Knee Ligaments – Anatomy, Types, Functions,

Knee Ligaments – Anatomy, Types, Functions,

Knee Ligaments/Ligaments are bands of tough, elastic connective tissue that surround a joint to give support and limit the joint’s movement. Knee ligaments are thick strands of tissue made of collagenous fibers that connect the upper leg bones to the lower ones. There are four main knee joint ligaments: the lateral collateral ligament (LCL), medial collateral ligament (MCL), anterior cruciate ligament (ACL), and the posterior cruciate ligament (PCL). Collectively, their main function is to restrain knee movement in order to provide joint stability.

The knee is the largest joint in the body. It is a compound synovial joint that consists of the tibiofemoral joint and the patellofemoral joint. It primarily serves as a hinge joint which allows flexion and extension as well as various other movements. It joins the lower leg and thigh bilaterally and is an essential component of efficient bipedal movements such as walking, running, and jumping. The anatomical function and stability of the knee depend on muscles, bones, ligaments, cartilage, synovial tissue, synovial fluid, and other connective tissues. The 4 main stabilizing ligaments of the knee are the anterior cruciate (ACL), posterior cruciate (PCL), medial collateral (MCL), and lateral collateral  (LCL). The ACL attaches at the lateral condyle of the femur and the intercondyloid eminence of the tibia, and functions to prevent anterior translation of the tibia on the femur. The PCL attaches at the medial condyle of the femur and the posterior intercondylar area of the tibia, and functions to prevent forward displacement of the femur on the tibia.

Ligaments Of Knee Joint

Ligaments and menisci

The ligaments of the knee joint can be divided into two groups; extracapsular ligaments and intracapsular ligaments. These ligaments connect the femur and tibia, holding them in place, providing stability, and preventing dislocation.

Extracapsular ligaments are found outside the joint capsule and include the patellar ligament, lateral and medial collateral ligaments, and oblique and arcuate popliteal ligaments. Intracapsular ligaments are found inside the joint capsule, with the cruciate ligaments being the most well known of this subgroup.

Patellar ligament

The patellar ligament is a strong, thick fibrous band that is a distal continuation of the quadriceps femoris tendon. It is found superficial/anterior to the infrapatellar bursa and extends from the apex of the patella to the tibial tuberosity.

Along its outer margins, the patellar ligament blends with the medial and lateral patellar retinacula, which are extensions of the vastus medialis and lateralis muscles, respectively, as well as the overlying fascia. The patellar ligament plays a major role in stabilizing the patella and preventing its displacement.

Lateral (fibular) collateral ligament

The lateral (fibular) collateral ligament is a strong ligament that originates from the lateral epicondyle of the femur, just posterior to the proximal attachment of the popliteus, and extends distally to attach on the lateral surface of the fibular head.

As it attaches to the fibular head, the ligament splits the tendon of biceps femoris muscle in two. The lateral collateral ligament is found deep to the lateral patellar retinaculum, and superficial to the tendon of popliteus muscle, which separates the ligament from the lateral meniscus.

Medial (tibial) collateral ligament

The medial( (tibial) collateral ligament is the strong, flat ligament of the medial aspect of the knee joint. The medial collateral ligament, in addition to its literal counterpart, acts to secure the knee joint and prevent excessive sideways movement by restricting external and internal rotation of the extended knee. The medial collateral ligament has sometimes divided the literature into superficial and deep parts:

  • Superficial medial collateral ligament – originates just proximal the medial epicondyle of the femur. This ligament has two attachment points; a proximal attachment on the medial condyle of the tibia, and a distal attachment on the medial shaft of the tibia. Anteriorly, the superficial medial collateral ligament blends with the medial patellar retinaculum and the medial patellofemoral ligament, which courses from the medial femoral condyle to attach onto the medial border of the patella.
  • Deep medial collateral ligament – a vertical thickening of the knee joint capsule found underneath the superficial medial collateral ligament. It originates from the area of the distal femur, then attaches to the medial meniscus, and terminates on the proximal tibia. These two parts of the ligament are defined as meniscofemoral and meniscotibial ligaments (see below).

Oblique popliteal ligament

The oblique popliteal ligament (Bourgery ligament) is an expansion of the semimembranosus tendon which originates posterior to the medial tibial condyle and reflects superiorly and laterally to attach on the lateral condyle of the femur. As it spans the intercondylar fossa, the oblique popliteal ligament reinforces the posterior part of the joint capsule and blends with its central portion.

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Arcuate popliteal ligament

Arcuate popliteal ligament is a thick, fibrous band that arises on the posterior aspect of the fibular head and arches superiorly and medially to attach on the posterior side of the joint capsule of the knee. The arcuate popliteal ligament reinforces the posterolateral part of the joint capsule, and together with the oblique popliteal ligament, prevents overextension of the knee joint.

Cruciate ligaments

The paired cruciate ligaments got their name due to the fact that they cross each other obliquely within the joint in a way that resembles a cross (latin = crux), or a letter X. They cross within the joint capsule, however remain external to the synovial cavity. The cruciate ligaments are divided as follows:

  • Anterior cruciate ligament – arises from the anterior intercondylar area of the tibia just behind the attachment of the medial meniscus, and extends posterolaterally and proximally to attach on the posterior part of the medial surface of the lateral femoral condyle. As it crosses to the other side of the knee joint, the ligament passes underneath the transverse ligament (see below) and blends with the anterior horn of the lateral meniscus. The anterior cruciate ligament is important to prevent posterior rolling and displacement of the femoral condyle during flexion, as well as to prevent hyperextension of the knee joint.
  • Posterior cruciate ligament – arises from the posterior intercondylar area of the tibia and extends anteromedially and proximally to attach on the anterior part of the lateral surface of the medial femoral condyle. This ligament is almost twice as strong and has better blood supply than the anterior cruciate ligament. The posterior cruciate ligament has the opposite function of the anterior cruciate ligament, serving to prevent anterior rolling and displacement of the femoral condyle during extension, as well as to prevent hyperflexion of the knee joint.

Menisci

The menisci are fibrocartilaginous crescent-shaped plates found between the articular surfaces of the femur and tibia and serve to provide their congruence and shock absorption. The menisci are thick and vascularized in their outer one third, while their inner two-thirds are thinner and avascular. Additionally, the inner two-thirds contain radially organized collagen bundles, whereas the outer third contains larger circumferentially arranged bundles. Thus, it is believed that the inner portion is more adapted for weight-bearing and resisting compressive forces, while the outer portions are suited for resisting tensional forces. The menisci are divided as follows:

  • Medial meniscus – a C-shaped, almost semicircular fibrocartilaginous plate that overlies the surface of the medial tibial plateau. Its anterior horn attaches on the anterior intercondylar area of tibia and blends with the anterior cruciate ligament. Its posterior horn is attached to the posterior intercondylar area of the tibia, between the attachments of the lateral meniscus and the posterior cruciate ligament.
  • Lateral meniscus – an almost circular fibrocartilaginous plate that overlies the surface of the lateral tibial plateau. Its anterior horn also attaches to the anterior intercondylar area of tibia and partially blends with the anterior cruciate ligament. Similarly, its posterior horn attaches to the posterior intercondylar areas anterior to the posterior horn of the medial meniscus.
  • Transverse ligament – connects the menisci anteriorly extending from the anterior margin of the lateral meniscus to the anterior horn of the medial meniscus. Its exact role is uncertain but it is thought that these ligaments stabilize the menisci during knee movements and decrease tension generated in the longitudinal circumferential fibers.
  • meniscofemoral ligaments – are the superior portions of the distal medial collateral ligament extending from the posterior horn of the lateral meniscus to the lateral aspect of the medial femoral condyle. They are divided into two ligaments; an anterior meniscofemoral ligament (of Humphry) that courses anterior to the posterior cruciate ligament; and a posterior menisco femoral ligament (of Wrisberg), that runs posterior to the posterior cruciate ligament.
  • Meniscotibial (coronary) ligaments – are the inferior portions of the distal medial collateral ligament, extend between the margin of the lateral meniscus and the peripheral area of the tibial condyles. It is comprised of a medial and lateral meniscotibial (coronary) ligament.
  • Patellomeniscal ligament – comprised of a medial and lateral patellomeniscal ligament, often described as simply medial and lateral ligaments. These ligaments run from the inferior third of the patella to insert on the anterior portion of the medial and lateral meniscus, respectively.
  • Ligamentum mucosum – consists of two alar folds that attach onto the infrapatellar fat pad, holding it in position. This structure is an embryonic remnant that separates the medial and lateral compartments of the knee.
  • Popliteofibular ligament – located on the posterolateral aspect of the knee joint, extending from the popliteus muscle to the medial aspect of the fibula.
  • Fabellofibular ligament – arises from a small sesamoid bone on the posterior aspect of the lateral supracondylar ridge of the femur and inserts distally on the posterolateral edge of the styloid process of the fibula.
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Knee Conditions

  • Chondromalacia patella (also called patellofemoral syndrome) – Irritation of the cartilage on the underside of the kneecap (patella), causing knee pain. This is a common cause of knee pain in young people.
  • Knee osteoarthritis – Osteoarthritis is the most common form of arthritis, and often affects the knees. Caused by aging and wear and tear of cartilage, osteoarthritis symptoms may include knee pain, stiffness, and swelling.
  • Knee effusion – Fluid buildup inside the knee, usually from inflammation. Any form of arthritis or injury may cause a knee effusion.
  • Meniscal tear – Damage to a meniscus, the cartilage that cushions the knee, often occurs with twisting the knee. Large tears may cause the knee to lock.
  • ACL (anterior cruciate ligament) strain or tear – The ACL is responsible for a large part of the knee’s stability. An ACL tear often leads to the knee “giving out,” and may require surgical repair.
  • PCL (posterior cruciate ligament) strain or tear – PCL tears can cause pain, swelling, and knee instability. These injuries are less common than ACL tears, and physical therapy (rather than surgery) is usually the best option.
  • MCL (medial collateral ligament) strain or tear – This injury may cause pain and possible instability to the inner side of the knee.
  • Patellar subluxation – The kneecap slides abnormally or dislocates along the thigh bone during activity. Knee pain around the kneecap results.
  • Patellar tendonitis – Inflammation of the tendon connecting the kneecap (patella) to the shin bone. This occurs mostly in athletes from repeated jumping.
  • Knee bursitis – Pain, swelling, and warmth in any of the bursae of the knee. Bursitis often occurs from overuse or injury.
  • Baker’s cyst – Collection of fluid in the back of the knee. Baker’s cysts usually develop from a persistent effusion as in conditions such as arthritis.
  • Rheumatoid arthritis – An autoimmune condition that can cause arthritis in any joint, including the knees. If untreated, rheumatoid arthritis can cause permanent joint damage.
  • Gout – A form of arthritis caused by buildup of uric acid crystals in a joint. The knees may be affected, causing episodes of severe pain and swelling.
  • Pseudogout – A form of arthritis similar to gout, caused by calcium pyrophosphate crystals depositing in the knee or other joints.
  • Septic arthritis – An infection caused by bacteria, a virus, or fungus inside the knee can cause inflammation, pain, swelling, and difficulty moving the knee. Although uncommon, septic arthritis is a serious condition that usually gets worse quickly without treatment.

Knee Tests

  • Physical examination – By examining the location of knee pain and looking for swelling or abnormal movement, a doctor gathers information about potential causes of damage or stress on the knee.
  • Drawer test – With the knee bent, a doctor can pull (anterior drawer test) and push (posterior drawer test) the lower leg while holding the foot stable to check the stability of the ACL and PCL knee ligaments.
  • Valgus stress test – Pushing the calf outward while holding the thigh stable, a doctor can check for injury to the medial collateral ligament (MCL). Pushing the calf inward (varus stress test), a doctor can look for injury to the lateral collateral ligament (LCL).
  • Knee X-ray – A plain X-ray film of the knee is typically the best initial imaging test for most knee conditions.
  • Magnetic resonance imaging (MRI scan) – Using high-energy magnetic waves, an MRI scanner creates highly detailed images of the knee and leg. An MRI scan is the most-often used method of detecting ligament and meniscal injuries.
  • Arthrocentesis of the knee (joint aspiration) – A needle is inserted into the joint space inside the knee, and fluid is drawn out. Various forms of arthritis may be diagnosed through knee arthrocentesis.
  • Arthroscopy – A surgical procedure that allows examination of the knee with an endoscope.
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Knee Treatments

  • RICE therapy – Rest (or reducing daily activities), Ice, Compression (as with bandage support) and Elevation. RICE is good initial therapy for many knee conditions.
  • Pain medicines – Over-the-counter or prescription pain relievers such as acetaminophen (Tylenol), ibuprofen (Motrin), and naproxen (Aleve) can treat most knee pain.
  • Physical therapy – An exercise program can strengthen the muscles surrounding the knee, increasing the knee’s stability.
  • Cortisone injection – Injecting steroids into the knee can help reduce pain and swelling.
  • Hyaluronan injection –  Injection of this “goo” material into the knee may reduce pain from arthritis and delay the need for knee surgery in some people.
  • Knee surgery – Surgery may be done to correct a variety of knee conditions. Surgery can replace or repair a torn ligament, remove an injured meniscus, or entirely replace a severely damaged knee. Surgery may be done with a large incision (open) or smaller incisions (arthroscopic).
  • Arthroscopic surgery – An endoscope (flexible tube with surgical tools on its end) is inserted into the knee joint. Arthroscopic surgery has a shorter recovery and rehabilitation period than open surgery.
  • ACL repair –  A surgeon uses a graft (cut from your own body or a donor’s body) to replace the torn ACL.

Movements

There are four main movements that the knee joint permits:

  • Extension:  Produced by the quadriceps femoris, which inserts into the tibial tuberosity.
  • Flexion: Produced by the hamstrings, gracilis, sartorius and popliteus.
  • Lateral rotation: Produced by the biceps femoris.
  • Medial rotation: Produced by five muscles; semimembranosus, semitendinosus, gracilis, sartorius and popliteus.

How do I get ready for a knee ligament repair?

  • Your healthcare provider will explain the procedure to you and offer you the chance to ask any questions that you might have about the procedure.
  • You will be asked to sign a consent form that gives your permission to do the procedure. Read the form carefully and ask questions if something is not clear.
  • In addition to complete medical history, your healthcare provider may perform a complete physical exam to ensure you are in good health before undergoing the procedure. You may undergo blood tests or other diagnostic tests.
  • Tell your healthcare provider if you are sensitive to or are allergic to any medicines, latex, tape, and anesthetic agents (local and general).
  • Tell your healthcare provider of all medicines (prescribed and over-the-counter) and herbal supplements that you are taking.
  • Tell your healthcare provider if you have a history of bleeding disorders or if you are taking any anticoagulant (blood-thinning) medicines, aspirin, or other medicines that affect blood clotting. It may be necessary for you to stop these medicines before the procedure.
  • If you are pregnant or suspect that you are pregnant, you should notify your healthcare provider.
  • You will be asked to fast for 8 hours before the procedure, generally after midnight.
  • You may receive a sedative prior to the procedure to help you relax. Because the sedative may make you drowsy, you will need to arrange for someone to drive you home.
  • You may meet with a physical therapist prior to your surgery to discuss rehabilitation.
  • Arrange for someone to help around the house for a week or two after you are discharged from the hospital.
  • Based on your health condition, your healthcare provider may request other specific preparations.

References

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