AAOS Orthopaedic Basic Science Self-Assessment Examination Q&A Book | Latest 2025/2026 Edition | American Academy of Orthopaedic Surgeons

2025

,1- In the context of joint arthroplasty, the alpha-defensin immunoassay test is useful for the
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O detection of? O




1*aseptic loosening. O




O 2*metal corrosion. O




O 3*periprosthetic

O infection. 4*bone O




O ingrowth.



Correct answer 3 O O




Alpha-defensin is a protein released by activated neutrophils in response to infection. The detection
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of alpha-defensin in synovial fluid is highly sensitive and specific as a marker of periprosthetic
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infection. Aseptic loosening and the bone ingrowth of prostheses generally are detected
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radiographically. Metal corrosion issues—in metal-on-metal prostheses, for example—generally are
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followed using blood metal ion levels.
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2- In posttraumatic arthritis, the initial injury stimulates the production of inflammatory cytokines.
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O Which cytokine is produced at the highest level on the first day after injury?
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1*Interleukin-6 (IL-6) O




O 2*Interleukin-1 beta (IL-1β) O O
IL -1B
TNF-a
O 3*Chemokine ligand 22 (CCL- O O O




22)

4*Damage-associated molecular patterns (DAMPs) O O O




Correct answer 2 O O




The development of arthritis after joint injury is common and can result from multiple causes,
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O including cartilage contusion, meniscal injury, ligament tear, or intra-articular fracture. The
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O accuracy of reduction does not necessarily prevent the development of posttraumatic arthritis.
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O Data from animal studies of posttraumatic arthritis demonstrate the production of inflammatory
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O cytokines that lead to chondrocyte death and matrix destruction. In the first few days after
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O injury IL- OO O



1β (predominantly) and tumor necrosis factor alpha are the primary cytokines produced, followed by
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nitric oxide, matrix metalloproteinases, and aggrecanases, which degrade the chondral matrix CCL-
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22 increases at around 5 days after injury, however. Other factors called DAMPs, which are
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O generated through the mechanical or enzymatic degradation of joint tissues, also stimulate an
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O innate inflammatory response.
O O

,3- What is the main function of lubricin in synovial joints?
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1*Serves as a component of the extracellular matrix
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O 2*Inhibits matrix metalloproteinase
O O




3*Increases cross-linking between collagen fibers
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O 4*Reduces the coefficient of friction in the joint
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Correct answer 4 O O




Lubricin reduces the friction between the surfaces in the joint, leading to decreased shear forces
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Ogoing through the hyaline cartilage. It is a glycoprotein that is produced by the chondrocytes in the
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Osuperficial zone and is not a primary component of the extracellular matrix. A lack of lubricin has
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Obeen associated with syndromes causing arthritic changes at an early age
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4- Anti-sclerostin antibody increases bone formation by targeting what molecular
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pathway? 1*Wnt
O OO




2*Bone morphogenetic protein (BMP)
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O 3*Notch

4*Indian hedgehog O




Correct answer 1 O O




All of the listed factors serve critical functions in bone formation. Only BMP-based therapies
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currently are FDA approved, however. Sclerostin is an extracellular antagonist of Wnt signaling and,
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to a lesser extent, BMP signaling. Blosozumab currently is an investigational antibody therapy
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designed to block sclerostin’s ability to inhibit Wnt signaling, netting a positive effect on bone
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formation. In a phase 2 trial involving 120 postmenopausal women, 1 year of blosozumab treatment
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resulted in a 17% increase in bone mineral density in the lumbar spine.
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, 5- Figures 1 through 3 display radiographs and an MRI from a 29-year-old man who has complained
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of left leg pain since sustaining a gunshot wound 18 months ago. He denies any fevers or chills but
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does have pain and drainage from his wound. His erythrocyte sedimentation rate (ESR) is 105
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mm/h (reference range: 0-20 mm/h), C-reactive protein (CRP) level is 12 mg/L (reference range:
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0.08-3.1 mg/L), white blood cell (WBC) count is 8,000 /µL (reference range: 4500-11000 /µL), and
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vitamin D level is 15 ng/mL (reference range: 20-40ng/ml).
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What is the tissue indicated by the arrow in Figure
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4? Figure 1
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