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Total Hip Arthroplasty (THA) MCQs

Practice Set 31 of 36

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

Question 601

Topic: Total Hip Arthroplasty (THA)

Which of the following intraoperative variables most significantly increases the risk of posterior dislocation following a primary THA performed via a posterior approach?

. Placement of the acetabular component in 30 degrees of anteversion
. Use of a 36-mm femoral head instead of a 28-mm head
. Failure to repair the short external rotators and posterior capsule
. Lengthening the operative leg by 10 mm relative to the contralateral side
. Increasing the femoral offset by 5 mm

Correct Answer & Explanation

. Placement of the acetabular component in 30 degrees of anteversion

Explanation

The posterior approach disrupts the posterior soft tissue envelope (capsule and short external rotators). Failure to perform a robust posterior soft-tissue repair significantly increases the risk of early posterior dislocation. Conversely, increased acetabular anteversion, larger femoral head size (increases jump distance), increased leg length, and increased offset all serve to increase soft tissue tension and mechanical stability, thereby decreasing dislocation risk.

Question 602

Topic: Total Hip Arthroplasty (THA)

A patient presents 6 months after a right THA complaining that the operative leg feels longer. On physical examination, the distance from the anterior superior iliac spine (ASIS) to the medial malleolus is strictly equal bilaterally. However, the distance from the umbilicus to the medial malleolus is 2 cm greater on the right. Anteroposterior pelvic radiographs demonstrate that the lesser trochanters are perfectly level relative to the ischial tuberosities. What is the most likely etiology of the patient's symptoms?

. Use of an oversized femoral head length (+8mm)
. Acetabular cup placed inferior to the anatomic tear drop
. Fixed pelvic obliquity secondary to spinal deformity or soft tissue contracture
. Subsidence of the femoral stem on the contralateral side
. Excessive offset of the femoral stem

Correct Answer & Explanation

. Use of an oversized femoral head length (+8mm)

Explanation

The patient has an apparent (functional) leg length discrepancy, not a true (anatomic) leg length discrepancy. True leg length is measured from ASIS to medial malleolus, which is equal here, and confirmed radiographically by level lesser trochanters. Apparent leg length is measured from the umbilicus to the medial malleolus. A discrepancy in apparent length with equal true length is caused by pelvic obliquity, often driven by lumbar scoliosis, fixed spinal deformity, or adductor/abductor contractures.

Question 603

Topic: Total Hip Arthroplasty (THA)

A surgeon aims to increase femoral offset during a total hip arthroplasty without increasing leg length. Which of the following techniques will best achieve this goal?

. Using a longer femoral head neck length
. Decreasing the depth of femoral stem insertion
. Using a lateralized (high-offset) femoral stem
. Decreasing the acetabular component abduction angle
. Increasing the anteversion of the acetabular component

Correct Answer & Explanation

. Using a longer femoral head neck length

Explanation

A lateralized or high-offset femoral stem is designed specifically to increase the offset (the perpendicular distance from the center of rotation to the anatomical axis of the femur) without changing the vertical height (leg length). Increasing the femoral head length or decreasing stem insertion depth would inadvertently increase leg length.

Question 604

Topic: Total Hip Arthroplasty (THA)

A 62-year-old male presents with groin pain and swelling 6 years after a metal-on-polyethylene total hip arthroplasty. Serum cobalt and chromium levels are elevated. Aspiration yields sterile fluid with a high macrophage count. Which of the following implant characteristics is most associated with this condition?

. Large diameter (>= 36mm) metal head on a standard trunnion
. Ceramic head on a titanium trunnion
. Highly cross-linked polyethylene liner
. Cemented femoral stem
. Increased acetabular cup anteversion

Correct Answer & Explanation

. Large diameter (>= 36mm) metal head on a standard trunnion

Explanation

This presentation describes mechanically assisted crevice corrosion (trunnionosis) at the modular head-neck junction. Risk factors include large diameter metal heads, which increase the torsional forces on the taper, mixed metal couples, and certain taper designs.

Question 605

Topic: Total Hip Arthroplasty (THA)

A 45-year-old active male underwent a THA with a ceramic-on-ceramic bearing. Three years postoperatively, he complains of an audible squeaking sound from his hip when walking or bending. Which of the following component positions is most strongly associated with the biomechanical phenomenon causing this sound?

. Excessive femoral anteversion
. Acetabular cup retroversion and edge loading
. Decreased global femoral offset
. Acetabular cup abduction angle < 35 degrees
. Placement of the center of rotation medial to the Kohler line

Correct Answer & Explanation

. Excessive femoral anteversion

Explanation

Squeaking in ceramic-on-ceramic bearings is strongly associated with edge loading, which disrupts the fluid lubrication film between the articular surfaces. Edge loading is often caused by malpositioning of the acetabular cup, particularly increased inclination (steep cup) or retroversion, which leads to stripe wear and subsequent squeaking.

Question 606

Topic: Total Hip Arthroplasty (THA)
A 75-year-old male requires a revision THA. Preoperative radiographs reveal a loose femoral stem with severe diaphyseal bone loss, a completely absent isthmus, and less than 4 cm of intact diaphyseal bone for distal fixation. According to the Paprosky classification, this is a Type IIIB defect. Which of the following femoral components is the most appropriate workhorse for this reconstruction?
. Fully porous-coated cylindrical non-modular stem
. Cemented long-stem revision prosthesis
. Modular fluted tapered titanium stem
. Standard geometry proximally coated wedge stem
. Impaction bone grafting with a standard short stem

Correct Answer & Explanation

. Modular fluted tapered titanium stem

Explanation

A Paprosky IIIB defect implies inadequate diaphyseal bone (<4 cm of 'scratch fit') to reliably support a fully porous-coated cylindrical stem. Modular fluted tapered titanium stems are the preferred choice, as their flutes provide rotational stability and the taper provides axial stability in the distal diaphyseal bone, bypassing the deficient proximal bone.

Question 607

Topic: Total Hip Arthroplasty (THA)
A 72-year-old male presents with a loose acetabular component. Imaging demonstrates an inferiorly migrated teardrop, a fracture line extending through the posterior column, and complete separation between the superior and inferior halves of the hemipelvis. What is the preferred contemporary management for this severe defect?
. Paprosky type IIIA defect; treat with a standard oversized hemispherical cup
. Paprosky type IIIB defect; treat with an unconstrained jumbo cup
. Pelvic discontinuity; treat with posterior column plating alone
. Pelvic discontinuity; treat with rigid spanning fixation such as a cup-cage construct or acetabular distraction with porous metal
. Paprosky type IIC defect; treat with a superior metal augment

Correct Answer & Explanation

. Pelvic discontinuity; treat with rigid spanning fixation such as a cup-cage construct or acetabular distraction with porous metal

Explanation

Complete separation of the superior and inferior hemipelvis is a pelvic discontinuity. It requires reconstruction that spans and rigidly fixes the superior and inferior segments. Contemporary techniques include custom triflange components, cup-cage constructs, or the acetabular distraction technique utilizing highly porous tantalum cups with augments to bridge the gap.

Question 608

Topic: Total Hip Arthroplasty (THA)

The Exeter femoral stem is a classic example of a collarless, polished, double-tapered cemented implant. By which biomechanical principle does this specific stem design achieve long-term stability?

. Shape-closed fixation, relying on rigid bonding between the stem and cement mantle.
. Force-closed fixation, allowing controlled subsidence of the stem within the cement mantle.
. Proximal load transfer, utilizing a collar to offload the distal cement mantle.
. Distal point loading, wedging the tip of the stem into the diaphyseal bone.
. Osseointegration, achieved through ongrowth onto the polished metallic surface.

Correct Answer & Explanation

. Shape-closed fixation, relying on rigid bonding between the stem and cement mantle.

Explanation

Collarless, polished, double-tapered stems (like the Exeter) are designed to function as 'force-closed' devices. Because they are highly polished, they do not bond to the cement. Instead, the double-taper design allows the stem to subside slightly within the intact cement mantle under axial load, effectively acting as a wedge that increases radial compressive forces and stabilizes the implant.

Question 609

Topic: Total Hip Arthroplasty (THA)

A 72-year-old woman experiences recurrent posterior dislocations following a primary total hip arthroplasty via a posterior approach. Radiographs show a well-fixed cup with 20 degrees of anteversion and 40 degrees of abduction, and a well-fixed stem with 5 degrees of retroversion. What is the most appropriate surgical intervention?

. Revision of the acetabular component to increase anteversion
. Revision of the femoral stem to increase anteversion
. Application of a constrained acetabular liner
. Trochanteric advancement
. Prescribing an abduction brace for 6 weeks

Correct Answer & Explanation

. Revision of the acetabular component to increase anteversion

Explanation

The femoral stem is retroverted (5 degrees), which significantly predisposes the patient to posterior instability. Since the acetabular component is already in an optimal position, revision of the femoral stem to correct the version is the definitive treatment.

Question 610

Topic: Total Hip Arthroplasty (THA)

A 72-year-old female sustains a fall 5 years after an uncemented THA. Radiographs reveal a periprosthetic fracture around the femoral stem extending from the distal aspect of the lesser trochanter to just proximal to the tip of the stem. The stem is radiographically loose, but the surrounding cortical bone stock is thick and adequate. How is this fracture classified according to the Vancouver system?

. Vancouver A
. Vancouver B1
. Vancouver B2
. Vancouver B3
. Vancouver C

Correct Answer & Explanation

. Vancouver A

Explanation

Vancouver B fractures occur around or just below the tip of the stem. B1 indicates a well-fixed stem; B2 indicates a loose stem but adequate bone stock; B3 indicates a loose stem with severely deficient bone stock. Since the stem is loose with adequate bone, it is a Vancouver B2 fracture, which typically requires revision using a long-stem prosthesis.

Question 611

Topic: Total Hip Arthroplasty (THA)

A 65-year-old female presents with an intractable Trendelenburg lurch and recurrent hip instability 2 years following a THA via a lateral approach. MRI confirms complete avulsion of the gluteus medius and minimus tendons with severe fatty infiltration and atrophy of the muscle bellies. What is the most reliable surgical salvage option for stability?

. Direct anatomical repair of the abductor tendons using bone anchors
. Gluteus maximus muscle transfer
. Revision to a constrained acetabular liner
. Revision to a dual mobility bearing articulation
. Fascia lata autograft augmentation of the deficient capsule

Correct Answer & Explanation

. Direct anatomical repair of the abductor tendons using bone anchors

Explanation

In the setting of chronic, irreparable abductor deficiency with severe fatty atrophy, direct repairs and muscle transfers have unacceptably high failure rates. To prevent dislocation while allowing a functional range of motion, revising the acetabular construct to a dual mobility bearing is highly reliable and preferred over constrained liners, which have higher rates of mechanical failure and loosening.

Question 612

Topic: Total Hip Arthroplasty (THA)

During a standard posterior approach to the hip (Moore or Southern approach), the short external rotators are sharply released. Which of the following vessels provides the primary blood supply to the adult femoral head and is at significant risk of injury if dissection is carried too close to the intertrochanteric crest or quadratus femoris?

. Medial femoral circumflex artery
. Lateral femoral circumflex artery
. Obturator artery
. Inferior gluteal artery
. Superior gluteal artery

Correct Answer & Explanation

. Medial femoral circumflex artery

Explanation

The medial femoral circumflex artery (MFCA), specifically its deep branch, provides the main arterial blood supply to the adult femoral head. It crosses posterior to the obturator externus tendon and anterior to the quadratus femoris. Dissection or release of the quadratus femoris too close to the femur can injure this crucial vessel.

Question 613

Topic: Total Hip Arthroplasty (THA)

During a primary THA, restoring the anatomic femoral offset (the horizontal distance from the center of rotation to the femoral anatomic axis) has which of the following biomechanical effects?

. Increases the abductor moment arm and decreases the joint reactive force
. Decreases the abductor moment arm and increases the joint reactive force
. Increases both the abductor moment arm and the joint reactive force
. Decreases the tension on the soft tissues, increasing dislocation risk
. Shifts the center of gravity medially

Correct Answer & Explanation

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

Explanation

Restoring or slightly increasing femoral offset increases the mechanical advantage (moment arm) of the abductor musculature. By the equation of static equilibrium in the coronal plane, an increased abductor moment arm means less abductor force is required to keep the pelvis level during the single-leg stance phase of gait. This subsequently decreases the overall compressive joint reactive force across the hip.

Question 614

Topic: Total Hip Arthroplasty (THA)

A 45-year-old active male with a ceramic-on-ceramic total hip arthroplasty presents to the ER after hearing a loud "crack" in his hip followed by sudden severe pain. Radiographs confirm a shattered ceramic head. During revision surgery, which of the following steps is critical to prevent early failure of the new bearing?

. Retaining the well-fixed titanium acetabular shell without any liner modifications
. Thorough synovectomy and using a new ceramic head with a titanium sleeve
. Placing a standard metal-on-polyethylene bearing to avoid repeat fracture
. Washing the joint with normal saline and replacing only the femoral head
. Performing a routine extended trochanteric osteotomy

Correct Answer & Explanation

. Retaining the well-fixed titanium acetabular shell without any liner modifications

Explanation

Ceramic fracture generates microscopic third-body shards that rapidly destroy non-ceramic bearings. A thorough synovectomy is critical to remove debris, and a new ceramic head (often with a titanium sleeve if the native trunnion is retained) must be used.

Question 615

Topic: Total Hip Arthroplasty (THA)

A 4-year-old boy presents with progressive bowing of his left leg. Radiographs reveal a prominent medial metaphyseal beak, lucency, and an epiphyseal-metaphyseal angle of 20 degrees. What is the most appropriate management?

. Observation and reassurance
. Prescription of a knee-ankle-foot orthosis (KAFO)
. Proximal tibial corrective osteotomy
. Guided growth (hemiepiphysiodesis) of the lateral tibia
. Epiphysiodesis of the contralateral leg to prevent leg length discrepancy

Correct Answer & Explanation

. Observation and reassurance

Explanation

The patient has infantile Blount disease with significant radiographic changes (epiphyseal-metaphyseal angle > 16 degrees). At age 4, bracing is ineffective, making a proximal tibial corrective osteotomy the treatment of choice to prevent permanent deformity.

Question 616

Topic: Total Hip Arthroplasty (THA)

A patient has pain 2 years after undergoing a metal-on-metal (MOM) left total hip arthroplasty (THA). Which

test(s) best correlate with a prognosis if this patient is having a reaction to metal debris?

. Erythrocyte sedimentation rate, C-reactive protein, and white blood cell count
. Serum cobalt and chromium ion levels
. MRI with metal artifact reduction sequence (MARS)
. CT of pelvis

Correct Answer & Explanation

. Erythrocyte sedimentation rate, C-reactive protein, and white blood cell count

Explanation

Painful MOM THA and taper corrosion can cause substantial damage to a patient's hip if left untreated. In this case, the workup for a painful MOM THA starts the same as a workup for a painful metal-on- polyethylene bearing couple. Infection must be ruled out in every case with a set of inflammatory markers. If these markers are remotely elevated, this is an indication for joint aspiration. In patients with metal debris, the pathology report often indicates too many cells to count or cellular debris. Metal ion levels do not seem to correlate with prognosis. There are well-functioning patients with high ion levels and poor- functioning patients with low ion levels. Advanced imaging with MARS MRI to evaluate for peritrochanteric fluid collection, a soft-tissue mass, or synovial/capsular hypertrophy will reveal signs of a metal reaction that indicate the need for a revision discussion. A CT scan can show more advanced bony destruction as an indicator of poor prognosis. These films can be used to determine the need for a structural graft or augments for reconstruction of bone loss attributable to metal debris.

Question 617

Topic: Total Hip Arthroplasty (THA)

A 59-year-old active woman undergoes elective total hip replacement in which a posterior approach is

used. She has minimal pain and is discharged to home 2 days after surgery. Four weeks later, she dislocates her hip while shaving her legs. She undergoes a closed reduction in the emergency department. Postreduction radiographs show a reduced hip with well-fixed components in satisfactory alignment. What is the most appropriate management of this condition from this point forward?

. Observation and patient education regarding hip dislocation precautions
. Revision to a larger-diameter femoral head
. Revision to a constrained acetabular component
. Application of a hip orthosis for 3 months

Correct Answer & Explanation

. Observation and patient education regarding hip dislocation precautions

Explanation

First-time early dislocations are often treated successfully without revision surgery, especially when no component malalignment is present. In this clinical scenario, it appears the patient would benefit from better education about dislocation precautions. Hip orthoses are of questionable benefit unless the patient is cognitively impaired. Revision surgery can be successful but is usually reserved for patients with recurrent dislocations.

Question 618

Topic: Total Hip Arthroplasty (THA)

A 70-year-old man undergoes removal of an infected total hip arthroplasty (THA) and insertion of an

articulating antibiotic-loaded spacer to treat a deep periprosthetic hip infection. While in a nursing home receiving intravenous antibiotics 3 weeks after surgery, the patient trips and falls. Examination reveals swelling in the mid and distal thigh, intact skin and neurovascular structures, and severe pain with knee

or hip movement. Radiographs of the femur are shown in Figures 1 through

. What is the most appropriate treatment for the fracture below the implant?
. Balanced traction to address concern for persistent infection with reoperation
. Open reduction and internal fixation of the fracture with a lateral plate and screws
. Removal of the articulating spacer and revision to a longer-stem antibiotic-loaded articulating spacer
. Removal of the articulating spacer and reimplantation using a long-stem fluted uncemented hip replacement

Correct Answer & Explanation

. What is the most appropriate treatment for the fracture below the implant?

Explanation

This patient has a type C periprosthetic femoral fracture. The articulating spacer is not involved in the fracture, which is well distal to the implant. The most appropriate treatment is open reduction and internal fixation of the fracture. Traction is not appropriate for this fracture because the injury can be treated surgically despite the history of previous hip infection. Traction would also be needed for at least 5 weeks and would delay the surgical treatment of the periprosthetic fracture until the time of second-stage revision THA. The fracture is fairly distal, and revision to a longer antibiotic-loaded implant or uncemented stem is not suitable for this fracture pattern, because it extends well past the isthmus. A femoral stem in the distal fragment would provide little stability for the fracture. Removal of the articulating spacer and reimplantation using a long-stem fluted uncemented hip replacement is not appropriate, because it would be premature to reimplant the man's hip while he is still receiving treatment for a deep hip infection.

Question 619

Topic: Total Hip Arthroplasty (THA)

Figures 1 and 2 show the radiographs obtained from a 68-year-old morbidly obese man who underwent

left total hip replacement 7 years ago and did well, with no symptoms prior to the current presentation. He recently rose from a seated position and felt a pop in the hip, with immediate pain and inability to bear weight. Any pressure on the left foot now produces a painful, grinding sensation with loss of left hip stability. What is the best next step?

. Revision of the acetabular implant to a constrained bearing with modular exchange of the femoral head and neck
. Revision of the acetabular and femoral implants
. Retention of the acetabular implant with modular exchange of the femoral head and neck
. Revision of the femoral component alone with a new ceramic head

Correct Answer & Explanation

. Revision of the acetabular implant to a constrained bearing with modular exchange of the femoral head and neck

Explanation

The modular femoral stem has fractured. Changing the liner to a constrained design is not warranted at this time based on the information provided. Revision of the acetabular implant is appropriate because of the potential for damage to the existing cup from metal debris and femoral implant contact and to convert from a metal-on-metal articulation. Nonsurgical management would not provide pain relief or improvement; revision of the total hip arthroplasty is recommended. The implant failed in a short time, and retention of the femoral stem is not recommended because of the concern for failure with only a neck exchange. A dual-mobility bearing may be a good option if the surgeon plans to retain the acetabular component. Extended trochanteric osteotomy is a useful technique for the removal of a well-fixed femoral implant. In this patient, femoral stem removal withoutosteotomy would be difficult due to the fracture of the implantโ€™s femoral neck and theinability to gain purchase for extraction.

Question 620

Topic: Total Hip Arthroplasty (THA)

Figure 1 shows the radiograph obtained from a 67-year-old man recently diagnosed with osteoarthritis, 8

years after receiving a left metal-on-metal total hip arthroplasty (THA). The acetabular component has a modular cobalt alloy acetabular liner. The patient states that he did very well postoperatively, but for the last 6 months has noted worsening pain and swelling in his left hip. Serum metal ion testing reveals a chromium level of 12.4 ng/mL, compared with a normal level of less than 0.3 ng/mL, and a cobalt level of 11.8 ng/mL, compared with a normal level less than 0.7 ng/mL. An MRI with metal artefact reduction sequence (MARS) was performed and is shown in Figure

. What is the most appropriate management at this time?
. Annual monitoring of serum metal ion levels
. Repeated MRI with MARS in 6 months
. Conversion of the THA to a cobalt alloy femoral head and polyethylene bearing
. Conversion of the THA to a ceramic femoral head with an inner titanium sleeve and polyethylene bearing

Correct Answer & Explanation

. What is the most appropriate management at this time?

Explanation

Metal-on-metal THA was initially introduced in the 1990s, with the proposed advantages of decreased wear and improved stability. However, catastrophic adverse local tissue reactions associated with their use has raised numerous concerns. The work-up of a patient with a prior metal-on-metal total hip arthroplasty involves a thorough history and physical examination; blood analysis, including the erythrocyte sedimentation rate, C-reactive protein, and metal ion levels; and secondary imaging, including ultrasonography, CT, and MRI. In a patient with clinical symptoms, elevated metal ion levels, and a large fluid collection seen on MRI, the most appropriate treatment would be removal of the metal-on-metal bearing. Given the presence of an adverse reaction involving cobalt and chromium, a revision ceramic head may be most appropriate to avoid the potential of trunnion-associated corrosion.

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