GENERAL CONCEPT OF TRIBOLOGY IN TKA

Abstract

‘Tribology’ is derived from the Greek word “tribos” and means the “science of rubbing”. Friction, lubrication, and wear mechanism in the common English language means the precise field of interest of tribology. Wear of PE insert has often been reported in TKA to be primary causes of complications and failure.

As a friction, the wear that occurs in TKA is system properties rather than intrinsic material properties and is therefore affected by multiple variables such as design, material properties, duration and alignment. The contact area on each condyles varies from about 150 mm² for moderate to high-conformity knees in flexion, down to 30 mm² for low-conformity. The corresponding maximum compressive pressure in activity is 10 to 50 MPa, which favor fatigue and deformation of UHMWPE (yield stress: 15MPa). In contrast, fully conforming mobile bearing knees have contact area of at least 300 mm² on each condyles, giving maximum pressure of only 5 MPa. There are several mechanisms whereby small PE particles are released in TKA. Some of these mechanisms are fatigue processes requiring numerous cycles of sliding. Multidirectional sliding is more damaging than sliding in same direction. The wear mechanisms in TKA are as follows:

• Adhesive wear

• Abrasive wear (2-body, 3-body)

• Third body wear

• Corrosion wear

• Fatigue wear (delamination): the most destructive of all wear mechanism

There have been a number of published studies on the in vivo wear measured on retrieved total knee bearings. These studies indicated more clinical wear on the medial side. Patterns of wear varied greatly among individual knees; a majority showed very similar extents of wear on the medial and lateral sides, however there were cases with significantly more wear on one condylar articulation than the other. Evidence of edge loading was common and seen most frequently in the central zone of the medial condylar area.