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.
Meniscal Tears
There are two wedge-shaped cartilage pieces present between the thighbone and the shinbone each called a meniscus. The menisci stabilize the knee joint and act as shock absorbers.
Posterior Cruciate Ligament (PCL) Injuries
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.
Osgood-Schlatter Disease
Osgood-Schlatter disease refers to an overuse injury that occurs in the knee of growing children and adolescents. This is caused by inflammation of the tendon located below the kneecap (patellar tendon). Children and adolescents who participate in sports such as soccer, gymnastics, basketball, and distance running are at a higher risk of this disease.
Runner's Knee
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. Patellofemoral pain is a common complaint among runners, jumpers, and other athletes such as skiers, cyclists, and soccer players; thus the common name, runner’s knee.
Shin Splints
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).
Bowed Legs
Bowed leg is a bony deformity resulting in outward curvature of one or both knees of the lower legs. It is commonly seen in toddlers and overweight adolescents.
Goosefoot Bursitis of the Knee
A bursa is a small fluid-filled sac found between soft tissues and bones. It lubricates and acts as a cushion, decreasing the friction between bones when they move. Bursitis refers to the inflammation and swelling of the bursa. Goosefoot bursitis or pes anserine bursitis is the inflammation of the bursa present between the tendons of the hamstring muscle and the tibia (shinbone) on the inner side of the knee.
Kneecap Bursitis
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.
Osteonecrosis of the Knee
Osteonecrosis is a condition in which the 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 60 years of age are commonly affected, three times more often than men.
Fractures of the Tibia
The lower leg is made up of two long bones called the tibia and fibula that extend between the knee and ankle. The tibia or shinbone is the larger of the two bones. It bears most of the body’s weight and helps form the ankle joint and knee joint.
Femur Fracture
The femur or thigh bone is the longest and strongest bone in the body, connecting the hip to the knee. A femur fracture is a break in the femur. The distal femur is the lower part of the thigh bone which flares out like an upside-down funnel and its lower end is covered by a smooth, slippery articular cartilage that protects and cushions the bone during movement.
Pediatric Femur Fracture
The femur or thighbone is the largest and strongest bone in the human body. Pediatric thighbone fractures can occur when your child falls hard on the ground and gets hit during sports, automobile accidents and child abuse. In a thighbone fracture, the broken bones may be aligned or displaced.
Growth Plate Fracture
Growth plates are areas of soft, cartilaginous tissues present at the end of long bones in growing children. These cartilage tissues or soft bones later harden to become solid bones in adulthood once growing has completed. A fracture of these bones is termed a growth plate fracture.
Knee arthroscopy
Knee arthroscopy is a common surgical procedure performed using an arthroscope, a viewing instrument, to diagnose or treat a knee problem. It is a relatively safe procedure and you will usually be discharged from the hospital on the same day of surgery.
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 an artificial prosthesis.
Anterior Cruciate Ligament Reconstruction
ACL (anterior cruciate ligament) 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.
Unicondylar Knee Replacement
Unicompartmental knee replacement or unicondylar 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. The knee can be divided into three compartments: patellofemoral, the compartment in front of the knee between the knee cap and thigh bone, medial compartment, on the inside portion of the knee, and lateral compartment which is the area on the outside portion of the knee joint.
Revision Knee Replacement
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.
Patient Specific Knee Replacement
Patient Specific Knee Replacement is a newer technology in total knee replacement surgery. It is an advanced procedure using an individualized patient-specific knee implant for replacement of all three components of the knee.
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Robotic Assisted Knee Replacement
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.
Minimally Invasive Knee Joint Replacement
Total knee replacement is a very successful surgical treatment for knee arthritis. Over the years, minimally invasive knee replacement surgical techniques have been developed to lessen tissue trauma and improve patient outcomes.