbone.
Combined Hyaluronic Therapy for the Knee
Combined hyaluronic therapy is the process of injecting hyaluronic acid (HA) along with platelet-rich plasma (PRP) into your knee to treat osteoarthritis.
Matrix Induced Autologous Chondrocyte Implantation (MACI)
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.
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.
Failed Anterior Cruciate Ligament (ACL) Reconstruction
Anterior cruciate ligament reconstruction failure may be due to the following problems:
Technical: This is the most common cause of failure and may involve incorrect drilling of a tunnel through the tibial or femoral bone for the attachment of the graft.
Failed Meniscus Repair
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.
Meniscal transplantation is a surgical procedure to replace the damaged meniscus of the knee with healthy cartilage.
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.
Weight-bearing joints, such as the knee, may develop defects in the articular cartilage (spongy tissue that lines and cushions joints during movement) due to stress, trauma or degenerative disease
Posterolateral Corner Reconstruction
Posterolateral corner injury is damage or injury to the structures of the posterolateral corner. The structures of the posterolateral corner include the lateral collateral ligament, the popliteus tendon, and the popliteo-fibular ligament.
The menisci are two C-shaped cartilages that act as shock absorbers between the thigh and shin bones that articulate at the knee joint. They provide stability and lubrication to the joint as well as nutrition for the articular cartilage.
Quadriceps Tendon Repair
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.
Tibial Eminence Fracture
The tibia or shin bone is a major bone of the leg which connects the knee to the ankle. A fracture or break in the upper part of the tibia is known as a proximal tibial fracture and commonly occurs just below the knee joint.
Before performing trochleoplasty, your doctor will ensure that the articular cartilage (spongy tissue that lines and cushions joints during movement) at the trochlea is normal and healthy.
Chondroplasty is a surgical procedure to repair and reshape damaged cartilage in a joint. The procedure involves smoothing degenerative cartilage and trimming any unstable flaps of cartilage.
Physeal Sparing Reconstruction of the Anterior Cruciate Ligament
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
Bone-Patellar Tendon-Bone (BPTB) Autograft
An autograft refers to using organ or tissue (bone, cartilage, tendon or skin) from the same person to transplant elsewhere on their body.
Bone-Patellar Tendon-Bone (BPTB) Allograft
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.
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 hamstring autograft method is a surgical procedure to replace the torn ACL with part of the hamstring tendon taken from your leg.
Knee arthroscopy is a common surgical procedure performed using an arthroscope, a viewing instrument, to diagnose or treat a knee problem.
Knee osteotomy is a surgical procedure in which the upper shinbone (tibia) or lower thighbone (femur) is cut and realigned. It is usually performed in arthritic conditions affecting only one side of your knee.
High Tibial Osteotomy
High tibial osteotomy is a surgical procedure performed to relieve pressure on the damaged site of an arthritic knee joint. It is usually performed in arthritic conditions affecting only one side of your knee and the aim is to take pressure off the damaged area and shift it to the other side of your knee with healthy cartilage.
Tibial Tubercle Osteotomy
Tibial tubercle osteotomy is a surgical procedure that is performed along with other procedures to treat patellar instability, patellofemoral pain, and osteoarthritis.
Patellar Tendon Repair
Patella tendon rupture is the rupture of the tendon that connects the patella (kneecap) to the top portion of the tibia (shinbone). The patellar tendon works together with the quadriceps muscle and the quadriceps tendon to allow your knee to straighten out.
Medial Patellofemoral Ligament Reconstruction
Medial patellofemoral ligament reconstruction is a surgical procedure indicated for severe patellar instability.
Distal Realignment Procedures
Distal realignment procedures, also known as tibial tubercle transfer (TTT) procedures, are performed to reposition the kneecap after subluxation or dislocation by realigning the tendon under the kneecap to the underlying tibial tubercle.
Arthroscopic Reconstruction of the Knee for Ligament Injuries
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.
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.
The lateral collateral ligament (LCL) is a thin set of tissues present on the outer side of the knee, connecting the thighbone (femur) to the fibula (bone of the lower leg).
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.
ACL Reconstruction of Patellar Tendon
Anterior cruciate ligament (ACL) reconstruction patellar tendon is a surgical procedure that replaces the injured ACL with a patellar tendon.
ACL Reconstruction Procedure of Hamstring Tendon
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.
Medial collateral ligament reconstruction is indicated for chronic MCL instability despite appropriate non-surgical treatment.
Cartilage replacement is a surgical procedure performed to replace the worn-out cartilage with new cartilage.
Autologous Chondrocyte Implantation
Autologous chondrocyte implantation (ACI) is a procedure to treat the articular cartilage defects of the knee. This procedure is effective for treating small areas of cartilage damage that causes pain and swelling and restricts range of motion.
Subchondroplasty is a minimally invasive procedure that is performed to specifically repair chronic BMLs by filling them with a bone substitute material.
Partial meniscectomy is a surgical procedure to remove the torn portion of the meniscus from the knee joint.
A meniscus tear is the commonest knee injury in athletes, especially those involved in contact sports. A sudden bend or twist in your knee can cause the meniscus to tear.
Partial Transphyseal Surgery
Partial transphyseal surgery is an arthroscopically assisted operative procedure to reconstruct the anterior cruciate ligament (ACL) in the knee of a child or adolescent with growth plates or physis (areas near the ends of long bones where growth is still occurring).