DEXA Anatomy & Physiology of Bone Structure 4 — Questions and Answers
Question 1: The femoral neck is a critical DEXA measurement site primarily because it:
- Is purely trabecular bone with no cortical shell
- Is a common fracture site with high morbidity and is rich in trabecular bone (Correct answer)
- Has the highest bone density of any skeletal site
- Is unaffected by degenerative changes that confound lumbar readings
Correct answer: Is a common fracture site with high morbidity and is rich in trabecular bone
The femoral neck is a major osteoporotic fracture site and contains significant trabecular bone, making it a key DEXA site for fracture risk assessment.
Question 2: Bone tissue that is rapidly deposited during fracture healing or in Paget's disease, characterized by disorganized collagen fibers, is called:
- Lamellar bone
- Woven (fiber) bone (Correct answer)
- Cortical bone
- Endochondral bone
Correct answer: Woven (fiber) bone
Woven bone has randomly oriented collagen fibers and is weaker than lamellar bone; it is laid down quickly in response to injury and is later remodeled.
Question 3: Volkmann's canals in compact bone run in what orientation relative to Haversian canals?
- Parallel (longitudinal)
- Perpendicular (transverse/oblique) (Correct answer)
- Concentric (circumferential)
- Diagonal at 45°
Correct answer: Perpendicular (transverse/oblique)
Volkmann's canals run perpendicular to the long axis of bone, connecting adjacent Haversian canals and the periosteum to the medullary cavity.
Question 4: Which hormone directly inhibits osteoclast activity and is secreted by thyroid parafollicular (C) cells?
- Parathyroid hormone
- Calcitonin (Correct answer)
- Aldosterone
- Cortisol
Correct answer: Calcitonin
Calcitonin, secreted by thyroid C cells, inhibits osteoclast-mediated bone resorption and lowers serum calcium, opposing the effects of PTH.
Question 5: In a long bone, the diaphysis refers to:
- The rounded end of the bone covered with articular cartilage
- The shaft (midportion) of the long bone (Correct answer)
- The flared region where the shaft meets the end
- The growth plate between shaft and end
Correct answer: The shaft (midportion) of the long bone
The diaphysis is the cylindrical shaft of a long bone, composed predominantly of compact cortical bone surrounding the medullary cavity.
Question 6: Cortical bone comprises approximately what percentage of total skeletal mass?
- 20%
- 50%
- 80% (Correct answer)
- 95%
Correct answer: 80%
Cortical (compact) bone accounts for approximately 80% of total skeletal mass, while trabecular bone makes up the remaining 20%.
Question 7: Which biochemical marker is primarily used as an index of bone resorption activity in clinical practice?
- Bone-specific alkaline phosphatase (BSAP)
- C-terminal telopeptide of type I collagen (CTX) (Correct answer)
- Osteocalcin
- Procollagen type I N-propeptide (P1NP)
Correct answer: C-terminal telopeptide of type I collagen (CTX)
CTX (C-terminal cross-linked telopeptide of type I collagen) is released into circulation during osteoclastic bone resorption and is a standard resorption biomarker.
DEXA Anatomy & Physiology of Bone Structure 4
The femoral neck is a critical DEXA measurement site primarily because it: