Courtesy: Zaid Al-Rab, Founder, OrthoPass, Leeds, UK
Overview
Catastrophic polyethylene wear is a serious complication in total knee replacement, often leading to implant failure.
Contributing Factors
1. Surgical Factors
- Component malalignment
- Instability
- Poor ligament balancing
2. Patient Factors
- High activity levels
- Obesity
3. Polyethylene Factors
- Thin inserts
- Sterilization method
- Implant design
Critical Threshold
Polyethylene thickness < 8 mm significantly increases risk
Important Concept
- Gamma irradiation in vacuum reduces oxidation
Does NOT increase wear
Common Site of Failure
- Posteromedial region due to increased load
Patellofemoral Tracking in TKA
Factors That Improve Tracking
- Lateralization of femoral component
- External rotation of femoral component
- Joint line preservation
- Medialization of patellar button
Incorrect Factor
Internal rotation of tibial component
Why?
- Causes lateral shift of tibial tuberosity
- Leads to patellar maltracking and instability
Femoral Component Rotation
Established Methods
- Transepicondylar axis
- Posterior condylar axis
- Whiteside’s line
- Gap balancing technique
Not Recommended
Femoral alignment axis
All-Polyethylene Tibial Component
Key Feature
- Non-modular design
Disadvantages
- No liner exchange
- No modular revision options
Other Facts
- Lower cost
- Comparable survivorship to metal-backed implants
Patellar Clunk Syndrome
Occurs In
- Posterior stabilized (PS) prosthesis
Pathology
- Hypertrophic fibrous tissue at superior patella
Mechanism
- Tissue gets trapped during flexion
- Releases during extension – audible clunk
Patellar Resurfacing
Evidence (KAT Trial)
Findings
- More cost-effective long term
No Difference In
- Functional outcome
- Range of motion
- Quadriceps strength
Complication
- Increased risk of patellar fracture
Femoral Component External Rotation (3° Rule)
Standard Practice
- ~3° external rotation relative to posterior condyles
Primary Purpose
- Balance the flexion gap
Biomechanical Basis
- Native tibia – varus alignment
- Tibial cut – trapezoidal flexion gap
External rotation – rectangular gap
Secondary Benefit
- Improves patellar tracking
Periprosthetic Joint Infection (PJI)
Major Diagnostic Criteria
Either confirms infection:
- Two positive cultures (same organism)
- Sinus tract communicating with joint
Minor Criteria
- Elevated CRP / ESR
- High synovial WBC
- Neutrophil percentage
- Positive histology
- Single positive culture
Key Exam Point
Sinus tract = definitive diagnosis
Unicompartmental vs Total Knee Replacement
TOPKAT Trial (2019)
Findings (5-Year Outcome)
Unicompartmental Knee Replacement (UKR)
- Lower cost
- Shorter hospital stay
- Similar functional outcomes
- Similar reoperation rates
Exam Point
UKR = lower surgical cost
Gap Balancing vs Measured Resection
Measured Resection
- Based on anatomical landmarks
Gap Balancing
- Based on ligament tension
Key Advantage
Better flexion gap stability
Requirements
- Accurate tibial cut
- Intact collateral ligaments
FRCS Part 1 Examination Pattern
Format
- Single Best Answer (SBA)
Structure
- 2 papers
- 120 questions each
- Total: 240 questions
Timing
- 135 minutes per paper
~65 seconds per question
Exam Strategy
Approach
- Eliminate 3 options quickly
- Choose between final 2
Preparation Strategy
- Combine:
- MCQ practice
- Concept-based reading
Recommended Practice Volume
- ~3,000 to 15,000 MCQs
Best Practice Tips
- Avoid repeating same questions
- Cover entire syllabus
- Maintain notes
- Focus on weak areas
Key Take-Home Messages
TKA Concepts
- Polyethylene < 8 mm – high wear risk
- External rotation of femur – key for balance
- Internal tibial rotation – harmful
Clinical Insights
- Sinus tract = infection
- UKR = cost-effective alternative
Exam Strategy
-
- Strong concepts + high MCQ exposure = success
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