Knee anatomy and pathology Flashcards
What are the features of typical synovial joint?
A typical synovial joint has articular cartilage covering the articular surfaces involved, a synovial membrane covering all other surfaces, synovial fluid and an articular capsule which has an outer fibrous layer lined by the serous synovial membrane. Joint capsules may have folds to facilitate movement and ligaments provide stability.
What is the function of articular cartilage?
made up of special hyaline cartilage, it ensures the ends of the bones in the joint ae lubricated, slightly compressible and that they experience almost no friction. It is not surrounded by perichondrium and is partly vascularised.
What is the function of the synovial membrane?
a serous membrane that lines all non-articular structures on the joint interior. It has a rich blood supply and secretes synovial fluid.
What is the function of synovial fluid?
Nutrient to the articular cartilage, contains hyaluronic acid, viscosity varies inversely to stress.
What is the function of ligaments?
provide stabilisation without limiting too much motion. Capsular ligaments are simply thickening of the joint capsule itself. They are either elongated bands or triangles. Their fibres radiate from a small spot on one articular bone to another.
What are the six classes of synovial joints?
Ball & socket, Condylar, Saddle (sellar), Plane (gliding), Hinge (ginglymi), pivot (trochoid).
Describe a ball and socket joint.
A spheroidal joint. Can move in three planes therefore is multi axial. Flexion and extension, adduction and abduction, medial and lateral rotation and circumduction. Eg hip joint.
Describe a condylar joint
Is an ellipsoid joint. An oval convex surface articulates with an elliptical concavity. Can move in two directions at right angles. Permits flexion, extension, adduction and abduction. Movement in one plane is usually freer than the other. Circumduction (axial rotation) is usually more restricted than saddle joints. The metacarpophalangeal joints (knuckles) are an example.
Describe a saddle joint
Primary movement occurs in two planes but because of the articular geometry there is a degree of axial rotation. They are bi axial joints. Eg first carpometcarpal joint. It allows adduction, abduction, flexion and extension.
Describe a plane joint
Gliding or sliding movements. Opposed surfaces are flat or almost flat. Almost always small. Eg ACJ.
Describe a hinge joint
Allows movement in one plane so is uni or mono axial. The joint capsule is thin and lax in the directions of movement (anterior and posterior) but are joined by strong laterally placed collateral ligaments. Eg elbow.
Describe a pivot joint
Permit rotation around a central axis and are thus uni axial. A rounded process of bone rotates within a sleeve or sling. Eg atlantoaxial joint.
What is a simple joint?
(most synovial joints) have one pair of articular surfaces.
What is a compound joint?
have more than one pair. Composed of more than two bones. Often synonymous with complex joints. For example, knee, elbow and radio carpal.
What is a complex joint?
A joint with a disc; a joint with 3 or more elements; 2 joints acting as one. Eg knee, elbow
Compare an articular disc and a meniscus.
An articular disc is made up of fibrocartilage that grows inwards from the joint capsule and forms a pad between the two articulating bones. Examples include TMJ, distal radioulnar joint and both ends of the clavicle.
A meniscus is fibrocartilage that grows inward from the joint capsule but does not cross the joint. For example, the knee joint.
What is a bursa?
A bursa is a fibrous sac filled with synovial fluid that separates adjacent muscles or where tendons passes over a bone.
What is the function of a bursa?
It cushions muscles, helps tendons slide more easily and can be tendon sheaths (elongated bursa that wrap around a tendon)
What are the five different bone shapes and examples?
Long bones are tubular eg humerus
Short bones are cuboidal and found only in the tarsus and carpus.
Flat bones usually serve protective functions. Eg cranium
Irregular bones have various chapes eg facial bones
Sesamoid bones develop in tendons and can be found where tendons cross the ends of long bones. The protect tendons from excessive wear and are often change the angles of tendons as they pass to their attachments. Eg patella
Where to bone landmarks occur?
Wherever tendons, ligaments and fascia are attached, or where arteries lie adjacent to or enter bones.
What is a condyle?
Rounded knuckle like articular area, often occurs in pairs eg lateral and medial femoral condyles.
What is a tuberosity?
Large rounded elevation.
What is a tubercle?
Small raised eminence eg greater tubercle of the humerus.
What is a groove?
Elongated depression or furrow eg radial groove of the humerus.
What type of joint is the knee joint?
Primarily hinge type synovial joint however there is an element of gliding and rolling with rotation about the vertical axis.
What is the most important muscle in stabilizing the knee joint?
the quadriceps femoris, in particular the inferior fibres of the vastus medialis and lateralis.
What is the most stable position of the knee?
The erect, extended position of the joint is most stable as the articular surfaces are congruent, the primary ligaments (cruciate and collateral) are taut and the many tendons around the joint provide a splinting effect.
Where is the opening in the fibrous layer of the knee joint capsule and why is it there?
posterior to the lateral tibial condyle where the Tendon of popliteus passes out of the joint capsule to attach to the tibia.
Describe the fibrous capsule of the knee anteriorly
The quadriceps tendon, Patella and patella ligament replace the fibrous layer anteriorly, that is to say the fibrous layer is continuous with the lateral and medial margins of these structures.
