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We provide information to help patients and caregivers to understand of knee anatomy, associated symptoms, and joint arthroplasty.

Knee Bones

  • There are four bones to make up the knee joint; the tibia (shine bone), femur (thigh bone), patella (kneecap) and fibular (on the outer side of the shine). They support the body and transfer forces between the hip and foot, allowing the leg to move smoothly and efficiently.


The knee is a modified hinge joint, a type of synovial joint, which is composed of three functional compartments: the patellofemoral articulation, consisting of the patella, or "kneecap", and the patellar groove on the front of the femur through which it slides; and the medial and lateral tibiofemoral articulations linking the femur, or thigh bone, with the tibia, the main bone of the lower leg. The joint is bathed in synovial fluid which is contained inside the synovial membrane called the joint capsule. The posterolateral corner of the knee is an area that has recently been the subject of renewed scrutiny and research.

The knee is the largest joint and one of the most important joints in the body. It plays an essential role in movement related to carrying the body weight in horizontal (running and walking) and vertical (jumping) directions.

At birth, the kneecap is just formed from cartilage, and this will ossify (change to bone) between the ages of three and five years. Because it is the largest sesamoid bone in the human body, the ossification process takes significantly longer.

  • Articular bodies
    • The articular bodies of the femur are its lateral and medial condyles. These diverge slightly distally and posteriorly, with the lateral condyle being wider in front than at the back while the medial condyle is of more constant width. The radius of the condyles' curvature in the sagittal plane becomes smaller toward the back. This diminishing radius produces a series of involute midpoints (i.e. located on a spiral). The resulting series of transverse axes permit the sliding and rolling motion in the flexing knee while ensuring the collateral ligaments are sufficiently lax to permit the rotation associated with the curvature of the medial condyle about a vertical axis.
    • The pair of tibial condyles are separated by the intercondylar eminence composed of a lateral and a medial tubercle.
    • The patella is inserted into the thin anterior wall of the joint capsule. On its posterior surface is a lateral and a medial articular surface, both of which communicate with the patellar surface which unites the two femoral condyles on the anterior side of the bone's distal end.
  • Articular capsule
    • The articular capsule has a synovial and a fibrous membrane separated by fatty deposits. Anteriorly, the synovial membrane is attached on the margin of the cartilage both on the femur and the tibia, but on the femur, the suprapatellar bursa or recess extends the joint space proximally. The suprapatellar bursa is prevented from being pinched during extension by the articularis genus muscle. Behind, the synovial membrane is attached to the margins of the two femoral condyles which produces two extensions similar to the anterior recess. Between these two extensions, the synovial membrane passes in front of the two cruciate ligaments at the center of the joint, thus forming a pocket direct inward.
  • Bursae
    • Numerous bursae surround the knee joint. The largest communicative bursa is the suprapatellar bursa described above. Four considerably smaller bursae are located on the back of the knee. Two non-communicative bursae are located in front of the patella and below the patellar tendon, and others are sometimes present.
  • Cartilage
    • Cartilage is a thin, elastic tissue that protects the bone and makes certain that the joint surfaces can slide easily over each other. Cartilage ensures supple knee movement. There are two types of joint cartilage in the knees: fibrous cartilage (the meniscus) and hyaline cartilage. Fibrous cartilage has tensile strength and can resist pressure. Hyaline cartilage covers the surface along which the joints move. Cartilage will wear over the years. Cartilage has a very limited capacity for self-restoration. The newly formed tissue will generally consist of a large part of fibrous cartilage of lesser quality than the original hyaline cartilage. As a result, new cracks and tears will form in the cartilage over time.
  • Menisci
    • The articular disks of the knee-joint are called menisci because they only partly divide the joint space. These two disks, the medial meniscus and the lateral meniscus, consist of connective tissue with extensive collagen fibers containing cartilage-like cells. Strong fibers run along the menisci from one attachment to the other, while weaker radial fibers are interlaced with the former. The menisci are flattened at the center of the knee joint, fused with the synovial membrane laterally, and can move over the tibial surface.
    • The menisci serve to protect the ends of the bones from rubbing on each other and to effectively deepen the tibial sockets into which the femur attaches. They also play a role in shock absorption, and may be cracked, or torn, when the knee is forcefully rotated and/or bent.
  • Ligaments
    • Intracapsular
      • The knee is stabilized by a pair of cruciate ligaments. The anterior cruciate ligament (ACL) stretches from the lateral condyle of femur to the anterior intercondylar area. The ACL is critically important because it prevents the tibia from being pushed too far anterior relative to the femur. It is often torn during twisting or bending of the knee. The posterior cruciate ligament (PCL) stretches from medial condyle of femur to the posterior intercondylar area. Injury to this ligament is uncommon but can occur as a direct result of forced trauma to the ligament. This ligament prevents posterior displacement of the tibia relative to the femur.
      • The transverse ligament stretches from the lateral meniscus to the medial meniscus. It passes in front of the menisci. It is divided into several strips in 10% of cases. The two menisci are attached to each other anteriorly by the ligament. The posterior and anterior meniscofemoral ligaments stretch from the posterior horn of the lateral meniscus to the medial femoral condyle. They pass posteriorly behind the posterior cruciate ligament. The posterior meniscofemoral ligament is more commonly present (30%); both ligaments are present less often.[15] The meniscotibial ligaments (or "coronary") stretches from inferior edges of the mensici to the periphery of the tibial plateaus.
    • Extracapsular
      • The patellar ligament connects the patella to the tuberosity of the tibia. It is also occasionally called the patellar tendon because there is no definite separation between the quadriceps tendon (which surrounds the patella) and the area connecting the patella to the tibia. This very strong ligament helps give the patella its mechanical leverage and also functions as a cap for the condyles of the femur. Laterally and medially to the patellar ligament the lateral and medial retinacula connect fibers from the vasti lateralis and medialis muscles to the tibia. Some fibers from the iliotibial tract radiate into the lateral retinaculum and the medial retinaculum receives some transverse fibers arising on the medial femoral epicondyle.
      • The medial collateral ligament (MCL) stretches from the medial epicondyle of the femur to the medial tibial condyle. It is composed of three groups of fibers, one stretching between the two bones, and two fused with the medial meniscus. The MCL is partly covered by the pes anserinus and the tendon of the semimembranosus passes under it. It protects the medial side of the knee from being bent open by a stress applied to the lateral side of the knee (a valgus force). The lateral collateral ligament (LCL a.k.a. "fibular") stretches from the lateral epicondyle of the femur to the head of fibula. It is separate from both the joint capsule and the lateral meniscus. It protects the lateral side from an inside bending force (a varus force). The anterolateral ligament (ALL) is situated in front of the LCL.

Meniscus and Cartilage

  • The ends of three bones (tibia, femur, and patella) where they touch are covered with articular cartilage, a smooth substance that protects the bones and enables them to move easily.
  • Cartilage is the important part of the knee joint that there are two types of cartilage in the knee: articular cartilage which lines the joint and the meniscus which is a special extra layer of thick cartilage. These act as shock absorbers to reduce the forces going through the bones and reduce friction allowing the bones to move smoothly.
  • The menisci are located between the femur and tibia. These C-shaped wedges act as "shock absorbers" that cushion the joint


  • Ligaments are tough, fibrous connective tissues made of collagen that link bone to bone. In the knee joint, there are the main stabilizing structures preventing excessive movements and instability.

All remaining surfaces of the knee are covered by a thin lining called the synovial membrane. This membrane releases a fluid that lubricates the cartilage, reducing friction to nearly zero in a healthy knee. Normally, all of these components work in harmony. But disease or injury can disrupt this harmony, resulting in pain, muscle weakness, and reduced function.

Knee Pain Associated Causes, Symptoms and Treatment

The knee joint is a weight-bearing joint that withstands large forces during activity, such as running and jumping. A damaged knee joint can cause great disability. Some diseases and injuries are described to the below and severe cases my require surgery.


Osteoarthritis (OA) is commonly known as “wear and tear arthritis” or “degenerative arthritis ".
OA is the most common cause of arthritis pain in knees. The knee joint is surrounded with cartilage that protects the joint and allows for smooth movement. It also absorbs the pressure and shock created by activities like running and walking. When this cartilage wears down from increasing age, obesity, joint injury or bone deformities, among other risk factors, the bones rub together, causing pain and stiffness.


The most common cause of osteoarthritis of the knee is age. Almost everyone will eventually develop some degree of osteoarthritis. However, several factors increase the risk of developing significant arthritis at an earlier age.

  • Age: The ability of cartilage to heal decreases as a person gets older.
  • Weight: Weight increases pressure on all the joints, especially the knees. Every pound of weight you gain adds 3 to 4 pounds of extra weight on your knees.
  • Heredity: This includes genetic mutations that might make a person more likely to develop osteoarthritis of the knee. It may also be due to inherited abnormalities in the shape of the bones that surround the knee joint.
  • Gender: Women ages 55 and older are more likely than men to develop osteoarthritis of the knee.
  • Repetitive stress injuries: These are usually a result of the type of job a person has. People with certain occupations that include a lot of activity that can stress the joint, such as kneeling, squatting, or lifting heavy weights (55 pounds or more), are more likely to develop osteoarthritis of the knee because of the constant pressure on the joint.
  • Athletics: Athletes involved in soccer, tennis, or long-distance running may be at higher risk for developing osteoarthritis of the knee. That means athletes should take precautions to avoid injury. However, it's important to note that regular moderate exercise strengthens joints and can decrease the risk of osteoarthritis. In fact, weak muscles around the knee can lead to osteoarthritis.
  • People with rheumatoid arthritis, the second most common type of arthritis, are also more likely to develop osteoarthritis. People with certain metabolic disorders, such as iron overload or excess growth hormone, also run a higher risk of osteoarthritis.


  • Deep, aching joint pain, sometimes sharp, with activity; the pain can persist at rest
  • A creaking or grating sound in the joint
  • Swelling and stiffness in one or more joints
  • Limited movement; loss of joint flexibility


The goal of treatment is to reduce joint pain and inflammation, and to enhance joint function. Treatments may include medications, dietary supplements, alternative therapies (e.g., acupuncture, relaxation therapy), medical aids (e.g., shock-absorbing shoes, splints or braces), losing weight, exercise and physical therapy and corticosteroid injections. Surgery is the most radical option if one joint is badly damaged or is causing severe symptoms.

  • Exercise: Strengthening the muscles around the knee makes the joint more stable and decreases pain. Stretching exercises help keep the knee joint mobile and flexible.
  • Weight loss: Losing even a small amount of weight, if needed, can significantly decrease knee pain from osteoarthritis.
  • Pain relievers and anti-inflammatory drugs: This includes over-the-counter choices such as acetaminophen (Tylenol), ibuprofen (Advil, Motrin), or naproxen sodium (Aleve). Don't take over-the-counter medications for more than 10 days without checking with your doctor. Taking them for longer increases the chance of side effects. If over-the-counter medications don't provide relief, your doctor may give you a prescription anti-inflammatory drug or other medication to help ease the pain.
  • Injections of corticosteroids: Steroids are powerful anti-inflammatory drugs. Hyaluronic acid is normally present in joints as a type of lubricating fluid.
  • Alternative therapies: Some alternative therapies that may be effective include topical creams with capsaicin, acupuncture, or supplements, including glucosamine and chondroitin.
  • Using devices: There are two types of braces: "unloader" braces, which take the weight away from the side of the knee affected by arthritis; and "support" braces, which provide support for the entire knee.
  • Physical and occupational therapy: If you are having trouble with daily activities, physical or occupational therapy can help. Physical therapists teach you ways to strengthen muscles and increase flexibility in your joint. Occupational therapists teach you ways to perform regular, daily activities, such as housework, with less pain.
  • Surgery: When other treatments don't work, surgery is a good option.


he followings can prevent the development of OA later on in life

  • Maintaining a healthy weight
  • Regular work out such as walking, stretching, swimming and yoga
  • Avoiding repetitive motions and risky activities that may cause joint pain

Rheumatoid Arthritis (RA)

Rheumatoid Arthritis (RA) is a chronic, systemic inflammatory disorder. RA causes when the function of does not work properly. The immune system normally makes antibodies (small proteins) to attack bacteria, viruses and other germs. Antibodies are formed against the synovium (the tissue that surrounds each joint) in people with RA. This causes inflammation in and around the affected joints.
The actual causes of this autoimmune disease are not clear.


Joint pain, stiffness, redness, warmth and swelling; joint deformity; and, small lumps or nodules under the skin.


Treatment for rheumatoid arthritis varies:

  • Relieving pain, improving functional ability and slowing down joint damage
  • Taking a rest can reduce active joint inflammation and pain, and fights fatigue.
  • Exercise is important to maintain muscle strength and flexibility as well as preserving joint mobility.
  • Relieving stress can ease the difficulties of living with a chronic, painful disease
    (e.g., joining a support group, cognitive behavioral therapy, meditation).
  • Joint replacement and Rendon reconstruction help to relieve severe joint damage.


There is no cure for rheumatoid arthritis, but a variety of treatments for RA can slow down the condition and keep joint damage to a minimum.

Anterior Cruciate Ligament (ACL) Injury

Anterior cruciate ligament injuries most commonly occur during sports and outdoor activities that involve sudden stops, jumping or changes in direction. When an ACL occurs, many people hear or feel a “pop” in their knee.


Signs and symptoms of an ACL injury usually include:

  • Extreme pain
  • A lot of immediate swelling from bleeding within the joint, which will feel warm
  • An audible pop or crack at the time of injury, and a feeling of instability
  • Restricted range of motion, with particular difficulty in straightening the leg


Prompt first-aid care can reduce pain and swell immediately after a knee injury. The fowling R.I.C.E. is the self-care model at home:

  • Rest: Taking a rest and protecting the injured or sore area for healing
  • Ice: Applying cold-pack or Ice at least three times (10-20 mins) in a day can reduce pain and swelling
  • Compression: Wrapping the injured or sore area with an elastic bandage (such as an Ace wrap), will help decrease swelling.
  • Elevation: Elevating the injured or sore area on pillows while applying ice when sitting or lying down

Also, seeking medical attention at the earliest possible day. The decision to forego surgery is based on the stability of the knee, the patient’s age, and the activities or occupations in which they are involved.
Many people choose to try to stabilize the knee by building up muscle strength, especially in the quadriceps. Recovering from ACL surgery or reconstruction is extremely variable, but generally, it can be expected that within four to five months, the knee will start to function normally, and kicking movements and sudden turns may be possible. One year post surgery, the knee may feel almost normal, but total perfection is rare.


Many ACL injuries can be prevented if the muscles that surround the knees are strong and flexible. Prevention focuses on proper nerve and muscle control of the knee. Exercises aim to increase muscle power, balance, and improve core strength and stability.

The fowling training tips can reduce the risk of an ACL injury:

  • Train and condition year round
  • Practice proper landing techniques after jumps. This involves bending your knees to absorb the force and keeping them in line with your feet.
  • When you pivot, crouch and bend at the knees and hips. This reduces stress on the ACL.
  • Strengthen your hamstrings and quadriceps. The hamstring muscle is at the back of the thigh; the quadriceps muscle is at the front. These muscles work together to bend or straighten the leg. Strengthening both muscles can better protect the leg against knee injuries.

Posterior Cruciate Ligament Injury – PCL Injury

The posterior cruciate ligament is located in the back of the knee. It is one of the several ligaments that connect the femur to the tibia. The posterior cruciate ligament keeps the tibia from moving backwards too far. An injury to the posterior cruciate ligament requires a powerful force. A common cause of injury is a bent knee hitting a dashboard in a car accident or a football player falling on a knee that is bent.

The typical symptoms of a posterior cruciate ligament injury are:

  • Pain with swelling that occurs steadily and quickly after the injury
  • Swelling that makes the knee stiff and may cause a limp
  • Difficult to walk
  • Feels unstable, like it may “give out”


Joint pain, limited joint function and abnormal appearance of broken leg (e.g., looks shorter, turns outward).


The PCL is torn less frequently than the ACL, although it is much more demanding to repair surgically.

  • Non-surgical treatment
    • ­If you have injured just your posterior cruciate ligament, your injury may heal quite well without surgery Your doctor may recommend simple, nonsurgical options.
    • ­RICE: When you are first injured, the RICE method - rest, ice, gentle compression and elevation — can help speed your recovery.
    • ­Immobilization: Your doctor may recommend a brace to prevent your knee from moving. To further protect your knee, you may be given crutches to keep you from putting weight on your leg.
    • Physical therapy: As the swelling goes down, a careful rehabilitation program is started. Specific exercises will restore function to your knee and strengthen the leg muscles that support it. Strengthening the muscles in the front of your thigh (quadriceps) has been shown to be a key factor in a successful recovery.
  • Surgical treatment
    • ­A doctor may recommend surgery if you have combined injuries. For example, if you have dislocated your knee and torn multiple ligaments including the posterior cruciate ligament, surgery is almost always necessary.­
    • ­Rebuilding the ligament. 
      • Because sewing the ligament ends back together does not usually heal, a torn posterior cruciate ligament must be rebuilt. Your doctor will replace your torn ligament with a tissue graft. This graft is taken from another part of your body, or from another human donor (cadaver). It can take several months for the graft to heal into your bone.
    • ­Procedure
      • Surgery to rebuild a posterior cruciate ligament is done with an arthroscope using small incisions. Arthroscopic surgery is less invasive. The benefits of less invasive techniques include less pain from surgery, less time spent in the hospital, and quicker recovery times. Surgical procedures to repair posterior cruciate ligaments continue to improve. More advanced techniques help patients resume a wider range of activities after rehabilitation.


The following methods may prevent a PCL injury:

  • Warm up and stretch before participating in athletic activities
  • Exercise to strengthen the leg muscles around knee
  • Wear comfortable, supportive shoes that fit your feet and fit your sport

Knee Arthroplasty

Knee arthroplasty is a complex procedure that requires an orthopedic surgeon to make precise measurements and skillfully remove the diseased portions of your bone, in order to shape the remaining bone to accommodate the knee implant. During the procedure, the surgeon builds the artificial knee inside your leg, one component at a time, to create a highly realistic artificial joint.

  • Indications for Knee Replacement Surgery
    • Severe knee pain or stiffness that limits your everyday activities, including walking, climbing stairs, and getting in and out of chairs.
    • Hard to walk more than a few blocks without significant pain and you may need to use a cane or walker
    • Moderate or severe knee pain while resting, either day or night
    • Chronic knee inflammation and swelling that does not improve with rest or medications
    • Failure to substantially improve with other treatments such as anti-inflammatory medications, cortisone injections, lubricating injections, physical therapy, or other surgeries
    • There are no absolute age or weight restrictions for total knee replacement.
  • Evaluation
    • A medical history: Your orthopedic surgeon will gather information about your general health and ask you about the extent of your knee pain and your ability to function.
    • A physical examination: This will assess knee motion, stability, strength, and overall leg alignment.
    • X-rays: These images help to determine the extent of damage and deformity in your knee.
    • Other tests. Occasionally blood tests, or advanced imaging such as a magnetic resonance imaging (MRI) scan, may be needed to determine the condition of the bone and soft tissues of your knee.
  • Preparing for Surgery
    • Medical Evaluation: If a patient decides to have the surgery, an orthopedic surgeon may ask to schedule a complete physical examination before the operation. This is needed to make sure the patient is healthy enough to have the surgery and complete the recovery process. Many patients with chronic medical conditions, like heart disease, may also be evaluated by a specialist, such as a cardiologist, before the surgery.
    • Test: Several tests, such as blood and urine samples, and an electrocardiogram.
    • Medications: Tell about the medications you are taking. He or she will tell which medications you should stop taking and which you should continue to take before surgery.
    • Dental Evaluation: Although the incidence of infection after knee replacement is very low, an infection can occur if bacteria enter your bloodstream. To reduce the risk of infection, major dental procedures (such as tooth extractions and periodontal work) should be completed before your total knee replacement surgery.
    • Urinary Evaluations: People with a history of recent or frequent urinary infections should have a urological evaluation before surgery. Older men with prostate disease should consider completing required treatment before undertaking knee replacement surgery.
    • Social Planning: Although you will be able to walk on crutches or a walker soon after surgery, you will need help for several weeks with such tasks as cooking, shopping, bathing, and doing laundry. If you live alone, your orthopedic surgeon's office, a social worker, or a discharge planner at the hospital can help you make advance arrangements to have someone assist you at home. They also can help you arrange for a short stay in an extended care facility during your recovery if this option works best for you.
    • Home Planning: Several modifications can make your home easier to navigate during your recovery. The following items may help with daily activities:
      • ­Safety bars or a secure handrail in your shower or bath
      • Secure handrails along your stairways
      • A stable chair for your early recovery with a firm seat cushion (and a height of 18 to 20 inches), a firm back, two arms, and a footstool for intermittent leg elevation
      • A toilet seat riser with arms, if you have a low toilet
      • A stable shower bench or chair for bathing
      • Removing all loose carpets and cords
      • A temporary living space on the same floor because walking up or down stairs will be more difficult during your early recovery
  • Surgery description
    • Prepare the bone. The damaged cartilage surfaces at the ends of the femur and tibia are removed along with a small amount of underlying bone.
    • Position the metal implants. The removed cartilage and bone is replaced with metal components that recreate the surface of the joint. These metal parts may be cemented or "press-fit" into the bone.
    • Chronic knee inflammation and swelling that does not improve with rest or medications
    • Resurface the patella. The undersurface of the patella (kneecap) is cut and resurfaced with a plastic button. Some surgeons do not resurface the patella, depending upon the case.
    • Insert a spacer. A medical-grade plastic spacer is inserted between the metal components to create a smooth gliding surface.
  • The information on this page is intended only for patients and caregivers
  • Trademarks appearing on the website are owned, licensed and distributed by Corentec Co., Ltd.
  • Reference : American Academy of Orthopaedic Surgeons (AAOS)