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What Type Of Joint Is The Knee

Functional Classification Of Joints

Types of Synovial Joints || why is the knee not a pure hinge joint?

The functional classification of joints is based on the type and degree of movement that they allow. There are three types of joints in the functional classification: immovable, partly movable, and movable joints.

  • Immovable joints allow little or no movement at the joint. Most immovable joints are fibrous joints. Besides the bones of the cranium, immovable joints include joints between the tibia and fibula in the lower leg and between the radius and ulna in the lower arm.
  • Partly movable joints permit slight movement. Most partly movable joints are cartilaginous joints. Besides the joints between vertebrae, they include the joints between the ribs and sternum .
  • Movable joints allow bones to move freely. All movable joints are synovial joints. Besides the knee, they include the shoulder, hip, and elbow. Movable joints are the most common type of joints in the body.
  • Anterior Cruciate Ligament Injury

    The anterior cruciate ligament is the most commonly injured ligament of the knee. The injury is common during sports. Twisting of the knee is a common cause of over-stretching or tearing the ACL. When the ACL is injured a popping sound may be heard, and the leg may suddenly give out. Besides swelling and pain, walking may be painful and the knee will feel unstable. Minor tears of the anterior cruciate ligament may heal over time, but a torn ACL requires surgery. After surgery, recovery is prolonged and low impact exercises are recommended to strengthen the joint.

    What Kind Of Joint Is The Knee Joint

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    There are three types of joints in the human body: fibrous, cartilaginous and synovial joints. This classification is based on the material used for making the joint. For example, fibrous joints are those that are joined by fibrous ligaments. Cartilaginous joints, on the other hand, are the joints in which…

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    Types Of Movable Joints

    Movable joints can be classified further according to the type of movement they allow. There are six classes of movable joints: pivot, hinge, saddle, plane, condyloid, and ball-and-socket joints. An example of each class, as well as the type of movement it allows, is shown in Figure \.

    Feature: My Human Body

    Of all the parts of the skeletal system, the joints are generally the most fragile and subject to damage. If the cartilage that cushions bones at joints wears away, it does not grow back. Eventually, all of the cartilage may wear away. This is the cause of osteoarthritis, which can be both painful and debilitating. In serious cases, people may lose the ability to climb stairs, walk long distances, perform routine daily activities, or participate in activities they love such as gardening or playing sports. If you protect your joints, you can reduce your chances of joint damage, pain, and disability. If you already have joint damage, it is equally important to protect your joints and limit further damage. Follow these five tips:

  • Maintain a normal, healthy weight. The higher your weight is, the more force you exert on your joints. When you walk, each knee has to bear a force equal to as much as six times your body weight. If a person weighs 200 pounds, each knee bears more than half a ton of weight with every step. Seven in ten knee replacement surgeries for osteoarthritis can be attributed to obesity.
  • Bones Of The Knee Joint

    3D Osteoporosis of the knee joint

    The knee joint is comprised of three bones that interact to allow for hinge-like motion:

    • The tibia . The tibia is the primary weight bearing bone of the lower leg and connects to the bottom of the femur, forming the hinge of the knee joint.
    • The femur . The femur is both the longest and strongest bone in the human body. It supports the upper body weight during standing, walking, or running. Injuries to the femur can take longer to heal than injuries to other bones. The femur is covered in cartilage where it meets with the tibia and patella .
    • The patella . The patella sits at the anterior-most of the knee joint. The patella anatomically lies in the front of the knee, in the groove formed by the two cartilage covered expansions of the lower femur .

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    Implications Of Hinge Joints

    • Unlike other joints, hinge joints permit movement across one plane.
    • Hinge joints allow straightening, bending and flexing of joints. For example, flexing of a finger or a toe.
    • The bones in hinge joints are covered with a protective cartilage and a thick fluid known as synovial fluid. This fluid helps in lubricating the bones, making them move without much friction.
    • All hinge joints include muscles, ligaments and other kinds of tissues that maintain the joint.
    • Hinge joints are considered more steady than ball-and-socket joints, such as hips and shoulder joints. But there is greater movement in ball-and-socket joints.
    • Unlike the movement in hinge joints, the movement in ball-and-socket joints is along more than one plane.
    • Even though hinge joints are considered stable, there are chances of dislocating them. The most commonly dislocated hinge joints occur in parts of hands and feet.
    • Performing regressive sport activities usually affect hinge joints. For example, runners knee.

    Factors That Oppose The Lateral Pull Of The Patella By The Quadriceps

    • The lateral facet of the intercondylar groove is steeper than the media facet, blocking the lateral shift of patella
    • The oblique fibers of vastus medialis oblique
    • Medial patellofemoral ligament


    Static examination

    The patient stands barefoot with knees exposed and the two feet slightly apart. First the patient is inspected while standing for symmetry, skin changes, scars, sinuses and soft tissue swelling.

    From anterior view, the alignment of the knee is inspected. Genu valgum has increased Q-angle which is associated with lateral patella maltracking and subluxation. The Q-angle should be measured to measure the laterally directed forces across the patella.

    The height and the position of the patella should be inspected. A high riding patella is associated with patella sublaxation while a low riding patella is associated with chondromalacia patella. Squinting patella have increased incidence of patellofemoral pain while outfacing patella is associated with habitual sublaxation of the patella.

    Leg Length discrepancy assessment can be done by comparing the level of the pelvic on both sides for pelvic tilt.

    From side view the knee is inspected for genus recarvatum which may indicate general hyperlaxity, in which the beighton score is determined. Lack of full knee extension is associated with patellofemoral arthrosis.

    The feet posture is assessed. Excessive foot pronation is associated with genu valgum and tibia internal rotation.

    Dynamic examination

    Static examination

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    Muscles Acting On The Knee Joint

    Muscles acting on the knee joint

    Popliteus, semimembranosus and semitendinosus, assisted by sartorius and gracilis.
    Lateral rotation Biceps femoris

    The prime flexors of the knee joint are biceps femoris, semitendinosus and semimembranosus, whereas popliteus initiates flexion of the âlocked kneeâ and gracilis and sartorius assist as weak flexors.

    The primary extensor of the knee joint is quadriceps femoris, assisted by the tensor fasciae latae. Quadriceps femoris of four muscle bellies rectus femoris, vastus lateralis, vastus medialis and vastus intermedius, all innervated by the femoral nerve.

    Medial rotation, as discussed earlier, occurs when the knee is in the last stage of extension, with some also occurring when the knee is flexed. It is primarily produced by the actions of popliteus, semimembranosus and semitendinosus, which are assisted by sartorius and gracilis. Lateral rotation is produced by biceps femoris and also occurs when the knee is flexed.

    Now that you have worked out all things knee joint, why not test your new knowledge with our quiz!

    Types Of Hinge Joints

    How knee arthroscopy is carried out
  • The Elbow: The elbow joint connects the upper part of the arm known as humerus, to the two bones in the lower part of the arm known as radius and ulna respectively. This is called the humeroulnar joint. The humeroulnar joint is situated between a notch in the ulna and a notch in the humerus.
  • The Jaw: The jaw is a hinge joint that allows one to open and close their mouth. The jaw can also move from side to side. Although the jawbone is not a hinge joint, the jawbone moves as a result of the hinge joint.
  • The Hand: The interphalangeal joints are the joints that all the fingers together. As human beings utilize hands for daily activities, it is considered to be the most important hinge joint. There are three sets of joints namely, metatarsophalangeal joints, proximal interphalangeal joints and distal interphalangeal joints.
  • The Foot: Just like the hands, the feet also consist of three interphalangeal joints. They have two planters, tendons and other ligaments. Even though toes appear different than fingers, they show two similar movements namely flexion and extension.
  • The Knee: The knee joint connects the thighs to the lower part of the leg. The knee joint is the largest joint in the human body and is different from the other hinge joints. It is different because it not only allows movement like flexion and extension, but also side-to-side movement.
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    Types Of Knee Replacement

    There are four designs of knee joint prostheses

    1. Cruciate-retaining ProsthesisFor the cruciate-retaining prosthesis to give strength in bending, the posterior cruciate ligament must be healthy. As a result, it should not be used in individuals who have pre-existing or intra-operatively diagnosed posterior cruciate impairment.

    Advantageso Tibial impingement and instability are prevented.o Theoretically, maintaining more regular architecture that mimics normal knee.o Bone stock that has been preserved o Posterior cruciate ligament kinesthetic awareness in its natural state

    Disadvantageso Earlier polyethylene degradation can be caused by a tight posterior cruciate ligament.o A weak or torn posterior cruciate ligament causes flexion imbalance and the risk of displacement or dislocation.

    2. Posterior-Stabilized ProsthesisThe posterior cruciate ligament must be sacrificed in the posterior-stabilized total knee replacement design, which is significantly more restricted.

    Advantageso Allows for greater knee flexiono Allows the knee to be more balanced overallo Lower axial rotation and condylar translation

    Disadvantageso Patellar clunk syndrome is a condition that affects the patellar tendon.o Erosion or fracture of the tibial bone

    3. Constrained Nonhinged ProsthesisThe constrained nonhinged prosthesis has a bigger tibial post and a wider femoral cage, which provides more stability and restraint in both the varus-valgus and internal-external rotatory planes.

    Additional Structures Associated With Synovial Joints

    A few synovial joints of the body have a fibrocartilage structure located between the articulating bones. This is called an articular disc, which is generally small and oval-shaped, or a meniscus, which is larger and C-shaped. These structures can serve several functions, depending on the specific joint. In some places, an articular disc may act to strongly unite the bones of the joint to each other. Examples of this include the articular discs found at the sternoclavicular joint or between the distal ends of the radius and ulna bones. At other synovial joints, the disc can provide shock absorption and cushioning between the bones, which is the function of each meniscus within the knee joint. Finally, an articular disc can serve to smooth the movements between the articulating bones, as seen at the temporomandibular joint. Some synovial joints also have a fat pad, which can serve as a cushion between the bones.

    Figure 9.4.2 Bursae:

    A tendon sheath is similar in structure to a bursa, but smaller. It is a connective tissue sac that surrounds a muscle tendon at places where the tendon crosses a joint. It contains a lubricating fluid that allows for smooth motions of the tendon during muscle contraction and joint movements.

    Homeostatic Imbalances Bursitis

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    Cartilage Of The Knee

    There are two types of the cartilage of the knee joint:

  • Articular cartilage is the smooth lining that covers the end of the bone. When the smooth articular cartilage is worn away, knee arthritis is the result. Cartilage is generally a resilient structure that resists damage, but when injured it has a difficult time healing. It can also wear down over time with age.
  • The other type of cartilage in the knee joint is called the meniscus. The meniscus is a shock absorber that sits between the end of the thigh bone and the top of the shin bone.
  • What Type Of Joint Is The Knee

    Knee Joint

    The knee is what is known as a synovial hinge joint, but what does that mean?

    A synovial joint has a joint capsule which is like a sac surrounding the joint. The capsule contains synovial fluid which nourishes and lubricates the joint allowing it to move smoothly and painlessly – a bit like the oil in your car.

    A hinge joint typically allows motion in one plane, flexion and extension. The knee is the largest hinge joint in the body and is slightly unusual as it also allows a small amount of rotation.

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    Osteoarthritis Of The Knee

    The knee is one of the joints most commonly affected by osteoarthritis. Cartilage in the knee may begin to break down after sustained stress, leaving the bones of the knee rubbing against each other and resulting in osteoarthritis. Nearly a third of US citizens are affected by osteoarthritis of the knee by age 70.

    Obesity is a known and very significant risk factor for the development of osteoarthritis. Risk increases proportionally to body weight. Obesity contributes to OA development, not only by increasing the mechanical stress exerted upon the knees when standing, but also leads to increased production of compounds that may cause joint inflammation.

    Parity is associated with an increased risk of knee OA and likelihood of knee replacement. The risk increases in proportion to the number of children the woman has birthed. This may be due to weight gain after pregnancy, or increased body weight and consequent joint stress during pregnancy.

    Flat feet are a significant risk factor for the development of osteoarthritis. Additionally, structural deformities, advanced age, female sex, past joint trauma, genetic predisposition, and certain at-risk occupations may all contribute to the development of osteoarthritis in general.

    What You Need To Know

    • The most common causes of knee pain are related to aging, injury or repeated stress on the knee.
    • Common knee problems include sprained or strained ligaments, cartilage tears, tendonitis and arthritis.
    • Diagnosing a knee injury or problem includes a medical examination and usually the use of a diagnostic procedure such as an x-ray, MRI, CT scan or arthroscopy.
    • Both non-operative and surgical treatment options are available to treat knee pain and problems depending on the type and severity of the condition.

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    Blood Supply And Lymphatics

    The structures of the knee receive much of their blood supply from a plexus of arteries with branches from the popliteal artery and femoral artery. The popliteal artery branches off the superficial femoral artery and runs posteriorly across the knee joint. The superior medial, inferior medial, superior lateral, and inferior lateral genicular arteries branch off the popliteal artery and travel anteriorly to anastomose with other parts of the plexus. Also, a descending genicular artery branches off the superficial femoral artery and anastomoses anteriorly with the other genicular arteries. The anterior and posterior tibial recurrent arteries travel laterally from the anterior tibial artery and also contribute to the plexus. The middle genicular artery travels directly into the joint. In addition, the sural arteries branch off the popliteal artery and travel inferiorly away from the midline. The flexor muscles are supplied mainly by the inferior gluteal, perforating, popliteal, deep femoral, and sural arteries. The femoral artery primarily supplies the extensor muscles.

    Much of the lymphatic drainage from the knee and lower leg travel to the popliteal lymph nodes in the popliteal fossa. The popliteal nodes, along with other knee and lower limb lymphatics, drain into the deep inguinal and sub inguinal nodes. The lymphatic system primarily follows vasculature.

    Assessment Of Posterior Cruciate Ligament

    Knee Joint – Part 1 – 3D Anatomy Tutorial

    Posterior drawer test and tibial sag tests can determine the integrity of the posterior cruciate ligament. Similar to anterior drawer test, the knee should be flexed 90 degrees and the tibia is pushed backwards. If the tibia can be pushed posteriorly, then the posterior drawer test is positive. In tibial sag test, both knees are flexed at 90 degrees with the person in supine position and bilateral feet touching the bed. Bilateral knees are then watch for posterior displacement of tibia. If the affected tibia slowly displaced posteriorly, the posterior cruciate ligament is affected.

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    How Knee Replacement Is Performed

    The surgery is usually done under general anesthesia. Other types of anesthesia include spinal, epidural, or regional nerve block.

    The steps of Knee Replacement are as follow:

    Preparing the JointBroken cartilaginous surfaces on the femur and tibia endings, as well as a small fragment of bone under them, are excised.

    Placing the Metallic ImplantMetallic components are used to replace the excised cartilage and bone, re-creating the joints surface. Metallic pieces can be glued or pressed-fit into the bone.

    Patellar ResurfacingWith a plastic screw, the undersurface of the patella is sliced and resurfaced. Based on the circumstances, sometimes, surgeons dont need to resurface the kneecap.

    Placing a SpacerTo produce a smoother sliding interface, a plastic spacer is put between the metallic components.

    What Aggravates Hip Bursitis

    Trochanteric bursitis can result from one or more of the following events: Injury to the point of the hip. This can include falling onto the hip, bumping the hip into an object, or lying on one side of the body for an extended period. Play or work activities that cause overuse or injury to the joint areas.

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