Shining Light on Tendonitis

Abstract

Biophysics Athletes, whether two- or four-legged, can develop tendonitis, a painful condition that requires a long recovery period. Fundamental imaging studies of damage to collagen in tendon often exploit its birefringence, but polarized light imaging usually requires chemical staining of the fibers. Sivaguru et al. exploited collagen's noncentrosymmetric organization to perform direct imaging through second-harmonic generation. In their technique, two near-infrared photons (780 nm wavelength) from an ultrashort pulsed laser combine in the sample to produce a photon at 390 nm. The resulting images, which were taken both with light transmitted through the sample (forward scans) and with reflected light (backward scans), were then Fourier-transformed to determine fiber orientations. They compared normal tendon from horse with tendon that had undergone a model for injury—degradation with collagenase. Degradation led to a decrease in fiber orientation and better spread in the forward and backward scan ratios. Such strain-free methods lend themselves to endoscopic approaches for assessing tendon damage. Opt. Express 18 , 24983 (2010).