MS Orthopaedics - Paper IV (Recent Advances) KNRUHS

Top 20 Expected Questions - Theory Examination 2025/2026

ESSAY QUESTIONS (Long Answer - 20 marks)

SHORT ESSAY QUESTIONS (10 marks each) - Most Expected

Summary Frequency Table

Very Recent Advances to Add (2024-2026, Campbell's 15th Ed)

• Robotic-Assisted Arthroplasty: MAKO (Stryker) for TKA/THA - haptic feedback, bone-saving cuts
• Augmented Reality (AR) Navigation: Intraoperative AR for implant positioning
• Unilateral Biportal Endoscopy (UBE): New MIS spine technique
• Cementless TKA: Data on outcomes vs cemented
• Unicompartmental Knee Arthroplasty (UKA): Indications, conversion to TKA
• Ibuprofen/NSAIDs effect on fracture healing: Reconsidered in recent literature
• JAK Inhibitors (tofacitinib, baricitinib): New biologics class for RA
• Exosome therapy: Newer than stem cells in cartilage/bone healing
• 3D Printing / Patient-Specific Implants: Custom cutting guides, patient-specific implants in revision surgery
• Enhanced Recovery After Surgery (ERAS) in Arthroplasty: Multimodal analgesia, early mobilization protocols

Exam Strategy Tips

1. Every answer in Paper 4 must mention "recent advances" - examiners expect the contemporary update even for a classical topic.
2. For any arthroplasty topic, mention robotic assistance and kinematic alignment as the current trend.
3. For biologics/PRP topics, mention classification systems and level of evidence - examiners love this.
4. Masquelet technique and BMP often come together - prepare them as a combined answer.
5. For spine topics, always contrast old approach vs new (open vs MIS, fusion vs motion preservation).

KNRUHS MS Orthopaedics - Paper IV (Recent Advances)

Top 20 Expected Questions

1. Autologous Chondrocyte Implantation (ACI) / MACI - (most repeated, asked 2013, 2015, multiple sessions)
2. Computer-Assisted Navigation in Orthopaedic Surgery - (asked 2013, 2014, 2015 - extremely high frequency)
3. Recent trends in management of injuries of the Cervical Spine - (asked in literally every paper - 2009, 2013, 2014, 2015, 2024)
4. Platelet-Rich Plasma (PRP) - types and uses in Orthopaedics - (asked 2013, 2015)
5. Bone Morphogenetic Protein (BMP) and its role in Orthopaedics - (asked 2014, 2015)
6. Minimally Invasive Spine Surgery (MISS) - (asked 2014, 2015)
7. Limb Salvage Surgery in Osteosarcoma / Malignant Bone Tumors - (asked 2008, 2013, 2014, 2015)
8. Tribology - What is it? How has it changed clinical orthopaedic practice? - (asked 2013 and 2015 in identical wording - likely to repeat)
9. Revision Knee Arthroplasty - recent developments - (asked 2014, 2015)
10. Locked Compression Plate (LCP) / LISS / MIPO technique - (asked 2008, 2014)
11. Induced Membrane Technique (Masquelet) in bone defects / osteomyelitis - (asked 2013)
12. TNF-alpha antagonists / Biologics in Rheumatoid Arthritis - (asked 2013)
13. Antibiotic-Impregnated Bone Cement / Local antibiotic delivery systems - (asked 2015)
14. Radiofrequency Ablation (RFA) in Osteoid Osteoma / bone tumors - (asked 2013)
15. Polytrauma management - Damage Control Orthopaedics (DCO) - (asked 2013)
16. Cruciate-sparing vs Cruciate-sacrificing Total Knee Arthroplasty - (asked 2013)
17. Recent advances in Total Hip Arthroplasty (bearing surfaces, approaches, ERAS) - (asked 2009, 2015 pseudotumor/MOM)
18. Periprosthetic fractures of femur / knee (Vancouver classification, management) - (asked 2014)
19. Rotator Cuff - recent trends in management - (asked 2013)
20. Robotic-Assisted Surgery / AI and 3D printing in Orthopaedics - (emerging topic, highest probability for 2025-2026 exams given global and KNRUHS syllabus updates)

Questions 1, 2, 3, 8 have appeared in near-identical wording across sessions - prepare these as priority. Q20 is the single most likely "new" topic the examiner will test in 2025-2026 that hasn't been asked before.

Robotic-Assisted Surgery, AI, and 3D Printing in Orthopaedics

Structured Answer - 15 Marks | MS Orthopaedics Paper IV

INTRODUCTION (1 mark)

I. ROBOTIC-ASSISTED ORTHOPAEDIC SURGERY (5 marks)

Classification of Robotic Systems

A. MAKO SmartRobotics (Stryker) - Most Widely Used

• Uses CT-based preoperative 3D planning
• Intraoperatively, a haptic boundary (AccuStop technology) constrains the cutting burr - prevents inadvertent bone removal outside the planned zone
• Applications: Total Knee Arthroplasty (TKA), Total Hip Arthroplasty (THA), Partial Knee (UKA)
• Advantages:
  • Improved component alignment and positioning
  • Reduced outliers in implant orientation
  • Lower revision rates for dislocation in THA (Bendich et al., J Arthroplasty 2022)
  • Bone-conserving, patient-specific cuts

B. ROSA Knee (Zimmer-Biomet)

• Registration using bone morphing (no preoperative CT required)
• Soft tissue balancing capability in real-time
• Approved for TKA and, since February 2024, for total shoulder arthroplasty (ROSA Shoulder) - first FDA-approved robot for shoulder replacement

C. Robotic Spine Surgery

• Mazor X (Medtronic) and ExcelsiusGPS (Globus Medical) for percutaneous pedicle screw placement
• CT-to-fluoroscopy image fusion guidance
• Reduces screw malposition and radiation exposure to surgeon

Clinical Advantages of Robotic Surgery

1. Reproducible bone cuts independent of surgeon fatigue
2. Real-time intraoperative feedback
3. Better soft tissue balancing in TKA
4. Reduced outliers in coronal, sagittal, and rotational alignment
5. Potentially improved implant longevity

Limitations

• High capital cost
• Steep learning curve
• Increased operative time initially
• Outcome benefit over conventional surgery still debated at long-term follow-up

II. ARTIFICIAL INTELLIGENCE (AI) IN ORTHOPAEDICS (4 marks)

Definition

Applications

• AI algorithms analyse radiographs/CT scans to automatically measure deformity, templating implant size
• AI-based systems (e.g., TraumaCad) for fracture classification and pre-op templating
• Predicts surgical complexity and estimated blood loss

• Real-time AI-assisted navigation superimposed on fluoroscopy
• Integration with robotic systems for dynamic force line optimization during TKA
• Augmented Reality (AR): AR headsets project CT/MRI anatomy onto the surgical field - under active development for spine and pelvis surgery

• Deep learning models detect radiographic fractures with accuracy comparable to experienced radiologists
• Automated AO/OTA fracture classification from X-rays

• ML models predict 90-day complications, readmission risk, implant failure
• Patient-specific discharge planning and rehabilitation protocols

• Smart implants with embedded microchips/sensors monitor load, temperature, and micromotion in real-time - early detection of periprosthetic loosening (emerging technology)

III. 3D PRINTING (ADDITIVE MANUFACTURING) IN ORTHOPAEDICS (4 marks)

Principle

Applications in Orthopaedics

• Custom prostheses for complex revision arthroplasty with significant bone loss
• Acetabular cage reconstructions in massive bone defects
• Custom cutting guides (PSI guides) for TKA and osteotomies - improve accuracy without robotic system

• 3D-printed bone models for complex fractures (acetabular, tibial plateau) allow surgeon to rehearse reduction and fixation
• Reduces intraoperative time and improves execution

• Titanium implants with 3D-printed trabecular (lattice) structures mimicking cancellous bone
• Porosity of 60-80% promotes osseointegration (bone ingrowth)
• Examples: Stryker Tritanium, Zimmer Biomet Trabecular Metal-equivalent structures

• Custom mega-prostheses for large tumour resections (after limb salvage surgery)
• Complex pelvis and sacral reconstructions

• 3D-printed titanium cages for interbody fusion (TLIF, ALIF)
• Surface porosity enhances fusion rates

• Printing of scaffold structures seeded with cells (chondrocytes, stem cells) for cartilage regeneration - preclinical stage, promising

Materials Used

SUMMARY / COMBINED ADVANTAGE (1 mark)

• Fewer outliers in implant alignment
• Reduced revision rates
• Shorter hospital stays (combined with ERAS protocols)
• Better functional scores and implant longevity

DIAGRAM TO DRAW IN EXAM

CT Scan → 3D Digital Model → AI Planning → Robotic Execution → Smart Implant Monitoring

Smart Implants in Orthopaedics

Structured Answer - 10 Marks | MS Orthopaedics Paper IV

INTRODUCTION (1 mark)

COMPONENTS OF A SMART IMPLANT (1 mark)

1. Sensor unit - measures load, pressure, strain, temperature, pH, or motion
2. Microprocessor - processes and encodes sensor data
3. Wireless telemetry module - transmits data (Bluetooth Low Energy / near-field communication)
4. Power source - micro-battery or energy-harvesting systems (motion-based piezoelectric, ultrasound-powered)

TYPES AND CLINICAL APPLICATIONS (4 marks)

1. Smart Knee Implants

• Persona IQ (Zimmer Biomet + Canary Medical) - the world's first FDA-approved smart knee replacement
• Embedded sensor measures: step count, walking speed, range of motion, gait symmetry, and cadence
• Data transmitted to the mymobility digital platform viewable by surgeon and patient
• Enables remote rehabilitation monitoring and personalised physiotherapy protocols
• Detects early loosening or malalignment by tracking progressive changes in load distribution

2. Smart Hip Implants

• VERASENSE (OrthAlign / Stryker) - intraoperative tibial/femoral sensor trial for soft tissue balancing during TKA and THA
• Measures compartment loading in real-time during trial reduction
• Allows surgeon to optimise soft tissue balance before final implantation
• Reduces postoperative instability and accelerated polyethylene wear

3. Smart Fracture Fixation Devices

• Instrumented intramedullary nails with strain gauges to monitor fracture healing progression
• Load-bearing data identifies when callus is sufficiently mineralised for full weight-bearing
• Reduces radiation exposure (replaces serial X-rays for healing assessment)
• Experimental systems used in clinical trials for tibial and femoral nail monitoring

4. Smart Spinal Implants

• Pedicle screw systems with embedded sensors detect toggling / loosening early
• Interbody cages with pressure sensors monitor fusion status
• Telemetric rods in growing spine constructs for scoliosis - adjust remotely without repeat surgery (remote adjustment systems)

5. Smart Bone Cement / Infection Monitoring

• Antibiotic-eluting cement with embedded electrochemical biosensors for early periprosthetic joint infection (PJI) detection
• Sensors measure inflammatory biomarkers (IL-6, CRP equivalents) locally
• Preclinical stage but highly promising for early PJI diagnosis

ADVANTAGES (1.5 marks)

LIMITATIONS AND CHALLENGES (1.5 marks)

1. Biocompatibility of electronic components over decades - microelectronics must withstand body fluids lifelong
2. Power supply - micro-batteries need replacement or energy harvesting remains insufficient for long-term use
3. Data security and privacy - wireless transmission of patient health data (cybersecurity risk)
4. Regulatory approval - demanding pathway for combination medical devices (implant + digital health software)
5. Cost - significantly more expensive than conventional implants; cost-effectiveness unproven long-term
6. MRI compatibility - metallic and electronic components may limit postoperative MRI use

FUTURE DIRECTIONS (1 mark)

• Bioresorbable smart implants for fracture fixation that degrade after healing while transmitting data during active healing phase
• AI-integrated dashboards that synthesise implant data with wearable device data for holistic joint health monitoring
• Drug-eluting smart implants that release antibiotics or anti-inflammatory agents on demand when sensor detects early infection signals
• Closed-loop smart implants - fully autonomous: sensor detects problem, microprocessor responds, actuator adjusts stiffness or releases drug

DIAGRAM TO DRAW

Tibial component → Embedded pressure sensor → Wireless transmitter → External receiver/smartphone → Surgeon dashboard

Bone Marrow Aspirate Concentrate (BMAC)

Structured Answer - 15 Marks | MS Orthopaedics Paper IV

INTRODUCTION (1 mark)

COMPOSITION OF BMAC (1 mark)

• Mesenchymal Stem Cells (MSCs) - multipotent, can differentiate into bone, cartilage, tendon, fat
• Hematopoietic progenitor cells
• Growth factors:
  • PDGF (Platelet-Derived Growth Factor) - cell proliferation
  • TGF-β (Transforming Growth Factor-beta) - matrix synthesis
  • BMP-2 and BMP-7 - osteoinduction, chondrogenesis
  • IL-1ra (Interleukin-1 receptor antagonist) - anti-inflammatory
  • VEGF - angiogenesis, neovascularisation
• Platelets and fibrin - scaffolding matrix

Red blood cells, mature granulocytes, and immature myeloid progenitors are removed by centrifugation (Rheumatology 2-Volume Set, Elsevier 2022)

DIAGRAM 1 - BMAC HARVESTING SITE

     ILIAC CREST (side view)
     ________________________
    /    Posterior Superior   \
   |      Iliac Spine (PSIS)   |
   |                           |
   |   [X] ← Aspiration        |
   |        point (2-4 cm      |
   |        anterior to PSIS)  |
    \_________________________ /
    
    Needle: Jamshidi bone marrow
    aspiration needle, 11-gauge
    Volume aspirated: 30-60 mL
    (multiple small aliquots of 
     2-4 mL each, reposition needle)

DIAGRAM 2 - CENTRIFUGATION / PROCESSING STEPS

  Bone Marrow Aspirate (60 mL)
           |
           ▼
   [CENTRIFUGE TUBE]
   ┌─────────────────┐
   │  TOP LAYER:     │  ← Plasma / fat (discarded)
   │  ─ ─ ─ ─ ─ ─   │
   │  MIDDLE LAYER:  │  ← BUFFY COAT = BMAC ✓
   │  (MSCs, platelets,│   (concentrated ~7x)
   │   growth factors)│
   │  ─ ─ ─ ─ ─ ─   │
   │  BOTTOM LAYER:  │  ← Red blood cells (discarded)
   └─────────────────┘
           |
           ▼
    BMAC (3-6 mL final volume)
    ~6-7 fold concentration of MSCs

MECHANISM OF ACTION (2 marks)

• Stimulate resident stem cells to proliferate
• Suppress local inflammation (via IL-1ra blocking IL-1β)
• Promote angiogenesis (via VEGF)
• Induce matrix synthesis

• Suppresses T-cell and macrophage activity
• Shifts macrophage phenotype from M1 (pro-inflammatory) to M2 (pro-healing)
• This is particularly important in osteoarthritis where chronic synovial inflammation perpetuates cartilage damage

DIAGRAM 3 - MECHANISM OF ACTION

    BMAC injected
    into joint
         |
    ┌────┴────────────────────────┐
    |                             |
    ▼                             ▼
MSC differentiates          MSC secretes
into CHONDROCYTE            GROWTH FACTORS
    |                        (PDGF, TGF-β,
    ▼                         BMP-2, IL-1ra)
New cartilage                    |
matrix formed               ┌───┴──────────┐
                             ▼              ▼
                      Resident cells  Inflammation
                      proliferate     suppressed

CLINICAL APPLICATIONS (4 marks)

1. Knee Osteoarthritis (Most studied)

• Intra-articular injection of BMAC
• Best results in Kellgren-Lawrence Grade II-III (mild to moderate OA)
• Meta-analysis (Chahla et al.): All 8 clinical trials showed good-to-excellent functional outcomes and significant pain reduction at 24 months
• 2025 expert opinion (Migliorini et al., J Orthop Surg Res): BMAC modulates knee inflammation but superiority over PRP remains unclear - high-quality RCTs still needed

2. Focal Chondral Defects

• BMAC combined with scaffold (collagen membrane, fibrin glue, or hyaluronic acid carrier)
• Used as adjunct to microfracture or as a standalone injection technique
• Superior to microfracture alone at 18-month follow-up (especially for defects >2 cm²)
• Also combined with MACI for enhanced cartilage repair

3. Fracture Nonunion / Delayed Union

• Percutaneous injection of BMAC at the nonunion site (Connolly technique)
• Avoids open surgery for biologically inert atrophic nonunions
• Works via osteoprogenitor cells + BMP-2/7 stimulating osteoblast activity
• Systematic review (Int Orthopaedics 2017): Effective in tibial and other long bone nonunions, particularly atrophic pattern

4. Osteonecrosis of Femoral Head (ONFH) - Early Stages

• Combined with core decompression (Hernigou technique)
• BMAC injected into decompressed channel
• Best results in Ficat Stage I and II
• Stimulates neovascularisation (VEGF) and prevents femoral head collapse
• Long-term results show significant delay or prevention of collapse vs core decompression alone

5. Tendon and Ligament Repair

• BMAC injection for chronic tendinopathy (rotator cuff, patellar tendon, Achilles)
• Augments surgical repair of massive rotator cuff tears
• MSC differentiation into tenocytes + anti-inflammatory effect reduces chronic tendon degeneration

6. Spinal Fusion Augmentation

• BMAC added to local autograft / allograft / cage to enhance interbody fusion
• Particularly useful when autograft volume is limited
• Used with demineralized bone matrix (DBM) as a biological enhancer

HARVESTING TECHNIQUE (1 mark)

• Alternative sites: proximal tibia, proximal humerus, distal femur

1. Patient prone / lateral, sterile prep
2. 11-gauge Jamshidi needle introduced 2-4 cm anterior to PSIS, into iliac crest marrow
3. Aspirate in small aliquots of 2-4 mL at each position (reposition needle between aspirates)
4. Total volume: 30-60 mL (larger volumes dilute MSC concentration)
5. Transfer to centrifuge tube → process at point-of-care
6. Final BMAC volume: 3-6 mL → injected or mixed with scaffold

COMPARISON: BMAC vs PRP (1 mark)

LIMITATIONS AND CURRENT STATUS (1 mark)

1. Variability in MSC concentration - depends on patient age, health, aspiration technique; elderly patients yield fewer and less potent MSCs
2. Lack of standardisation - different centrifuge systems produce different concentrations
3. Evidence quality - most trials are level III-IV; high-quality RCTs are still limited (2025 consensus)
4. Regulatory status - classified as "more than minimally manipulated" in some countries if combined with scaffold; subject to strict cell therapy regulations
5. Cost - centrifuge systems are expensive; not universally available
6. No proven superiority over PRP for all indications

CONCLUSION (0.5 mark)

1. Iliac crest aspiration site - lateral view
2. Centrifuge tube with three layers (buffy coat = BMAC)
3. Mechanism of action flowchart

Tribology and Bearing Surfaces in Total Hip Replacement (THR)

Structured Answer - 15 Marks | MS Orthopaedics Paper IV

I. TRIBOLOGY - DEFINITION AND BASIC CONCEPTS (2 marks)

Key Tribological Terms

Modes of Lubrication in THR

1. Hydrodynamic lubrication - full fluid film, no surface contact (ideal; occurs at high speed)
2. Boundary lubrication - thin molecular film only; surfaces in partial contact (occurs at low speed / start-up)
3. Mixed lubrication - combination; most common in walking cycle

DIAGRAM 1 - BEARING SURFACE OVERVIEW

        ACETABULAR COMPONENT
        ┌──────────────────────┐
        │   SHELL (Titanium)   │
        │  ┌────────────────┐  │
        │  │  LINER         │  │  ← Polyethylene / Ceramic
        │  │  ○  ←Head      │  │
        │  └────────────────┘  │
        └──────────────────────┘
        
        FEMORAL HEAD
        ○ ← Metal (CoCr) or Ceramic
        |
        | Femoral neck / trunnion
        |
    [STEM - cemented or cementless]

  BEARING COUPLE = Head material ON Liner material
  e.g., Metal-on-Poly / Ceramic-on-Poly / Ceramic-on-Ceramic

II. BEARING SURFACES - TYPES AND PROPERTIES (8 marks)

A. METAL-ON-CONVENTIONAL POLYETHYLENE (MoP) - Historical Standard

• Introduced by Sir John Charnley in the 1960s - the "low friction arthroplasty"
• UHMWPE sterilised by gamma irradiation in air - generated free radicals → oxidative degradation
• Wear rate: 0.1-0.2 mm/year (linear)
• Over time, polyethylene particles (0.1-1 µm) released into joint
• Macrophages engulf particles → cytokine release (IL-1, TNF-α, PGE2) → osteoclast activation → periprosthetic osteolysis → aseptic loosening

B. HIGHLY CROSS-LINKED POLYETHYLENE (HCLPE) - Current Standard (Campbell's 15th Ed 2026)

1. UHMWPE irradiated at 5-15 Mrad (high-dose gamma or electron-beam radiation)
2. Irradiation ruptures PE molecular bonds → creates free radicals
3. In absence of oxygen → free radicals cross-link adjacent chains = highly cross-linked PE
4. Post-irradiation thermal treatment eliminates residual free radicals:
   • Remelting (above 135°C) - virtually eliminates free radicals but reduces crystallinity and mechanical strength
   • Annealing (below melting point) - preserves mechanical properties but less effective at eliminating free radicals
5. Newer method: Vitamin E doping - antioxidant scavenges free radicals without remelting; preserves mechanical properties

DIAGRAM 2 - HCLPE MANUFACTURING

 UHMWPE
    |
    ▼
  Irradiation
  (5-15 Mrad, inert environment)
    |
    ▼
 Free radicals formed
    |
    ├──── [+O₂] → Oxidised PE (BAD - chain scission)
    |
    └──── [-O₂] → Cross-linked PE (GOOD ✓)
    |
    ▼
 Post-irradiation heat treatment
    ├── Remelting (>135°C): eliminates free radicals, ↓crystallinity
    └── Annealing (<135°C): preserves strength, some radicals remain
    |
    ▼
 Vitamin E doping (newest): scavenges radicals, best of both
    |
    ▼
 HCLPE LINER (80-90% wear reduction vs conventional PE)

• 80-90% reduction in wear rate vs conventional PE (hip simulator data, Campbell's 15th Ed)
• Lower osteolysis rates - adopted widely from late 1990s
• Allows use of larger femoral heads (32-40 mm) without increasing volumetric wear
• Larger heads = greater jump distance = reduced dislocation risk
• 10-20 year clinical studies confirm superior survivorship vs conventional PE

C. CERAMIC-ON-POLYETHYLENE (CoP)

• Ceramic head advantages:
  • Harder than metal → resists scratching from third-body particles
  • Smoother surface finish (Ra 0.002-0.005 µm) vs CoCr (Ra 0.02 µm)
  • Hydrophilic - maintains better fluid film lubrication
  • No metal ion release → no trunnion corrosion
  • No adverse local tissue reaction (ALTR)
• Wear rate: Lower than CoCr-on-HCLPE
• 4th generation Biolox delta (CeramTec): composite of alumina + zirconia + strontium aluminate - highest burst strength, lowest fracture risk
• Preferred combination for young patients: ceramic head on HCLPE liner

D. CERAMIC-ON-CERAMIC (CoC)

• Wear rate: 4000 times less than CoCr-on-PE (Campbell's 15th Ed 2026)
• Alumina wear: <0.025 mm/year at 18.5-year follow-up (Hamadouche et al.)
• Ceramic wear particles are biologically inert - do not activate macrophages significantly
• No osteolysis in long-term studies

1. Ceramic fracture - rare with modern 4th generation ceramics; more common with small heads (28 mm) and short neck lengths; proof testing of each implant before release reduces risk
2. Squeaking - incidence generally low but up to 10% in some series; caused by stripe wear from microseparation during swing phase; multifactorial (stem flexibility, malposition, fluid film disruption)
3. Stripe wear - edge loading at extremes of flexion (rising from chair, stair-climbing)
4. Sensitivity to malposition - excessive cup verticality worsens wear; more sensitive than other bearings
5. No revision option if ceramic fractures into head - metal sleeves available for ceramic heads on damaged trunnions

E. METAL-ON-METAL (MoM) - LARGELY ABANDONED

• Large head size → increased jump distance → very low dislocation rate
• Low linear wear rate (due to "running-in" and fluid film lubrication with large heads)
• Marketed for young active patients

• Adverse Local Tissue Reaction (ALTR) - cobalt and chromium ions released as nano-particles
• Processed by T-lymphocytes → hypersensitivity reaction
• Pseudotumour - benign inflammatory mass or frank soft tissue necrosis around the hip
• Systemic cobalt toxicity (cobalt cardiomyopathy, neuropathy in extreme cases)
• Elevated serum cobalt and chromium ions - threshold of concern: >7 ppb
• High revision rates (ASR/DePuy implant recall 2010)
• FDA issued safety warnings on metal-on-metal hip implants

F. DUAL MOBILITY COMPONENTS (DMC)

• Combines large effective head size (stability) with small head wear characteristics
• Lowest dislocation rate of all bearing types
• Particularly useful for: revision THA, cognitively impaired patients, abductor dysfunction, after femoral neck fractures in elderly
• No sacrifice of wear characteristics

III. OSTEOLYSIS - WEAR DEBRIS PATHWAY (2 marks)

  Bearing surface wear
         |
         ▼
  Wear particles (0.1-10 µm)
  released into joint space
         |
         ▼
  Macrophage phagocytosis
  (particle size determines response:
   0.1-1 µm most biologically active)
         |
         ▼
  Macrophage activation →
  IL-1β, TNF-α, PGE2 release
         |
         ▼
  RANKL upregulation
         |
         ▼
  Osteoclast recruitment and activation
         |
         ▼
  PERIPROSTHETIC OSTEOLYSIS
  (balloon-like lucencies on X-ray)
         |
         ▼
  Implant loosening → Revision surgery

IV. TRUNNION CORROSION (1 mark)

• Trunnion = the Morse taper junction between femoral head and stem
• Corrosion occurs due to fretting (micromotion) + crevice corrosion at the metal-metal junction
• CoCr head on titanium stem taper = galvanic corrosion (dissimilar metals)
• Releases metal ions locally → ALTR, pain, soft tissue damage even with non-MOM bearing
• Solution: Use ceramic heads on titanium stems - eliminates galvanic corrosion

V. IDEAL BEARING SURFACE - CURRENT RECOMMENDATION (1 mark)

CONCLUSION (1 mark)

1. Acetabular shell + liner + femoral head labelled diagram
2. HCLPE manufacturing flowchart (irradiation → cross-linking → free radical elimination)
3. Osteolysis pathway (wear debris → macrophage → osteoclast → bone loss)

Examiner's Full-Mark Checklist

Tribology & Bearing Surfaces of THR - 15 Marks

WHAT EXAMINERS SPECIFICALLY LOOK FOR

1. DEFINITION OF TRIBOLOGY - Non-negotiable (must write)

• Greek origin "tribos" = rubbing
• Science of friction, lubrication, and wear
• This exact word has appeared in KNRUHS as "What is Tribology? How has it changed clinical orthopaedic practice?" - the definition IS the first mark

2. MODES OF LUBRICATION - Distinguishes average from good answers

• Hydrodynamic lubrication - full fluid film
• Boundary lubrication - thin molecular layer
• Mixed lubrication - most common in gait
• Elastohydrodynamic lubrication - deformation of surfaces improves film

3. CHARNLEY'S CONTRIBUTION - Always expected

• Low friction arthroplasty (1962)
• First to apply tribological principles to hip replacement
• Chose small head (22 mm) + UHMWPE + cemented stem
• Small head = reduced frictional torque (Charnley's reasoning)

4. ALL FOUR BEARING COUPLES WITH WEAR RATES - Core content

• Material composition
• Wear rate (numerical figure)
• Specific advantage
• Specific complication/failure mode

5. HCLPE MANUFACTURING PROCESS - Distinguishes good from excellent

• Irradiation dose: 5-15 Mrad
• Cross-linking mechanism (in absence of oxygen)
• Free radical problem
• Annealing vs Remelting - this comparison is frequently probed in viva too
• Vitamin E doping - the most recent advance - shows updated reading

6. OSTEOLYSIS PATHWAY - Mandatory

• Must name the macrophage-cytokine-osteoclast cascade
• Specifically: IL-1, TNF-α, PGE2, RANKL
• "Effective joint space" concept - particles travel along implant-bone interface
• This links tribology back to why it matters clinically

7. PSEUDOTUMOUR / ALTR IN MoM - High yield

• Specific term: Adverse Local Tissue Reaction (ALTR)
• T-lymphocyte mediated (not macrophage - different from PE wear)
• Monitoring: serum cobalt/chromium ions (threshold 7 ppb)
• MARS MRI protocol for surveillance
• 2010 DePuy ASR recall - shows clinical awareness

8. DUAL MOBILITY - Modern advance that most candidates miss

• Bousquet's concept (1974, France)
• Two articulations explained clearly
• Primary indication: high dislocation risk
• Lowest dislocation rate of all bearings
• Complication: intraprosthetic dislocation (must name this)

9. TRUNNION CORROSION - Recent concept (post-2010)

• Most candidates do not write this
• Fretting + crevice corrosion at Morse taper
• CoCr head on titanium stem = galvanic corrosion
• Relevant even without MoM bearing
• Solution: ceramic heads on titanium stems

10. CURRENT RECOMMENDATION / CLINICAL APPLICATION

• A clear statement of what bearing is used when and why
• Young active patient vs elderly low-demand patient comparison
• How tribology knowledge drove the abandonment of MoM
• How it led to development of HCLPE and ceramic bearings

11. DIAGRAMS - Carry 2-3 marks

1. Cross-section of acetabular cup showing shell/liner/head with labels
2. Osteolysis pathway (macrophage cascade)

• HCLPE manufacturing flowchart
• Lubrication modes diagram

INSTANT MARK-LOSERS (What causes deductions)

MARK DISTRIBUTION - How to plan your 15-mark answer

ONE-LINE EXAMINER MINDSET

"I want to see that you understand WHY bearing surfaces evolved, not just WHAT they are - and that you can connect tribological science directly to clinical decision-making."

Tribology & Bearing Surfaces of THR - 10 Marks

Exact Points to Write + Points NOT to Miss

STRUCTURE FOR 10 MARKS (write in this order)

BLOCK 1 - Definition (1 mark)

• Tribology = science of friction, lubrication, wear (Greek: tribos = rubbing)
• Applied to orthopaedics: governs bearing surface performance and implant longevity

BLOCK 2 - Lubrication Modes (1 mark)

• Hydrodynamic - full fluid film (no contact)
• Boundary - thin molecular film (surfaces touch)
• Mixed - combination, most common in walking

BLOCK 3 - Charnley's Contribution (0.5 mark)

• Sir John Charnley, 1962 - "Low Friction Arthroplasty"
• 22 mm small head + UHMWPE liner + cemented stem
• Small head reduces frictional torque - applied tribology to THA first

BLOCK 4 - Bearing Surfaces with Wear Rates (4 marks - core of answer)

• CoCr head + UHMWPE liner
• Wear rate: 0.1-0.2 mm/year
• Failure: PE particles → macrophages → IL-1, TNF-α → osteoclast activation → osteolysis → aseptic loosening

• Irradiation at 5-15 Mrad → cross-linking of PE chains
• 80-90% reduction in wear vs conventional PE
• Free radical problem → eliminated by remelting or annealing or Vitamin E doping (latest)
• Current dominant bearing worldwide

• Alumina ceramic (Biolox delta = 4th generation)
• Wear rate: <0.025 mm/year, 4000x less than CoCr-on-PE
• Complication: Squeaking (up to 10%), ceramic fracture (rare)
• Best for: young active patients

• Large head (36-60 mm), low linear wear
• Failed due to: ALTR (Adverse Local Tissue Reaction), pseudotumour, cobalt toxicity
• Monitor: serum Co/Cr ions >7 ppb = concern
• DePuy ASR recall 2010

BLOCK 5 - Dual Mobility (1 mark)

• Bousquet concept (1974): small inner head inside mobile PE, PE inside metal shell
• Two articulations → large effective head size + small head wear
• Lowest dislocation rate of all bearing types
• Indication: high dislocation risk, revision THA, elderly
• Complication: intraprosthetic dislocation

BLOCK 6 - Trunnion Corrosion (0.5 mark)

• Fretting at Morse taper junction → metal ion release even without MoM bearing
• CoCr head on titanium stem = galvanic corrosion
• Prevention: ceramic head on titanium stem

BLOCK 7 - Clinical Application / How Tribology Changed Practice (1 mark)

• Tribology drove abandonment of MoM after ALTR recognised
• Led to development of HCLPE - reduced revision rates by 50%+
• Ceramic heads now preferred to eliminate trunnion corrosion
• Dual mobility for dislocation prevention
• Current recommendation: Ceramic head + HCLPE = dominant couple worldwide

BLOCK 8 - One Diagram (1 mark)

  [ TITANIUM SHELL ]
  [ LINER: PE/Ceramic ]
       ○  ← FEMORAL HEAD (CoCr or Ceramic)
       |
   [STEM]

CRITICAL POINTS NOT TO MISS (exam score separators)

POINTS TO NOT WASTE TIME ON (for 10-mark version)

• Do NOT write full manufacturing flowchart of HCLPE (save for 15 marks)
• Do NOT write detailed history of each generation of ceramics
• Do NOT write MoM hip resurfacing in detail
• Do NOT write osteolysis radiographic classification
• Do NOT draw elaborate diagrams - one clean labelled diagram is enough

TIME PLAN FOR 10-MARK ANSWER

One sentence that gets you full marks mentally: "Write the definition, 4 bearing couples with wear rates and one complication each, ALTR for MoM, dual mobility, trunnion corrosion, and one diagram - nothing else."