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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 304 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 6061

Topic: 3. Adult Reconstruction (Hip & Knee)

During a total knee arthroplasty, the surgeon notes that the knee is well-balanced in extension, but the flexion gap is unacceptably tight. Which of the following surgical adjustments will best correct this imbalance?

. Resect more distal femur
. Resect more proximal tibia
. Increase the size of the femoral component
. Decrease the size of the femoral component and use a thicker polyethylene insert
. Decrease the anteroposterior size of the femoral component while maintaining the anterior cortex reference

Correct Answer & Explanation

. Decrease the anteroposterior size of the femoral component while maintaining the anterior cortex reference

Explanation

A tight flexion gap with a balanced extension gap requires altering only the flexion gap. Downsizing the femoral component (reducing posterior condylar offset) while maintaining the anterior reference will selectively increase the flexion gap without affecting extension.

Question 6062

Topic: 3. Adult Reconstruction (Hip & Knee)

In total hip arthroplasty, the use of highly cross-linked polyethylene (HXLPE) has significantly reduced wear rates compared to conventional polyethylene. What is the primary trade-off or disadvantage associated with the high levels of radiation used to cross-link the polyethylene?

. Increased oxidative degradation over time
. Decreased ultimate tensile strength and fatigue crack propagation resistance
. Increased risk of early catastrophic component debonding
. Reduced biocompatibility leading to increased osteolysis per particle
. Increased friction coefficient against ceramic heads

Correct Answer & Explanation

. Decreased ultimate tensile strength and fatigue crack propagation resistance

Explanation

While irradiation creates cross-links that drastically reduce adhesive and abrasive wear, it also reduces the mechanical properties of the polyethylene. Specifically, it decreases ductility, ultimate tensile strength, and resistance to fatigue crack propagation.

Question 6063

Topic: 3. Adult Reconstruction (Hip & Knee)

A 70-year-old female experiences recurrent posterior dislocations of her total hip arthroplasty. Intraoperatively, the acetabular component is found to be solidly fixed but retroverted. What is the most appropriate surgical management?

. Revision of the femoral head to a larger diameter
. Revision of the acetabular component to increase anteversion
. Conversion to a bipolar hemiarthroplasty
. Advancement of the greater trochanter
. Application of an abduction brace for 6 weeks

Correct Answer & Explanation

. Revision of the acetabular component to increase anteversion

Explanation

Recurrent posterior dislocations due to a retroverted acetabular cup require revision of the cup to proper anteversion (typically 15-20 degrees) to restore stability. Increasing head size alone does not correct the underlying mechanical malposition and will likely fail.

Question 6064

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total knee arthroplasty for a fixed valgus deformity, the surgeon notes a tight lateral compartment in both flexion and extension. Which structure should be released first to effectively balance the gap?

. Medial collateral ligament
. Popliteus tendon
. Iliotibial band
. Lateral collateral ligament
. Posterolateral capsule

Correct Answer & Explanation

. Iliotibial band

Explanation

For a fixed valgus knee that is tight in both flexion and extension, the iliotibial band (ITB) and the posterolateral capsule are typically released first. Releasing the LCL or popliteus initially can lead to severe instability, particularly in flexion.

Question 6065

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old female presents with progressive groin pain 5 years after receiving a metal-on-metal total hip arthroplasty. Radiographs show a well-fixed implant. MRI with metal artifact reduction demonstrates a large, thick-walled cystic mass communicating with the joint. What is the most likely histologic finding of the periprosthetic tissue?

. Abundant neutrophils and extracellular gram-positive cocci
. Extensive foreign-body giant cell reaction surrounding birefringent particles
. Perivascular lymphocytic infiltrate with macrophage accumulation and extensive tissue necrosis
. Sheets of pleomorphic spindle cells with atypical mitoses and osteoid matrix
. Predominance of eosinophils, mast cells, and IgE-mediated degranulation

Correct Answer & Explanation

. Perivascular lymphocytic infiltrate with macrophage accumulation and extensive tissue necrosis

Explanation

Metal-on-metal implants can cause Aseptic Lymphocytic Vasculitis-Associated Lesions (ALVAL) or adverse local tissue reactions (ALTR). Histologically, these lesions typically feature a robust perivascular lymphocytic infiltrate, prominent macrophages, and extensive local tissue necrosis.

Question 6066

Topic: 3. Adult Reconstruction (Hip & Knee)

In total hip arthroplasty (THA), accurately restoring the hip center of rotation is critical for optimizing biomechanics. Compared to a superiorly and laterally placed center of rotation, moving the center of rotation medially and inferiorly achieves which of the following effects?

. Decreases the abductor moment arm and increases the joint reaction force
. Increases the body weight moment arm and increases the joint reaction force
. Increases the abductor moment arm and decreases the joint reaction force
. Decreases the body weight moment arm and increases the abductor force required
. Increases the abductor force required and increases the joint reaction force

Correct Answer & Explanation

. Increases the abductor moment arm and decreases the joint reaction force

Explanation

Placing the acetabular component medially and inferiorly (anatomic position) increases the abductor moment arm and decreases the body weight moment arm. According to biomechanical equilibrium, a larger abductor moment arm decreases the required abductor force, which in turn significantly decreases the overall joint reaction force across the hip.

Question 6067

Topic: 3. Adult Reconstruction (Hip & Knee)

During a posterior-stabilized total knee arthroplasty (TKA), trial components are placed. The surgeon notes that the knee is well-balanced in extension, but the flexion gap is unacceptably tight (lift-off and difficult to flex past 90 degrees). Which of the following intraoperative maneuvers is most appropriate to resolve this specific imbalance?

. Recut the proximal tibia with more posterior slope or downsize the femoral component
. Resect an additional 2 mm from the distal femur
. Release the posterior capsule
. Increase the thickness of the polyethylene insert
. Upsize the femoral component using an anterior referencing system

Correct Answer & Explanation

. Recut the proximal tibia with more posterior slope or downsize the femoral component

Explanation

A tight flexion gap with a balanced extension gap means the posterior aspect of the femoral component is too prominent or the tibia is lacking slope. Options to increase the flexion gap without affecting the extension gap include downsizing the femoral component (with anterior referencing, this moves the posterior condylar cut anteriorly) or increasing the posterior slope of the tibial cut. Resecting more distal femur or releasing the posterior capsule affects the extension gap.

Question 6068

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old female with long-standing rheumatoid arthritis is undergoing preoperative evaluation for a total hip arthroplasty. Flexion-extension cervical spine radiographs reveal an anterior atlantodens interval (ADI) of 11 mm and a posterior atlantodens interval (PADI) of 13 mm. She is neurologically intact. What is the most appropriate management regarding her cervical spine?

. Proceed with total hip arthroplasty with awake fiberoptic intubation
. Prescribe a hard cervical collar and proceed with THA
. Postpone THA and perform C1-C2 posterior spinal fusion
. Postpone THA and perform occipitocervical fusion
. Administer high-dose corticosteroids before THA

Correct Answer & Explanation

. Postpone THA and perform C1-C2 posterior spinal fusion

Explanation

In patients with rheumatoid arthritis, an anterior atlantodens interval (ADI) > 9-10 mm or a posterior atlantodens interval (PADI, or space available for the cord) < 14 mm are strong indications for surgical stabilization (C1-C2 fusion) due to the high risk of catastrophic neurological injury, even if currently asymptomatic. The hip arthroplasty should be postponed until the cervical spine is stabilized.

Question 6069

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient undergoes a primary total hip arthroplasty via a posterior approach. Postoperatively, the patient experiences recurrent posterior dislocations. Radiographic evaluation shows that the acetabular component is placed in 5 degrees of anteversion. Which of the following best explains the etiology of this instability?

. Excessive acetabular anteversion relative to the safe zone
. Acetabular component placed in relative retroversion
. Impingement of the greater trochanter on the ilium
. Excessive femoral offset
. Anterior pelvic tilt in the seated position

Correct Answer & Explanation

. Acetabular component placed in relative retroversion

Explanation

The normal 'safe zone' for acetabular cup anteversion is approximately 15 to 20 degrees. A cup placed in 5 degrees of anteversion is functionally retroverted, which significantly predisposes the patient to posterior dislocation, particularly with hip flexion and internal rotation.

Question 6070

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the Musculoskeletal Infection Society (MSIS) criteria for periprosthetic joint infection (PJI), which of the following is considered a 'major' criterion, sufficient to definitively establish a diagnosis of PJI on its own?

. Elevated serum C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR)
. Purulence in the affected joint
. A single positive intraoperative periprosthetic tissue culture
. A sinus tract communicating with the prosthesis
. Elevated synovial fluid white blood cell (WBC) count greater than 3,000 cells/µL

Correct Answer & Explanation

. A sinus tract communicating with the prosthesis

Explanation

According to the MSIS criteria, there are two major criteria for definitive diagnosis of PJI: 1) A sinus tract communicating with the prosthesis, or 2) A pathogen isolated by culture from at least two separate tissue or fluid samples. The other options are minor criteria.

Question 6071

Topic: 3. Adult Reconstruction (Hip & Knee)
A 60-year-old male with a history of a metal-on-metal total hip arthroplasty presents with groin pain and a palpable mass. Workup reveals an adverse local tissue reaction (ALTR) or pseudotumor. Which type of hypersensitivity reaction is primarily responsible for this pathology?
. Type I (IgE-mediated)
. Type II (Cytotoxic)
. Type III (Immune complex)
. Type IV (Delayed cell-mediated)
. Type V (Stimulatory autoantibody)

Correct Answer & Explanation

. Type IV (Delayed cell-mediated)

Explanation

Adverse local tissue reactions (ALTR) or pseudotumors associated with metal-on-metal implants are characterized pathologically by an ALVAL (aseptic lymphocytic vasculitis-associated lesion) response, which is a Type IV (delayed, T-cell mediated) hypersensitivity reaction to metal ions (cobalt and chromium).

Question 6072

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient with a modular primary total hip arthroplasty (THA) utilizing a titanium stem and a cobalt-chrome head presents with groin pain. Workup reveals an adverse local tissue reaction (ALTR) or pseudotumor. Which specific pathophysiologic mechanism is most responsible for this failure at the modular head-neck taper junction?

. Galvanic corrosion exclusively
. Pitting corrosion driven by macrophage activation
. Pure fretting without chemical interaction
. Mechanically assisted crevice corrosion (MACC)
. Hydrogen embrittlement of the titanium alloy

Correct Answer & Explanation

. Mechanically assisted crevice corrosion (MACC)

Explanation

Trunnionosis at the modular head-neck junction of a THA is classically driven by mechanically assisted crevice corrosion (MACC). The cyclical micromotion at the taper junction mechanically disrupts the protective oxide passivation layer (fretting). The restricted fluid exchange in this enclosed local geometry (crevice) allows for oxygen depletion and a localized drop in pH, creating an acidic, aggressive environment that accelerates the release of metal ions. This combination of mechanical wear and chemical corrosion is termed MACC.

Question 6073

Topic: 3. Adult Reconstruction (Hip & Knee)
A 65-year-old man presents with groin pain 10 years after a total hip arthroplasty. Radiographs show eccentric wear of the polyethylene liner and large periacetabular radiolucencies. Which of the following cells is the primary mediator of the osteolysis seen in this patient?
. Osteoblasts
. Osteoclasts
. Macrophages
. T-lymphocytes
. Polymorphonuclear leukocytes

Correct Answer & Explanation

. Macrophages

Explanation

Macrophages are the primary mediators of particle-induced osteolysis. They phagocytose UHMWPE wear debris (optimal size 0.1-1.0 micrometers) and subsequently release inflammatory cytokines (such as TNF-alpha, IL-1, IL-6), which then stimulate osteoclasts to resorb bone.

Question 6074

Topic: 3. Adult Reconstruction (Hip & Knee)
In total joint arthroplasty, aseptic loosening is predominantly driven by a macrophage-mediated inflammatory response to wear debris. Which of the following sizes of ultra-high-molecular-weight polyethylene (UHMWPE) particles are most biologically active in initiating this osteolytic cascade?
. Particles larger than 10 micrometers
. Particles smaller than 0.1 micrometers
. Particles between 0.1 and 1.0 micrometers
. Needle-shaped particles between 10 and 20 micrometers
. Macroscopic chunks larger than 1 millimeter

Correct Answer & Explanation

. Particles between 0.1 and 1.0 micrometers

Explanation

Macrophage activation and subsequent osteolysis is highly dependent on the size and concentration of wear particles. UHMWPE particles in the submicron to small micron range (0.1 to 1.0 micrometers) are readily phagocytosed by macrophages but cannot be digested, leading to maximal release of pro-inflammatory cytokines (TNF-alpha, IL-1, IL-6) and subsequent osteoclast activation.

Question 6075

Topic: 3. Adult Reconstruction (Hip & Knee)

In total hip arthroplasty, which of the following bearing surface combinations is associated with the lowest volumetric wear rate but carries the highest risk of squeaking and catastrophic component fracture?

. Ceramic-on-polyethylene
. Metal-on-metal
. Ceramic-on-ceramic
. Metal-on-polyethylene
. Oxinium-on-polyethylene

Correct Answer & Explanation

. Ceramic-on-ceramic

Explanation

Ceramic-on-ceramic bearings have the lowest volumetric and linear wear rates of all available combinations. However, they are associated with unique complications, most notably a risk of catastrophic ceramic fracture and an audible squeaking sound during gait.

Question 6076

Topic: Total Knee Arthroplasty (TKA)

During a total knee arthroplasty (TKA), the surgeon inadvertently internally rotates the femoral component relative to the surgical epicondylar axis. What is the most likely biomechanical consequence of this technical error?

. Medial patellar subluxation
. Lateral patellar tracking and potential dislocation
. Increased flexion gap laxity medially
. Decreased extension gap
. Symmetric tightness in both medial and lateral compartments in flexion

Correct Answer & Explanation

. Lateral patellar tracking and potential dislocation

Explanation

Internal rotation of the femoral component in TKA mediatizes the trochlear groove, thereby increasing the Q angle. This leads to lateral patellar tracking, tilt, and an increased risk of lateral patellar subluxation or dislocation. It also creates a tight medial flexion gap.

Question 6077

Topic: 3. Adult Reconstruction (Hip & Knee)

A 70-year-old female undergoes a total hip arthroplasty via a posterior approach. Postoperatively, she is noted to have a complete foot drop and sensory loss over the anterolateral leg and the dorsum of the foot. Which specific component of the sciatic nerve is most vulnerable to injury during this procedure?

. Tibial division
. Common peroneal division
. Sural nerve
. Posterior femoral cutaneous nerve
. Saphenous nerve

Correct Answer & Explanation

. Common peroneal division

Explanation

The common peroneal division of the sciatic nerve is significantly more vulnerable to injury during THA than the tibial division. This is due to its more lateral anatomic position, fewer supporting connective tissue elements, and its tethering at the fibular head, making it highly susceptible to stretch injuries during limb lengthening or retractor placement.

Question 6078

Topic: 3. Adult Reconstruction (Hip & Knee)

In total knee arthroplasty (TKA), polyethylene wear differs significantly from that seen in total hip arthroplasty (THA). Which of the following best describes the predominant mechanism of polyethylene wear in TKA and its primary biomechanical cause?

. Adhesive wear due to third-body particulate debris
. Abrasive wear due to multidirectional, crossed-path motion
. Delamination and pitting due to high subsurface cyclic shear stresses
. Corrosive wear secondary to synovial fluid infiltration into the matrix
. Galvanic wear due to mixed metal ion deposition on the articular surface

Correct Answer & Explanation

. Delamination and pitting due to high subsurface cyclic shear stresses

Explanation

Polyethylene wear in TKA is primarily due to subsurface fatigue resulting in delamination and pitting. This is caused by the non-conforming nature of the tibiofemoral joint (flat on round), which creates extremely high subsurface cyclic shear stresses just below the contact area. In contrast, THA wear is predominantly abrasive and adhesive (volumetric) due to the highly conforming ball-and-socket articulation and multidirectional (crossed-path) motion.

Question 6079

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old active male underwent a total hip arthroplasty with a ceramic-on-ceramic bearing surface. Two years later, he complains of a loud, reproducible squeaking sound from the hip during specific movements, without associated pain. What is the most critical biomechanical factor associated with this phenomenon?

. Micro-fractures of the ceramic head leading to third-body wear
. Fluid-film lubrication failure due to systemic metal ion release
. Edge loading secondary to acetabular component malposition
. Impingement of the anterior femoral neck against a retained anterior capsule
. Osteolysis leading to micromotion of the cementless acetabular shell

Correct Answer & Explanation

. Edge loading secondary to acetabular component malposition

Explanation

Squeaking is a well-documented specific complication of ceramic-on-ceramic (CoC) total hip arthroplasty. It is most strongly associated with stripe wear caused by edge loading. Edge loading typically occurs due to acetabular component malposition (such as excessive steepness/inclination or incorrect version), leading to a loss of the protective fluid-film lubrication and localized high-friction contact between the ceramic head and the edge of the ceramic liner.

Question 6080

Topic: 3. Adult Reconstruction (Hip & Knee)
In total hip arthroplasty, aseptic loosening is most frequently driven by the biological response to ultra-high-molecular-weight polyethylene (UHMWPE) wear debris. Which specific particle size range is most readily phagocytosed by macrophages, initiating the osteolytic cascade?
. < 0.1 micrometers
. 0.1 to 10 micrometers
. 15 to 25 micrometers
. 30 to 50 micrometers
. > 50 micrometers

Correct Answer & Explanation

. 0.1 to 10 micrometers

Explanation

Macrophages preferentially phagocytose UHMWPE wear particles in the 0.1 to 10 micrometer range. Particles smaller than this often do not stimulate an aggressive immune response, while particles larger than 10-15 micrometers are too large for individual macrophage phagocytosis and typically elicit a foreign body giant cell response. Macrophage activation by 0.1-10 μm particles leads to the release of osteolytic cytokines such as TNF-alpha, IL-1, IL-6, and PGE2.

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