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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 226 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 4501

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient with a chronic periprosthetic joint infection (PJI) following total hip arthroplasty (THA) is found to have a Staphylococcus epidermidis infection. The femoral component is well-fixed, but the acetabular component shows evidence of loosening. The patient is otherwise healthy with no significant comorbidities. What is the most appropriate treatment strategy?

. Debridement, antibiotics, and implant retention (DAIR)
. One-stage exchange arthroplasty
. Two-stage exchange arthroplasty
. Excision arthroplasty (Girdlestone procedure)
. Chronic antibiotic suppression without surgery

Correct Answer & Explanation

. Two-stage exchange arthroplasty

Explanation

For a chronic PJI with a loose component (in this case, the acetabular component), and especially with a low-virulence organism likeStaphylococcus epidermidis(thoughS. epidermidiscan form biofilm), a two-stage exchange arthroplasty is generally considered the gold standard. The first stage involves removal of all prosthetic components, thorough debridement, and placement of an antibiotic-loaded cement spacer. After a period of intravenous antibiotics and normalization of infection markers, the second stage involves reimplantation of new components. DAIR is typically reserved for acute infections (<3-6 weeks post-op or acute hematogenous spread) with stable components. One-stage exchange can be considered for specific organisms or patient profiles but is not the standard for chronic PJI with a loose component. Excision arthroplasty is a salvage procedure for patients who cannot tolerate or fail exchange arthroplasty. Chronic antibiotic suppression is for patients unfit for surgery or who have failed other treatments, but carries its own risks and high failure rates.

Question 4502

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient with a metal-on-metal (MoM) hip arthroplasty presents with chronic groin pain, an elevated serum cobalt level, and MRI findings consistent with an adverse local tissue reaction (ALTR) or 'pseudotumor' around the joint. The prosthetic components appear well-fixed on radiographs. What is the most appropriate definitive management for this patient?

. Observation with serial monitoring of cobalt levels and imaging
. Revision of only the femoral head and acetabular liner to ceramic/polyethylene
. Revision of both the femoral and acetabular components
. Arthroscopic debridement and excision of the pseudotumor only
. Intra-articular steroid injections for pain management

Correct Answer & Explanation

. Revision of both the femoral and acetabular components

Explanation

For symptomatic ALTR/pseudotumor associated with MoM hip arthroplasty, even if components appear well-fixed, the definitive management is revision of both the femoral and acetabular components. The pseudotumor is a consequence of continuous wear and corrosion from both metal surfaces. Simply revising the head and liner (Option 1) leaves the metal shell, which can continue to generate metal ions. Observation is inappropriate for a symptomatic ALTR with elevated metal ions, which can lead to progressive tissue damage. Arthroscopic debridement addresses only the pseudotumor, not the source of the problem. Steroid injections offer only temporary symptomatic relief and do not treat the underlying pathology.

Question 4503

Topic: 3. Adult Reconstruction (Hip & Knee)

A common complication in total knee arthroplasty is patellofemoral pain. From a biomechanical perspective, which of the following best describes the primary effect of increased patellar component lateralization on patellofemoral joint mechanics?

. Decreased patellofemoral contact area and increased contact pressure
. Increased congruency and decreased stress on the lateral facet
. Reduced quadriceps moment arm, improving extension strength
. Medial shift of the Q-angle, reducing lateralizing forces
. Enhanced tracking within the trochlear groove throughout range of motion

Correct Answer & Explanation

. Decreased patellofemoral contact area and increased contact pressure

Explanation

Increased patellar component lateralization (or external rotation) disrupts the normal tracking of the patella within the trochlear groove. This typically leads to a decrease in the patellofemoral contact area, concentrating the load over a smaller surface. This concentration of force results in increased patellofemoral contact pressure, particularly on the lateral facet, which can cause pain and accelerated wear. Increased congruency is incorrect. Reduced quadriceps moment arm would impair extension strength. A medial shift of the Q-angle is unlikely with lateralization. Enhanced tracking is contrary to what happens with maltracking.

Question 4504

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient undergoes total hip arthroplasty with an extensively coated, stiff femoral stem. Over time, radiographs demonstrate proximal cortical thinning around the stem. This phenomenon is best explained by which of the following biomechanical principles?

. Creep deformation
. Stress concentration
. Fatigue failure
. Stress shielding
. Wear debris osteolysis

Correct Answer & Explanation

. Stress shielding

Explanation

Stress shielding occurs when a stiffer implant (like a stiff metallic femoral stem) carries a disproportionately large share of the load, reducing the stress experienced by the surrounding bone. According to Wolff's Law, bone adapts to the loads placed upon it. Reduced stress on the proximal femur leads to bone resorption and cortical thinning, as the bone perceives less mechanical demand. Creep is time-dependent deformation under constant stress. Stress concentration is an area of increased stress. Fatigue failure is material failure due to cyclic loading. Wear debris osteolysis is caused by particulate matter leading to inflammation and bone resorption, typically around the implant-bone interface, but not necessarily proximal cortical thinning due as a primary mechanism to the stem's stiffness.

Question 4505

Topic: 3. Adult Reconstruction (Hip & Knee)

The concept of 'stress shielding' is a significant concern in orthopedic implant design. It occurs when a rigid implant bears a disproportionate amount of load, leading to a reduction in stress experienced by the surrounding bone. According to Wolff's Law, the primary long-term consequence of stress shielding on the adjacent bone is:

. Increased bone remodeling and enhanced mineralization due to adaptive response.
. Peri-implant osteolysis due to excessive bone resorption.
. Stimulation of osteoblast activity and new bone formation to strengthen the interface.
. Reduced bone density and cortical thinning (osteopenia) distal to the implant.
. A shift towards intramembranous ossification to compensate for stress reduction.

Correct Answer & Explanation

. Reduced bone density and cortical thinning (osteopenia) distal to the implant.

Explanation

Wolff's Law states that bone adapts its structure to the loads it is subjected to. If loading on a bone decreases, bone mass and density will decrease. Stress shielding occurs when a stiff implant (e.g., a total hip arthroplasty stem) takes up too much of the load, reducing the stress on the surrounding bone. In response to this reduced stress, the bone will resorb and decrease its density, leading to osteopenia or cortical thinning in the shielded areas. Option D is correct. Option A is incorrect; increased remodeling would likely involve both formation and resorption, but reduced load would lead to net resorption. Option B describes osteolysis, which can occur for other reasons (e.g., wear particles) but not typically as a direct consequence of stress shielding unless severe enough to cause local ischemia. Option C is the opposite of the effect. Option E is incorrect; intramembranous ossification is a mode of bone formation, not a response to stress reduction in mature bone in this context.

Question 4506

Topic: 3. Adult Reconstruction (Hip & Knee)

An 8-year-old boy with severe SMA Type II presents with unilateral right hip dislocation. He has an asymptomatic windswept pelvic deformity and does not walk. He sits in a customized wheelchair. What is the most appropriate management for his right hip dislocation?

. Open reduction and Dega osteotomy
. Closed reduction and spica casting
. Observation and continuation of physical therapy
. Varus derotational osteotomy (VDRO) alone
. Total hip arthroplasty

Correct Answer & Explanation

. Observation and continuation of physical therapy

Explanation

In non-ambulatory children with SMA, hip subluxation and dislocation are extremely common due to muscle weakness and imbalance. Unlike in cerebral palsy where a dislocated hip can become highly painful, dislocated hips in SMA are usually painless. Surgical reconstruction has a high rate of failure, high complication rates, and generally does not improve function or sitting balance. Therefore, observation is the most appropriate management for an asymptomatic hip dislocation in a non-ambulatory SMA patient.

Question 4507

Topic: 3. Adult Reconstruction (Hip & Knee)

You are evaluating a 5-year-old male with SMA Type II. He presents with bilateral knee flexion contractures of 40 degrees and equinovarus foot deformities. He is non-ambulatory. What is the primary indication for surgical intervention for lower extremity contractures in non-ambulatory SMA patients?

. To attempt to make the child a community ambulator
. To prevent the development of neuromuscular scoliosis
. To alleviate pain, facilitate hygiene, and improve wheelchair positioning
. To reverse the progression of alpha motor neuron loss
. To prepare for total knee arthroplasty

Correct Answer & Explanation

. To alleviate pain, facilitate hygiene, and improve wheelchair positioning

Explanation

In non-ambulatory patients with SMA, severe lower extremity contractures are common due to immobility and muscle imbalance. Surgical release of contractures is generally not indicated to achieve ambulation, as the primary issue is profound weakness, not just restricted motion. Surgery is reserved for cases where the contractures cause pain, interfere with wearing orthoses, compromise hygiene, or prevent comfortable wheelchair seating and positioning.

Question 4508

Topic: 3. Adult Reconstruction (Hip & Knee)

A 7-year-old non-ambulatory child with SMA Type II presents with an asymptomatic, unilateral dislocated hip. Pelvic obliquity is minimal. What is the most appropriate management for this hip?

. Open reduction and spica casting
. Varus derotational osteotomy and pelvic osteotomy
. Observation
. Proximal femoral resection (Girdlestone)
. Total hip arthroplasty

Correct Answer & Explanation

. Observation

Explanation

In non-ambulatory patients with SMA, unilateral or bilateral hip dislocations are typically painless and do not significantly impair sitting balance. Observation is the standard of care due to high surgical failure rates and lack of functional benefit.

Question 4509

Topic: 3. Adult Reconstruction (Hip & Knee)

A 7-year-old girl with SMA Type II, who is a non-ambulator and utilizes a customized wheelchair, is found to have an asymptomatic, unilateral dislocated hip on routine radiographic screening. What is the most appropriate orthopedic management?

. Immediate closed reduction and spica casting
. Open reduction with femoral varus derotational osteotomy
. Open reduction with a Salter innominate osteotomy
. Observation and supportive care
. Girdlestone resection arthroplasty

Correct Answer & Explanation

. Observation and supportive care

Explanation

Hip instability and dislocation are exceedingly common in severe, non-ambulatory SMA. Because these dislocations are generally painless and surgical intervention has a high recurrence rate and complication profile, observation is the recommended management.

Question 4510

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old female with severe rheumatoid arthritis undergoes a linked (semi-constrained) total elbow arthroplasty (TEA).

Three years later, she develops rapid early polyethylene wear and aseptic loosening of the components. What is the most common iatrogenic cause of early bushing wear and failure in a linked TEA?

. Ulnar component malrotation leading to excessive varus stress
. Triceps insufficiency resulting in anterior subluxation forces
. Leaving the radial head intact, causing impingement on the humeral component
. Mismatch between the humeral component's axis of rotation and the anatomic axis of rotation
. Over-resection of the distal humerus shortening the lever arm

Correct Answer & Explanation

. Mismatch between the humeral component's axis of rotation and the anatomic axis of rotation

Explanation

In a linked or semi-constrained total elbow arthroplasty, the prosthesis acts as a hinge that allows some varus/valgus toggle. If the humeral component is placed with its axis of rotation malaligned compared to the natural anatomic axis of the elbow, it creates a kinematic mismatch. This generates excessive stress on the polyethylene bushings during flexion and extension, leading to accelerated wear, osteolysis, and early aseptic loosening.

Question 4511

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old female with advanced rheumatoid arthritis undergoes a primary linked semi-constrained total elbow arthroplasty (TEA).

Following comprehensive postoperative rehabilitation, what specific lifelong functional limitation must she be advised to adhere to in order to minimize the risk of aseptic loosening?

. Avoidance of active elbow extension against gravity
. A permanent lifting restriction of no more than 5 to 10 pounds (single event)
. Avoidance of elbow flexion past 90 degrees
. Requirement to wear a static progressive splint at night indefinitely
. Avoidance of any forearm supination while the elbow is extended

Correct Answer & Explanation

. A permanent lifting restriction of no more than 5 to 10 pounds (single event)

Explanation

Patients who undergo total elbow arthroplasty (TEA) are traditionally placed on lifelong lifting restrictions to prevent accelerated polyethylene wear, bushing failure, and aseptic loosening, which remain the most common long-term complications. The standard recommendation is a lifting limit of 5 to 10 pounds for a single event and 1 to 2 pounds for repetitive lifting.

Question 4512

Topic: 3. Adult Reconstruction (Hip & Knee)

A 72-year-old female with a history of a cementless total hip arthroplasty presents with thigh pain after a ground-level fall. Radiographs show a periprosthetic femur fracture that occurs around the stem, extending just distal to its tip. The femoral stem is noted to be clinically loose, but the bone stock surrounding the proximal femur is robust and adequate. According to the Vancouver classification, what is the injury type and the most appropriate standard surgical treatment?

. Vancouver A; Nonoperative management with protected weight-bearing
. Vancouver B1; Open reduction and internal fixation with a locking plate
. Vancouver B2; Revision arthroplasty with a long-stem femoral component
. Vancouver B3; Revision arthroplasty with proximal femoral replacement
. Vancouver C; Open reduction and internal fixation with a locking plate

Correct Answer & Explanation

. Vancouver B2; Revision arthroplasty with a long-stem femoral component

Explanation

This is a Vancouver B2 periprosthetic fracture. The fracture occurs around or just below the stem (Type B), the stem is loose (sub-type 2), but the proximal bone stock is adequate (differentiating it from B3, which has poor bone stock). The standard of care for a Vancouver B2 fracture is revision of the femoral component to a long-stem prosthesis (usually cementless, fully porous-coated, or fluted tapered) that bypasses the fracture by at least two cortical diameters.

Question 4513

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total hip arthroplasty using a direct lateral (Hardinge) approach, the surgeon splits the gluteus medius and vastus lateralis. To avoid denervation of the anterior portion of the gluteus medius and tensor fasciae latae, the proximal splitting of the gluteus medius should not exceed what distance from the tip of the greater trochanter?

. 1 - 2 cm
. 3 - 5 cm
. 7 - 9 cm
. 10 - 12 cm
. 15 cm

Correct Answer & Explanation

. 3 - 5 cm

Explanation

The direct lateral (Hardinge) approach to the hip does not use a true internervous plane, as it splits the gluteus medius and vastus lateralis (both innervated by the superior gluteal nerve for the former, and femoral nerve for the latter, but the split is within the substance of the gluteus medius). The superior gluteal nerve courses from posterior to anterior and supplies the gluteus medius, gluteus minimus, and TFL. Its inferior branch runs approximately 3 to 5 cm proximal to the tip of the greater trochanter. Extending the split further proximal than 5 cm risks severing this nerve, leading to a postoperative Trendelenburg gait.

Question 4514

Topic: Total Hip Arthroplasty (THA)

During a Kocher-Langenbeck approach for a posterior wall acetabular fracture, the short external rotators of the hip are tagged and tenotomized near their femoral insertion. Which muscle should be preserved or have its femoral insertion left intact to protect the main blood supply to the femoral head?

. Piriformis
. Superior gemellus
. Obturator internus
. Quadratus femoris
. Inferior gemellus

Correct Answer & Explanation

. Quadratus femoris

Explanation

The deep branch of the medial femoral circumflex artery (MFCA) provides the primary blood supply to the adult femoral head. It runs anterior to the quadratus femoris and posterior to the obturator externus. To protect the MFCA during a posterior approach, the quadratus femoris (or at least its inferior half) and the obturator externus should be preserved. Tenotomizing the piriformis and the triceps coxae (superior gemellus, obturator internus, inferior gemellus) is standard and safe.

Question 4515

Topic: 3. Adult Reconstruction (Hip & Knee)

A direct lateral (Hardinge) approach is used for a total hip arthroplasty. The gluteus medius is split during the approach. To avoid denervating the anterior portion of the gluteus medius and tensor fasciae latae, the proximal split should not extend beyond what distance from the tip of the greater trochanter?

. 1 cm
. 3 cm
. 5 cm
. 7 cm
. 10 cm

Correct Answer & Explanation

. 5 cm

Explanation

The superior gluteal nerve innervates the gluteus medius, minimus, and TFL. Its branches traverse the deep surface of the gluteus medius approximately 3 to 5 cm proximal to the tip of the greater trochanter. Splitting the muscle beyond 5 cm places the nerve at significant risk.

Question 4516

Topic: 3. Adult Reconstruction (Hip & Knee)

A 50-year-old patient presents with rapidly progressive, severe hip and knee osteoarthritis out of proportion to their age. During total knee arthroplasty, the articular cartilage is noted to be distinctly black and brittle. The underlying systemic disease is caused by an inherited deficiency in which enzyme?

. Uricase
. Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)
. Homogentisate 1,2-dioxygenase
. Phenylalanine hydroxylase
. Tyrosinase

Correct Answer & Explanation

. Homogentisate 1,2-dioxygenase

Explanation

Ochronosis (alkaptonuria) results from a deficiency of homogentisate 1,2-dioxygenase. This causes homogentisic acid to accumulate and polymerize into a black pigment that deposits in articular cartilage, leading to early, severe degeneration.

Question 4517

Topic: 3. Adult Reconstruction (Hip & Knee)

During a total hip arthroplasty on a 55-year-old man with severe degenerative joint disease and a history of dark urine, the surgeon notes that the articular cartilage is stark black. This condition is caused by a deficiency in which of the following enzymes?

. Homogentisate 1,2-dioxygenase
. Galactosamine-6-sulfatase
. Lysyl hydroxylase
. Glucocerebrosidase
. Tyrosine kinase

Correct Answer & Explanation

. Homogentisate 1,2-dioxygenase

Explanation

Alkaptonuria (ochronosis) is an autosomal recessive disorder caused by a deficiency in homogentisate 1,2-dioxygenase. This leads to the accumulation of homogentisic acid, which binds to collagen, causing black pigmentation (ochronosis) and early-onset severe osteoarthritis.

Question 4518

Topic: 3. Adult Reconstruction (Hip & Knee)

An orthopedic researcher is evaluating a new diagnostic test for periprosthetic joint infection (PJI). The prevalence of PJI in the study population is artificially increased from 5% to 20%. Assuming the sensitivity and specificity of the diagnostic test remain unchanged, what is the effect on the predictive values of the test?

. Both PPV and NPV will increase
. PPV will increase and NPV will decrease
. PPV will decrease and NPV will increase
. Both PPV and NPV will decrease
. Predictive values are independent of disease prevalence

Correct Answer & Explanation

. PPV will increase and NPV will decrease

Explanation

Positive predictive value (PPV) and negative predictive value (NPV) are highly dependent on disease prevalence. As the prevalence of a disease increases in a population, the PPV of a test increases and the NPV decreases. Sensitivity and specificity are intrinsic properties of the test and do not change with disease prevalence.

Question 4519

Topic: 3. Adult Reconstruction (Hip & Knee)

During a prolonged total knee arthroplasty, the pneumatic tourniquet is suddenly deflated after 100 minutes of ischemia time. Which of the following physiological changes is most likely to be observed immediately by the anesthesia team?

. Increase in core body temperature
. Decrease in end-tidal carbon dioxide (ETCO2)
. Increase in central venous pressure (CVP)
. Increase in end-tidal carbon dioxide (ETCO2)
. Increase in mean arterial blood pressure (MAP)

Correct Answer & Explanation

. Increase in end-tidal carbon dioxide (ETCO2)

Explanation

Tourniquet deflation leads to the release of ischemic, acidotic, and hypercarbic blood back into systemic circulation. This results in an immediate increase in end-tidal CO2 (ETCO2), a transient decrease in core body temperature, a decrease in mean arterial pressure (due to vasodilation and redistribution of blood volume), and an increase in serum potassium.

Question 4520

Topic: 3. Adult Reconstruction (Hip & Knee)
The primary mode of wear in a well-functioning metal-on-polyethylene total hip arthroplasty that produces billions of submicron polyethylene particles, ultimately leading to osteolysis, is best classified as:
. Third-body wear
. Abrasive wear
. Adhesive wear
. Fretting wear
. Corrosive wear

Correct Answer & Explanation

. Adhesive wear

Explanation

Adhesive wear occurs between the smooth metal head and the ultra-high-molecular-weight polyethylene (UHMWPE) liner during normal articulation. It is the primary generator of the submicron-sized particulate debris that triggers macrophage-mediated periprosthetic osteolysis.

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