ABOS Part I Comprehensive Orthopaedic Review: Ankle, Knee PJI, Hip Arthroplasty | Part 22307

Correct Answer: B

A positive anterior drawer test with a 'clunk' and apprehension is a key indicator of mechanical instability, specifically ATFL insufficiency, which is the most common cause of recurrent lateral ankle instability. The 'clunk' suggests significant talar translation, and apprehension indicates the patient's recognition of the instability. While other findings like sinus tarsi pain, hypermobility, limited dorsiflexion, and pain on hop test are relevant to chronic ankle problems, they do not directly demonstrate the mechanical laxity of the lateral ankle ligaments as strongly as a positive anterior drawer test in this context. Generalized hypermobility might suggest a need for a reconstructive rather than just a repair procedure, but the mechanical instability is primarily shown by the drawer test.

Correct Answer: D

The anterior talofibular ligament (ATFL) is the weakest and most commonly injured of the lateral ankle ligaments. It primarily resists anterior translation of the talus and internal rotation, especially when the ankle is in plantarflexion, which is the position of typical inversion injury. The CFL primarily resists inversion in dorsiflexion, the PTFL resists posterior talar translation, the AITFL (part of the syndesmosis) stabilizes the distal tibiofibular joint, and the deltoid ligament stabilizes the medial ankle.

Correct Answer: C

The Modified Brostrom procedure, often referred to as Brostrom-Gould, is the most common and gold standard surgical procedure for primary repair of chronic lateral ankle instability. It involves direct repair of the attenuated ATFL and CFL, often augmented with the inferior extensor retinaculum. Chrisman-Snook and Watson-Jones are older tenodesis procedures using peroneal tendons, which are non-anatomical reconstructions. Anatomical reconstruction with allograft is typically reserved for revision cases or patients with poor tissue quality/generalized laxity. Peroneal tendon transfer isn't a primary repair technique for instability.

Correct Answer: D

Magnetic Resonance Imaging (MRI) is the most sensitive imaging modality for evaluating the integrity of soft tissue structures like the ATFL and CFL. It can show attenuation, scarring, or complete tears of these ligaments. While stress radiographs are excellent for demonstrating functional mechanical instability by measuring talar tilt and anterior translation, they don't directly visualize the ligaments' integrity as well as MRI. Plain radiographs are for bony anatomy, and CT scans are superior for bony detail but less so for soft tissues.

Correct Answer: D

The anterior drawer test for the ankle is best performed with the ankle in slight plantarflexion (approximately 10-20 degrees). This position relaxes the CFL and PTFL, thereby isolating the ATFL, which is taut in plantarflexion and anterior translation. In dorsiflexion, the ATFL is relaxed, and the CFL becomes more taut, making assessment of the ATFL less specific.

Correct Answer: C

The calcaneofibular ligament (CFL) is the primary static restraint to varus (inversion) stress of the ankle, particularly when the ankle is in a neutral or dorsiflexed position. While it also contributes to subtalar stability, its main role in ankle stability is resisting inversion. The ATFL limits anterior translation and internal rotation. The deltoid ligament prevents eversion, and syndesmotic ligaments stabilize the distal tibiofibular joint.

Correct Answer: B

In the modified Brostrom-Gould procedure, the attenuated ATFL and CFL are directly repaired and imbricated. The repair is then augmented by incorporating a flap of the inferior extensor retinaculum over the repaired ligaments. This provides additional strength and stability to the lateral ankle complex. The peroneal tendons are used in tenodesis procedures (e.g., Chrisman-Snook), not typically in a Brostrom-Gould repair. The spring ligament is on the medial side, and the superior peroneal retinaculum stabilizes the peroneal tendons.

Correct Answer: C

Osteochondral lesions (OCLs) of the talus are the most common concomitant injury found in patients with chronic lateral ankle instability, occurring in up to 50% of cases. The repeated episodes of 'giving way' and abnormal biomechanics can lead to impaction injuries of the talar dome. While other conditions listed can occur, OCLs are specifically and highly associated with chronic ankle instability. It is crucial to evaluate for these lesions pre-operatively, often requiring an MRI.

Correct Answer: C

For patients with generalized ligamentous laxity (like a high Beighton score) or poor tissue quality, a primary repair (like a modified Brostrom-Gould) may not provide sufficient long-term stability due to the inherent laxity. In such cases, an anatomical reconstruction using an autograft (e.g., gracilis, semitendinosus) or allograft is often preferred to provide a stronger and more durable repair. Non-anatomical reconstructions are generally less favored due to altered biomechanics. Arthroscopic debridement addresses impingement but not instability, and isolated PTFL repair is rare.

Correct Answer: C

Most guidelines recommend a minimum of 3 to 6 months of comprehensive non-operative management, including bracing, proprioceptive training, strengthening, and activity modification, before considering surgical intervention for chronic lateral ankle instability. A shorter trial may be considered in elite athletes or specific cases, but generally, conservative measures should be exhausted first.

Correct Answer: C

This patient presents with an acute periprosthetic joint infection (PJI) within 3 months of primary TKA, high WBC count in synovial fluid, and positive Gram stain, suggesting bacterial infection (likely Staphylococcal). DAIR (Debridement, Antibiotics, and Implant Retention) is the preferred initial management for acute PJI, especially if symptoms are present for less than 3-6 weeks, the components are stable, and the soft tissues are healthy. Exchange of modular components (polyethylene liner) significantly improves DAIR success rates by removing the biofilm burden from these surfaces. Long-term suppressive antibiotics are for chronic, incurable cases or patients unsuitable for surgery. Single-stage revision is considered for acute PJI in selected cases, but DAIR is often preferred first given the short symptom duration. Two-stage revision is typically reserved for chronic PJI or failed DAIR. Arthrodesis is a salvage procedure for recurrent failed infections.

Correct Answer: C

The most critical step to confirm infection eradication before proceeding to the second stage of reimplantation is obtaining at least two, preferably three, consecutive negative synovial fluid cultures from the knee, ideally after a period off antibiotics (e.g., 2 weeks) to reduce false negatives. While inflammatory markers (ESR, CRP) can guide treatment, they are not definitive for eradication. Imaging (MRI, CT) may be useful for assessing bone stock or identifying occult infection but does not replace microbiological confirmation. Serum alpha-defensin is a diagnostic marker for PJI, not typically used for confirming eradication post-treatment. Empirically continuing antibiotics without microbiological clearance increases the risk of resistance and does not confirm eradication.

Correct Answer: C

According to the 2018 International Consensus Meeting (ICM) criteria for PJI, synovial fluid white blood cell (WBC) count >3,000 cells/µL and synovial fluid polymorphonuclear neutrophil (PMN) percentage >80% are major criteria for diagnosing PJI. While other thresholds exist (e.g., AAOS guidelines suggest >2,500 WBC/µL with >60% PMN for acute PJI, and >1,700 WBC/µL with >65% PMN for chronic PJI), a WBC count of 50,000 cells/µL with 80% neutrophils far exceeds all thresholds and is highly specific for PJI. The other options, while possibly elevated, are less definitively indicative of PJI, with some (like 1,500 WBC) potentially falling into indeterminate zones depending on the PMN%.

Correct Answer: C

To maximize the yield for diagnosing PJI, especially in cases where synovial fluid culture is negative, it is crucial to send at least 5-6 periprosthetic tissue samples for both aerobic and anaerobic culture. Additionally, extending the incubation time to 10-14 days (or even longer for suspected fungal/mycobacterial infections) significantly increases the detection rate of slow-growing or fastidious organisms that may form biofilms. A single sample is insufficient due to sampling error and low bacterial load in biofilm. Fungal and mycobacterial cultures should be considered but not as the sole focus. Rapid PCR can be helpful but does not replace culture as the gold standard for guiding antibiotic therapy.

Correct Answer: B

Obesity (BMI >30 kg/m²) is a consistently recognized and significant independent risk factor for PJI following TKA, primarily due to factors like increased soft tissue bulk, compromised wound healing, altered immune response, and higher incidence of comorbidities. While rheumatoid arthritis, COPD, and psoriasis can contribute to overall surgical risk, obesity has a more direct and stronger epidemiological link to PJI. History of DVT is a thrombotic risk, not directly a PJI risk factor.

Correct Answer: C

A draining sinus tract that communicates with a prosthetic joint is considered pathognomonic for a periprosthetic joint infection (PJI), even if inflammatory markers are only mildly elevated or aspirations are not possible. In such chronic cases, the biofilm is well established, and DAIR is typically ineffective. Therefore, a two-stage revision arthroplasty is the gold standard for managing chronic PJI with a sinus tract. This involves implant removal, debridement, spacer placement, and a subsequent reimplantation after infection eradication. DAIR is not appropriate here given the chronic nature and established sinus. Oral or topical antibiotics alone are insufficient.

Correct Answer: C

According to the 2018 ICM criteria, a positive alpha-defensin test in synovial fluid is considered a major diagnostic criterion for PJI, with high sensitivity and specificity. Elevated ESR and CRP are minor criteria. Fever and localized pain are clinical signs but not major diagnostic criteria on their own. A history of wound dehiscence is a risk factor, not a diagnostic criterion.

Correct Answer: C

Group A Streptococcus (GAS) causes rapidly progressive, highly virulent infections, often associated with significant soft tissue necrosis and systemic toxicity. In such cases, the infection is often fulminant, and the biofilm forms quickly and aggressively. While DAIR can be considered for very early acute PJI, the presence of extensive necrotic tissue and a highly virulent organism like GAS often warrants more aggressive treatment. Immediate implant removal and placement of an antibiotic-loaded cement spacer (first stage of a two-stage revision) is often necessary to adequately address the infection and necrotic burden, especially when the infection is aggressive and destructive. DAIR success rates are low for GAS infections with significant soft tissue involvement. Single-stage revision is generally not recommended for such aggressive acute infections where eradication is uncertain. Wound debridement and washout alone are insufficient. Antibiotics alone cannot penetrate a mature biofilm and necrotic tissue effectively.

Correct Answer: C

The primary mechanism by which antibiotic-loaded bone cement (ALBC) spacers aid in infection eradication is by creating a very high local concentration of antibiotics at the infection site. This local delivery allows for concentrations far exceeding what can be achieved systemically, which is crucial for penetrating biofilms and effectively killing bacteria. While some structural support is offered, and they maintain the joint space, their main therapeutic benefit is antibiotic elution. They do not directly absorb cytokines, mechanically remove biofilm (though debridement does), or primarily stimulate local immune responses in this context.

Correct Answer: C

Following a successful DAIR (Debridement, Antibiotics, and Implant Retention) for acute PJI, the typical recommendation is 2-4 weeks of targeted intravenous antibiotic therapy, followed by an extended course of oral antibiotics for several months (e.g., 3-6 months, sometimes longer, depending on the organism and patient factors). This prolonged systemic therapy is crucial to suppress residual bacteria and prevent recurrence. Shorter durations are insufficient for eradicating PJI. 6-12 weeks of IV antibiotics is typically reserved for two-stage revisions where the implant is removed, or for very complex cases.

Correct Answer: C

Explanation:

The case explicitly describes first-generation cementing techniques as involving 'hand mixing of cement and finger packing of bone cement in the doughy phase into an unplugged, unwashed femoral canal,' leading to 'disappointing results due to the inability to produce a consistent cement mantle.' Second-generation techniques are defined by 'plugging the medullary canal, cleaning the canal with pulsed lavage and inserting cement in a retrograde manner using a cement gun.' This directly 'reduced the incidence of gross voids and filling defects in the mantle,' which is the core problem identified with first-generation techniques regarding mantle consistency.

• A. Porosity reduction via vacuum mixing or centrifugation: This is a characteristic of third-generation cementing techniques, which primarily aimed at improving the mechanical properties of the cement itself by reducing porosity, rather than directly addressing the consistency of the mantle's application or filling of the canal. While important, it's not the most direct answer to the problem of gross voids and inconsistent mantle filling.
• B. Stem centralization both proximally and distally: This is a characteristic of fourth-generation cementing techniques, designed to ensure an adequate and symmetrical cement mantle. While crucial for long-term success, the primary issue with first-generation techniques was the presence of voids and filling defects due to poor application, which plugging and retrograde insertion (second-generation) directly addressed. Centralization builds upon a foundation of a well-filled canal.
• C. Plugging the medullary canal and retrograde cement insertion with a cement gun: This is the defining feature of second-generation cementing techniques. As stated in the case, these advancements 'reduced the incidence of gross voids and filling defects in the mantle,' directly improving the consistency and completeness of the cement mantle compared to first-generation techniques.
• D. Hand mixing of cement in the doughy phase: This is a characteristic of first-generation cementing techniques, as described in the case, and is precisely what led to the inconsistent cement mantle and disappointing results. Therefore, it would not address the issue.
• E. Use of a metal-on-polyethylene bearing surface: This refers to the type of articulation used in the THA and has no direct relation to the cementing technique or the quality of the cement mantle.

Correct Answer: E

Explanation:

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.'

Correct Answer: C

Explanation:

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.

Correct Answer: B

Explanation:

The Paprosky classification system for femoral defects is described in the case:

• Type I: Minimal metaphyseal cancellous bone loss/normal intact diaphysis. Usually seen after removal of uncemented components without biological ingrowth.
• Type II: Extensive metaphyseal cancellous bone loss/normal intact diaphysis. Often seen after removal of cemented prosthesis. Calcar deficiency and major AP bone loss.
• Type IIIA: Metaphysis severely damaged/> 4 cm diaphyseal bone for distal fixation. Grossly loose femoral component. First-generation cementing techniques.
• Type IIIB: Metaphysis severely damaged/< 4 cm diaphyseal bone for distal fixation. Extends slightly further than type IIIA.
• Type IV: Extensive metaphyseal and diaphyseal bone loss/isthmus non-supportive.

The question describes 'extensive metaphyseal cancellous bone loss and intact diaphysis often seen after removal of a cemented prosthesis.' This description directly matches Paprosky Type II.

• A. Type I: This involves minimal metaphyseal bone loss and is typically associated with uncemented components, not cemented ones with extensive loosening.
• B. Type II: This type is characterized by 'extensive metaphyseal cancellous bone loss/normal intact diaphysis' and is 'Often seen after removal of cemented prosthesis,' which perfectly fits the scenario described.
• C. Type IIIA: This involves severe metaphyseal damage and requires more than 4 cm of diaphyseal bone for distal fixation. While the patient had first-generation cementing, the description in the question focuses on metaphyseal loss with an intact diaphysis, making Type II a more precise fit for the given information. Type IIIA implies more severe metaphyseal damage than just 'extensive metaphyseal cancellous bone loss.'
• D. Type IIIB: This is even more severe than Type IIIA, with less than 4 cm of diaphyseal bone for distal fixation.
• E. Type IV: This involves extensive metaphyseal and diaphyseal bone loss with a non-supportive isthmus, which is a much more severe defect than described.

Correct Answer: E

Explanation:

The Paprosky classification of acetabular bone defects (Table 2.5) is described with specific radiographic findings:

• Type 1: No substantial loss of bone stock (not explicitly detailed in the provided text, but implied as minimal).
• Type 2: (Subdivided into A, B, C, though not fully detailed in the provided text, the general characteristic is contained defects).
• Type 3: 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.

The case text provides specific radiographic findings for Paprosky acetabular defects, which are used to determine the type:

• '1. Superior migration of the hip centre'
• '2. Ischial osteolysis'
• '3. Teardrop osteolysis Inferior anterior column and medial wall.'
• '4. Position of the implant relative to Kohler’s line Deficiency of anterior column and/or medial wall deficiency.'

While the table doesn't explicitly list 'Type III' with these findings, the description of 'Superior migration of the hip centre' and 'Ischial osteolysis' are listed as key radiographic findings within the Paprosky classification system, which are typically associated with more severe, uncontained defects, specifically Paprosky Type III acetabular defects. The provided text lists these as general radiographic findings for the Paprosky classification, implying they are indicators of higher-grade defects. In the context of the Paprosky system, superior migration and ischial osteolysis are hallmarks of Type III defects, indicating significant bone loss requiring specialized reconstruction.

• A. Type I: This implies minimal bone loss, which is inconsistent with superior migration and ischial osteolysis.
• B, C, D. Type IIA, IIB, IIC: These are typically contained defects, or less severe than Type III. Superior migration and ischial osteolysis indicate more extensive, uncontained bone loss.
• E. Type III: Although the table provided is incomplete in its explicit breakdown of Type III, the listed radiographic findings of 'Superior migration of the hip centre' and 'Ischial osteolysis' are classic indicators of a Paprosky Type III acetabular defect, which represents severe bone loss requiring significant reconstructive challenges.

Correct Answer: D

Explanation:

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.

Correct Answer: B

Explanation:

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 the primary rationale given in the case for this specific scenario involving 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 is more reliable specifically 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.

Correct Answer: C

Explanation:

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.

Correct Answer: C

Explanation:

The case describes the femoral component removal process: 'It is important to clear the shoulder of the prosthesis removing any cement or bone overhanging the proximal aspect of the greater trochanter as either stem removal will be obstructed or a greater trochanter fracture will occur with stem removal.'

• A. Using cement splitters to remove cement radially: Cement splitters are used later in the process to break up the cement mantle, but not as the initial critical step to prevent proximal complications.
• B. Performing an extended trochanteric osteotomy (ETO): While an ETO 'will greatly simplify implant and cement removal,' it is a major surgical step and not the initial critical step for preventing immediate complications during stem removal itself. The ETO is a method of access and removal, not a preparatory step for the stem removal itself.
• C. Clearing the shoulder of the prosthesis by removing any overhanging cement or bone: This is explicitly stated as the 'important' initial step to prevent 'stem removal will be obstructed or a greater trochanter fracture will occur with stem removal.' This is crucial for safe and effective stem extraction.
• D. Utilizing ultrasonic tools to disrupt the cement: Ultrasonic tools are used to disrupt cement, but this comes after the initial clearance of the proximal shoulder and often in conjunction with other tools.
• E. Applying flexible osteotomes to disrupt the cement/implant interface: Flexible osteotomes are used to further disrupt the cement/implant interface, but this is done after the initial clearance of the shoulder.

Correct Answer: B

Explanation:

The case describes the acetabular component removal: 'The safest way is to disrupt the PE cup from the cement using curved gouges. This prevents inadvertent damage to the bone of the acetabulum bed. After removal of the cup the cement is removed piecemeal.'

• A. To allow for easier visualization of anchoring holes for burring: While visualization is important, the primary reason stated for this initial step is bone protection, not specifically visualization for burring. Burring comes later for debulking cement.
• B. To prevent inadvertent damage to the bone of the acetabulum bed: This is the explicit reason given in the case for disrupting the PE cup from the cement first with curved gouges. Protecting the host bone is paramount in revision surgery.
• C. To facilitate the use of a threaded extractor through a drill hole: A threaded extractor is mentioned as an alternative method ('Sometimes a threaded extractor through a drill hole in the PE can be used'), not the primary reason for the initial gouge technique.
• D. To reduce operating time and blood loss: While efficient removal can contribute to this, the primary stated reason for this specific technique is safety and bone preservation, not necessarily a reduction in time or blood loss.
• E. To ensure complete removal of all polyethylene debris: While removing the PE cup is part of the process, the stated reason for this specific initial technique is bone protection, not debris removal.

Correct Answer: C

Explanation:

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 discusses cementing techniques) point to the importance of cemented fixation 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 on cementing techniques and loosening.
• 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.

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.

The duration of symptoms is the most critical determinant of DAIR success, with significantly higher failure rates if symptoms have been present for more than 3 to 4 weeks. Early intervention is paramount before a mature biofilm can fully establish on the implant surfaces.

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.

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.

The direct anterior approach (Smith-Petersen) exploits the internervous plane between the TFL, innervated by the superior gluteal nerve, and the sartorius, innervated by the femoral nerve. Using this true internervous plane helps minimize postoperative muscle denervation.

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.

The posterior inferior tibiofibular ligament (PITFL) provides the greatest resistance (approximately 42%) to posterior translation and overall stability of the syndesmosis. The AITFL contributes approximately 35%, and the interosseous ligament provides about 22%.

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.

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.

Medial talar osteochondral lesions are typically deep and cup-shaped, located posteromedially, and are less often associated with a distinct traumatic event compared to lateral lesions. Lateral lesions are usually anterior, shallow, wafer-shaped, and strongly associated with a history of trauma.

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.

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.

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.

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.

The posterior inferior tibiofibular ligament (PITFL) is the strongest component of the syndesmotic complex and provides the greatest resistance (approximately 42%) to lateral displacement of the distal fibula. The AITFL is typically the first to tear but is structurally weaker.

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.

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.

Osteochondral lesions of the talus larger than 1.5 cm in diameter or those with deep subchondral cysts are poorly responsive to simple marrow stimulation techniques. Osteochondral autograft transfer (OATS) restores the structural bone defect and provides viable hyaline cartilage.

This is a Vancouver B2 periprosthetic fracture, characterized by a fracture around the stem with an unstable/loose implant but adequate proximal bone stock. The standard of care is revision arthroplasty utilizing a long stem that bypasses the fracture to achieve diaphyseal fixation.

A stiff lumbopelvic junction prevents the pelvis from naturally tilting posteriorly during sitting, which normally increases functional acetabular anteversion. To compensate for this lack of dynamic clearance and prevent anterior impingement/posterior dislocation, the cup should be implanted with increased anteversion.

Rifampin is uniquely highly effective against staphylococcal species residing within biofilms on orthopedic implants. It penetrates the biofilm matrix and kills slow-growing, stationary-phase bacteria by inhibiting DNA-dependent RNA polymerase.

The optimal position for an ankle arthrodesis is neutral dorsiflexion (0 degrees), slight valgus (0-5 degrees), and slight external rotation (5-10 degrees) matching the contralateral side. This maximizes forward progression during stance phase and minimizes stress on the midfoot.

The superficial interval of the direct anterior approach is between the sartorius (supplied by the femoral nerve) and the tensor fasciae latae (supplied by the superior gluteal nerve), making it a true internervous and intermuscular plane.

In cases of strongly suspected culture-negative PJI, molecular diagnostics such as Next-Generation Sequencing (NGS) or 16S rRNA PCR of the synovial fluid offer significantly higher sensitivity than traditional cultures for identifying elusive, fastidious, or previously treated organisms.

The sural nerve courses distally and crosses the lateral border of the Achilles tendon approximately 10 to 12 cm proximal to its calcaneal insertion. Sutures placed percutaneously in this region carry a high risk of nerve entrapment.

Squeaking in ceramic-on-ceramic THA is highly associated with component malposition, specifically excessive cup inclination (>50-55 degrees) or anteversion. This leads to edge loading, disruption of the fluid film lubrication, and subsequent stripe wear on the ceramic head.

Fungal periprosthetic joint infections are notoriously difficult to eradicate and form robust biofilms. The gold standard treatment is a two-stage exchange arthroplasty with an extended interval (often longer than bacterial PJI) of targeted systemic antifungal therapy.

During intraoperative stress testing of the syndesmosis (the Cotton or Hook test), widening of the medial clear space or the tibiofibular clear space by greater than 2 mm compared to the unstressed state indicates syndesmotic instability requiring operative stabilization.

An increased distance from the lesser trochanter to the center of rotation of the femoral head, with symmetric acetabular positioning, indicates that the femoral component sits too high. This is typically caused by a femoral neck cut that was made too proximally, retaining excessive calcar length.

Alpha-defensin is an antimicrobial peptide released by neutrophils that has extremely high sensitivity and specificity for PJI. It is particularly valuable for confirming infection in cases where standard cultures remain negative or when patients have recently taken antibiotics.

Squeaking in ceramic-on-ceramic THA is strongly correlated with edge-loading of the bearing surfaces. Edge-loading typically results from component malposition, specifically steep acetabular inclination or improper anteversion/retroversion.

Acute hematogenous periprosthetic joint infections presenting within days of symptom onset in a well-fixed implant are best managed with a DAIR procedure. Exchanging the modular polyethylene liner is critical to effectively reduce the biofilm burden.

The lateral femoral cutaneous nerve is at highest risk during the direct anterior approach to the hip due to its anatomical course over the sartorius muscle. Injury to this nerve results in meralgia paresthetica, presenting as anterolateral thigh numbness and dysesthesia.

Active Charcot neuroarthropathy, severe peripheral neuropathy, and lack of protective sensation are absolute contraindications for total ankle arthroplasty. These patients have an unacceptably high risk of catastrophic implant failure, subsidence, and deep infection, making arthrodesis the preferred procedure.

Static spacers are indicated in two-stage revisions when there is massive bone loss, severe ligamentous instability, an incompetent extensor mechanism, or inadequate soft-tissue coverage. Articulating spacers are generally preferred otherwise to maintain joint mobility and facilitate reimplantation.

Posterior dislocation in THA is frequently caused by inadequate anteversion or overt retroversion of the acetabular component. Proper 'safe zone' component positioning requires approximately 15-20 degrees of anteversion and 40 degrees of inclination.

Arthroscopic bone marrow stimulation (microfracture) is the first-line surgical treatment for small, primary osteochondral lesions of the talus measuring less than 1.5 cm in diameter. Larger, cystic, or failed lesions typically require OATS or fresh allografting.

Current AAOS and MSIS guidelines recommend discontinuing antibiotics for a minimum of 14 days prior to obtaining synovial fluid cultures. This antibiotic holiday maximizes the diagnostic yield and minimizes the risk of a false-negative culture.

Trunnionosis occurs via mechanically assisted crevice corrosion (MACC) at the head-neck junction in THA. It is classically diagnosed by elevated serum cobalt levels that are disproportionately higher than serum chromium levels.

Articulating spacers maintain joint mobility, prevent extensor mechanism contracture, and facilitate exposure during the reimplantation stage. Both static and articulating spacers demonstrate comparable infection eradication rates.

For an isolated retroacetabular osteolytic lesion with a well-fixed, optimally positioned acetabular component, the gold standard treatment is isolated polyethylene liner exchange combined with curettage and bone grafting of the cyst.

Increasing femoral anteversion increases the combined anteversion of the total hip construct. This effectively compensates for an excessively retroverted acetabular component, mitigating the risk of posterior dislocation.

Severe, rigid coronal plane deformities (typically >10-15 degrees) are considered a relative contraindication to primary TAA due to the high risk of edge-loading, component subsidence, and early failure.

DAIR is indicated for acute postoperative infections (within 4 weeks of index surgery) or acute hematogenous infections. For acute hematogenous PJI, DAIR is most successful when performed within 3 to 4 weeks of symptom onset.

Trunnionosis, or mechanically assisted crevice corrosion at the modular head-neck junction, characteristically presents with elevated serum cobalt disproportionate to chromium in metal-on-polyethylene THA, leading to adverse local tissue reactions.

Plain radiographs are notably inaccurate for assessing the distal tibiofibular syndesmosis. Axial CT is the most sensitive and specific imaging modality for evaluating syndesmotic reduction within the incisura fibularis.

The irradiation used to cross-link polyethylene improves wear resistance but decreases important mechanical properties, including fatigue resistance, yield strength, and ultimate tensile strength, which increases the risk of component fracture.

High-dose antibiotic loading (typically >2g per 40g bag of PMMA) creates significant stress risers within the cement mantle, substantially decreasing its compressive strength and overall structural integrity.