Basic anatomy of MSK Flashcards
Define joints
Joints
are the space or connection or junction between two bones (or bone-cartilage, bone-teeth or bone-ligament).
What determines range of motion at a given joint?
The tighter the bones fit at the point of contact, the stronger and more stable the joint.
The looser the fit, the greater the range of movement at the joint. ^[range of movement is also dependent on how the articulating bones fit together, the flexibility of soft tissues that bind the bones together, and the position of surrounding ligaments, muscles and tendons]
How are joints named and classified?
- joints are commonly named according to bones or portions of bones articulating at the joint e.g. glenoid fossa of scapula and head of humerus = glenohumeral joint
Joints are classified by the type of connective tissue that connects the bones and this determines the balance of mobility and stability.
There are three key types of joints, synarthroses, amphiarthroses, and diarthrodial or synovial joints.
Define synarthroses
Synarthroses or fibrous joints
are joints where adjacent bones are directly connected by fibrous connective tissue. There is no synovial cavity.
Examples include:
- an interlocking suture line between adjacent bones (e.g. skull). Sutures consists of strong fibrous tissue between skull bones e.g. sagittal suture
- Syndesmoses which consist of a fibrous ligament or membrane connecting bones e.g. interosseous membrane between the radius and ulna
- Gomphoses which consists of periodontal ligaments tethering teeth onto sockets e.g. roots of teeth in sockets of mandible
What is another name for synarthroses?
Fibrous joints
Define and describe amphiarthroses
Amphiarthroses or cartilaginous joints
can be defined by the presence of cartilage, either hyaline or fibro-, between articulating bones. There is no synovial joint cavity.
- synchrondrosis or primary cartilaginous joints are connected by hyaline cartilage. Some are temporary e.g. epiphyseal plate, first sternocostal joint, or permanent e.g. costochrondral joints
- symphysis or secondary cartilaginous joints are joined by fibrocartilage e.g. pubic symphysis, interbody joints between vertebral bodies and intervertebral discs
What is another name for amphiarthroses?
Cartilaginous joints
Describe synovial joints
Synovial or Diarthrodial Joints
are freely movable, but limited by surrounding joint capsule, ligaments and muscles.
Synovial joints are characterized by:
- articular cartilage covers the surfaces of the articulating bones, protects the ends of the bones and enables them to move against each other with minimal friction. Hyaline cartilage does not receive a blood supply or innervation. Therefore, it relies on synovial fluid for nutrition or waste removal.
- synovial membrane lines the capsule’s inner surface and covers all surfaces within the capsule, except for the articular cartilage. The synovial membrane secretes synovial fluid. It is well vascularised.
- synovial fluid
- joint capsule, which is fibrous, passes between articulating bones and attaches at the articular margins. The fibrous capsule is flexible, and permits considerable movement at a joint, while its tensile strength resists dislocation. The capsule can be strengthened by ligaments or muscles that cross the joint.
- ligaments are dense bundles of collagen fibres that pass between bones. They may arise from thickenings of the fibrous capsule, or maybe distinct from the capsule. Ligaments limit movement in unwanted directions. This maintains the normal relationship between articulating bones, and limits the damage to the joint. However, excessive movement or movement in the wrong direction can cause a sprain or tearing of the ligament, resulting in pain and instability
- Synovial joints are the most common type of joint in the body
- They are well innervated. Nerve endings are located in capsule, synovial membrane and ligaments.
- The main types of sensation from joints include proprioception and nociception.
- Note Hilton’s Law: the nerves supplying a joint are branches of a nerve supplying the overlying skin and muscles that move the joint
- Types: Hinge, Ball and socket, Saddle (as well as ellipsoid/condyloid, pivot, plane)
What is another name for synovial joint?
Diarthrodial joint
Define and describe the synovium, its role and its components
Synovium
- Internal lining of the joint.
- Two layers – lining or intima, and subintima - fibroblasts.
#### Intima
- Synoviocyte layer is only 3 cells thick
- Synoviocytes secrete hyaluronic acid.
#### Subintima
- Subintima consists of fibroblasts, producing a stroma of collagen fibrils and proteoglycans
Define and describe synovial fluid
- An ultrafiltrate of blood.
- Hyaluronic acid from synoviocytes increases viscosity
- Clear to pale yellow, relatively acellular
- Covers the surface of synovium and cartilage
- Lubricant, nutrient transport.
- Knee – 0.5 -1.5 ml.
Describe synovitis and its stages
Synovitis
- is an inflammation of the synovium
- an example is Rheumatoid arthritis, which is characterised by an immune attack on the synovium
- Early synovitis is characterised by:
- Changes to the synovium, becoming oedematous, thickened, hyperplastic, with projections. It is also characterised by dense infiltration of inflammatory cells.
- Late synovitis is characterised by a Pannus – hyperaemic, fibrovascular granulation tissue invading and destroying articular cartilage and bone.
Describe the types of cartilage
- Growth plate.
- Articular – synovial joints.
- Fibrocartilage – attaches tendons and ligaments to bone.
- Elastic cartilage – auricles, nose, epiglottis, trachea.
- Fibroelastic cartilage – intervertebral discs and intraarticular menisci (load bearing and shock absorption).
Define and briefly describe proteoglycans
- Components of the ground substance.
- Secreted by chondrocytes
- Among collagen fibrils
- 15-40% of dry weight
- Hydrophilic
- Core protein plus side chains of glycosaminoglycans
- Chondroitin and keratin sulphate
- Attach to hyaluronic acid filaments (aggregation)
Describe collagen
- Collagen is produced by fibroblasts, as well as chondroblasts and osteoblasts
- 28 types, 90% is type 1.
- All composed of three alpha polypeptide chains arranged like a three stranded rope
- Type 1 - skin, fascia, tendon, ligament, bone.
- Type 2 – all forms of cartilage.
- Type 3 - in association with type 1, found in skin, artery, uterus
- Type 4 - basement membrane
- Type 5- placenta, blood vessels
- Determines the tensile strength of tissues
- Provides a framework
- Limits movement of other tissue components
- Induces platelet aggregation and clot formation
- Regulates hydroxyapatite deposition in bone
