TEST BANK AAOS ORTHOPAEDIC BASIC
SCIENCE SELF-ASSESSMENT EXAMINATION
2025/2026 EDITION
Total Questions: 200
Question Type: Multiple Choice
Answer Key: Correct answer indicated in bold after each question
Rationales: Provided for every correct answer with textbook references
Reference Key:
[OKU-15] = Orthopaedic Knowledge Update 15
[OBS-5] = Orthopaedic Basic Science: Foundations of Clinical Practice, 5th Ed.
[RES] = ResStudy / AAOS SAE question bank
SECTION 1 – BONE BIOLOGY AND PHYSIOLOGY
1. Which cell type is primarily responsible for bone resorption?
A) Osteoblast
B) Osteocyte
C) Osteoclast
D) Chondrocyte
Answer: C
Rationale: Osteoclasts are large, multinucleated cells that resorb bone by
secreting acid and proteolytic enzymes. Osteoblasts form bone; osteocytes
are mature bone cells that maintain the matrix; chondrocytes form cartilage.
[OBS-5, Chapter 3]
2. The organic component of bone matrix is primarily composed of:
A) Hydroxyapatite
B) Calcium phosphate
C) Type I collagen
D) Proteoglycans
Answer: C
Rationale: Type I collagen constitutes approximately 90% of the organic
matrix of bone, providing tensile strength and flexibility.
, Hydroxyapatite and calcium phosphate are inorganic components.
[OBS-5, Chapter 2]
3. Which hormone is the primary regulator of calcium homeostasis by
increasing serum calcium levels?
A) Calcitonin
B) Parathyroid hormone (PTH)
C) Vitamin D
D) Estrogen
Answer: B
Rationale: Parathyroid hormone (PTH) increases serum calcium by stimulating
osteoclastic bone resorption, increasing renal calcium reabsorption, and
activating vitamin D. Calcitonin decreases serum calcium.
[OBS-5, Chapter 5]
4. The process of woven bone being remodeled into lamellar bone is called:
A) Osteogenesis
B) Modeling
C) Remodeling
D) Ossification
Answer: C
Rationale: Remodeling is the process by which woven bone (immature,
disorganized) is replaced by lamellar bone (mature, organized) through
coupled osteoclastic resorption and osteoblastic formation.
[OBS-5, Chapter 4]
5. Which growth factor is most potent for stimulating osteoblast
proliferation and differentiation?
A) BMP-2 (Bone Morphogenetic Protein-2)
B) TGF-β (Transforming Growth Factor-beta)
C) IGF-1 (Insulin-like Growth Factor-1)
D) FGF (Fibroblast Growth Factor)
Answer: A
Rationale: BMP-2 is one of the most potent osteoinductive factors,
stimulating mesenchymal stem cells to differentiate into osteoblasts.
TGF-β, IGF-1, and FGF also play roles but are less specific.
[OBS-5, Chapter 6]
6. Osteocytes communicate with each other and with osteoblasts/osteoclasts
through:
A) Gap junctions and canaliculi
, B) Synaptic junctions
C) Desmosomes
D) Tight junctions
Answer: A
Rationale: Osteocytes are connected to each other and to surface bone cells
via gap junctions within canaliculi, allowing for communication and
mechanosensing. [OBS-5, Chapter 3]
7. Which of the following is a marker of bone formation?
A) N-telopeptide (NTX)
B) Deoxypyridinoline (DPD)
C) Bone-specific alkaline phosphatase (BSAP)
D) Hydroxyproline
Answer: C
Rationale: Bone-specific alkaline phosphatase (BSAP) is a marker of
osteoblast activity and bone formation. NTX, DPD, and hydroxyproline are
markers of bone resorption. [OBS-5, Chapter 5]
8. The principal inorganic component of bone is:
A) Calcium carbonate
B) Hydroxyapatite [Ca10(PO4)6(OH)2]
C) Calcium oxalate
D) Magnesium phosphate
Answer: B
Rationale: Hydroxyapatite is the main crystalline mineral in bone,
providing compressive strength. It is composed of calcium and phosphate.
[OBS-5, Chapter 2]
9. Which cell type is derived from hematopoietic stem cells?
A) Osteoblast
B) Osteocyte
C) Osteoclast
D) Chondrocyte
Answer: C
Rationale: Osteoclasts are derived from hematopoietic stem cells of the
monocyte/macrophage lineage. Osteoblasts, osteocytes, and chondrocytes are
derived from mesenchymal stem cells. [OBS-5, Chapter 3]
10. The RANK/RANKL/OPG system regulates:
A) Bone formation
, B) Bone resorption
C) Cartilage formation
D) Muscle contraction
Answer: B
Rationale: RANKL (produced by osteoblasts) binds to RANK on osteoclasts to
stimulate osteoclastogenesis and bone resorption. OPG (osteoprotegerin) is
a decoy receptor that inhibits this interaction. [OBS-5, Chapter 5]
11. Which vitamin is essential for intestinal calcium absorption?
A) Vitamin A
B) Vitamin C
C) Vitamin D
D) Vitamin K
Answer: C
Rationale: Vitamin D (specifically 1,25-dihydroxyvitamin D) increases
intestinal absorption of calcium and phosphate. Vitamin K is involved in
bone matrix protein carboxylation. [OBS-5, Chapter 5]
12. What is the primary mechanical function of cancellous (trabecular) bone?
A) Resist tensile forces
B) Resist compressive forces and provide shock absorption
C) Provide attachment for tendons
D) Protect bone marrow
Answer: B
Rationale: Cancellous bone has a high surface area-to-volume ratio and is
designed to resist compressive forces and absorb shock, particularly in
the vertebral bodies and metaphyses of long bones. [OBS-5, Chapter 2]
13. Which of the following is NOT a stage of fracture healing?
A) Inflammatory phase
B) Reparative phase (soft and hard callus)
C) Remodeling phase
D) Necrotic phase
Answer: D
Rationale: The three stages of fracture healing are: (1) inflammatory
(hematoma formation, inflammation), (2) reparative (soft callus, hard
callus), and (3) remodeling. Necrotic phase is not a recognized stage.
[OBS-5, Chapter 10]
14. The primary blood supply to the femoral head in adults is the:
SCIENCE SELF-ASSESSMENT EXAMINATION
2025/2026 EDITION
Total Questions: 200
Question Type: Multiple Choice
Answer Key: Correct answer indicated in bold after each question
Rationales: Provided for every correct answer with textbook references
Reference Key:
[OKU-15] = Orthopaedic Knowledge Update 15
[OBS-5] = Orthopaedic Basic Science: Foundations of Clinical Practice, 5th Ed.
[RES] = ResStudy / AAOS SAE question bank
SECTION 1 – BONE BIOLOGY AND PHYSIOLOGY
1. Which cell type is primarily responsible for bone resorption?
A) Osteoblast
B) Osteocyte
C) Osteoclast
D) Chondrocyte
Answer: C
Rationale: Osteoclasts are large, multinucleated cells that resorb bone by
secreting acid and proteolytic enzymes. Osteoblasts form bone; osteocytes
are mature bone cells that maintain the matrix; chondrocytes form cartilage.
[OBS-5, Chapter 3]
2. The organic component of bone matrix is primarily composed of:
A) Hydroxyapatite
B) Calcium phosphate
C) Type I collagen
D) Proteoglycans
Answer: C
Rationale: Type I collagen constitutes approximately 90% of the organic
matrix of bone, providing tensile strength and flexibility.
, Hydroxyapatite and calcium phosphate are inorganic components.
[OBS-5, Chapter 2]
3. Which hormone is the primary regulator of calcium homeostasis by
increasing serum calcium levels?
A) Calcitonin
B) Parathyroid hormone (PTH)
C) Vitamin D
D) Estrogen
Answer: B
Rationale: Parathyroid hormone (PTH) increases serum calcium by stimulating
osteoclastic bone resorption, increasing renal calcium reabsorption, and
activating vitamin D. Calcitonin decreases serum calcium.
[OBS-5, Chapter 5]
4. The process of woven bone being remodeled into lamellar bone is called:
A) Osteogenesis
B) Modeling
C) Remodeling
D) Ossification
Answer: C
Rationale: Remodeling is the process by which woven bone (immature,
disorganized) is replaced by lamellar bone (mature, organized) through
coupled osteoclastic resorption and osteoblastic formation.
[OBS-5, Chapter 4]
5. Which growth factor is most potent for stimulating osteoblast
proliferation and differentiation?
A) BMP-2 (Bone Morphogenetic Protein-2)
B) TGF-β (Transforming Growth Factor-beta)
C) IGF-1 (Insulin-like Growth Factor-1)
D) FGF (Fibroblast Growth Factor)
Answer: A
Rationale: BMP-2 is one of the most potent osteoinductive factors,
stimulating mesenchymal stem cells to differentiate into osteoblasts.
TGF-β, IGF-1, and FGF also play roles but are less specific.
[OBS-5, Chapter 6]
6. Osteocytes communicate with each other and with osteoblasts/osteoclasts
through:
A) Gap junctions and canaliculi
, B) Synaptic junctions
C) Desmosomes
D) Tight junctions
Answer: A
Rationale: Osteocytes are connected to each other and to surface bone cells
via gap junctions within canaliculi, allowing for communication and
mechanosensing. [OBS-5, Chapter 3]
7. Which of the following is a marker of bone formation?
A) N-telopeptide (NTX)
B) Deoxypyridinoline (DPD)
C) Bone-specific alkaline phosphatase (BSAP)
D) Hydroxyproline
Answer: C
Rationale: Bone-specific alkaline phosphatase (BSAP) is a marker of
osteoblast activity and bone formation. NTX, DPD, and hydroxyproline are
markers of bone resorption. [OBS-5, Chapter 5]
8. The principal inorganic component of bone is:
A) Calcium carbonate
B) Hydroxyapatite [Ca10(PO4)6(OH)2]
C) Calcium oxalate
D) Magnesium phosphate
Answer: B
Rationale: Hydroxyapatite is the main crystalline mineral in bone,
providing compressive strength. It is composed of calcium and phosphate.
[OBS-5, Chapter 2]
9. Which cell type is derived from hematopoietic stem cells?
A) Osteoblast
B) Osteocyte
C) Osteoclast
D) Chondrocyte
Answer: C
Rationale: Osteoclasts are derived from hematopoietic stem cells of the
monocyte/macrophage lineage. Osteoblasts, osteocytes, and chondrocytes are
derived from mesenchymal stem cells. [OBS-5, Chapter 3]
10. The RANK/RANKL/OPG system regulates:
A) Bone formation
, B) Bone resorption
C) Cartilage formation
D) Muscle contraction
Answer: B
Rationale: RANKL (produced by osteoblasts) binds to RANK on osteoclasts to
stimulate osteoclastogenesis and bone resorption. OPG (osteoprotegerin) is
a decoy receptor that inhibits this interaction. [OBS-5, Chapter 5]
11. Which vitamin is essential for intestinal calcium absorption?
A) Vitamin A
B) Vitamin C
C) Vitamin D
D) Vitamin K
Answer: C
Rationale: Vitamin D (specifically 1,25-dihydroxyvitamin D) increases
intestinal absorption of calcium and phosphate. Vitamin K is involved in
bone matrix protein carboxylation. [OBS-5, Chapter 5]
12. What is the primary mechanical function of cancellous (trabecular) bone?
A) Resist tensile forces
B) Resist compressive forces and provide shock absorption
C) Provide attachment for tendons
D) Protect bone marrow
Answer: B
Rationale: Cancellous bone has a high surface area-to-volume ratio and is
designed to resist compressive forces and absorb shock, particularly in
the vertebral bodies and metaphyses of long bones. [OBS-5, Chapter 2]
13. Which of the following is NOT a stage of fracture healing?
A) Inflammatory phase
B) Reparative phase (soft and hard callus)
C) Remodeling phase
D) Necrotic phase
Answer: D
Rationale: The three stages of fracture healing are: (1) inflammatory
(hematoma formation, inflammation), (2) reparative (soft callus, hard
callus), and (3) remodeling. Necrotic phase is not a recognized stage.
[OBS-5, Chapter 10]
14. The primary blood supply to the femoral head in adults is the:
