Loco PBLs

Question 1

Briefly explain why a DEXA scan is used to measure bone mineral density.

Answer 1

A DEXA (Dual-energy X-ray Absorptiometry) scan is used because it provides a highly accurate and low-radiation method for quantifying bone mineral density (BMD), particularly at the hip and lumbar spine. It is the gold standard for diagnosing osteoporosis and assessing fracture risk.

Question 2

What type of bone is most susceptible to developing osteoporosis and explain why?

Answer 2

Trabecular (spongy) bone is most susceptible to osteoporosis because it has a higher surface area and faster turnover rate than cortical bone. This makes it more prone to resorption and thinning, especially in areas like the vertebrae and femoral neck.

Question 3

What are the 4 main signs of osteoarthritis (OA) that you would find on an x-ray?

Answer 3

Joint space narrowing
Subchondral sclerosis
Osteophyte formation
Subchondral cysts

Question 4

What biochemical changes are observed in the osteoarthritic articular cartilage?

Answer 4

There is degradation of type II collagen and aggrecan, leading to decreased proteoglycan content. Matrix metalloproteinases (MMPs) and inflammatory cytokines (e.g. IL-1, TNF-α) are upregulated, promoting cartilage breakdown.

Question 5

What is the mode of action of the alendronate and what is long term potential side effect for patients taking this drug?

Answer 5

Alendronate is a bisphosphonate that inhibits osteoclast-mediated bone resorption by inducing osteoclast apoptosis. A potential long-term side effect is osteonecrosis of the jaw or atypical femoral fractures due to oversuppression of bone remodeling

Question 6

Tc-99m MDP (Technetium-99m Methylene Diphosphonate)

Answer 6

Tc-99m MDP (Technetium-99m Methylene Diphosphonate)

Definition: A radiopharmaceutical used in bone scintigraphy (bone scans).

Function: Binds to hydroxyapatite crystals in bone, especially at sites of active bone turnover.

Relevance: In Paget’s disease, Tc-99m MDP shows increased uptake in areas of excessive remodeling.

Question 7

Diaphysis

Answer 7

Diaphysis

Definition: The shaft or central part of a long bone (e.g., femur).

Relevance: Paget’s disease often affects long bones, and stress fractures can occur in the diaphyseal region due to abnormal remodeling and weakened structure.

Question 8

Coarse Trabeculae

Answer 8

Coarse Trabeculae

Definition: Thickened, irregular bony struts (trabeculae) within cancellous (spongy) bone.

Normal Function: Provide support and distribute mechanical loads.

In Paget’s Disease:
- Trabeculae become disorganized, thick, and coarse due to abnormal bone formation.
- Leads to weak, structurally unsound bone.

Question 9

Bisphosphonate Therapy

Answer 9

Bisphosphonate Therapy

Definition: A class of drugs that inhibit osteoclast-mediated bone resorption.

Mechanism:
- Attach to bone mineral
- Are ingested by osteoclasts, leading to their apoptosis

Common Agents: Zoledronic acid, alendronate, risedronate

In Paget’s Disease:
- Reduce bone turnover
- Alleviate pain
- Promote structural normalization of bone

Question 10

Paget’s Disease (of Bone)

Answer 10

Paget’s Disease (of Bone)

Definition: A chronic disorder of focal bone remodeling, where bone becomes enlarged, weak, and structurally abnormal.

Pathology:
- Excessive osteoclastic resorption
- Compensatory disorganized osteoblastic formation

Clinical Features:
- Bone pain, deformity, fractures, nerve compression
- Elevated ALP

Diagnosis: Based on imaging, biochemical markers, bone biopsy

Treatment: Primarily bisphosphonates