Introduction to MSK pathology

Question 1

Learning outcomes

Answer 1

(1) Describe the four phases of fracture healing Compare and contrast the pathological features of (2) osteoarthritis and (3) rheumatoid arthritis(4) Describe the pathophysiology of gout
Compare and contrast the pathological features of (5) benign and (6) malignant bone tumours

Question 2

Fracture callus

Answer 2

Definition- A connective tissue mass of haemorrhagic bony and cartilaginous material which attempts to repair a gap in a broken bone.

Question 3

Fracture healing

Answer 3

Initial phase –week 1 Immediately after a fracture, blood flows from blood vessels which have been damaged by the break. Blood which has leaked from these vessels forms a haemorrhagic swelling called a haematoma.
Soft (provisional) callus –week 2
During the first few weeks there is a proliferation of new small blood vessels called granulation tissue, immature cartilaginous matrix (produced by chondrocytes) and immature new bone (produced by osteoblasts).
Bony Callus –weeks 3 and 4
New bone is formed by osteoblasts and also new cartilage is transformed into bone via a process of endochondral ossification.
Remodelling- Over several months a process of remodelling or refining of the callus occurs.

Question 4

Osteoarthritis

Answer 4

Osteoarthritis is the most common type of arthritis.
Pathogenesis –Older patient (+/-family history, overweight, previous injury) –degeneration and thinning and fracture of articular cartilage.
Articular cartilage is a smooth type of cartilage which allows for lubricated joint movement, distribution of weight and shock absorption.
Osteoarthritis is accompanied by considerable loss of cartilage, the generation of wear particles, thickening of synovium and capsule disturbances in the subchondral bone and the growth of osteophytes at the margins of the joint.

Question 5

4 cardinal signs of OA on x-ray

Answer 5

• Asymmetric joint space narrowing
• Osteophytes
• Subchondral sclerosis
• Subchondral cysts

Question 6

Rheumatoid arthritis

Answer 6

Definition- an autoimmune disease which affects joints primarily but can often involve other organs such as eyes, lungs, heart, blood vessels, skin.
- IgM auto-antibody directed against the Immunoglobulin IgG
Anti-CCP Citrullinated peptides are found in various normal connective tissues

Question 7

Gout

Answer 7

Definition
Inflammation of joints and tissue around joints due to deposits of urate crystals
Uric acid is produced by the breakdown of RNA and DNA and is also produced from purines. It is normally excreted by the kidneys and gastrointestinal tract.
Elevated levels of uric acid can be caused by:
Consuming food which is rich in purine such as liver, anchovies and sardines.
Kidney disease
Medication eg: diuretics
Alcohol

Question 8

Benign bone tumours

Answer 8

Osteoma –a benign surface bone forming tumour
Enchondroma –a benign cartilage forming tumour present inside the medullary cavity of bone
Osteochondroma (exostosis) –a benign surface bone forming tumour with a cartilaginous cap

Question 9

Malignant tumours

Answer 9

Primary malignant bone tumours
Osteosarcoma- cancerous cells produce immature osteoid
Mean age at diagnosis = 15
Most common site of tumour: distal femur / proximal tibia

Chondrosarcoma- cancerous cells show cartilaginous differentiaton
Mean age at diagnosis = 50 y
Most common site: pelvis, scapula, sternum, and ribs, proximal femur and proximal humerus

Secondary / metastatic carcinoma involving bone