Infrared and Raman spectroscopy methods are used to assess the tension of ligaments, tendons and other tissue. The device includes an electromagnetic radiation source for directing radiation energy onto a sample, either directly or using a probe. Between the radiation source and the sample, emitted electromagnetic energies pass through a filtering device and are directed to the sample using optical components such as mirrors, lenses and optical fibers. After impacting the tissue, scattered emissions are collected by a collecting lens at a predetermined geometry. The scattered emissions are collected by a collection means such as lens and optical fibers directed to another filtering device and a spectrum-analyzing device, and detected with a photon-detecting device. The collected scattering signals are analyzed using a computing device such as a computer or a microprocessor. The tension in the tissue is obtained from the analysis of the scattered emissions.