Hindawi Publishing Corporation he Scientiic World Journal Volume 2013, Article ID 514743, 8 pages http://dx.doi.org/10.1155/2013/514743 Clinical Study Patellar Tendon Properties and Lower Limb Function in Rheumatoid Arthritis and Ankylosing Spondylitis versus Healthy Controls: A Cross-Sectional Study Verena Matschke, 1,2,3 Jeremy G. Jones, 1,2 Andrew B. Lemmey, 1 Peter J. Maddison, 1,2 and Jeanette M. Thom 1 1 School of Sport, Health and Exercise Sciences, Bangor University, Bangor LL57 2DG, UK 2 Department of Rheumatology, Betsi Cadwaladr University Health Board, Llandudno Hospital, Llandudno LL30 1LB, UK 3 CERN, European Organization for Nuclear Research, 1211 Geneva 23, Switzerland Correspondence should be addressed to Verena Matschke; verena.matschke@cern.ch Received 30 March 2013; Accepted 15 May 2013 Academic Editors: S. Ruta and E. R. Soriano Copyright © 2013 Verena Matschke et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Objective. Rheumatoid arthritis (RA) and ankylosing spondylitis (AS) lead to inlammation in tendons and peritendinous tissues, but efects on biomechanical tendon function are unknown. his study investigated patellar tendon (PT) properties in stable, established RA and AS patients. Methods. We compared 18 RA patients (13 women, 59.0 ± 2.8 years, mean ± SEM) with 18 age- and sex-matched healthy controls (58.2 ± 3.2 years), and 12 AS patients (4 women, 52.9 ± 3.4 years) with 12 matched controls (54.5 ± 4.7 years). Assessments with electromyography, isokinetic dynamometry, and ultrasound included quadriceps muscle force and cross-sectional area (CSA), PT stifness, and PT CSA. Additionally, measures of physical function and disease activity were performed. Results. PT stifness and physical function were lower in RA and AS patients compared to healthy controls, without a signiicant diference in force production. PT CSA was signiicantly larger leading to reduction in Young’s modulus (YM) in AS, but not in RA. Conclusion. he adverse changes in PT properties in RA and AS may contribute to their impaired physical function. AS, but not RA, leads to PT thickening without increasing PT stifness, suggesting that PT thickening in AS is a disorganised repair process. Longitudinal studies need to investigate the time course of these changes and their response to exercise training. 1. Introduction Chronic autoimmune arthritides are characterised by joint inlammation and progressive joint destruction and are accompanied by impaired physical function [1]. Inlamma- tion also afects other musculoskeletal structures includ- ing tendons and their insertions into bone (entheses), but whether this leads to chronic alterations in the biomechanical function of the tendon-muscle complex is unknown. he function of a tendon is determined by its stifness, that is, its elastic properties, which in turn inluence skeletal muscle force output and function. When the force of the con- tracting muscle is transmitted via the tendon, the resulting elongation of the tendon attenuates the impact of the con- traction on the connected bone. he force output is thereby reduced by a small amount, but this is stored as elastic energy and released on relaxation of the muscle [2]. hus, this mech- anism plays an essential part in the eicient performance of complex movements. Tendon properties also inluence joint stability and the ability to make postural adjustments [3] and consequently play a major role in maintaining balance and preventing falls. In exercise physiology, ultrasound is used to investigate the biomechanical properties of healthy tendons (especially the load-bearing patellar and achilles tendons) and how they adapt to high intensity exercise, immobilisation, and changes with ageing [3–5]. In the elderly and ater immobilisation, alterations in collagen content and cross linking lead to reduced tendon stifness and size with a consequent reduction in collagen ibril diameter and number [6, 7].