Lereim, Paul, et al. “A Biochemical Analysis of Subchondral Bone of the Medial Tibial Condyle in the Normal State and in Osteoarthritis and Rheumatoid Arthritis”. Acta Orthopaedica, vol. 46, no. 4, Jan. 1975, pp. 672-84, doi:10.3109/17453677508989250.