Question 1

According to the 2018 International Consensus Meeting on Periprosthetic Joint Infection, which of the following findings is considered a definitive major criterion for diagnosing a periprosthetic joint infection (PJI)?

Explanation

The 2018 ICM criteria define a major criterion as either a sinus tract communicating with the joint or two positive periprosthetic cultures with phenotypically identical organisms. The presence of either major criterion is diagnostic for PJI.

Question 2

A 45-year-old female presents with severe hand stiffness, progressive dysphagia, and fingertip ulcerations. Radiographs of her hands demonstrate acro-osteolysis and subcutaneous soft tissue calcifications.

Which of the following autoantibodies is most specific for the diffuse cutaneous form of this systemic disease?

Explanation

The clinical and radiographic presentation is consistent with systemic sclerosis (scleroderma). Anti-Scl-70 antibodies are highly specific for the diffuse cutaneous form of systemic sclerosis, which carries a higher risk of interstitial lung disease.

Question 3

A 7-year-old boy presents with right groin pain and a limp. Radiographs demonstrate a solitary lytic lesion in the proximal femur with endosteal scalloping. A biopsy is performed, revealing a proliferation of histiocytes with folded, "coffee-bean" nuclei mixed with eosinophils. Immunohistochemical staining will most likely be positive for which of the following pairs of markers?

Explanation

The biopsy findings describe Langerhans cell histiocytosis (eosinophilic granuloma). The pathologic Langerhans cells characteristically stain positive for CD1a, S-100, and Langerin (CD207).

Question 4

A 68-year-old man develops acute onset of right knee pain, swelling, and erythema 18 days after a primary total knee arthroplasty. Aspiration yields a synovial WBC count of 55,000 cells/uL. He is scheduled for debridement, antibiotics, and implant retention (DAIR). To maximize the success rate of this procedure, what intraoperative step MUST be performed?

Explanation

During a DAIR procedure for an acute periprosthetic joint infection, exchanging the modular polyethylene insert is critical. This allows access to the posterior joint space for thorough debridement and removes the biofilm adherent to the polymer.

Question 5

A 6-year-old girl presents with progressive mid-back pain. Neurological examination is unremarkable. Radiographs reveal a uniform collapse of the T7 vertebral body with preservation of the adjacent intervertebral disc spaces, consistent with vertebra plana. Which of the following is the most appropriate initial management?

Explanation

Vertebra plana in a child is highly characteristic of eosinophilic granuloma (Langerhans cell histiocytosis). Without neurologic deficit, the condition is typically self-limiting, and the vertebral body often spontaneously reconstitutes over time, making observation and symptomatic care the treatment of choice.

Question 6

A 38-year-old woman with a known history of CREST syndrome presents to the orthopedic clinic with exquisitely painful, pale fingertips triggered by cold weather. Which of the following is the most appropriate first-line pharmacologic therapy to manage the vasospastic component of her condition?

Explanation

The patient is experiencing Raynaud phenomenon, a hallmark of CREST syndrome (limited cutaneous systemic sclerosis). Calcium channel blockers, such as nifedipine, are the first-line medical therapy to induce vasodilation and prevent digital ischemia.

Question 7

Synovial fluid alpha-defensin testing is an important adjunct in diagnosing periprosthetic joint infection. What is the precise biological origin and function of alpha-defensin?

Explanation

Alpha-defensin is an antimicrobial peptide released by host neutrophils in response to the presence of pathogens. It is a highly sensitive and specific biomarker for PJI and is not significantly affected by prior antibiotic administration.

Question 8

A 4-year-old boy presents with a painful, enlarging scalp mass. Imaging reveals a solitary lytic skull lesion with a "beveled edge" appearance. If an electron microscopic analysis of the lesion tissue were performed, what pathognomonic ultrastructural finding would be expected?

Explanation

The clinical and radiographic presentation is classic for Langerhans cell histiocytosis of the skull. On electron microscopy, Langerhans cells contain Birbeck granules, which are distinctive "tennis racket"-shaped intracytoplasmic organelles.

Question 9

When treating a chronic periprosthetic knee infection with a two-stage exchange arthroplasty, what is a primary biomechanical or surgical advantage of utilizing an articulating antibiotic spacer rather than a static spacer?

Explanation

Articulating spacers maintain the length of collateral ligaments and allow interval range of motion, which prevents severe soft-tissue contractures. This significantly facilitates joint exposure and functional recovery during the second-stage reimplantation.

Question 10

A 52-year-old patient with limited cutaneous systemic sclerosis presents with firm, painful, palpable subcutaneous nodules over the extensor surfaces of the forearms and proximal interphalangeal joints.

What is the primary chemical composition of these particular deposits?

Explanation

The image and clinical description represent calcinosis cutis, a classic feature of the CREST variant of systemic sclerosis. These dystrophic calcifications are primarily composed of insoluble calcium hydroxyapatite.

Question 11

Langerhans cell histiocytosis can present in various clinical forms. Which of the following triads classically defines Hand-Schüller-Christian disease?

Explanation

Hand-Schüller-Christian disease is the chronic disseminated form of Langerhans cell histiocytosis. It is classically characterized by the triad of exophthalmos, diabetes insipidus (due to pituitary involvement), and multiple lytic skull lesions.

Question 12

In the management of a staphylococcal periprosthetic joint infection treated with DAIR, rifampin is frequently added to the oral antibiotic regimen after initial intravenous therapy. What is the mechanism of action of rifampin that makes it critical for biofilm-associated infections?

Explanation

Rifampin exerts its bactericidal effect by binding to the beta subunit of DNA-dependent RNA polymerase, thereby inhibiting RNA synthesis. It is highly effective in penetrating biofilms and eradicating stationary-phase staphylococci.

Question 13

A 60-year-old woman with a long-standing history of systemic sclerosis presents with severe, fixed flexion contractures of her proximal interphalangeal (PIP) joints bilaterally. At the cellular level, this joint deformity is primarily driven by the overproduction of which substance by hyperactive fibroblasts?

Explanation

Systemic sclerosis is characterized by widespread microvascular damage and excessive fibrosis. The fibrosis and resulting joint contractures are driven by hyperactive fibroblasts overproducing extracellular matrix proteins, predominantly collagen types I and III.

Question 14

A 62-year-old man undergoes revision of an anatomic total shoulder arthroplasty due to aseptic loosening. Preoperative aspiration was negative. However, 12 days after the revision surgery, 4 out of 5 intraoperative tissue cultures become positive for an organism. Which of the following is the most likely pathogen?

Explanation

Cutibacterium (formerly Propionibacterium) acnes is an indolent, anaerobic, Gram-positive bacillus commonly implicated in shoulder periprosthetic joint infections. It is slow-growing and frequently requires cultures to be held for up to 14 days to be detected.

Question 15

An 8-year-old boy is diagnosed with a solitary, painful eosinophilic granuloma of the clavicle confirmed by core needle biopsy. The lesion is structurally sound without an impending risk of fracture. What is the most appropriate next step in management?

Explanation

For a symptomatic, structurally stable solitary eosinophilic granuloma (LCH), minimally invasive treatments are preferred. Intralesional corticosteroid injection is highly effective at relieving pain and promoting lesion healing without the morbidity of surgical resection.

Question 16

A rapid colorimetric leukocyte esterase strip test is frequently used in the evaluation of periprosthetic joint infection. What is the major limitation of using this test on aspirated synovial fluid?

Explanation

Leukocyte esterase strips are inexpensive and provide rapid results by detecting an enzyme released by neutrophils. However, their major limitation is that heavy red blood cell contamination (bloody aspirate) makes the colorimetric change uninterpretable.

Question 17

A 50-year-old woman presents with calcinosis cutis, esophageal dysmotility, sclerodactyly, and telangiectasia.

Laboratory testing reveals the presence of anti-centromere antibodies. This patient is at the highest risk for developing which of the following life-threatening complications?

Explanation

The patient has CREST syndrome (limited cutaneous systemic sclerosis), marked by anti-centromere antibodies. These patients are at a particularly high risk for developing isolated pulmonary arterial hypertension, a leading cause of mortality in this subset.

Question 18

Which of the following variants of Langerhans cell histiocytosis predominantly affects infants under the age of 2, presents with diffuse hepatosplenomegaly, severe skin rash, and bone marrow infiltration, and frequently has a fatal clinical course?

Explanation

Letterer-Siwe disease is the acute, disseminated, multisystem form of Langerhans cell histiocytosis. It primarily strikes infants and is characterized by a rapid, frequently fatal course involving the skin, liver, spleen, and bone marrow.

Question 19

According to the 2018 International Consensus Meeting (ICM) criteria, which of the following is considered a definitive major criterion for diagnosing a periprosthetic joint infection (PJI)?

Explanation

The 2018 ICM criteria define two major criteria for definitive PJI: a communicating sinus tract or two positive periprosthetic cultures with phenotypically identical organisms. Purulence, elevated serum markers, and synovial WBC are considered minor criteria.

Question 20

A 7-year-old boy presents with a solitary lytic lesion in the proximal femur. Biopsy reveals mononuclear cells with grooved nuclei and abundant eosinophils. Which of the following genetic mutations is most frequently implicated in the pathogenesis of this disease?

Explanation

The described histology is classic for Langerhans Cell Histiocytosis (LCH). The BRAF V600E somatic mutation is identified in up to 60% of LCH cases, marking it as a clonal neoplastic process rather than a purely reactive one.

Question 21

A 45-year-old woman presents with the hand deformity shown, alongside dysphagia and severe cold intolerance in her fingers. Which autoantibody is most highly specific for her likely underlying condition?

Explanation

The image and clinical vignette describe CREST syndrome (Limited Cutaneous Systemic Sclerosis), characterized by calcinosis cutis, Raynaud's, esophageal dysmotility, sclerodactyly, and telangiectasia. Anti-centromere antibodies are highly specific for CREST syndrome.

Question 22

A 62-year-old man presents with insidious shoulder stiffness 2 years after an anatomic total shoulder arthroplasty. Aspiration yields no fluid, so intraoperative tissue cultures are obtained during revision. How long must these cultures be held to reliably detect the most likely causative organism?

Explanation

Cutibacterium acnes is a slow-growing, Gram-positive anaerobic rod that is the most common cause of shoulder PJI. Cultures must be held for a minimum of 14 days to minimize false-negative results.

Question 23

A biopsy of a solitary lytic skull lesion in a 5-year-old child demonstrates cells containing 'tennis-racket' shaped Birbeck granules on electron microscopy. Immunohistochemical staining of these cells will be characteristically positive for which of the following?

Explanation

Langerhans Cell Histiocytosis (LCH) is characterized by the presence of Birbeck granules on electron microscopy. The pathological Langerhans cells characteristically stain positive for S-100, CD1a, and CD207 (langerin).

Question 24

Which of the following is an absolute contraindication to performing a Debridement, Antibiotics, and Implant Retention (DAIR) procedure for a periprosthetic joint infection?

Explanation

A loose prosthesis is an absolute contraindication for a DAIR procedure, as biofilm cannot be adequately eradicated and the implant requires revision for mechanical stability. DAIR is best reserved for acute infections (<3-4 weeks) with well-fixed implants.

Question 25

A patient with systemic sclerosis presents with progressive shortening of her distal digits. Radiographs reveal resorption of the terminal phalangeal tufts. Which pathophysiology primarily drives this specific musculoskeletal manifestation?

Explanation

Acro-osteolysis in systemic sclerosis is primarily driven by chronic microvascular ischemia resulting from intimal proliferation and endothelial injury (Raynaud phenomenon). This chronic ischemia leads to atrophy and resorption of the distal phalangeal tufts.

Question 26

A 6-year-old boy presents with back pain but intact neurology. Radiographs reveal a 'coin-on-edge' appearance of the T8 vertebral body (vertebra plana). MRI confirms a solitary lesion confined to the vertebral body. What is the most appropriate initial management?

Explanation

Vertebra plana in a child without neurologic compromise is a classic presentation of eosinophilic granuloma (LCH). These solitary lesions are typically self-limiting and tend to reconstitute height over time, making observation and symptomatic care the best initial approach.

Question 27

A 68-year-old male presents with chronic knee pain and a draining sinus tract 2 years after a total knee arthroplasty.

According to the Musculoskeletal Infection Society (MSIS) criteria, what is the next most appropriate step in diagnosing a periprosthetic joint infection (PJI)?

Explanation

According to MSIS criteria, the presence of a sinus tract communicating with the prosthesis is a major criterion and is considered definitive evidence of a PJI. No further diagnostic testing is required to establish the diagnosis.

Question 28

A 7-year-old boy presents with a painful, lytic lesion in the proximal femur with periosteal reaction. Biopsy reveals cells with characteristic "coffee bean" grooved nuclei and electron microscopy demonstrates Birbeck granules. Which of the following immunohistochemical marker profiles is most specific for this diagnosis?

Explanation

The clinical and histologic findings describe Langerhans Cell Histiocytosis (LCH). The neoplastic cells in LCH characteristically stain positive for CD1a, S100, and Langerin (CD207).

Question 29

A 45-year-old female presents with tightening of the skin over her fingers, dysphagia, and painful calcium deposits in her digits. Hand radiographs are obtained.

Which autoantibody is most commonly associated with this patient's specific syndromic presentation?

Explanation

This patient has CREST syndrome (limited cutaneous systemic sclerosis), characterized by Calcinosis cutis, Raynaud's, Esophageal dysmotility, Sclerodactyly, and Telangiectasia. Anti-centromere antibodies are highly specific for CREST syndrome.

Question 30

A 72-year-old female with a well-functioning total hip arthroplasty (THA) placed 5 years ago develops sudden onset severe hip pain and fevers starting 5 days ago following a dental procedure. Radiographs show well-fixed components. What is the most appropriate management?

Explanation

DAIR is indicated for acute hematogenous PJI (symptoms <3-4 weeks) or acute postoperative PJI (within 4 weeks of index surgery) in patients with well-fixed implants and stable soft tissues. The modular components (e.g., polyethylene liner) must be exchanged during the procedure.

Question 31

A 6-year-old boy is evaluated for mild, progressive back pain. Radiographs reveal an isolated, completely flattened vertebral body (vertebra plana) at T8 with no associated soft tissue mass or kyphotic deformity. The patient is neurologically intact. What is the most appropriate initial management?

Explanation

Isolated vertebra plana in a pediatric patient is the classic presentation of Eosinophilic Granuloma (LCH) of the spine. In the absence of neurologic deficits or severe instability, these typically reconstitute height over time, making observation and symptomatic management the standard of care.

Question 32

The synovial fluid alpha-defensin test is increasingly utilized in the diagnosis of periprosthetic joint infections. Which of the following cells is the primary source of alpha-defensin in the synovial fluid?

Explanation

Alpha-defensin is an antimicrobial peptide released by activated neutrophils in response to infection. It is highly sensitive and specific for diagnosing PJI, even in the setting of concurrent antibiotic administration.

Question 33

A 50-year-old female with known systemic sclerosis complains of progressive shortening and pain in her fingertips. Radiographs reveal significant resorption of the distal phalangeal tufts (acro-osteolysis). What is the primary underlying pathophysiology driving this skeletal finding?

Explanation

Acro-osteolysis in systemic sclerosis is caused by chronic ischemia resulting from severe digital microangiopathy and Raynaud's phenomenon. The lack of blood flow leads to resorption of the distal phalangeal tufts.

Question 34

When formulating polymethyl methacrylate (PMMA) antibiotic-loaded bone cement for a spacer in a two-stage exchange for PJI, which characteristic is an absolute requirement for the admixed antibiotics?

Explanation

Antibiotics added to PMMA must be heat-stable because the exothermic polymerization reaction of bone cement reaches high temperatures. Vancomycin, tobramycin, and gentamicin are heat-stable and commonly used for this purpose.

Question 35

In the staging and prognosis of Langerhans Cell Histiocytosis (LCH), which of the following clinical scenarios carries the worst prognosis?

Explanation

The worst prognosis in LCH is seen in children under 2 years of age who have disseminated disease with multi-organ involvement, particularly involving 'risk organs' such as the liver, spleen, and bone marrow.

Question 36

A 60-year-old male is undergoing revision of a reverse total shoulder arthroplasty due to suspected indolent infection. Intraoperative cultures are sent. To maximize the yield for detecting Cutibacterium (Propionibacterium) acnes, how long should the microbiology laboratory hold the cultures?

Explanation

Cutibacterium acnes is a slow-growing, Gram-positive anaerobic bacillus frequently implicated in shoulder PJI. Cultures must be held for 14 to 21 days to ensure accurate detection.

Question 37

A patient with a history of MRSA PJI of the knee is currently 6 weeks status-post first-stage resection and placement of an articulating antibiotic spacer. They have completed a 6-week course of IV antibiotics. What is the most reliable method to confirm eradication of infection prior to proceeding with the second-stage reimplantation?

Explanation

Diagnosing the eradication of infection between stages of a two-stage exchange remains challenging, and there is no single highly reliable test. Surgeons typically use a combination of declining inflammatory markers, clinical appearance, and joint aspiration, though all have high false-negative or false-positive rates in this specific setting.

Question 38

A 42-year-old woman presents with diffuse skin thickening extending proximal to her elbows and knees. She complains of progressive dyspnea on exertion. Serologic testing is positive for Anti-Scl-70 antibodies. What is the most likely pulmonary complication associated with this specific autoantibody profile?

Explanation

Anti-Scl-70 (anti-topoisomerase I) antibodies are associated with diffuse cutaneous systemic sclerosis, which carries a high risk of interstitial lung disease (pulmonary fibrosis). In contrast, anti-centromere antibodies (CREST) are more associated with isolated pulmonary arterial hypertension.

Question 39

A 4-year-old girl is evaluated for a skull mass. Radiographs reveal a lytic lesion with a "beveled edge" or "hole-within-a-hole" appearance. Which of the following is the most likely diagnosis?

Explanation

The "beveled edge" or "hole-within-a-hole" appearance on a skull radiograph is classic for Langerhans Cell Histiocytosis (Eosinophilic Granuloma). This occurs due to unequal destruction of the inner and outer tables of the skull.

Question 40

A 82-year-old male with severe heart failure and a well-fixed total knee arthroplasty develops a coagulase-negative Staphylococcus PJI. Due to his prohibitive surgical risk, chronic suppressive oral antibiotic therapy is chosen. Which of the following is a strict prerequisite for the success of this treatment modality?

Explanation

For chronic suppressive antibiotic therapy to be a viable option, the implant must be well-fixed, the organism must be of low virulence and susceptible to oral antibiotics, and the patient must be able to tolerate the medication. A draining sinus tract is a relative contraindication.

Question 41

Biofilm formation plays a critical role in the pathogenesis of periprosthetic joint infections. Within a mature biofilm, which characteristic best explains the extreme resistance of the embedded bacteria to systemic antibiotic therapy?

Explanation

Bacteria within a mature biofilm exhibit a markedly altered phenotype, entering a dormant, stationary growth phase. Because most antibiotics target active cell division and metabolic processes, these dormant bacteria are highly resistant to standard antimicrobial therapy.

Question 42

A 55-year-old female with systemic sclerosis desires surgical correction of severe proximal interphalangeal (PIP) joint flexion contractures in her hands to improve hygiene. What is the most significant perioperative risk that must be extensively discussed with this patient?

Explanation

Patients with systemic sclerosis have profound digital microangiopathy. Any surgical intervention on the digits carries an extremely high risk of postoperative digital ischemia, necrosis, and severe wound healing complications.

Question 43

A 65-year-old female with a long-standing history of severe Rheumatoid Arthritis (RA) presents with acute knee pain 3 years after a total knee arthroplasty. Her baseline serum ESR and CRP are chronically elevated due to her RA. Which synovial fluid marker is the most accurate diagnostic tool for distinguishing PJI from an acute RA flare?

Explanation

Alpha-defensin maintains highly accurate sensitivity and specificity for diagnosing PJI even in the setting of systemic inflammatory diseases like rheumatoid arthritis, whereas synovial WBC counts and serum inflammatory markers may be falsely elevated by the underlying disease.

Question 44

A 9-year-old boy presents with localized pain in his clavicle. Imaging reveals a solitary, well-circumscribed, 'punched-out' lytic lesion. Biopsy confirms Eosinophilic Granuloma. If the lesion remains symptomatic despite brief observation, what is the most appropriate first-line intervention?

Explanation

Symptomatic, solitary Eosinophilic Granuloma (LCH) bone lesions that do not resolve with observation are effectively treated with intralesional corticosteroid (methylprednisolone) injection. Wide resection or radiation is overly aggressive for this benign condition.

Question 45

According to the updated 2018 Evidence-Based Definition of Periprosthetic Joint Infection, which of the following combinations satisfies the criteria for definitively diagnosing a PJI?

Explanation

The isolation of the exact same organism from two separate periprosthetic tissue or fluid cultures is a major criterion and definitively establishes the diagnosis of PJI.

Question 46

A patient with long-standing systemic sclerosis presents with severe, fixed flexion contractures of the PIP joints. Non-operative management has failed.

If surgery is deemed absolutely necessary despite the high risks, what is the preferred surgical procedure to provide stable, pain-free digits?

Explanation

In systemic sclerosis, PIP joint contractures are driven by the unyielding, fibrotic skin envelope rather than primary articular disease. Soft tissue releases and arthroplasties have high failure rates; therefore, PIP joint arthrodesis in a functional position is the most reliable surgical option if conservative care fails.

Question 47

A 65-year-old man presents with a painful total knee arthroplasty 3 years post-op. Serum CRP is 15 mg/L and ESR is 45 mm/hr. Joint aspiration yields a WBC count of 2,800 cells/uL with 75% PMNs. Which of the following synovial fluid biomarkers provides the highest specificity for diagnosing a periprosthetic joint infection?

Explanation

Alpha-defensin is an antimicrobial peptide released by neutrophils that has demonstrated >95% specificity and sensitivity for diagnosing PJI. It outperforms other markers in equivocal cases and is now a key minor criterion in modern diagnostic algorithms.

Question 48

A 72-year-old female presents 3 weeks after a primary total hip arthroplasty with acute onset of hip pain, erythema, and a draining sinus tract. Radiographs show well-fixed components. What is the most appropriate surgical management?

Explanation

DAIR is indicated for acute postoperative infections (within 4 weeks of surgery) with well-fixed implants and an intact soft-tissue envelope. Modular components should be exchanged to disrupt forming biofilms and allow thorough joint washout.

Question 49

A 50-year-old female with systemic sclerosis presents with progressive shortening of her distal fingers and painful, chalky subcutaneous nodules. Radiographs demonstrate resorption of the distal phalangeal tufts. What autoantibody is most commonly associated with her localized disease variant?

Explanation

Anti-centromere antibodies are strongly associated with limited cutaneous systemic sclerosis (CREST syndrome), which classically presents with calcinosis cutis and acro-osteolysis. Anti-Scl-70 is associated with diffuse systemic sclerosis and a higher risk of interstitial lung disease.

Question 50

An 8-year-old boy presents with back pain. Radiographs reveal a severe compression fracture of the T6 vertebral body (vertebra plana). Biopsy of the lesion shows sheets of eosinophils and mononuclear cells. Electron microscopy reveals tennis-racket shaped intracytoplasmic organelles. Which immunohistochemical marker will be definitively positive?

Explanation

The clinical presentation of vertebra plana with "tennis-racket" Birbeck granules on electron microscopy is pathognomonic for Langerhans Cell Histiocytosis (LCH). These histiocytic cells characteristically stain positive for CD1a, S-100, and Langerin (CD207).

Question 51

A 68-year-old man undergoes DAIR for an acute hematogenous periprosthetic joint infection of his knee. Intraoperative cultures grow methicillin-sensitive Staphylococcus aureus (MSSA). Which of the following oral antibiotic regimens is best supported by evidence for long-term suppression after initial IV therapy?

Explanation

Rifampin has excellent biofilm penetration and is highly effective against staphylococcal species in PJI. It must be combined with a companion drug (such as a fluoroquinolone like ciprofloxacin) to prevent the rapid emergence of resistance.

Question 52

A 6-year-old boy presents with a painful, isolated lytic lesion in the clavicle with mild periosteal reaction. Biopsy confirms eosinophilic granuloma. There is no impending fracture or neurological deficit. What is the most appropriate initial management?

Explanation

Isolated eosinophilic granuloma (LCH of bone) in children is a benign, often self-limiting process. Asymptomatic or mildly symptomatic lesions without high risk of pathologic fracture are typically managed with observation or intralesional corticosteroid injection.

Question 53

According to the Musculoskeletal Infection Society (MSIS) criteria, which of the following is considered a major (definitive) criterion for diagnosing a periprosthetic joint infection?

Explanation

The major criteria for PJI are either a sinus tract communicating with the prosthesis or the isolation of identical pathogens from at least two separate tissue or fluid samples. All other listed options represent minor criteria.

Question 54

A 55-year-old woman with a 15-year history of diffuse systemic sclerosis requires a total knee arthroplasty for severe secondary osteoarthritis. Which of the following perioperative complications is she at significantly higher risk for compared to the general population?

Explanation

Systemic sclerosis is characterized by microvascular obliteration and dense dermal collagen deposition. This compromises local skin perfusion, leading to a markedly increased risk of wound dehiscence and necrosis following surgical incisions.

Question 55

A 4-year-old girl is diagnosed with multifocal Langerhans Cell Histiocytosis. She presents with lytic skull lesions and exophthalmos. What endocrine abnormality is classically associated with this clinical triad?

Explanation

The classic Hand-Schüller-Christian triad of multifocal LCH includes lytic skull lesions, exophthalmos, and diabetes insipidus. The diabetes insipidus results from histiocytic infiltration of the pituitary stalk or hypothalamus.

Question 56

During a 2-stage revision for a chronic periprosthetic knee infection, an articulating antibiotic spacer is placed.

Compared to static spacers, articulating spacers in the knee have been shown to provide which of the following benefits?

Explanation

Articulating spacers maintain joint mobility, preventing severe capsular contracture and preserving the length of the extensor mechanism. This significantly facilitates surgical exposure during the second stage, yielding comparable infection eradication rates to static spacers.

Question 57

A 65-year-old male is 8 weeks out from the first stage of a 2-stage revision for a total hip PJI. His spacer is in place, and he has completed 6 weeks of IV antibiotics. His ESR and CRP have normalized, and his hip is clinically benign. What is the most appropriate next step?

Explanation

Following completion of IV antibiotics during a 2-stage revision, an "antibiotic holiday" of at least 2 to 4 weeks is recommended. This allows for clinical observation and re-evaluation of inflammatory markers to ensure the infection remains suppressed off therapy prior to reimplantation.

Question 58

According to the 2018 International Consensus Meeting (ICM) criteria, which of the following is considered a major criterion for diagnosing a periprosthetic joint infection?

Explanation

A sinus tract communicating with the prosthesis or two positive periprosthetic cultures with phenotypically identical organisms are the only major criteria for PJI. The others represent minor criteria.

Question 59

A 50-year-old female presents with severe Raynaud's phenomenon, esophageal dysmotility, and the findings shown in the clinical image.

Which autoantibody is most specifically associated with her likely diagnosis?

Explanation

The image and clinical presentation describe CREST syndrome (limited cutaneous systemic sclerosis). Anti-centromere antibodies are highly specific for CREST syndrome.

Question 60

A 6-year-old boy presents with mid-back pain. Radiographs reveal a "coin lesion" (vertebra plana) at T7 without posterior element involvement. Neurological exam is completely normal. What is the most appropriate initial management?

Explanation

Vertebra plana in a child without neurological deficit is classically associated with eosinophilic granuloma (Langerhans Cell Histiocytosis). It is typically self-limiting, and observation with bracing often leads to partial reconstitution of vertebral height.

Question 61

Which of the following scenarios is the most appropriate indication for Debridement, Antibiotics, and Implant Retention (DAIR) in the setting of periprosthetic joint infection?

Explanation

DAIR is most successful for acute postoperative infections (<4 weeks from index surgery) or acute hematogenous infections (<3 weeks of symptoms) with well-fixed implants and exchangeable modular parts. A sinus tract is a contraindication to DAIR.

Question 62

According to the 2018 International Consensus Meeting (ICM) criteria for periprosthetic joint infection, which of the following serum markers is heavily weighted as a minor criterion alongside C-reactive protein (CRP)?

Explanation

The 2018 ICM criteria introduced serum D-dimer as a minor criterion for PJI diagnosis. It is weighted with 2 points, equivalent to an elevated CRP, making it a highly useful adjunct in the diagnostic workup.

Question 63

A 68-year-old male presents with acute onset of severe right knee pain and swelling 3 weeks after a dental procedure. He underwent a right total knee arthroplasty 5 years ago. Aspiration yields 65,000 WBCs/uL with 95% neutrophils.

What is the most appropriate surgical management?

Explanation

Acute hematogenous PJI (symptoms lasting less than 3-4 weeks) in a well-fixed prosthesis is best managed with DAIR and modular component exchange. This strategy provides a high likelihood of eradicating the infection while preserving the well-fixed implants.

Question 64

Which of the following antibiotics is most critical to include in the treatment regimen for a retained total joint arthroplasty infected with methicillin-sensitive Staphylococcus aureus, owing to its efficacy against biofilm-associated bacteria?

Explanation

Rifampin has unique activity against staphylococcal species residing within a mature biofilm. It is universally recommended as an adjunct in the medical management of staphylococcal PJI treated with debridement and implant retention.

Question 65

When fabricating an articulating cement spacer for a two-stage revision total knee arthroplasty to treat a fungal PJI (Candida species), which of the following antimicrobial agents should be mixed into the polymethylmethacrylate (PMMA) bone cement?

Explanation

Amphotericin B and voriconazole are commonly used in PMMA for fungal PJI. Amphotericin B has a well-documented release profile and is heat-stable, making it the most suitable and traditional choice for cement spacers in fungal infections.

Question 66

A 55-year-old male undergoes a revision anatomic total shoulder arthroplasty for presumed aseptic loosening. At 10 days, 3 out of 5 intraoperative cultures grow Cutibacterium acnes. Which of the following describes the most characteristic trait of this organism in periprosthetic shoulder infections?

Explanation

Cutibacterium (formerly Propionibacterium) acnes is an anaerobic, slow-growing, gram-positive bacillus commonly implicated in shoulder PJI. Cultures should be held for at least 14 days to maximize the detection of this indolent organism.

Question 67

The optimal initial and sustained elution of antibiotics from a polymethylmethacrylate (PMMA) cement spacer is best achieved by which of the following preparation techniques?

Explanation

Antibiotic elution from PMMA is highly dependent on the surface area and porosity of the cement. Hand mixing (avoiding vacuum mixing) increases porosity, thereby enhancing the release of the admixed antibiotics.

Question 68

Chronic antibiotic suppression is most appropriate for which of the following patients with a confirmed periprosthetic joint infection?

Explanation

Chronic antibiotic suppression is reserved for patients who are medically unfit for surgery or refuse further operations, provided the implant is radiographically stable and the organism is susceptible to a tolerated oral antibiotic. A loose implant or a chronic sinus tract are relative contraindications.

Question 69

A 42-year-old woman presents with tightening of the skin on her face and hands, Raynaud's phenomenon, and dysphagia. She notes painful ulcerations at the tips of her fingers.

Which of the following antibodies is associated with an increased risk of developing pulmonary arterial hypertension in this specific disease subset?

Explanation

Anti-centromere antibodies are highly associated with the limited cutaneous form of systemic sclerosis (CREST syndrome). This specific subset has a significantly increased risk of developing isolated pulmonary arterial hypertension compared to patients with diffuse disease.

Question 70

Which of the following radiographic findings in the hand is considered a classic hallmark of systemic sclerosis?

Explanation

Acro-osteolysis, which is the resorption of the terminal phalangeal tufts, is a classic radiographic feature of systemic sclerosis. It is often accompanied by soft tissue thinning and calcinosis cutis.

Question 71

A 55-year-old female with limited cutaneous systemic sclerosis presents with painful, firm subcutaneous nodules on her fingertips that occasionally extrude a chalky white material.

What is the initial recommended medical therapy to manage these symptomatic lesions?

Explanation

Calcinosis cutis in systemic sclerosis is notoriously difficult to treat. Calcium channel blockers, such as diltiazem, are often considered first-line medical therapy to reduce calcium influx into cells, though surgical excision may be required for recalcitrant lesions.

Question 72

A patient with advanced systemic sclerosis is scheduled to undergo an elective orthopedic procedure. The surgical team must be hypervigilant regarding which of the following perioperative complications directly related to the disease pathophysiology?

Explanation

Patients with systemic sclerosis suffer from severe microvascular disease and Raynaud's phenomenon. Perioperative stress, cold exposure, or the use of epinephrine-containing local anesthetics can precipitate severe vasospasm leading to digital ischemia or necrosis.

Question 73

Flexion contractures of the fingers in patients with systemic sclerosis are primarily driven by which of the following pathologic processes?

Explanation

In systemic sclerosis, the overproduction and accumulation of collagen result in extensive fibrosis of the skin and deeper connective tissues. This fibrotic process leads to severe, progressive tethering and flexion contractures of the digits without primary articular destruction.

Question 74

In differentiating the diffuse cutaneous form of systemic sclerosis from the limited form (CREST syndrome), which of the following clinical features is highly typical of the diffuse form?

Explanation

Diffuse cutaneous systemic sclerosis is characterized by rapid progression of skin thickening (both proximal and distal) and early, severe internal organ involvement. This notably includes interstitial lung disease (pulmonary fibrosis) and scleroderma renal crisis.

Question 75

A patient with scleroderma-associated Raynaud's phenomenon presents with an acute, extremely painful ischemic digital ulcer. Conservative measures and oral therapies have failed. Which of the following is the most appropriate next step in management to prevent autoamputation?

Explanation

For severe, limb-threatening Raynaud's phenomenon with ischemic digital ulcers in systemic sclerosis, intravenous prostacyclin analogues (e.g., epoprostenol or iloprost) are indicated. They promote intense vasodilation and inhibit platelet aggregation to salvage the digit.

Question 76

A 6-year-old child presents with back pain and a normal neurologic examination. Radiographs of the thoracic spine demonstrate a severe, uniform collapse of the T7 vertebral body, with preservation of the adjacent disc spaces. Which of the following is the most likely diagnosis?

Explanation

A severely flattened vertebral body (vertebra plana) with intact adjacent disc spaces in a child is the classic radiographic presentation of eosinophilic granuloma. This is a localized form of Langerhans cell histiocytosis.

Question 77

Which of the following somatic genetic mutations is found in approximately 50-60% of patients with Langerhans cell histiocytosis, supporting its modern classification as a myeloid neoplastic disorder?

Explanation

The BRAF V600E somatic mutation is identified in more than half of patients with Langerhans cell histiocytosis. This discovery has led to its reclassification as a neoplastic disorder rather than a reactive process, and it offers a target for specific inhibitor therapies.

Question 78

A biopsy of a lytic skull lesion in a 5-year-old boy reveals clusters of histiocytes with abundant eosinophilic cytoplasm and indented nuclei. On electron microscopy, rod-like intracytoplasmic inclusion bodies with a central striated line are identified. What are these structures called?

Explanation

Birbeck granules are the hallmark electron microscopic finding in Langerhans cell histiocytosis. They are frequently described as "tennis-racket" shaped intracytoplasmic organelles.

Question 79

Which of the following conditions is most likely to cause a false-positive synovial alpha-defensin test in the workup of a painful total hip arthroplasty?

Explanation

Metallosis and adverse local tissue reactions to metal debris can cause a false-positive alpha-defensin result. Although alpha-defensin is an antimicrobial peptide highly specific for PJI, severe metallic debris reactions mimic the inflammatory profile sufficiently to trigger false positives.

Question 80

A 6-year-old boy presents with back pain and a normal neurologic exam. Radiographs reveal complete collapse of the T8 vertebral body (vertebra plana). Laboratory studies are within normal limits. Which of the following is the most appropriate initial management?

Explanation

Solitary vertebra plana in a child is strongly suggestive of Langerhans cell histiocytosis (eosinophilic granuloma). In neurologically intact patients, it is a self-limiting process that often reconstitutes over time, making observation with or without an extension brace the treatment of choice.

Question 81

Staphylococcus epidermidis is a common pathogen in periprosthetic joint infections. Which of the following components is primarily responsible for the structural integrity of the biofilm produced by this organism?

Explanation

The biofilm of S. epidermidis is primarily composed of polysaccharide intercellular adhesin (PIA), which is synthesized by the icaADBC operon. This extracellular polymeric substance protects the bacteria from host immune responses and antibiotics.

Question 82

A 42-year-old woman with a history of systemic sclerosis presents with progressive shortening and pain in her fingertips. Radiographs show resorption of the distal phalangeal tufts.

What vascular phenomenon is most characteristically associated with the pathogenesis of this skeletal finding?

Explanation

The radiograph demonstrates acro-osteolysis, which in systemic sclerosis is driven by chronic ischemia. This ischemia results from Raynaud's phenomenon (an exaggerated sympathetic vasoconstrictive response) coupled with progressive digital microvasculopathy.

Question 83

Recent molecular advancements have classified Langerhans cell histiocytosis (LCH) as an inflammatory myeloid neoplasm. Which of the following genetic mutations is present in over 50% of LCH cases and serves as a potential target for molecular therapy?

Explanation

The BRAF V600E somatic mutation is found in 50-60% of LCH cases, leading to constitutive activation of the MAPK/ERK pathway. Targeted therapies, such as the BRAF inhibitor vemurafenib, are utilized for severe, refractory multisystem cases.

Question 84

In a patient undergoing Debridement, Antibiotics, and Implant Retention (DAIR) for a periprosthetic joint infection, which of the following factors is considered an absolute contraindication to the procedure?

Explanation

The presence of a sinus tract indicates a chronic infection with an established, mature biofilm. This is an absolute contraindication to a DAIR procedure, as eradication cannot be achieved without complete implant removal.

Question 85

You are contemplating surgical release for severe PIP joint flexion contractures in a patient with long-standing systemic sclerosis. Which of the following is the most significant localized risk regarding this surgical intervention?

Explanation

Patients with systemic sclerosis have profound digital microvasculopathy and poor tissue perfusion. Surgical interventions in the hand carry an exceptionally high risk of digital ischemia, delayed wound healing, and frank necrosis.

Question 86

A 65-year-old male develops a delayed periprosthetic joint infection 1 year following a reverse total shoulder arthroplasty. Cultures eventually grow Cutibacterium acnes. Which of the following best describes the microbiological characteristics of this organism?

Explanation

Cutibacterium (formerly Propionibacterium) acnes is a slow-growing, Gram-positive, anaerobic (or microaerophilic) bacillus commonly found in the sebaceous glands of the shoulder. Extended culture incubation (up to 14 days) is required to maximize detection.

Question 87

A 65-year-old male presents with acute onset knee pain and swelling 3 weeks after an uncomplicated total knee arthroplasty. Aspiration yields 55,000 WBC/uL with 95% neutrophils. What is the most appropriate surgical management?

Explanation

Irrigation and debridement with modular exchange (DAIR) is indicated for acute postoperative periprosthetic joint infections, typically defined as occurring within 4 weeks of the index surgery. It is also indicated for acute hematogenous infections with well-fixed implants.

Question 88

Which of the following synovial fluid biomarkers is an antimicrobial peptide produced by neutrophils and serves as an important adjunctive test for diagnosing periprosthetic joint infection due to its high accuracy, even in the setting of concurrent systemic inflammatory diseases?

Explanation

Alpha-defensin is a biomarker released by neutrophils in response to pathogens. It demonstrates high sensitivity and specificity for diagnosing PJI, remaining reliable even if the patient has received prior antibiotics or has an underlying inflammatory arthropathy.

Question 89

A 9-year-old boy has a biopsy of a solitary lytic clavicle lesion. Electron microscopy of the specimen demonstrates characteristic cytoplasmic organelles resembling "tennis rackets." These structures are pathognomonic for which of the following conditions?

Explanation

Birbeck granules are characteristic cytoplasmic organelles shaped like tennis rackets seen on electron microscopy. They are pathognomonic for Langerhans cell histiocytosis (LCH).

Question 90

A 40-year-old female with diffuse systemic sclerosis presents with palpable grating over the flexor tendons of her wrists and ankles during active motion. The presence of these tendon friction rubs is most strongly associated with an increased risk for which of the following?

Explanation

Tendon friction rubs are highly specific to the diffuse cutaneous form of systemic sclerosis. Their presence is a poor prognostic marker, strongly associated with severe skin thickening, restrictive lung disease, renal crisis, and reduced overall survival.

Question 91

A 50-year-old woman with a history of systemic sclerosis presents with worsening fingertip pain.

Radiographs show resorption of the terminal phalangeal tufts. What is this radiographic finding termed?

Explanation

Acro-osteolysis refers to the resorption of the distal phalangeal tufts, a finding commonly seen in scleroderma, Raynaud's phenomenon, and secondary hyperparathyroidism. In scleroderma, it is primarily driven by chronic digital ischemia.

Question 92

A patient is undergoing revision of a loose total hip arthroplasty. Preoperative aspirates were culture-negative despite elevated serum inflammatory markers. To improve diagnostic yield, the explanted components are subjected to sonication. What is the primary mechanism by which sonication increases the sensitivity of cultures?

Explanation

Sonication uses low-frequency ultrasound to physically disrupt and dislodge biofilms adhering to explanted hardware. This process releases sessile bacteria into the fluid, significantly improving culture sensitivity in PJI.

Question 93

A 6-year-old girl presents with mid-back pain. Radiographs of the thoracic spine demonstrate severe, uniform collapse of the T7 vertebral body with preservation of the adjacent disc spaces. A diagnosis of eosinophilic granuloma is suspected. What is the most appropriate initial management for this spinal lesion without neurological deficits?

Explanation

Eosinophilic granuloma often presents as vertebra plana (Calvé disease) in children. Without neurological compromise or significant instability, observation and conservative care is the standard, as the lesion typically heals and the vertebral body often reconstitutes.

Question 94

A 72-year-old diabetic male is diagnosed with a Candida albicans periprosthetic joint infection of the knee. What is the generally recommended surgical and medical management strategy for a chronic fungal PJI?

Explanation

Fungal PJIs are notoriously difficult to eradicate due to robust biofilm formation and lack of approved antifungal-loaded cements for spacers. A two-stage exchange, typically combined with extended systemic antifungal therapy, is the gold standard for treatment.

Question 95

A 42-year-old female with systemic sclerosis presents with severe flexion contractures of the proximal interphalangeal (PIP) joints and limited hand function.

Which of the following best describes the pathogenesis of her joint contractures?

Explanation

Joint contractures in systemic sclerosis primarily result from the progressive fibrosis, thickening, and tightening of the skin and periarticular soft tissues. This contrasts with rheumatoid arthritis, where primary synovial pannus drives joint destruction.

Question 96

A 4-year-old child presents with a triad of exophthalmos, diabetes insipidus, and multiple lytic skull lesions. This classic clinical triad is indicative of which variant of Langerhans cell histiocytosis?

Explanation

Hand-Schüller-Christian disease is a chronic disseminated form of LCH. It is classically characterized by the clinical triad of diabetes insipidus, exophthalmos, and lytic bone lesions of the skull.

Question 97

A 68-year-old female undergoes first-stage explantation and placement of an articulating antibiotic cement spacer for a chronic PJI of the knee. The cement is loaded with high doses of vancomycin and tobramycin. Postoperatively, she develops rising serum creatinine and oliguria. Which of the following is the most likely cause?

Explanation

Antibiotics locally eluted from PMMA spacers can reach high systemic concentrations. When large amounts of cement and high doses of nephrotoxic antibiotics (like vancomycin and tobramycin) are used, patients are at significant risk for acute kidney injury.

Question 98

A 12-year-old girl is diagnosed with a symptomatic, solitary eosinophilic granuloma of the proximal humerus confirmed by biopsy. Which of the following is the most appropriate minimally invasive treatment option that has demonstrated high rates of resolution?

Explanation

For a solitary, symptomatic eosinophilic granuloma, intralesional injection of corticosteroids (e.g., methylprednisolone) is a highly effective, minimally invasive treatment. It promotes rapid pain relief, healing, and ossification of the lesion.

Question 99

According to the Musculoskeletal Infection Society (MSIS) criteria, a diagnosis of "culture-negative" periprosthetic joint infection can be established definitively if which of the following is present?

Explanation

A communicating sinus tract is a definitive major criterion for PJI. Its presence alone confirms the diagnosis, establishing a "culture-negative" PJI even if intraoperative cultures fail to grow an organism.

Question 100

A 55-year-old female with limited cutaneous systemic sclerosis (CREST syndrome) presents with hard, painful subcutaneous nodules over her extensor forearms and fingertips.

Excision is considered due to frequent skin breakdown. What is the primary composition of these deposits?

Explanation

The lesions described represent calcinosis cutis, a classic feature of CREST syndrome (Calcinosis, Raynaud's, Esophageal dysmotility, Sclerodactyly, Telangiectasia). These subcutaneous deposits are primarily composed of insoluble calcium hydroxyapatite crystals.

Orthopaedic Surgery Board Exam Review: ABOS Part I & AAOS OITE Prep Questions | Part 22210

ABOS Board Review: Periprosthetic Infections, Systemic Sclerosis, LCH | Part 25

Key Takeaway

ABOS Board Review: Periprosthetic Infections, Systemic Sclerosis, LCH | Part 25

Chapter Index