In situ observation of lubricant film formation in THR considering real conformity: The effect of model synovial fluid composition

- In situ observation of film thickness development in THR considering real conformity.
- Pendulum hip joint simulator in combination with colorimetric interferometry.
- Investigation of the effect of synovial fluid composition on lubricant film formation.
- Two tests focused on protein adsorption and film formation during flexion-extension.
- Substantial effect of hyaluronic acid and phospholipids on lubricant film thickness.

The present paper explores the effect of synovial fluid composition on lubricant film formation in hip replacements. The measurements were realized utilizing pendulum hip joint simulator, while the film thickness was evaluated using optical interferometry. Contact couples consisted of metal and ceramic femoral heads articulating with glass acetabular cups. As the test lubricants, various model fluids were employed. Initially, static tests, aimed on the effect of material and load on adsorption, were conducted. It was found that adsorbed film thickness increases independently of the head material. Consequently, swinging flexion-extension experiments were realized, revealing that the film formation is substantially affected by composition of model fluid. The thickest film was observed when higher concentration of hyaluronic acid and phospholipids was applied.