The Effect of Surface Active Phospholipids on the Lubrication of Osteoarthritic Sheep Knee Joints: Wear

Abstract

As a result of wear in the synovial joint, cartilaginous and osseous wear particles are produced. Previous research has shown that wear-particle shape may be correlated with joint disease status. In addition, phospholipids, present naturally in the joint, have been implicated as major contributors to joint lubrication. This study aimed to investigate the effect of phospholipids, as surface-active boundary lubricants, on the wear characteristics of the synovial joint by the application of numerical shape descriptors to cartilage wear particles. Artificially worn, lipid-depleted, sheep knee joints were injected with two concentrations of the phospholipid dipalmitoyl phosphatidylcholine (Lα-DPPC) and worn further in a mechanical rig. Particles were harvested from the joint, extracted from solution by ferrography, and analyzed in a field-emission scanning electron microscope (FESEM). After binary processing, the particle images were numerically analyzed for shape parameters such as boundary fractal dimension, shape factor, convexity, elongation and area. The condylar surfaces were also extracted and viewed in their hydrated state in an environmental scanning electron microscope (ESEM). The results of numerical particle analysis indicate that a synthetic solution of Lα-DPPC in propylene glycol may have a significant effect on the wear characteristics of synovial joints. Statistically significant differences between pre- and post-lubricated particles for convexity, elongation and formfactor have been found for 35 mg/ml Lα-DPPC and synovial fluid. In addition, similar trends for synovial fluid and the phospholipid solutions were noted for the boundary fractal dimension and curl. Particles have been of similar shape and morphology as described in the literature. The condyle surface morphology observed was characteristic of worn articular cartilage.