Bearing Surfaces in Total Hip Arthroplasty
DNB Orthopaedics • October 2023 • Paper IV • Question 2 • 10 Marks [3+4+3]
Introduction
The bearing surface in total hip arthroplasty (THA) refers to the articulating couple formed between the prosthetic femoral head and the acetabular liner/cup. Its tribological characteristics strongly influence friction, wear, generation of particulate debris, osteolysis and long-term implant survival.
An ideal bearing should have:
- Very low wear
- Low coefficient of friction
- High scratch and corrosion resistance
- High toughness
- Biocompatible wear particles
- Ability to accommodate larger femoral heads safely
- Long-term mechanical reliability
- Reasonable cost
The major modern bearing options are: metal-on-polyethylene, ceramic-on-polyethylene and ceramic-on-ceramic. Metal-on-metal is now largely of historical/selected relevance because of adverse reactions to metal debris.
Basic Tribology
Tribology is the science of friction, lubrication and wear between interacting surfaces. In THA, wear is influenced by:
- Bearing material
- Femoral head size
- Surface roughness
- Component position
- Lubrication
- Patient activity
- Third-body particles
- Material processing and oxidation
The clinical consequence of wear is not simply loss of material: wear debris can trigger macrophage-mediated osteolysis and aseptic loosening.
1. Types of Bearing Surfaces [3 Marks]
| Bearing Couple | Common Abbreviation | Current Role |
|---|---|---|
| Metal-on-Polyethylene | MoP | Common, established bearing |
| Ceramic-on-Polyethylene | CoP | Common modern option |