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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 31 of 326

This practice set contains high-yield board review questions covering key concepts in 3. Adult Reconstruction (Hip & Knee). Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 601

Topic: Total Hip Arthroplasty (THA)

The patient's radiographs show radiolucent lines at the bone–cement interface located circumferentially around all seven DeLee and Charnley zones in the acetabulum and lucencies in all seven Gruen zones around the femoral component. Based on the Harris and Barrack grading system for cement mantle quality, what grade would most accurately describe the femoral component's cement mantle in this scenario?

. A. Grade A
. B. Grade B
. C. Grade C
. D. Grade C2
. E. Grade D

Correct Answer & Explanation

. E. Grade D

Explanation

Correct Answer: EExplanation:The case describes the femoral component as having 'separated from the femoral cement with lucencies in all seven Gruen zones.' The Harris and Barrack grading system defines:Grade A:Complete filling of the medullary cavity by cement, a so-called ‘white-out’ at the cement–bone interface.Grade B:Slight radiolucency of the cement–bone interface.Grade C:Radiolucency involving 50% to 99% of the cement–bone interface or a defective or incomplete cement mantle.Grade C2:A defect where the tip of the stem abuts the cortex with no intervening cement.Grade D:Radiolucency at the cement–bone interface of 100% in any projection, or a failure to fill the canal with cement such that the tip of the stem is not covered.Since the case states 'lucencies in all seven Gruen zones,' this indicates 100% radiolucency at the cement-bone interface, which directly corresponds to a Grade D cementing technique according to Harris and Barrack.A. Grade A:This describes a perfect cement mantle ('white-out'), which is clearly not the case here.B. Grade B:This describes slight radiolucency, which is less severe than 'lucencies in all seven Gruen zones.'C. Grade C:This describes radiolucency involving 50% to 99% or a defective mantle, but 'all seven Gruen zones' implies 100% involvement, making Grade D more accurate.D. Grade C2:This is a specific type of Grade C defect where the stem tip abuts the cortex. While possible in severe loosening, the description of 'lucencies in all seven Gruen zones' more broadly and definitively points to Grade D, which encompasses 100% radiolucency.E. Grade D:This grade is defined by 'Radiolucency at the cement–bone interface of 100% in any projection,' which perfectly matches the description of 'lucencies in all seven Gruen zones.'

Question 602

Topic: 3. Adult Reconstruction (Hip & Knee)

The patient reports severe pain after walking 200 yards, which improves with rest. He denies fever, chills, or a sinus tract. He also denies night pain or constant pain. On examination, he has an antalgic gait and a positive Trendelenburg sign. Based on this clinical presentation, what is the most likely diagnosis?

. A. Septic loosening of the THA
. B. Trochanteric bursitis
. C. Aseptic loosening of the THA
. D. Lumbar radiculopathy
. E. Vascular claudication

Correct Answer & Explanation

. C. Aseptic loosening of the THA

Explanation

Correct Answer: CExplanation:The case provides clear differentiating features between aseptic and septic loosening, as well as other causes of hip pain:Aseptic loosening:Typically, pain is aggravated by weightbearing, significant with the first few steps of walking (start-up pain) which improves slightly with further walking only to worsen again with more walking. The pain is always improved with rest and rarely constant. Examination may reveal shortening, antalgic gait, and positive Trendelenburg sign.Septic loosening:Suggested by a history of fever, chills, sinus tract, night pain, rest pain, or constant pain.The patient's symptoms of 'severe pain after walking 200 yards,' which 'improves with rest,' and the absence of fever, chills, sinus tract, night pain, or constant pain, strongly point towards aseptic loosening. The physical exam findings of 'antalgic gait and a positive Trendelenburg sign' further support this diagnosis.A. Septic loosening of the THA:This is less likely given the absence of fever, chills, sinus tract, night pain, or constant pain. The pain pattern (worse with activity, better with rest) is classic for aseptic loosening.B. Trochanteric bursitis:While a possibility for hip pain, the description of severe pain with walking, improving with rest, and signs of instability (Trendelenburg) are more indicative of component loosening rather than isolated bursitis. Bursitis pain is often localized to the greater trochanter and can be worse with direct pressure or lying on the affected side.C. Aseptic loosening of the THA:This aligns perfectly with the patient's symptoms: pain aggravated by weightbearing (walking 200 yards), improvement with rest, and the absence of infectious signs. The antalgic gait and positive Trendelenburg sign are classic findings for hip pathology, including loosening.D. Lumbar radiculopathy:This would typically present with neurogenic features such as radiation below the knee, numbness, paraesthesia, or dysaesthesias, which are not mentioned in the patient's presentation.E. Vascular claudication:While pain with walking that improves with rest is characteristic of claudication, it is typically described as cramping in the calf or thigh, and pulses/skin temperature would need to be checked. The patient's symptoms are localized to the hip, and the presence of an antalgic gait and Trendelenburg sign points to hip joint pathology.

Question 603

Topic: 3. Adult Reconstruction (Hip & Knee)
The patient requires revision hip surgery due to aseptic loosening. Given the extensive metaphyseal cancellous bone loss and intact diaphysis often seen after removal of a cemented prosthesis, which Paprosky classification type for femoral defects would most accurately describe this patient's likely bone loss?
. Type I
. Type II
. Type IIIA
. Type IIIB
. Type IV

Correct Answer & Explanation

. Type II

Explanation

The Paprosky classification system for femoral defects is as follows: Type I: Minimal metaphyseal cancellous bone loss/normal intact diaphysis. Type II: Extensive metaphyseal cancellous bone loss/normal intact diaphysis. Often seen after removal of cemented prosthesis. Type IIIA: Metaphysis severely damaged/> 4 cm diaphyseal bone for distal fixation. Type IIIB: Metaphysis severely damaged/< 4 cm diaphyseal bone for distal fixation. Type IV: Extensive metaphyseal and diaphyseal bone loss/isthmus non-supportive. The question describes extensive metaphyseal cancellous bone loss and intact diaphysis, which matches Paprosky Type II.

Question 604

Topic: 3. Adult Reconstruction (Hip & Knee)
During surgical planning for this patient's revision THA, the examiner asks about bone loss. The candidate mentions the Paprosky classification for acetabular defects. If the preoperative radiographs show superior migration of the hip center and ischial osteolysis, which Paprosky acetabular defect type is most likely?
. Type I
. Type IIA
. Type IIB
. Type IIC
. Type III

Correct Answer & Explanation

. Type III

Explanation

The Paprosky classification of acetabular bone defects categorizes defects based on severity. Type III defects are characterized by significant bone loss, often involving superior migration of the hip center, ischial osteolysis, teardrop osteolysis, and deficiency of the anterior column and/or medial wall. These findings indicate severe bone loss requiring specialized reconstruction.

Question 605

Topic: Total Hip Arthroplasty (THA)

The patient requires an extended trochanteric osteotomy (ETO) for cement removal. When consenting the patient for this procedure, which of the following complications is *specifically* increased or unique to the use of an ETO compared to a standard revision THA without osteotomy?

. A. Dislocation
. B. Nerve palsy (e.g., sciatic nerve)
. C. Heterotopic ossification
. D. Malunion or non-union of the osteotomy site
. E. Deep vein thrombosis (DVT)

Correct Answer & Explanation

. D. Malunion or non-union of the osteotomy site

Explanation

Correct Answer: DExplanation:The case specifically lists complications associated with the ETO: 'In addition the patient is going to require an extended trochanteric osteotomy (ETO) to remove the cement distally and this will increase operating time and blood loss. There is always the concern that the osteotomy site will go on to either malunion or non-union. Osteotomy migration or fracture can also occur.'A. Dislocation:Dislocation is a general complication of THA revision, but not specifically increased or unique to the ETO itself. The case mentions 'Usually component malpositioning or laxity of soft tissues around the hip' as causes.B. Nerve palsy (e.g., sciatic nerve):Nerve palsy is a known complication of THA revision surgery in general (2–7%), but not specifically or uniquely linked to the ETO itself more than other aspects of the revision.C. Heterotopic ossification:Heterotopic ossification is a general complication of hip surgery, including primary and revision THA, but not specifically unique to or significantly increased by an ETO compared to other revision approaches.D. Malunion or non-union of the osteotomy site:This is a direct and unique complication of performing an osteotomy. The case explicitly states, 'There is always the concern that the osteotomy site will go on to either malunion or non-union. Osteotomy migration or fracture can also occur.' This is a specific risk introduced by the ETO.E. Deep vein thrombosis (DVT):DVT is a general complication of major orthopedic surgery, including THA revision, but not specifically or uniquely increased by the ETO itself.

Question 606

Topic: Total Hip Arthroplasty (THA)

During surgical planning for this patient's revision THA, the candidate states a preference for uncemented components. Given the need for an ETO to remove distal cement, what is the primary rationale for choosing an uncemented femoral implant in this specific scenario?

. A. Uncemented components are generally preferred if previously cement was used.
. B. Cement would be relatively contraindicated if using an ETO as it may get into the osteotomy site and prevent healing.
. C. Uncemented stems allow for easier future revisions.
. D. The patient's age (78 years old) makes uncemented fixation more reliable.
. E. Uncemented components have a lower risk of postoperative infection.

Correct Answer & Explanation

. B. Cement would be relatively contraindicated if using an ETO as it may get into the osteotomy site and prevent healing.

Explanation

Correct Answer: BExplanation:The case explicitly addresses the choice of uncemented components in the context of an ETO: 'I would use uncemented components as generally they are preferred if previously cement was used. Cement would be relatively contraindicated if using an ETO as it may get into the osteotomy site and prevent healing.'A. Uncemented components are generally preferred if previously cement was used:While the candidate states this as a general preference, it's not theprimaryrationale given in the case forthis specific scenarioinvolving an ETO. The ETO introduces a more direct and specific contraindication to cement.B. Cement would be relatively contraindicated if using an ETO as it may get into the osteotomy site and prevent healing:This is the direct and specific reason provided in the case for preferring uncemented components when an ETO is performed. The presence of cement in the osteotomy site can impair bone healing, leading to complications like non-union.C. Uncemented stems allow for easier future revisions:While uncemented stems can sometimes be easier to remove in future revisions compared to well-fixed cemented stems, this is not the primary rationale given in the case for the current decision regarding ETO.D. The patient's age (78 years old) makes uncemented fixation more reliable:Patient age is a factor in bone quality, but the case does not state that uncemented fixation ismore reliablespecifically due to the patient's age. In fact, older patients with poorer bone quality might sometimes benefit from cemented fixation, though modern uncemented options are robust. The primary reason given is ETO-specific.E. Uncemented components have a lower risk of postoperative infection:There is no evidence presented in the case, nor is it a generally accepted principle, that uncemented components inherently have a lower risk of postoperative infection compared to cemented components. Infection risk is multifactorial.

Question 607

Topic: 3. Adult Reconstruction (Hip & Knee)

For this revision THA, the candidate plans to use a multihole revision acetabular shell. Regarding the bearing surface and femoral head size, what is the most appropriate choice to significantly reduce the risk of postoperative dislocation, as discussed in the case?

. A. Ceramic-on-ceramic bearing with a 28 mm head
. B. Metal-on-metal bearing with a 32 mm head
. C. Metal-on-polyethylene bearing with a 36 mm head
. D. Ceramic-on-polyethylene bearing with a 28 mm head
. E. Dual mobility bearing with a 32 mm head

Correct Answer & Explanation

. C. Metal-on-polyethylene bearing with a 36 mm head

Explanation

Correct Answer: CExplanation:The case explicitly states the candidate's plan for the bearing surface and head size: 'A long stem femoral implant, multihole revision (tantulum) acetabular shell and a metal-on-polyethylene bearing surface. I would attempt to use at least 32 mm head but preferably a 36 mm head as this significantly reduces the risk of postoperative dislocation.'A. Ceramic-on-ceramic bearing with a 28 mm head:While ceramic-on-ceramic offers low wear, a 28 mm head is smaller and associated with a higher risk of dislocation compared to larger heads. The case specifically mentions preferring a 36 mm head.B. Metal-on-metal bearing with a 32 mm head:Metal-on-metal bearings have fallen out of favor due to concerns about metal ion release and pseudotumor formation. While a 32 mm head is better than 28 mm, the case prefers 36 mm.C. Metal-on-polyethylene bearing with a 36 mm head:This option directly matches the candidate's stated preference: 'metal-on-polyethylene bearing surface' and 'preferably a 36 mm head as this significantly reduces the risk of postoperative dislocation.'D. Ceramic-on-polyethylene bearing with a 28 mm head:Similar to option A, a 28 mm head is not the preferred size for reducing dislocation risk in this scenario.E. Dual mobility bearing with a 32 mm head:While dual mobility bearings are excellent for reducing dislocation risk, they are not explicitly mentioned as the chosen bearing surface in the candidate's plan. The candidate specifically states 'metal-on-polyethylene bearing surface' and a preference for a 36 mm head.

Question 608

Topic: 3. Adult Reconstruction (Hip & Knee)

The case references Barrack RL, Mulroy RD Jr, Harris WH. 'Improved cementing techniques and femoral component loosening in young patients with hip arthroplasty: a 12 year radiographic review. J Bone Joint Surg Br 1992;74:385–389.' The examiner notes this is a classic hip paper and the candidate 'should know the key message, relevance and why it is important.' Based on the context of the entire case discussion, what is the key message of this paper?

. A. The superiority of uncemented femoral components in young patients.
. B. The importance of dual mobility bearings in reducing dislocation rates.
. C. The correlation between improved cementing techniques and reduced femoral component loosening.
. D. The efficacy of extended trochanteric osteotomy for cement removal.
. E. The classification of acetabular bone defects for revision surgery.

Correct Answer & Explanation

. C. The correlation between improved cementing techniques and reduced femoral component loosening.

Explanation

Correct Answer: CExplanation:The title of the paper itself, 'Improved cementing techniques and femoral component loosening in young patients with hip arthroplasty,' directly indicates its key message. The case further reinforces this by discussing first, second, third, and fourth-generation cementing techniques and the Harris and Barrack grading system for cement mantle quality, all of which are related to the quality and impact of cementing techniques on component longevity.A. The superiority of uncemented femoral components in young patients:While uncemented components are often used in young patients, the paper's title and the context of the case (which heavily discussescementing techniques) point to the importance ofcementedfixation quality, not necessarily the superiority of uncemented.B. The importance of dual mobility bearings in reducing dislocation rates:This is a separate topic related to bearing surfaces and stability, not directly addressed by the paper's title or the primary focus of the cementing technique discussion.C. The correlation between improved cementing techniques and reduced femoral component loosening:This directly aligns with the paper's title and the extensive discussion in the case about the evolution and importance of proper cementing techniques to prevent loosening, particularly in the context of the patient's first-generation cementing failure.D. The efficacy of extended trochanteric osteotomy for cement removal:ETO is a surgical technique for revision, but not the primary focus of a paper oncementing techniquesandloosening.E. The classification of acetabular bone defects for revision surgery:While bone defect classification is discussed in the case, it's a separate topic from the specific paper referenced, which focuses on femoral cementing.

Question 609

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old male presents with a painful total knee arthroplasty (TKA) 4 years postoperatively. His ESR and CRP are elevated, and a joint aspiration is performed. According to the 2018 International Consensus Meeting (ICM) criteria, what synovial fluid white blood cell (WBC) count is the threshold for diagnosing chronic periprosthetic joint infection?

. Greater than 500 cells/muL
. Greater than 1,500 cells/muL
. Greater than 3,000 cells/muL
. Greater than 10,000 cells/muL
. Greater than 50,000 cells/muL

Correct Answer & Explanation

. Greater than 3,000 cells/muL

Explanation

The 2018 ICM criteria established the threshold for synovial fluid WBC count in chronic knee periprosthetic joint infection as greater than 3,000 cells/muL. For acute infections (within 6 weeks of surgery or acute hematogenous), the threshold is higher at 10,000 cells/muL.

Question 610

Topic: 3. Adult Reconstruction (Hip & Knee)

A 72-year-old female undergoes a two-stage exchange arthroplasty for a chronic knee periprosthetic joint infection. An articulating cement spacer is planned. Compared to a static spacer, an articulating spacer is generally contraindicated in which of the following scenarios?

. Extensive bone loss with lack of collateral ligament stability
. Infection with methicillin-resistant Staphylococcus aureus (MRSA)
. Patients over 80 years of age
. Polymicrobial infections
. Prior history of a patellectomy

Correct Answer & Explanation

. Extensive bone loss with lack of collateral ligament stability

Explanation

Static spacers are preferred over articulating spacers in cases of massive bone loss, severe ligamentous instability, or compromised soft-tissue envelopes requiring flap coverage. Articulating spacers require adequate bone stock and collateral stability to function correctly without dislocating or causing periprosthetic fractures.

Question 611

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old male presents with end-stage ankle osteoarthritis and a concomitant varus deformity of 20 degrees. Which of the following is an absolute contraindication for a total ankle arthroplasty (TAA) in this patient?

. Patient age under 60 years
. Avascular necrosis involving more than 50% of the talar body
. History of a previous medial malleolar fracture
. Ankle varus deformity of 20 degrees
. Body mass index (BMI) of 32

Correct Answer & Explanation

. Avascular necrosis involving more than 50% of the talar body

Explanation

Avascular necrosis of greater than 50% of the talar body is an absolute contraindication for TAA due to a high risk of component subsidence and failure. While severe deformities require correction, they can often be managed with concurrent procedures, whereas massive talar AVN necessitates an ankle arthrodesis.

Question 612

Topic: 3. Adult Reconstruction (Hip & Knee)

A 62-year-old female presents with squeaking from her total hip arthroplasty, which utilizes a ceramic-on-ceramic bearing. She is otherwise asymptomatic. Squeaking in ceramic-on-ceramic hips is most strongly associated with which of the following?

. Acetabular component retroversion
. Femoral stem subsidence
. Edge loading due to component malposition
. Use of an oversized femoral head
. Concurrent low-grade periprosthetic joint infection

Correct Answer & Explanation

. Edge loading due to component malposition

Explanation

Squeaking in ceramic-on-ceramic bearings is strongly correlated with edge loading, which typically occurs due to acetabular component malposition (e.g., steep inclination or excessive anteversion/retroversion). Edge loading leads to loss of fluid film lubrication and stripe wear, producing the characteristic noise.

Question 613

Topic: 3. Adult Reconstruction (Hip & Knee)

A synovial fluid alpha-defensin test is ordered to evaluate a patient for a periprosthetic joint infection (PJI) of the knee. What is the physiological role and cellular source of alpha-defensin?

. An antimicrobial peptide released by activated neutrophils
. A cytokine released by macrophages in response to metal wear debris
. An acute phase reactant produced by the liver
. An endotoxin produced by Gram-positive bacteria
. A degradation product of the articular cartilage matrix

Correct Answer & Explanation

. An antimicrobial peptide released by activated neutrophils

Explanation

Alpha-defensin is a host-derived antimicrobial peptide secreted by activated neutrophils in response to infection. It serves as a highly sensitive and specific biomarker for diagnosing PJI, remaining reliable even in the setting of concurrent antibiotic use.

Question 614

Topic: 3. Adult Reconstruction (Hip & Knee)

A 66-year-old male with a metal-on-polyethylene total hip arthroplasty utilizing a modular large-diameter cobalt-chromium head presents with groin pain and an expanding soft tissue mass. Aspiration yields sterile, cloudy fluid. What is the primary mechanism responsible for this presentation?

. Type IV delayed hypersensitivity to polyethylene debris
. Mechanically assisted crevice corrosion at the head-neck junction
. Aseptic loosening secondary to poor cement technique
. Undiagnosed indolent fungal periprosthetic joint infection
. Galvanic corrosion between the titanium shell and cobalt-chromium liner

Correct Answer & Explanation

. Mechanically assisted crevice corrosion at the head-neck junction

Explanation

The clinical picture of an adverse local tissue reaction (ALTR) or pseudotumor in a metal-on-polyethylene THA with a modular head is indicative of trunnionosis. This is caused by mechanically assisted crevice corrosion (MACC) at the modular head-neck junction (trunnion), releasing toxic metal ions.

Question 615

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient is undergoing the first stage of a two-stage revision for a chronic knee PJI. High-dose antibiotics are mixed into the polymethyl methacrylate (PMMA) cement spacer. To maximize antibiotic elution while maintaining structural integrity, which mixing technique is most appropriate?

. Vacuum mixing the cement to eliminate porosity
. Hand mixing the cement to increase porosity and surface area
. Adding more than 20% by weight of liquid antibiotics to the cement powder
. Waiting for the cement to fully cure before adding the antibiotics
. Adding the antibiotics exclusively to the liquid monomer before mixing

Correct Answer & Explanation

. Hand mixing the cement to increase porosity and surface area

Explanation

For antibiotic spacers, hand mixing is preferred over vacuum mixing because it increases the porosity of the cement, thereby maximizing the surface area and subsequent antibiotic elution. High doses of powdered (not liquid) antibiotics must be added to the polymer powder to ensure a robust local release.

Question 616

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old man presents with a painful total knee arthroplasty (TKA) 3 years postoperatively. Serum ESR is 45 mm/hr and CRP is 25 mg/L. Joint aspiration yields a white blood cell count of 4,500 cells/µL with 85% polymorphonuclear neutrophils. Excluding metallosis and inflammatory arthropathies, which of the following synovial fluid markers offers the highest specificity for confirming a diagnosis of periprosthetic joint infection (PJI)?

. Interleukin-6 (IL-6)
. Alpha-defensin
. Leukocyte esterase colorimetric strip
. Synovial C-reactive protein (CRP)
. Synovial fluid polymorphonuclear cell percentage

Correct Answer & Explanation

. Alpha-defensin

Explanation

Alpha-defensin is an antimicrobial peptide released by neutrophils that demonstrates extremely high specificity (>95%) for diagnosing periprosthetic joint infection. It remains highly accurate even in the presence of systemic antibiotics and is a major criterion in the 2018 ICM scoring system.

Question 617

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old female presents with acute onset of severe left knee pain, fever, and localized erythema 21 days after undergoing an uncomplicated primary total knee arthroplasty. Aspiration yields purulent fluid, and Gram stain shows Gram-positive cocci in clusters. Which of the following is the most appropriate initial surgical management?

. Suppressive oral antibiotic therapy for 6 weeks followed by single-stage revision
. Arthroscopic joint lavage and drain placement
. Debridement, antibiotics, and implant retention (DAIR) with polyethylene exchange
. Immediate two-stage exchange arthroplasty with an articulating antibiotic spacer
. Immediate single-stage exchange arthroplasty with a cemented constrained implant

Correct Answer & Explanation

. Debridement, antibiotics, and implant retention (DAIR) with polyethylene exchange

Explanation

For an acute postoperative PJI occurring within 4 weeks of the index arthroplasty, Debridement, Antibiotics, and Implant Retention (DAIR) with modular polyethylene exchange is the standard of care. This approach offers a high success rate while avoiding the morbidity of implant extraction.

Question 618

Topic: Total Hip Arthroplasty (THA)

A 72-year-old male experiences his third posterior dislocation of a primary total hip arthroplasty initially performed via a posterior approach. Radiographs demonstrate that the acetabular component is well-fixed but positioned in 45 degrees of inclination and 5 degrees of retroversion. What is the most appropriate surgical strategy to establish stability?

. Revision of the femoral head to a larger diameter head with an elevated lip liner
. Conversion to a constrained acetabular liner without altering the shell
. Revision of the acetabular shell to increase anteversion to approximately 15-20 degrees
. Advancement of the greater trochanter to increase abductor tension
. Revision of the femoral stem to a high-offset stem to increase tissue tension

Correct Answer & Explanation

. Revision of the acetabular shell to increase anteversion to approximately 15-20 degrees

Explanation

Recurrent posterior dislocations in the setting of an overtly retroverted acetabular component require surgical correction of the malposition. Revising the acetabular shell to appropriate anteversion directly addresses the mechanical cause of the impingement and posterior instability.

Question 619

Topic: 3. Adult Reconstruction (Hip & Knee)

A 64-year-old man presents with progressive anterior groin pain 7 years after undergoing a primary total hip arthroplasty using a metal-on-polyethylene bearing with a titanium stem and cobalt-chromium head. Inflammatory markers are normal. Serum cobalt is 12 ppb and chromium is 1 ppb. MRI demonstrates a large cystic mass extending into the iliopsoas bursa. What is the most likely etiology?

. Polyethylene wear-induced osteolysis
. Adverse local tissue reaction from head-neck mechanically assisted crevice corrosion
. Chronic indolent periprosthetic joint infection
. Impingement of the iliopsoas tendon on an uncovered anterior acetabular rim
. Aseptic loosening of the femoral component

Correct Answer & Explanation

. Adverse local tissue reaction from head-neck mechanically assisted crevice corrosion

Explanation

Elevated serum cobalt levels with normal chromium levels in a metal-on-polyethylene THA indicate mechanically assisted crevice corrosion (MACC), or trunnionosis, at the modular head-neck junction. This can cause an adverse local tissue reaction (ALTR) presenting as a pseudotumor.

Question 620

Topic: 3. Adult Reconstruction (Hip & Knee)

When planning a two-stage exchange arthroplasty for a chronic periprosthetic joint infection of the knee, which of the following clinical scenarios represents the strongest relative contraindication to utilizing an articulating antibiotic cement spacer over a static spacer?

. Infection with Methicillin-resistant Staphylococcus aureus (MRSA)
. Patient age greater than 80 years with multiple comorbidities
. Massive uncontained femoral and tibial metaphyseal bone loss with a compromised extensor mechanism
. A history of previous ipsilateral deep vein thrombosis
. The presence of a well-fixed cementless tibial component

Correct Answer & Explanation

. Massive uncontained femoral and tibial metaphyseal bone loss with a compromised extensor mechanism

Explanation

Articulating spacers rely on adequate bone stock for stability and an intact extensor mechanism to function properly and prevent anterior soft tissue breakdown. Massive bone loss and extensor mechanism deficiency dictate the use of a static spacer to maintain length and stability.

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