Knee
- Anatomy
- Conditions
- Treatment
Knee Anatomy
The knee is a complex joint made up of different structures including bones, tendons, ligaments and muscles. They all work together to maintain 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
The Knee is a hinge joint made up of two bones, the thigh bone (femur) and the shinbone (tibia). There are two round knobs at the end of the femur called femoral condyles which articulate with the flat surface of the tibia called the tibial plateau. The tibia plateau on the inside of the leg is called the medial tibial plateau, and on the outside of the leg it is called 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 knee cap. 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 form 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
Movement of the bones causes friction between the articulating surfaces. To reduce this friction, all articulating surfaces involved in 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 which 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 there 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 by preventing 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
Ligaments are tough bands of tissue that connect one bone to another bone. The ligaments of the knee function to stabilize the knee joint. There are two important groups of ligaments that hold the bones of the knee joint together, collateral ligaments and the cruciate ligament.
Collateral ligaments are present on either side of the knee. They function to 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- This group of 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 or ACL and the cruciate ligament in the back of the knee is called posterior cruciate ligament or PCL.
Muscles
Muscles: There are two major muscles, the quadriceps and the hamstrings, which enable movement of the knee joint. The quadriceps muscles are in the front of the thigh. When the quadriceps muscles contract, the knee straightens. The hamstrings are in the back of the thigh. When the hamstring muscles contract, the knee bends.
Tendons
Tendons are structures that attach muscles to the 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.
Conditions
Knee Pain
The knee is one of the largest joints in the body, formed by the lower end of the femur, upper end of the tibia and the patella or knee cap. Several ligaments and muscles attach to the bones of the knee joint to maintain normal motion of the joint. Special cartilaginous tissues known as menisci are placed between the two articular ends of the joint. These act as a cushion between the articular surfaces and absorb the shock during movement.
Anterior Knee Pain
Anterior knee pain is a characterized by a 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 a variety of conditions which include runner's knee or patellar tendinitis and chondromalacia of the patella. There is an inter-individual variation in the duration and presentation of pain.
Jumper’s Knee
Jumper’s knee, also known as “patellar tendinitis" is an inflammation of the patellar tendon that connects your kneecap (patella) to your shinbone. This tendon helps in extension of the lower leg.
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. Articular cartilage does not have a direct blood supply to it so has less capacity to repair itself.
Meniscal Tears
The knee is one of the most complex and largest joint in the body, and is more susceptible to injury. Meniscal tears are one among the common injuries to the knee joint. It can occur at any age, but are more common in athletes playing contact sports.
Knee Anterior Cruciate Ligament (ACL) Injury
The anterior cruciate ligament, or ACL, is one of the major ligaments of the knee that is in the middle of the knee and runs from the femur (thigh bone) to the tibia (shin bone). It prevents the tibia from sliding out in front of the femur. Together with posterior cruciate ligament (PCL) it provides rotational stability to the knee.
Knee Medical Collateral Ligament (MCL) Injury
The medial collateral ligament (MCL), a band of tissue present on the inside of your knee joint, connects your thigh bone and shin bone (bone of your lower leg). The MCL maintains the integrity of the knee joint and prevents it from bending inward.
Knee Posterior Cruciate Ligament (PCL) Injury
Posterior cruciate ligament (PCL), one of four major ligaments of the knee are 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.
Knee Lateral Collateral Ligament (LCL) Injury
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 (side bone of lower leg). It provides stability as well as limits the sidewise rotation of the knee. Tear or injury of LCL may cause instability of the knee that can be either reconstructed or repaired to regain the strength and movement of the knee.
Patellofemoral Instability
Patellar (knee cap) instability results from one or more dislocations or partial dislocations (subluxations). Patella is the small piece of bone in front of the knee that slides up and down the femoral groove (groove in the femur bone) during bending and stretching movements. The ligaments on the inner and outer sides of patella hold it in the femoral groove and avoid dislocation of patella from the groove.
Knee Arthritis
Arthritis is a general term covering numerous conditions where the joint surface or cartilage wears out. The joint surface is covered by a smooth articular surface that allows pain free movement in the joint. This surface can wear out for several reasons; often the definite cause is not known.
Runner’s Knee
Runner's knee, also called patellofemoral pain syndrome refers to pain under and around your kneecap. Runner’s knee includes several medical conditions such as anterior knee pain syndrome, patellofemoral malalignment, and chondromalacia patella that cause pain around the front of the knee. As the name suggests, runner’s knee is a common complaint among runners, jumpers, and other athletes such as skiers, cyclists, and soccer players.
Osgood Schlatter Disease
Osgood-Schlatter disease refers to a condition of an overuse injury that occurs in the knee region of growing children and adolescents. This is caused by inflammation of the tendon located below the knee cap (patellar tendon). Children and adolescents who participate in sports such as soccer, gymnastics, basketball and distance running are at higher risk of this disease.
Chondromalacia Patella
The patella, also called the kneecap is a small bone present on the front of your knee joint. The underside of the patella is covered by cartilage that allows smooth gliding of the knee with movement. Overuse or misalignment of the patella can cause wear and tear of the cartilage.
Prepatellar/ Kneecap Bursitis
A bursa is a small fluid-filled sac found between soft tissues and bones. It lubricates and acts as a cushion to decrease friction between bones when they move. Bursitis refers to the inflammation and swelling of the bursa. Inflammation of the bursa in front of the kneecap (patella) is known as kneecap bursitis or prepatellar bursitis.
Baker’s Cyst
The knee consists of a fluid called synovial fluid, which reduces friction between the bones of the knee joint while you move your leg. Sometimes this fluid is produced in excess, resulting in its accumulation in the back of your knee. A Baker’s cyst or popliteal cyst is a fluid-filled swelling that develops into a lump behind the knee. This causes stiffness, tightness and pain behind your knee. It is commonly seen in women and people aged over 40 (although it can develop at any age).
Iliotibial Band Syndrome
Iliotibial band syndrome is an overuse injury resulting from the inflammation of iliotibial band. Iliotibial band is a tough group of fibers that begins at the iliac crest of hip and runs along the outside of the thigh, to get attached to the outer side of the shin bone just below the knee joint. Its function is to coordinate with the thigh muscles and provide stability the knee joint.
Osteochondritis Dissecans
Osteochondritis dissecans is a joint condition in which a piece of cartilage, along with a thin layer of the bone separates from the end of the bone because of inadequate blood supply. The separated fragments are sometimes called “joint mice”. These fragments may be localized, or may detach and fall into the joint space causing pain and joint instability.
Patella Fracture
The knee cap or patella is the largest sesamoid bone in the body and one of the components of the knee joint, present at the front of the knee. 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. The knee cap protects the knee and provides attachment to various muscle groups of the thigh and leg. Fracture of knee cap is rare and is more common in adult males.
Patella Tendon Rupture
Patella tendon rupture is the rupture of the tendon that connects the patella (knee cap) to the top portion of the tibia (shin bone). The patellar tendon works together with the quadriceps muscle and the quadriceps tendon to allow your knee to straighten out.
Quadriceps Tendon Rupture
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. The quadriceps muscles are the muscles located in front of the thigh.
Osteonecrosis of the Knee
Osteonecrosis is a condition in which death of a section of bone occurs because of lack of blood supply to it. It is one of the most common causes of knee pain in older women. Women over the age of 60 years of age are commonly affected, three times more often than men.
Shin Splints
“Shin splints” is used to describe the pain and inflammation of the tendons, muscles and bone tissue around the tibia or shine bone (a large bone in the lower leg). It occurs because of vigorous physical activity such as exercise or sports. The condition is also referred to as medial tibial stress syndrome (MTSS).
Knee Angular Deformities
Angular deformities of the knee are common during childhood and usually are variations in the normal growth pattern. Angular deformity of the knee is a part of normal growth and development during early childhood. Physiologic angular deformities vary with age
Patellar Tendinitis
Patellar tendinitis, also known as “jumper’s knee” is an inflammation of the patellar tendon that connects your kneecap (patella) to your shinbone. This tendon helps in extension of the lower leg.
Multi-Ligament Injury
The knee is a complex joint of the body which is vital for movement. The four major ligaments of the knee are anterior cruciate ligament, posterior cruciate ligament, medial collateral ligament and lateral collateral ligament.
Tibial Eminence Spine Avulsions
Tibial eminence spine avulsion fracture is avulsion (tear away) of the tibial eminence (an extension on the bone for attachment of muscles) which most commonly involves the anterior cruciate ligament (ACL) insertion site.
Treatment
Non-surgical Treatments
Pharmacological
The knee is a complex joint which consists of bone, cartilage, ligaments and tendons that make joint movements easy and at the same time 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. Injuries to the knee can be caused by degenerative disease such as arthritis, traumatic injuries and sports injuries.
PRP
Our blood consists of a liquid component known as plasma. It also consists of three main solid components which include the red blood cells (RBCs), white blood cells (WBCs), and platelets. Platelets play an important role in forming blood clots. They also consist of special proteins, known as growth factors, which help with our body’s healing process. Platelet-rich plasma or PRP is a high concentration of platelets and plasma.
Viscosupplementation
Viscosupplementation refers to the injection of a gel-like fluid called hyaluronic acid into the joint. Hyaluronan is a natural substance present in the joint fluid that assists in lubrication. It allows smooth movement of the cartilage covered articulating surfaces of the joint. With arthritis the level of hyaluronic acid decreases. By adding hyaluronic acid to an arthritis joint, the theory is that this will help with movement and pain.
Cortisone Injection
Cortisone is a corticosteroid released by the adrenal gland in response to stress and is a potent anti-inflammatory agent. Artificial preparations containing cortisone are injected directly into the affected joint to relieve pain and reduce inflammation.
Physical Therapy
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. The main aim of physical therapy is to make your daily activities such as walking, getting in and out of bed, or climbing stairs easier.
Surgical Treatment
Knee Arthroscopy
Knee Arthroscopy is a common surgical procedure performed using an arthroscope, a viewing instrument, to consider the knee joint to diagnose or treat a knee problem. It is a relatively safe procedure and most the patient’s discharge from the hospital on the same day of surgery.
Knee Reconstructive Procedures
Anterior Cruciate Ligament (ACL) Reconstruction
The anterior cruciate ligament is one of the major stabilizing ligaments in the knee. It is a strong rope like structure located in the centre of the knee running from the femur to the tibia.
Posterior Cruciate Ligament (PCL) Reconstruction
Posterior cruciate ligament (PCL), one of four major ligaments of the knee are 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.
Lateral Collateral Ligament (LCL) Reconstruction
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 (side bone of lower leg). It provides stability as well as limits the sidewise rotation of the knee. Tear or injury of LCL may cause instability of the knee that can be either reconstructed or repaired to regain the strength and movement of the knee.
Medial Collateral Ligament (MCL) Reconstruction
Medial collateral ligament (MCL) is one of four major ligaments of the knee that connects the femur (thigh bone) to the tibia (shin bone) and is present on the inside of the knee joint. This ligament helps stabilize the knee. An injury to the MCL may occur as a result of direct impact to the knee. An MCL injury can result in a minor stretch (sprain) or a partial or complete tear of the ligament. The most common symptoms following an MCL injury include pain, swelling, and joint instability.
Multi-Ligament Knee Reconstruction
Ligaments are fibrous tissue bands that connect bones and stabilize joints. The knee joint has four major ligaments – the anterior cruciate ligament, posterior cruciate ligament, lateral collateral ligament, and medial collateral ligament.
Medial Patellofemoral Ligament (MPFL) Reconstruction
Medial patellofemoral ligament reconstruction is a surgical procedure indicated in patients with more severe patellar instability. Medial patellofemoral ligament is a band of tissue that extends from the femoral medial epicondyle to the superior aspect of the patella. Medial patellofemoral ligament is the major ligament which stabilizes the patella and helps in preventing patellar subluxation (partial dislocation) or dislocation. This ligament can rupture or get damaged when there is patellar lateral dislocation.
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. During the surgery, your surgeon will remove or add a wedge of bone either below or above the knee joint depending on the site of arthritic damage.
Tibial Tubercle Osteotomy
Tibial tubercle osteotomy is a surgical procedure which is performed along with other procedures to treat patellar instability, patellofemoral pain, and osteoarthritis. This is a quite safe procedure and provides excellent access and surgical exposure during a difficult primary or revision total knee arthroplasty. Surgical treatment is indicated when physical therapy and other nonsurgical methods have failed and there is history of multiple knee dislocations.
Distal Femoral Osteotomy
An osteotomy is a surgical procedure that involves cutting and reshaping of a bone. Distal femoral osteotomy is indicated to correct deformities and malalignments such as valgus knee, a deformity where the knee angles out from the center of the body. It is also performed to treat osteoarthritis in young active patients contraindicated for joint replacement.
Cartilage Restoration
Advanced Cartilage Restoration
Cartilage replacement is a surgical procedure performed to replace the worn-out cartilage with the new cartilage. It is usually performed to treat patients with small areas of cartilage damage usually caused by sports or traumatic injuries. It is not indicated for those patients who have advanced arthritis of knee.
OATS
OATS is “osteochondral autograft transfer system”. It is one of the two types of cartilage transfer procedures and the other procedure is “Mosaicplasty”. Cartilage transfer procedures involve moving healthy cartilage from a non-weight bearing area of the knee to a damaged area of the cartilage in the knee.
Osteochondral Allograft Transplantation
Osteochondral grafting is a method of treating cartilage injuries that expose underlying bone.
An osteochondral allograft is a piece of tissue containing bone and cartilage that is taken from a deceased donor to replace damaged cartilage that lines the ends of bones in a joint. The allograft tissue is shaped to precisely fit the defect in the damaged joint of the patient and then transplanted to repair the damage.
MACI
Matrix-Induced autologous chondrocyte implantation (MACI) 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.
Knee Replacement Procedures
Total Knee Replacement
Total knee replacement, also called total knee arthroplasty, is a surgical procedure in which the worn out or damaged surfaces of the knee joint are removed and replaced with artificial parts. The knee is made up of the femur (thigh bone), the tibia (shin bone), and patella (kneecap). The meniscus, the soft cartilage between the femur and tibia, serves as a cushion and helps absorb shock during motion.
Knee Replacement
Unicompartmental knee replacement is a minimally invasive surgery in which only the damaged compartment of the knee is replaced with an implant. It is also called a partial knee replacement.
Others
Patellar Tendon Repair
Patella tendon rupture is the rupture of the tendon that connects the patella (knee cap) to the top portion of the tibia (shin bone). The patellar tendon works together with the quadriceps muscle and the quadriceps tendon to allow your knee to straighten out.
Click on the topics below to find out more from the orthopaedic connection website of American Academy of Orthopaedic Surgeons.
- ACL Injury: Should it be fixed?
- Activities After a Knee Replacement
- Additional Resources on the Knee
- Adolescent Anterior Knee Pain
- Arthritis of the Knee
- Care of the Aging Knee: Baby Boomers May Need Lifestyle Changes
- Cemented and Cementless Knee Replacement
- Deep Vein Thrombosis
- Frequently Asked Questions about Osteoarthritis of the Knee
- Goosefoot (Pes Anserine) Bursitis of the Knee
- Knee Arthroscopy
- Knee Arthroscopy Exercise Guide
- Knee Implants
- Knee Replacement Exercise Guide
- Kneecap (Prepatellar) Bursitis
- Meniscal Tear
- Meniscal Transplants
- Minimally Invasive Total Knee Replacement
- Nonsurgical Treatment Options for Osteoarthritis of the Knee
- Orthopaedists Research Female Knee Problems
- Osgood-Schlatter Disease (Knee Pain)
- Osteonecrosis of the Knee
- Posterior Cruciate Ligament (PCL) Tear
- Rotating Platform/Mobile-bearing Knees
- Runner’s Knee (Patellofemoral Pain)
- Surgical Treatment of Osteoarthritis of the Knee
- The Knee
- Total Knee Replacement
- Unstable Kneecap
- Viscosupplementation Treatment for Arthritis