ScienceDirect. The impact of the severity of knee osteoarthritis on the postural stability

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1 Available online at ScienceDirect Materials Today: Proceedings 3 (2016 ) DAS 2015 The impact of the severity of knee osteoarthritis on the postural stability G. Nagymate a, A. Pethes b, G. Szabo a, Z. Bejek c, R. Paroczai d, R.M. Kiss a * a Budapest University of Technology and Economics, Dept of Mechatronics, Optics and Mechanical Engineering Informatics, Bertalan Lajos str. 4-6, Budapest 1111, Hungary b Szent János Hospital Dept of Orthopedics and Traumatology, Diósárok 1-3., Budapest 1125, Hungary c Semmelweis University, Dept of Orthopedics, Karolina str 27, Budapest 1113, Hungary d Budapest University of Technology and Economics, Department of Applied Mechanics, Műegyetem rkp. 5., Budapest 1111, Hungary Abstract Knee osteoarthritis is one of the most widespread orthopedic diseases among elderly people. Biomechanical effects of this disorder are widely studied. In case of very intense knee osteoarthritis, typical measurements such as gait analysis are no longer possible. On the other hand stance tests can be performed even in these very severe cases. In our research, the biomechanical effects of knee osteoarthritis on postural stability in respect to the degree of abrasion were studied. The participants were divided into two groups according to the degree of osteoarthritis on Kellgren-Lawrence scale (KL3 and KL4+). The load distribution was measured during 30 seconds long bipedal stance. Load distribution between the affected and non-affected leg was determined. From measured parameters the coordinates of the center of pressure (COP) and the axes length and area of the 95% confidence ellipse of COP are also calculated. It was found that the confidence ellipse parameters are significantly increasing in respect to the severity of osteoarthritis which means the deterioration of osteoarthritis causes worsening the balancing capability. It could be established, the affected leg is less loaded compared to the healthy leg in both groups Elsevier Ltd. All rights reserved Elsevier Ltd. All rights reserved. Advanced in in Experimental Experimental Mechanics Mechanics (DAS (DAS 2015) 2015). Keywords: Knee osteoarthritis; stabilometry * Corresponding author. Tel.: ; fax: address: rita.kiss@mogi.bme.hu Elsevier Ltd. All rights reserved. Advanced in Experimental Mechanics (DAS 2015) doi: /j.matpr

2 1070 G. Nagymate et al. / Materials Today: Proceedings 3 ( 2016 ) Introduction Knee osteoarthritis is one of the most widespread orthopedic disorders among the elderly (above 65 years old) [1]. Treatment of knee osteoarthritis is an increasingly important health issue due to the aging population. Previous researches have clearly demonstrated that the deterioration of knee osteoarthritis comes along with narrowing knee joint movement and significantly changes the gait parameters [2, 3, 4, 5]. The gait analysis are asset and time consuming, thus are performed in special gait labs. Among biomechanical assessments the different equilibrium ability tests, especially the stability test during stance are the simplest and widely used nowadays. These stance tests are usually performed on force plates or force distribution plates for a specified time interval that are usually 30 or 60 seconds in bipedal or single limb stance with eyes open and closed. From the measurements of these platforms the coordinates of the instantaneous center of pressure (COP) are calculated. As these coordinates are time variant their motion can be described with different statistical parameters. The most widely used descriptive parameter is the sway path which is defined by the axes length and area of a confidence ellipse covering 95% of the COP points [6-9]. Researchers often used for characterization of stability the length of the sway path, and standard deviation of the COP points in the antero-posterior and medio-lateral directions [6-9]. Previous studies demonstrated that the postural stability of patients with knee OA measured during unipedal or bipedal stance significantly degrades compared to healthy individuals of similar ages [6-13]. However, in the literature no studies could be found comparing the specific postural stability parameters of patients with varying severity of knee osteoarthritis. Our research is intended to study the differences in postural stability between patients with severe (KL III) and intense (KL IV+) unilateral knee osteoarthritis. Based on our hypothesis the postural stability deteriorates, where especially the axes of the 95% confidence ellipse traveled by the COP and its area increases. Fig. 1. (a) Stabilometry measurement of very severe knee osteoarthritis patient; (b) Parameters of the 95% confidence ellipse of the time variant center of pressure

3 G. Nagymate et al. / Materials Today: Proceedings 3 ( 2016 ) Materials and methods 2.1. Patients Patients involved in the study were divided into two groups based on the two-ways X-ray examination. In case of the first group the osteoarthritis were rated as III on the Kellgren-Lawrence scale. This group of patients suffering from severe osteoarthritis consisted of eight patients. The members of the other group were diagnosed with very severe (intense) KL IV+ knee osteoarthritis, where the level of pain and disability makes an unaided few minutes walk impossible. This group was formed by 10 patients. Table 1 demonstrates the anthropometrical data of both groups of patients. All participants were informed in writing about the risks and benefits of the study; each gave signed informed consent and was given the opportunity to withdraw from the study at any time. The study was approved by the National Science and Research Ethics Committee (114/2004). Table 1. Anthropometrical data of the two groups Parameters KL III KL IV+ Male/Female 1/7 (8) 5/5 (10) Age (years) 69.5± ±7.2 Body weight (kg) 75.4± ±12.8 Height (cm) 162.3± ±12.3 BMI (kg/m 2 ) 31.54± ± Method The postural stability was examined by a stance test using Zebris FDM-S Multifunctional Force-measuring Plate (320mm x 470mm measuring surface with 1504 pcs. load cells). The load distribution was measured during 30 second long bipedal standing (Fig. 1. (a)). First, the load distribution between the affected and non-affected side was determined. Secondly, the coordinates of the instantaneous center of pressure (COP) were calculated during the measuring duration (Fig. 1. (b)). The width (w), height (h) and area of 95% confidence ellipse were calculated with WinPDMS processing software v1.2.1 (Zebris GmbH, Isny, Germany). The statistical comparison of the data belonging to the two patient groups was performed by Student s t-test. The necessary homogeneity of variances on the parameters of the two groups was proven by F-tests. The statistical power of the t-tests was calculated using IBM SPSS Statistics program v22. Statistical power for the tests was calculated by G*Power v software which is the probability that the t-tests correctly reject the identity of groups based on the analyzed parameter when there is actual significant difference. In case of the ellipse parameters we used two-sample two-tail t-test assuming equal variances based on the F-test results. To assess the statistical differences on distribution of the two feet paired t-test was used. Significance level (α) was set to Results All patients were able to carry out the test, no one has been excluded. The mean value and standard deviation of characteristic values of postural stability are summarized in Table 2 and displayed in Fig 2. Based on the results of F-test t-test could be performed.

4 1072 G. Nagymate et al. / Materials Today: Proceedings 3 ( 2016 ) Table 2. Descriptive statistics of the measured parameters Group ellipse width, mm ellipse height, mm ellipse Affected side % Non-affected side area, mm 2 % KL3 7.09± ± ± ± ±4.02 KL ± ± ± ± ± p< U nilateral K L III U nilateral K L IV p K L III = p KL IV+ = p= p< e llip se w id th, mm ellipse height, mm e llip se are a, mm 2 Affe cte d limb % Healthy limb % Fig. 2. The average and SD of different parameters in both patients group. In both groups the load-bearing capacity was significantly smaller on the affected side than on the non-affected side. The deterioration of the knee osteoarthritis entails the significant increase of the width, height and area of the 95% confidence ellipse. The most effective difference could be established in parameter of area of the 95% confidence ellipse, when the area increased more than 2 times (Fig. 2 and Table 2). The results of statistical comparisons and significance levels are summarized in Table 3. Table 3. Statistical differences Parameter Mean difference Significance Statistical power ellipse width, mm 5,79 p = 0, ellipse height, mm 11,80 p< 0, ellipse area, mm 2 176,89 p< 0, Force distribution difference between limbs (KL3), % Force distribution difference between limbs (KL4+), % p= p= Discussion The tests showed that the 30 seconds bipedal stance could be performed even by the very severe knee osteoarthritis patients. The results show that in both groups of patients significantly less load is put on the affected side than on the non-affected side. In accordance with our assumption the postural stability significantly deteriorates with the worsening knee osteoarthritis as represented by the COP confidence ellipse parameters. It means that the biomechanical effect of the osteoarthritis can be analysed by stabilometry at patients with varying severity of knee osteoarthritis.

5 G. Nagymate et al. / Materials Today: Proceedings 3 ( 2016 ) Our research showed firstly that, the balancing ability during bipedal stance is deteriorated by worsening of knee osteoarthritis. It should be taken into account in conservative rehabilitation protocol and in use of different aids. Secondly it could be established that, the balancing capacity measurement during bipedal stance could be used safely in patients with intense (KL IV+) knee osteoarthritis, where the use of gait analysis is not feasible. Acknowledgements This project is supported by the Hungarian Scientific Fund K References [1] C.F. Dillon et al., Prevalence of knee osteoarthritis in the United States: Arthritis data from the Third National Health and Nutrition Examination Survey, J Rheumatol Nov;33(11): [2] S.C. Huang et al., Effects of severity of degeneration on gait patterns in patients with medial knee osteoarthritis, Med Eng Phys Oct;30(8): [3] H.R. Yakhdani et al., Stability and variability of knee kinematics during gait in knee osteoarthritis before and after replacement surgery, Clin Biomech (Bristol, Avon) Mar;25(3): [4] Z. Bejek, R. Paroczai, A. Illyes, R.M. Kiss, The influence of walking speed on gait parameters in healthy people and in patients with osteoarthritis, Knee Surg Sports Traumatol Arthrosc Jul;14(7): [5] R.M. Kiss, Effect of severity of knee osteoarthritis on the variability of gait parameters, J Electromyogr Kinesiol Oct;21(5): [6] G.C. Gauchard et al., On the role of knee joint in balance control and postural strategies: Effects of total knee replacement in elderly subjects with knee osteoarthritis, Gait Posture Jun;32(2): [7] D. Vahtrik et al., Postural stability in relation to anthropometric and functional characteristics in women with knee osteoarthritis following total knee arthroplasty, Arch Orthop Trauma Surg May;134(5): [8] T. Masui et al., Gender differences in platform measures of balance in rural community-dwelling elders, Arch Gerontol Geriatr Sep- Oct;41(2): [9] T. Lyytinen et al., Postural control and thigh muscle activity in men with knee osteoarthritis, J Electromyogr Kinesiol Dec;20(6): [10] R.M.Kiss, Effect of degree of knee osteoarthritis on balancing capacity after sudden perturbation, J Electromyogr Kinesiol Aug;22(4): [11] B.S. Hassan et al., Effect of pain reduction on postural sway, proprioception and quadriceps strength in subject with knee osteoarthritis, Ann Rheum Dis 2002; 61: [12] B.S. Hassan et al., Static postural sway, proprioception and maximal voluntary quadriceps contraction in patients with knee osteoarthritis and normal subjects, Ann Rheum Dis 2001; 60: [13] T. Masui et al., Increasing postural sway in rural-community-dwelling elderly persons with knee osteoarthritis, J Orthop Sci 2006; 11: