A hypothesis matrix for studying biomechanical factors associated with the initiation and progression of posttraumatic osteoarthritis Ashvin Thambyah * Department of Orthopaedic Surgery, National University of Singapore, Singapore 119074, Singapore Received 6 November 2004; accepted 1 December 2004 Summary In this paper the current theories on how osteoarthritis (OA) may be initiated and progressed is described. This is done in relation to the biomechanical events that would predispose the joint to the degenerative process, as well as further progression of the process within an ‘OA’ cycle. The relationship between the types of loading to the type of joint damage that occurs is discussed. Subsequently the influence on the rate at which OA progresses from the trauma, is presented within a hypotheses matrix. For the type of tissue damage, four phases are distinguished, phase I: superficial cells or matrix only, phase II: deeper chondral region, phase III: the tidemark or calcified region, and phase IV: subchondral bone region. The biomechanical event (A) is stipulated as having a possibility of six outcomes. (A3) is the direct damage to the calcified cartilage near the tidemark that leads most rapidly into the cycle for OA to develop and progress. Another three outcomes (A1, A2 and A4) involve damage to regions other than the calcified cartilage near the tidemark. These three outcomes involve the cells or matrix, chondral or subchondral regions. It is hypothesised that damage involved in one of these three outcomes results in all likelihood to a new level of joint deficiency or vulnerability. This new predisposition could lead to A3 type outcome and directly into the OA progression cycle or result in more A1, A2 or A4 type outcomes which remains out of the OA cycle. The biomechanical events are therefore used to predict the risk of mechanically driven OA and the rapidity in which it progresses in relation to joint loading.  c 2004 Elsevier Ltd. All rights reserved. Introduction In this paper the current theories on how osteoar- thritis (OA) may be initiated and progressed is de- scribed in relation to the different injury and damage modes. The development of OA is dis- cussed as being initiated or propagated via one of several ways. These are based on theories on how cartilage damage may be initiated and propagated from (i) subchondral bone changes [1], (ii) micro- damage in the subchondral plate and calcified car- tilage that leads to enchondral ossification [2], and (iii) altered mechanics that cause a shift in contact 0306-9877/$ - see front matter  c 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.mehy.2004.12.004 * Tel.: +65 68746521; fax: +65 67780720. E-mail address: dosta@nus.edu.sg. Medical Hypotheses (2005) 64, 1157–1161 http://intl.elsevierhealth.com/journals/mehy