Medical Engineering & Physics 27 (2005) 329–335 Contact stresses in the knee joint in deep flexion Ashvin Thambyah, James C.H. Goh ∗ , Shamal Das De Department of Orthopaedic Surgery, National University of Singapore, Singapore 119074, Singapore Received 25 August 2004; accepted 2 September 2004 Abstract The contact stresses in the knee that arise from activities involving deep flexion have not been given due consideration in view of social and cultural practice amongst many Asians that frequently cause the engagement of these activities. Excessively large stresses (>25 MPa) can cause cartilage damage and may be the precursor to the development of degenerative disease of the joint. In this study, forces in the knee derived from previous studies of human walking and squatting were applied to five cadaver knees that underwent quasi-static mechanical testing. This was conducted using a materials-testing machine and a custom-made apparatus that allowed secure and consistent loading of the knee specimen in flexion beyond 120 ◦ . A thin-film electronic pressure transducer was inserted into the cadaver tibiofemoral joint space to measure force and area. Throughout the various positions simulating specific phases of walking, it was found that stresses peaked to 14 MPa (standard deviation was 2.5MPa). In deep flexion, the peak stresses were significantly larger by over 80%, reaching the damage limits of cartilage. The results from this biomechanical study suggest that the adequacy of articular cartilage to support loads in the knee joint during deep flexion may be questionable. © 2004 IPEM. Published by Elsevier Ltd. All rights reserved. Keywords: Biomechanics; Tibiofemoral; Squat; Osteoarthritis 1. Introduction Accurate and functionally relevant intra articular contact stresses in the natural knee joint is difficult to determine and there are no known published data on the stresses that result in the tibiofemoral knee joint in walking and squatting. The knee joint reaction forces from walking have been estimated to be as high as three to five times bodyweight [1,2]. This duly raises concern when strength studies of cartilage explants have shown that damage occurs with as low as 5–10MPa of cyclic stress [3]. Furthermore, given the evidence that os- teoarthritis and cartilage damage can occur in the knee as a result of frequent or high contact stresses [3,4], the relevance in measuring these stresses becomes especially significant for population groups where cultural and social habits commonly include high weight-bearing daily activities of deep flexion such as squatting and kneeling. The role of the meniscus, cartilage and soft tissue to neutralise high stresses becomes ∗ Corresponding author. Tel.: +65 67724424; fax: +65 67744082. E-mail address: dosgohj@nus.edu.sg (J.C.H. Goh). increasingly diminished in larger flexion angles where the tibiofemoral contact is largely reduced [5]. Studies of deep flexion biomechanics in the past have been largely focused on the patellofemoral joint [6–9], looking at forces and stresses in this joint and its impact on cartilage. The possibility of fail- ure in the tibiofemoral articular cartilage from high stresses in deep flexion, perhaps a cause for the development of knee osteoarthritis in these compartments, has not been investi- gated. Evidence shows that the tibiofemoral compartments are commonly involved in knee osteoarthritis where clinical ob- servation indicates that the medial side is the compartment most frequently affected [10,11] resulting in varus-knee de- formities. Recent findings show that Chinese subjects have significantly more varus alignment of the lower extremity compared with Westerners [12]. The concurrence of varus- knee deformity and knee osteoarthritis [13] and the influence of race on the prevalence of knee osteoarthritis [14,15] point- ing to a significantly higher incidence of knee osteoarthritis among the Chinese and Japanese, raises some questions. If not at least it makes it relevant to further understand the re- 1350-4533/$ – see front matter © 2004 IPEM. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.medengphy.2004.09.002