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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 98 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 1941

Topic: 3. Adult Reconstruction (Hip & Knee)

Stress shielding in cementless total hip arthroplasty leads to proximal femoral bone resorption over time due to the transfer of mechanical load distally. Which of the following femoral stem designs is associated with the highest degree of proximal stress shielding?

. A short, proximally coated metaphyseal-fitting titanium stem
. A fully porous-coated, large-diameter, rigid cylindrical cobalt-chromium stem
. A tapered-wedge titanium stem with proximal plasma spray
. A cemented, highly polished, double-tapered stainless steel stem
. A proximally hydroxyapatite-coated, non-porous titanium stem

Correct Answer & Explanation

. A fully porous-coated, large-diameter, rigid cylindrical cobalt-chromium stem

Explanation

According to Wolff's Law, bone remodels in response to mechanical stress. Stress shielding occurs when the stiff femoral stem bypasses the proximal femur and transfers load directly to the diaphysis. This is most pronounced with fully porous-coated stems (which achieve rigid diaphyseal fixation), large-diameter stems (which have a very high bending stiffness), and cobalt-chromium alloys (which possess a much higher modulus of elasticity than titanium). A fully porous-coated, large-diameter CoCr stem provides rigid distal fixation, completely unloading the proximal femur and leading to significant proximal cortical osteolysis/stress shielding.

Question 1942

Topic: Total Knee Arthroplasty (TKA)

When performing patellar resurfacing during a primary TKA, careful attention must be paid to the remaining thickness of the native patellar bone after the resection. To minimize the risk of a catastrophic postoperative patellar fracture, what is the generally accepted absolute minimum composite thickness of the remaining native anterior patellar bone shell?

. 5 to 7 mm
. 8 to 10 mm
. 12 to 15 mm
. 18 to 20 mm
. 22 to 24 mm

Correct Answer & Explanation

. 12 to 15 mm

Explanation

The native, unresurfaced patella is typically 22 to 26 mm thick in adults. When resurfacing the patella, the goal is to resect an amount of bone equal to the thickness of the polyethylene button being implanted to restore the native patellar composite thickness. However, if the native patella is thin or asymmetric, the surgeon must prioritize leaving an adequate residual bony shell. The established biomechanical threshold to prevent catastrophic patellar fracture is leaving an absolute minimum of 12 to 15 mm of native anterior patellar bone.

Question 1943

Topic: 3. Adult Reconstruction (Hip & Knee)

In modern total hip arthroplasty, highly cross-linked polyethylene (HXLPE) is frequently doped with Vitamin E (alpha-tocopherol). What is the primary biochemical purpose of adding Vitamin E to the polyethylene prior to or after irradiation?

. To increase the degree of crystalline cross-linking for enhanced wear resistance
. To act as a free radical scavenger, preventing oxidation without the need for post-irradiation remelting
. To increase the overall elastic modulus of the bearing surface
. To enhance the hydrophilicity of the bearing surface for better fluid film lubrication
. To lower the melting temperature of the polyethylene during manufacturing

Correct Answer & Explanation

. To act as a free radical scavenger, preventing oxidation without the need for post-irradiation remelting

Explanation

Irradiation is used to cross-link polyethylene to improve wear resistance, but it creates free radicals that can oxidize over time, leading to degradation and embrittlement. Historically, post-irradiation thermal treatment (remelting or annealing) was used to eliminate free radicals, but remelting reduces mechanical strength. Vitamin E acts as an antioxidant (free radical scavenger) that neutralizes these free radicals, preventing oxidation while avoiding the mechanical property loss associated with remelting.

Question 1944

Topic: 3. Adult Reconstruction (Hip & Knee)

A modern total knee arthroplasty utilizes a 'medial pivot' design. In a normal native knee during active flexion from 0 to 90 degrees, how does the kinematics of the femoral condyles on the tibia typically behave to justify this implant design?

. Both condyles translate anteriorly symmetrically
. Both condyles translate posteriorly symmetrically
. The medial condyle remains relatively stationary while the lateral condyle translates posteriorly
. The lateral condyle remains relatively stationary while the medial condyle translates posteriorly
. Both condyles exhibit equal internal rotation relative to the tibia

Correct Answer & Explanation

. The medial condyle remains relatively stationary while the lateral condyle translates posteriorly

Explanation

Native knee kinematics involve a 'medial pivot' mechanism. During knee flexion, the medial femoral condyle exhibits minimal anteroposterior translation (acting as a pivot point), while the lateral femoral condyle rolls and translates posteriorly. This differential translation results in the internal rotation of the tibia relative to the femur during flexion.

Question 1945

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old male complains of a sense of giving way and recurrent effusions one year after a primary posterior-stabilized total knee arthroplasty. On examination, the knee is perfectly stable in full extension but exhibits excessive anteroposterior laxity at 90 degrees of flexion. Radiographs show well-fixed components with no loosening. What is the most appropriate surgical management to address this specific instability pattern?

. Isolated polyethylene insert exchange to a thicker insert
. Revision of the femoral component to a larger anteroposterior size with posterior augments
. Revision of the tibial component to significantly increase the posterior slope
. Lateral retinacular release and patellar resurfacing
. Medial collateral ligament reconstruction

Correct Answer & Explanation

. Revision of the femoral component to a larger anteroposterior size with posterior augments

Explanation

The patient presents with isolated flexion instability, indicating that the flexion gap is unacceptably loose while the extension gap is stable. Placing a thicker polyethylene insert would tighten the flexion gap but would simultaneously over-tighten the extension gap, causing a flexion contracture. Increasing the tibial slope would paradoxically increase the flexion gap, making the instability worse. The correct management is to increase the anteroposterior dimension of the femur by upsizing the femoral component or adding posterior femoral augments; this tightens the flexion gap exclusively without affecting the extension gap.

Question 1946

Topic: 3. Adult Reconstruction (Hip & Knee)

Intra-prosthetic dislocation (IPD) is a unique and major complication associated with dual mobility total hip arthroplasty constructs. Which of the following best describes the pathomechanics of this specific complication?

. Dislocation of the large mobile polyethylene head from the metal acetabular shell
. Dissociation of the small inner metal/ceramic head from the large mobile polyethylene liner
. Impingement of the femoral neck on the acetabular rim leading to late component loosening
. Fretting corrosion at the trunnion leading to catastrophic failure of the femoral neck
. Failure of the locking mechanism holding the highly cross-linked polyethylene into the titanium shell

Correct Answer & Explanation

. Dissociation of the small inner metal/ceramic head from the large mobile polyethylene liner

Explanation

Intra-prosthetic dislocation (IPD) is unique to dual mobility bearings and refers specifically to the failure of the retentive rim of the large polyethylene component, causing the small inner metal or ceramic head to dislocate from within the polyethylene liner. The patient typically presents with sudden pain and limp. Radiographs will show the inner head eccentrically located or articulating directly with the metal acetabular shell.

Question 1947

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total knee arthroplasty, the surgeon notes severe lateral patellar tracking requiring a lateral retinacular release. Postoperatively, the patient continues to experience anterior knee pain. A CT scan is obtained to evaluate component rotation. Internal rotation of which of the following component pairs is the most frequent surgical cause of this patellar maltracking?

. Internal rotation of the femoral component and external rotation of the tibial component
. Internal rotation of the femoral component and internal rotation of the tibial component
. External rotation of the femoral component and internal rotation of the tibial component
. External rotation of both the femoral and tibial components
. Medialization of the femoral component and lateralization of the tibial component

Correct Answer & Explanation

. Internal rotation of the femoral component and internal rotation of the tibial component

Explanation

Patellar maltracking (lateral tracking and subluxation) in TKA is frequently caused by errors in component rotation that increase the Q-angle. Internal rotation of the femoral component medializes the trochlear groove relative to the extensor mechanism. Internal rotation of the tibial component externally rotates the tibial tubercle relative to the rest of the knee. Both of these specific technical errors effectively lateralize the tibial tubercle relative to the trochlear groove, increasing the Q-angle and causing lateral patellar maltracking.

Question 1948

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total knee arthroplasty for a severe fixed varus deformity, the surgeon resects the proximal tibia and distal femur. The knee remains tight medially in both flexion and extension. After releasing the deep medial collateral ligament (MCL) and removing all medial osteophytes, what is the most appropriate next step in the standard stepwise medial release to balance the knee?

. Release the superficial MCL off its distal tibial insertion
. Release the semimembranosus insertion
. Release the posteromedial capsule
. Perform a medial epicondylar osteotomy
. Resect the posterior cruciate ligament (PCL) completely

Correct Answer & Explanation

. Release the posteromedial capsule

Explanation

The standard step-wise medial soft-tissue release for balancing a varus TKA begins with comprehensive osteophyte resection. The deep MCL is then released. If the knee remains tight, particularly in extension, the next structure in the sequence is the posteromedial capsule (and semimembranosus insertion). Releasing the superficial MCL completely off its distal tibial insertion is reserved as a last resort, as it can lead to catastrophic medial instability requiring constrained inserts.

Question 1949

Topic: 3. Adult Reconstruction (Hip & Knee)

A 60-year-old male complains of persistent groin pain 1 year following an uncemented total hip arthroplasty. The pain is worst when initiating movement, specifically when actively lifting his leg to get into a car. Examination reveals pain with an active straight leg raise. Radiographs demonstrate an acetabular cup with 10 degrees of anteversion and 12 mm of anterior overhang beyond the bony anterior acetabular rim. What is the most definitive surgical management?

. Endoscopic iliopsoas tenotomy
. Acetabular cup revision to properly seat the cup and increase anteversion
. Revision of the femoral stem to a high-offset option
. Open adductor longus tenotomy
. Exchange to a larger diameter femoral head

Correct Answer & Explanation

. Acetabular cup revision to properly seat the cup and increase anteversion

Explanation

This patient is suffering from classic iliopsoas impingement after THA, characterized by start-up groin pain and pain with active hip flexion. It is mechanically caused by a prominent anterior edge of the acetabular component. While an iliopsoas tenotomy can be considered for minor overhang, significant anterior cup overhang (>8 mm) combined with relative retroversion (10 degrees anteversion) represents a gross mechanical block. The definitive treatment with the lowest recurrence rate for this degree of mechanical impingement is revision of the acetabular cup to sink it completely into the bone and correct the version.

Question 1950

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old female is scheduled for a primary total knee arthroplasty. She reports a severe, blistering skin reaction to cheap jewelry, and a formal patch test is intensely positive for nickel and cobalt hypersensitivity. To minimize the risk of a hypersensitivity reaction, what is the best combination of implant materials for her TKA?

. Standard cobalt-chromium femur and a standard titanium tibial tray
. Oxidized zirconium femur and an all-polyethylene tibia or pure titanium tray
. Stainless steel femur and a standard titanium tibial tray
. Cobalt-chromium femur with a highly cross-linked polyethylene tibial insert
. Titanium-aluminum-vanadium femur and a standard cobalt-chromium tibial tray

Correct Answer & Explanation

. Oxidized zirconium femur and an all-polyethylene tibia or pure titanium tray

Explanation

In a patient with documented severe metal hypersensitivity, particularly to cobalt or nickel, standard cobalt-chromium implants must be avoided. Stainless steel also contains nickel. Oxidized zirconium (Oxinium) is an ideal femoral component material for these patients; it consists of a zirconium alloy core with a transformed ceramic-like surface of zirconium oxide, virtually eliminating metal ion exposure. This should be paired with a titanium or all-polyethylene tibial component to avoid cobalt entirely.

Question 1951

Topic: Total Hip Arthroplasty (THA)

A patient presents 6 months after a right THA complaining that the right leg feels too long. On examination, the true leg length (measured from the ASIS to the medial malleolus) is equal bilaterally. However, the apparent leg length (measured from the umbilicus to the medial malleolus) is 2 cm longer on the right. What is the most likely etiology of this discrepancy?

. The femoral neck cut was made too high during surgery
. The acetabular component was placed too inferiorly
. Abductor weakness and an adduction contracture of the operative hip
. An abduction contracture of the operative hip
. Excessive femoral offset of the implanted stem

Correct Answer & Explanation

. An abduction contracture of the operative hip

Explanation

If the true leg lengths (ASIS to medial malleolus) are equal, the actual bony lengths of the lower extremities are identical. An apparent leg length discrepancy (umbilicus to medial malleolus) is caused by pelvic obliquity. An abduction contracture of the right hip forces the patient to tilt the right side of the pelvis downward to bring the legs parallel for standing/walking. This downward tilt of the right hemipelvis makes the right leg appear longer when measured from a central point (the umbilicus). Conversely, an adduction contracture results in an apparent shortening of the limb.

Question 1952

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following specific design modifications in modern posterior-stabilized total knee arthroplasty systems has been most instrumental in reducing the incidence of 'patellar clunk syndrome'?

. Moving the femoral intercondylar box further anteriorly
. Lengthening the trochlear groove proximally and smoothing the transition into the intercondylar box
. Significantly increasing the height and width of the tibial post
. Utilizing a highly asymmetric, anatomic patellar component instead of a dome-shaped one
. Decreasing the overall anteroposterior dimension of the femoral component

Correct Answer & Explanation

. Lengthening the trochlear groove proximally and smoothing the transition into the intercondylar box

Explanation

Patellar clunk syndrome occurs in posterior-stabilized (PS) knee designs when a fibrotic nodule forms at the superior pole of the patella or deep quadriceps tendon, which drops into the femoral intercondylar box during flexion and catches as the knee extends, causing a painful 'clunk.' Modern PS implants have significantly reduced this complication by lengthening the trochlear groove more proximally and lowering/smoothing the anterior lip of the intercondylar box, allowing the patella to track smoothly over the box without impingement.

Question 1953

Topic: 3. Adult Reconstruction (Hip & Knee)

During a posterior-stabilized total knee arthroplasty, the knee is found to be tight in extension and loose in flexion after the initial bone cuts. Which of the following is the most appropriate technical adjustment to balance the gaps?

. Upsize the femoral component
. Downsize the femoral component
. Release the posterior capsule
. Recut the distal femur, removing more bone
. Recut the proximal tibia, removing more bone

Correct Answer & Explanation

. Recut the distal femur, removing more bone

Explanation

A tight extension gap with a loose flexion gap requires increasing the extension gap without affecting the flexion gap. Recutting the distal femur achieves this, whereas resecting the proximal tibia would affect both gaps equally.

Question 1954

Topic: Total Hip Arthroplasty (THA)

A 65-year-old male presents with groin pain 5 years after a primary metal-on-polyethylene total hip arthroplasty. Joint aspiration yields fluid with a high cobalt-to-chromium ratio and negative cultures. Which of the following implant characteristics most increases the risk of this specific complication?

. Use of a 28-mm femoral head
. Standard offset femoral stem
. Increased femoral head diameter (e.g., 36-mm or larger)
. Use of a ceramic femoral head
. Highly cross-linked polyethylene liner

Correct Answer & Explanation

. Increased femoral head diameter (e.g., 36-mm or larger)

Explanation

The patient is experiencing trunnionosis (taper corrosion). Utilizing larger diameter metal femoral heads increases the frictional torque at the head-neck junction, exacerbating fretting and corrosion at the trunnion.

Question 1955

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old female reports a painful 'catching' sensation at the anterior aspect of her knee when actively extending from a flexed position, 1 year following a total knee arthroplasty. Which of the following component designs is most commonly associated with this complication?

. Cruciate-retaining design
. Medial pivot design
. Posterior-stabilized design
. Mobile-bearing design
. Hinged knee design

Correct Answer & Explanation

. Posterior-stabilized design

Explanation

Patellar clunk syndrome is most commonly associated with posterior-stabilized (PS) knee designs. It occurs when a fibrous nodule forms in the suprapatellar pouch and catches within the intercondylar box of the femoral component during extension.

Question 1956

Topic: 3. Adult Reconstruction (Hip & Knee)
A 76-year-old female sustains a distal femur fracture superior to her total knee arthroplasty. Radiographs show a displaced fracture, and the femoral component is clinically loose with loss of medial condyle bone stock. What is the most appropriate surgical management?
. Open reduction and internal fixation with a lateral locking plate
. Retrograde intramedullary nailing
. Revision arthroplasty with a distal femoral replacement
. Hinged total knee arthroplasty with short diaphyseal stems
. Nonoperative management with a hinged knee brace

Correct Answer & Explanation

. Revision arthroplasty with a distal femoral replacement

Explanation

A periprosthetic distal femur fracture with a loose component and poor distal bone stock (Lewis-Rorabeck Type III) requires revision arthroplasty. Distal femoral replacement (tumor prosthesis) is the standard of care to bypass the compromised bone and provide immediate stability.

Question 1957

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old female complains of persistent groin pain and a catching sensation with active hip flexion 1 year after an uncomplicated primary total hip arthroplasty. An ultrasound-guided injection of local anesthetic into the iliopsoas bursa completely relieves her pain. What radiographic finding is most likely present?

. Acetabular component retroversion
. Posterior overhang of the acetabular component
. Excessive femoral offset
. Subsynovial radiolucent lines
. Acetabular component placed in excessive anteversion

Correct Answer & Explanation

. Acetabular component retroversion

Explanation

Iliopsoas impingement is a common cause of groin pain after THA. It is frequently caused by a prominent anterior edge of the acetabular component, which typically results from cup retroversion, under-seating, or oversizing.

Question 1958

Topic: 3. Adult Reconstruction (Hip & Knee)

A 79-year-old male sustains a Vancouver B2 periprosthetic femur fracture around a cemented total hip arthroplasty. The stem has subsided 3 cm, but the diaphyseal bone stock distal to the fracture is robust. What is the optimal surgical management?

. Open reduction internal fixation with a lateral plate and cables
. Revision with a fluted, tapered, modular titanium long stem
. Revision with a fully porous-coated cylindrical long stem
. Proximal femoral replacement
. Impaction bone grafting with a cemented long stem

Correct Answer & Explanation

. Revision with a fluted, tapered, modular titanium long stem

Explanation

A Vancouver B2 fracture is characterized by a fracture around a loose stem with adequate bone stock. The standard of care is revision arthroplasty utilizing a fluted, tapered, modular titanium stem to achieve diaphyseal bypass fixation.

Question 1959

Topic: 3. Adult Reconstruction (Hip & Knee)

During a total knee arthroplasty for a severe, rigid varus deformity, the deep medial collateral ligament and posteromedial capsule have been released. The knee remains tight medially in both flexion and extension. Which structure should typically be released next to balance the knee?

. Superficial medial collateral ligament
. Pes anserinus tendons
. Semimembranosus insertion
. Posterior cruciate ligament
. Popliteus tendon

Correct Answer & Explanation

. Superficial medial collateral ligament

Explanation

In the stepwise medial release sequence for severe varus deformity, if release of the deep MCL and posteromedial capsule is insufficient, the next structure to be addressed is the superficial medial collateral ligament (sMCL), often performed via a pie-crusting technique or subperiosteal stripping.

Question 1960

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following best describes the primary biomechanical advantage of a dual-mobility construct in total hip arthroplasty compared to a standard unipolar construct?

. Increased frictional torque at the head-neck junction
. Elimination of polyethylene wear debris
. Increased effective head size and jump distance
. Decreased incidence of intra-prosthetic dislocation
. Enhanced biological fixation of the acetabular shell

Correct Answer & Explanation

. Increased effective head size and jump distance

Explanation

Dual-mobility components use a large polyethylene liner that articulates within a metal shell, effectively acting as a massive femoral head. This significantly increases the jump distance to dislocation, making it highly stable.

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