The present invention relates to an improved method and system for segmenting an ultrasound image for detecting osteoarthritis using an active contour technique. The method basically relates to local region scalable active contour using expandable kernel, or simply LREK. The LREK involves setting a kernel scale for the convolution kernel; computing standard deviation of pixel intensity of a region inside and outside the contour; establishing a linear combination for the first standard deviation and the second standard deviation; determining homogeneity of the region inside and outside the contour by comparing an absolute difference between the first linear combination and the second linear combination against an adaptive threshold value which is kernel-driven.