ORTHO 119 Shoulder Trauma Flashcards
What is bone?
A specialised form of connective tissue
What are the two types of bone?
Trabecullar (cancellous) and cortical (compact) bone
Describe trabecular bone
Spongy bone with high turnover axially. Site of bone remodelling and mineral homeostasis
Describe cortical bone
Compact bone with low turnover, found peripherally. Has trabecullar shell and has mainly mechanical and protective functions. Contain lacunae, haversian canals, osteons and canniliculi
Describe lacunae and where are they found?
Concentric layers of dense connective tissue in cortical bone
What type of collage comprises most of organic bone?
Type 1 from osteoblasts
What is inorganic bone?
Bone with high mineral content of calcium hydroxyapetitie crystals
What is an osteoid?
It is an area of newly formed unmineralised bone
What are the 4 types of bone cells?
Osteoprojenitor, Osteoblasts, osteocytes and osteoclasts
What are osteoprojenitor cells?
Self replicating precursor cells that differentiate into bone forming cells
What are osteoblasts?
Bone forming cells that deposit osteoid and control mineralisation
What are osteocytes?
Modified osteoblasts which have become surrounded by newly formed bone
What are osteoclasts?
Macrophage like cells that resorb bone
What is the role of canniliculi?
They permeate through the new bone and link lacunae between adjacent osteocyte processes
Act as mechanotransducting cells
What controls bone resorption and remodelling?
The RANK/OPG system
What causes increased OPG and therefore decreased bone resorption?
Oestrogen, IL1 and TNF alpha
What causes increased RANK and therefore increased resorption?
PTH, Vit D3 and PgE2
How does cartilage work as a shock absorber?
Collagen forms a meshwork holding in the proteoglycans. Proteoglycans have a high osmotic potential drawing water into the joint
What is the dry weight of cartilage?
3/4 collagen and 1/4 proteoglycans
What is the wet weight of cartilage?
70% water, 20% collagen, 7% PG’s, 2% cells and 1% of other proteins
What is the major proteoglycan in cartilage?
Aggrecan
What is the structure of aggrecan?
Protein core surrounded by covalently attached glycosaminoglycans. Contains hydroxyl and sulfate groups as well as chondroitin, keratin sulfate and hyaluronan groups
What enables the strong binding of water to aggrecan?
Its negatively charged hydroxyl and sulfate groups
What is the difference between adult and young cartilage?
Adult: hypocellular, aneural, avascular, extensive matrix, zonal morphology and tidemark
Young: hypercellular, little organisational matrix, no zonal morphology or tidemark
What is the function of the tidemark?
Prevents cartilage from utilitsing blood supply and therefore nutrients from subchondral bone
What are the two main classes of proteolytic enxymes involved in the degradation of cartilage?
ADAMTS and MMP’s
Name the 3 matrix metalloproteinases and what they degrade
Collagenases- triple helix collagens, gelatinases - denatured collagens and stromelysins - non-collagenous matrix proteins (not aggrecan though)
Where is the specific activity of ADAMTs
Between the glutamate and alanine in aggrecans interglobular domain
What occurs to cartilage in ageing?
Slowed cell metabolism Increased collagen and matrix protein cross linking Decreased collagen IX synthesis Changes in aggrecan Accumulation of degradation products
What is arthritis?
Joint space narrowing can cause pain, swelling, loss of function
What is RA due to?
Deposition of immune complexes in joint space, therefore influx of inflammatory cells and secretion of cytokine which degrade cartilage
What is OA usually as a result of?
Increased mechanical stresses on the joint, often after injury or trauma
What is the commonest cause of shoulder pain?
Rotator cuff tendonosis - often following trauma worse on arm abduction and elevation
= painful arc
What is dupytrens contracture?
Painless palpable fibrosis of the palmar aponeurosis with fibroblasts invading the dermis.
