Knee Arthroplasty MCQs for the FRCS Orth

Courtesy: Zaid Al-Rab, Founder, OrthoPass, Leeds, UK

1. Catastrophic Polyethylene Wear in Total Knee Replacement

Factors Contributing to Catastrophic Wear

Polyethylene wear can be influenced by:

1. Surgical factors

• Component malalignment
• Instability
• Poor ligament balancing

2. Patient factors

• High activity level
• Obesity

3. Polyethylene-related factors

• Thin polyethylene inserts
• Sterilization method
• Implant design

Important Threshold

• Polyethylene thickness < 8 mm increases risk of catastrophic wear.

Correct Concept

• Gamma irradiation of polyethylene in vacuum does NOT increase wear
  (It actually reduces oxidation compared with irradiation in air).

Key Point

• Catastrophic failure often occurs posteromedially due to increased load.

2. Patellofemoral Tracking in Total Knee Arthroplasty

Factors Improving Patellar Tracking

• Lateralization of femoral component
• External rotation of femoral component
• Joint line preservation
• Medialization of patellar button

Incorrect Factor

• Internal rotation of the tibial component

Why?

Internal tibial rotation:

• Causes lateral displacement of tibial tuberosity
• Leads to patellar maltracking and instability

3. Determining Femoral Component Rotation

Established Techniques

1. Transepicondylar axis
2. Posterior condylar axis
3. Whiteside’s line (anteroposterior axis)
4. Gap balancing technique

Not an Established Method

• Femoral alignment axis method

Clinical Note

• Each method may be affected by anatomical variation and difficulty identifying landmarks.

4. All-Polyethylene Tibial Component

Common Design in Modern TKA

• Metal-backed modular tibial component

Disadvantage of All-Polyethylene Tibial Component

• Lack of modularity

Clinical Implications

• Cannot perform:
  • Polyethylene liner exchange
  • Modular insert replacement in infection
  • Isolated insert revision for wear

Other Facts

• Cost is generally lower, not higher.
• Survivorship is comparable to metal-backed designs.

5. Patellar Clunk Syndrome

Occurs in

• Posterior Stabilized (PS) Knee Prosthesis

Pathology

• Formation of hypertrophic fibrous tissue at the superior pole of the patella.

Mechanism

• Fibrous tissue becomes trapped in the intercondylar box during knee flexion.
• On extension, it suddenly releases ? audible clunk.

Correct Concept

• Caused by impingement of hypertrophic scar tissue at the superior pole of the patella during extension.

6. Patellar Resurfacing in Total Knee Replacement

Evidence from Literature

Key study:

• KAT Trial (Knee Arthroplasty Trial – UK)

Findings

• Patellar resurfacing is more cost-effective long term.

Other Observations

• No significant difference in:
  • Functional outcome
  • Range of motion
  • Quadriceps strength

Complications

• Patellar fracture is more common with resurfacing.

7. Femoral Component External Rotation (3° Rule)

Standard Practice

• Femoral component placed in ~3° external rotation relative to posterior condyles.

Primary Purpose

• Balancing the flexion gap

Biomechanical Reason

• Native proximal tibia often has varus alignment.
• After tibial cut perpendicular to mechanical axis:
  • Flexion gap becomes trapezoidal.

External rotation of femoral component:

• Converts trapezoidal gap into rectangular balanced flexion gap.

Secondary Benefit

• Improved patellar tracking.

8. Diagnosis of Periprosthetic Joint Infection (PJI)

Major Diagnostic Criteria (International Consensus Meeting)

Either one confirms infection:

1. Two positive cultures with the same organism
2. Sinus tract communicating with the joint

Minor Criteria (Examples)

• Elevated CRP and ESR
• Elevated synovial WBC
• Elevated synovial neutrophil percentage
• Positive histology
• Single positive culture

Exam Point

• Sinus tract communicating with joint = diagnostic of infection.

9. Unicompartmental vs Total Knee Arthroplasty

Key Study

• TOPKAT Trial (Lancet, 2019)

Findings at 5 Years

Unicompartmental Knee Replacement (UKR):

• Lower surgical cost
• Shorter hospital stay
• Similar functional outcomes compared to TKR
• Similar reoperation rates

Important Exam Point

• UKR associated with lower surgical cost

10. Gap Balancing vs Measured Resection

Measured Resection

• Bone cuts based on anatomical landmarks

Gap Balancing

• Bone cuts adjusted to achieve equal ligament tension in flexion and extension

Evidence

Gap balancing technique:

• Better at reproducing flexion gap stability

Important Considerations

• Accurate tibial cut is essential
• Collateral ligament integrity is important

FRCS Part 1 Examination Pattern (Key Points)

Format

• Single Best Answer (SBA) questions
• Five options per question

Structure

• 2 papers on the same day
• 120 questions per paper
• Total: 240 questions

Time

• 135 minutes per paper

Average time per question:

• ~ 65 seconds

Strategy

• Usually 3 options can be eliminated easily
• Final choice between two close answers
• Requires strong conceptual knowledge

Study Strategy for FRCS MCQs

Recommended Approach

Balanced preparation:

1. Large number of MCQs
2. Concept-based reading

Suggested Practice Volume

• Approximate range reported by candidates:
  • 3,000 – 15,000 questions

Best Method

• Avoid repeating identical questions
• Focus on covering the entire curriculum
• Keep notes of topics encountered in MCQs
• Identify weak areas for focused reading