[An optical method for investigation of thickness of damaged articular cartilage]

The aim of this study was to develop an optical system to measure damaged cartilage thickness in-vivo and real time using an optical fiber probe and conducting ex-vivo elastic light-scattering spectroscopy experiments on different thicknesses of damaged calf's patella cartilage.

An elastic light-scattering spectroscopy system was assembled with a miniature UV-VIS spectrometer, halogen-tungsten light source, laptop and optical fiber probe. Elastic light-scattering spectra were taken on the control and damaged calf's patella cartilages of 40 samples. The samples were grouped into four; in the first group cartilages were not damaged, in the 2nd, 3rd and 4th groups cartilage thickness was reduced approximately 25%, 50% and 100% respectively. The probe consisted of six fibers; one for light delivery and the other five to detect diffuse back-reflected light from the cartilage. Diameter of the fibers was 400 microm, and distance of the detector fibers from the source fibers were 0.8, 1.6, 2.4, 3.2, 4.0 mm.

Our results showed a correlation between cartilage thickness and hemoglobin absorption in the wavelength range of 500-600 nm. We defined an absorption index using the spectral data of the diffuse back-reflected light to make a correlation between the thickness of the cartilage and absorption of hemoglobin. The index is inversely proportional to the thickness of the cartilage and can be used to estimate the cartilage thickness.

This study showed that measuring elastic light-scattering spectra utilizing the designed optical fiber probe can be used to estimate cartilage thickness. The effect of variation of hemoglobin content of subchondral bone on the estimated cartilage thickness was not clearly known. More ex-vivo experiments should be conducted to test the system efficiency in defining cartilage thickness. The system has the potential to be used in practice as a new product for non-invasively measuring cartilage thickness in-vivo.