The Knee 19 (2012) 32–35 Contents lists available at ScienceDirect The Knee Can single limb support objectively assess the functional severity of knee osteoarthritis?☆ Avi Elbaz a, Amit Mor a, Ofer Segal a, Gabriel Agar b, Nahum Halperin b, Amir Haim c, Eytan Debbi a, Ganit Segal a, Ronen Debi b,⁎ a b c AposTherapy Research Group, Herzliya, Israel Assaf Harofeh Medical Center, Zerifin, Israel Sourasky Medical Center, Tel Aviv, Israel a r t i c l e i n f o Article history: Received 25 July 2010 Received in revised form 29 November 2010 Accepted 13 December 2010 Keywords: Single limb support Osteoarthritis Pain Knee a b s t r a c t There is a lack in objective measurements that can assess the symptoms of knee osteoarthritis (KOA). In a previous study it was shown that pain and function are in higher correlation with the single-limb support gait parameter than with radiographic KOA stage. Single limb support represents a phase in the gait cycle when the body weight is entirely supported by one limb, while the contra-lateral limb swings forward. The purpose of this study was to further examine the relationship between single-limb support and the level of pain and function in patients with KOA. 125 adults with bilateral KOA underwent a physical and radiographic evaluation, and completed the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the SF-36 health survey. Patients walked barefoot at a self-selected speed on a computerized mat. Statistical analysis was used to divide the patients into quintiles based on single-limb support phase value and determine the differences in WOMAC and SF-36 scores between quintiles. Significant differences were found in WOMAC and SF-36 sub-category scores between the single-limb support quintiles. The means of the WOMAC-pain and WOMAC-function sub-categories decreased gradually over single-limb support quintiles (P b 0.001), and the means of the SF-36 sub-categories increased gradually over the quintiles (P b 0.001). Results show that single-limb support quintiles can help determine the level of pain, function and quality of life in patients with KOA. These results suggest that single-limb support quintiles may be added as an additional scale for generally assessing the symptomatic stage of KOA. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Patients suffering from knee osteoarthritis (KOA) experience knee pain, stiffness and decreased range of motion, all of which affect their body locomotion. These symptoms can significantly limit daily activities and lead to a loss of functional independence [1]. Patients express these limitations in terms of pain, function and quality of life. The clinical assessment of KOA therefore includes self-evaluation questionnaires to help qualify the symptoms of pain, function and quality of life. These include the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), the SF-36 health survey and others [2,3]. These questionnaires, however, subjectively measure the severity of KOA symptoms. ☆ The study was approved by the Institutional Helsinki Committee Registry at Assaf Harofeh Medical Center, Zerifin, Israel (Helsinki registration number 185/07, NIH no. NCT00599729). ⁎ Corresponding author. Department of Orthopedic Surgery, Assaf Harofeh Medical Center, P.O. Beer Yaacov, Zerifin 70600, Israel. Tel.: + 972 8 9779432; fax: + 972 8 9779434. E-mail address: debbi.ronen@gmail.com (R. Debi). 0968-0160/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.knee.2010.12.004 The American College of Rheumatology (ACR) has attempted to use radiographic findings to objectively measure the severity of symptomatic KOA. Their classification guidelines integrate the radiographic assessment with other clinical findings [4,5]. These guidelines, however, are limited because the interpretation of radiographic findings is by nature subjective and has intra and inter observer error [6]. Measurements of gait can objectively assess an individual's function. Studies have shown differences in gait patterns between patients with KOA and healthy individuals. Specifically, differences were found in the gait parameters of self-selected speed, step length and single limb support (SLS) (% of gait cycle) [7–9]. SLS represents a phase in the gait cycle when the body weight is entirely supported by one limb, while the contra-lateral limb swings forward. This phase usually accounts for 38–40% of the gait cycle [10,11]. In a previous study it was shown that pain and function are in higher correlation with SLS than with radiographic KOA stage. The purpose of this study was to further examine the relationship between single-limb support and the level of pain and function in patients with KOA. Specifically, the study was designed to test the hypothesis that SLS will decrease as pain and function worsen in patients with KOA. 33 A. Elbaz et al. / The Knee 19 (2012) 32–35 2. Methods 2.1. Study population A total of 125 patients participated in this study (79 women and 46 men; mean age (SD), 66 (SD 11.2) years, mean body mass index, 31.9 (SD 5.9)). All patients signed a written informed consent before entering the study. The protocol was approved by the Institutional Helsinki Committee Registry (Helsinki registration number 185/07, NIH protocol no. NCT00599729). The study was conducted at the Orthopedics Outpatient Clinic of Assaf Harofeh Medical Center in Zerifin, Israel and at the AposTherapy Center in Herzliya, Israel. Eligibility was defined as having symptomatic KOA for at least 6 months, qualifying under the American College of Rheumatology clinical criteria for OA of the knee [5], and having radiographically assessed KOA according to the Kellgren and Lawrence scale [12]. Exclusion criteria included the following: acute septic arthritis, corticosteroid injection within 3 months of the study, avascular necrosis, inflammatory arthritis, history of knee buckling, recent knee injury, neuropathic arthropathy, increased tendency to fall, lack of physical or mental ability to perform or comply with the study procedure, a history of pathological osteoporotic fractures, spinal or vascular claudication, and symptomatic degenerative arthritis in lower limb joints other than the knees. 2.2. Protocol All participants were instructed to refrain from taking pain medication, including paracetamol and NSAIDs, for a period of 3 days prior to the examination. All patients underwent a physical examination, including manual muscle testing to verify neurological deficits as a contraindication to patient inclusion, and a radiographic evaluation conducted by the senior orthopedic surgeon. Measurements of height, weight and leg length were taken. The leg length was measured from the tip of the greater trochanter to the floor through the lateral malleolus in upright standing position [13]. Patients were required to walk barefoot at a self-selected speed on a computerized mat (GAITRite®, CIR Systems Inc.). Patients walked 3 m before and after the walkway mat to allow sufficient acceleration and deceleration time outside the measurement area. Six trials were conducted and acquired data was stored for further analysis. The mean value of the six trials was calculated for each parameter. Following the gait test patients were asked to complete the WOMAC Osteoarthritis Index and the SF-36 health survey. The following gait parameters were evaluated: SLS (% gait cycle), normalized velocity (cm/s/leg length), normalized step length (cm/leg length), cadence (steps/min) and toe out angle (degrees). The original gait velocity and step length were normalized to leg length in order to eliminate the effect of height differences between patients. The WOMAC was divided into two categories: pain and function. These scales are scored from 0 cm to 10 cm, with 0 = no pain and 10 = worst pain. The SF-36 quality of life health survey is divided into eight subcategories: physical functioning, role limitation due to physical health, role limitation due to emotional problems, energy/fatigue, emotional well being, social functioning, pain and general health. The score ranges from 0 to 100, with higher scores indicating a better state of health and quality of life. 2.3. Statistical analysis Data was analyzed using SPSS statistic software version 17.0. The distributions of gait characteristics were examined using the Kolmogorov–Smirnov non-parametric test. Based on the results we used parametric or nonparametric statistical tests. The relationship between gait parameters and the WOMAC Osteoarthritis Index and the SF-36 health survey were analyzed using the Spearman or Pearson correlation with 95% confidence intervals (CI). Values of r ≤ 0.25 were considered low, values of 0.25 b r ≤ 0.50 were considered moderate and values of r ≥ 0.75 were considered high [14]. We further used partial linear correlation tests to adjust for age and BMI. A quintile analysis was then carried out in order to clarify the presentation of the correlations between SLS and the questionnaire results. This analysis would help reveal any non-linear changes (i.e. exponential) that occur within SLS at very high or very low data points in the questionnaire outcomes. The SLS value of the six walks between limbs was used to divide the patients into quintiles of equal sample size. Quintiles were generated by ranking the lowest values of SLS and creating 5 groups of equal sample size. The reason for taking the lowest SLS value was the assumption that patients will complete the questionnaire according to their worst symptom perception and therefore, the worse SLS value should be included in the analysis. The Kruskal–Wallis test was used to evaluate differences between groups in the nonparametric subcategories of the SF-36 quality of life health survey (role limitation due to physical health, role limitation due to emotional problems, and social functioning). One way analysis of variance (ANOVA) tests were used in continuous variables with normal distribution to evaluate decreasing or increasing trend between the groups followed by polynomial contrasts to evaluate the significance of the linear trend. All statistical tests were two-sided. A P value of ≤0.05 was considered to be statistically significant for all statistical tests. Table 1 Correlations and partial correlation between the gait parameters and the WOMAC Osteoarthritis Index and the SF-36 health survey. WOMAC-pain WOMAC-function WOMAC-stiffness SF-36 overall score Physical functioning Energy/fatigue Emotional well being Pain General health Limitation due to physical healtha Limitation due to emotional problemsa Social functioninga SLS r [95% CI] Cadence r [95% CI] Left toe out angle r [95% CI] Right toe out angle r [95% CI] − 0.50 − 0.53 − 0.39 0.53 0.49 0.33 0.29 0.50 0.36 0.41 0.39 0.24 − 0.39 − 0.42 − 0.23 0.44 0.42 0.28 0.30 0.41 0.32 0.31 0.32 0.23 0.19 0.19 0.11 − 0.13 − 0.14 − 0.04 0.04 − 0.21 − 0.10 − 0.14 − 0.04 − 0.13 0.17 (− 0.01,0.34) 0.18 (0.01,0.35) 0.06 (− 0.12,0.23) − 0.12 (− 0.29,0.06) − 0.14 (− 0.31,0.04) − 0.12 (− 0.29,0.06) − 0.04 (− 0.21,0.14) − 0.14 (− 0.31,0.04) − 0.003 (− 0.18,0.17) − 0.05 (− 0.22,0.13) − 0.10 (− 0.27,0.08) − 0.15 (− 0.32,0.03) (− 0.62,−0.36) (− 0.65,−0.39) (− 0.53,−0.23) (0.39,0.65) (0.34,0.61) (0.16,0.48) (0.12,0.44) (0.36,0.62) (0.20,0.50) (0.25,0.55) (0.23,0.53) (0.07,0.40) (− 0.53,−0.23) (− 0.56,−0.26) (− 0.39,−0.06) (0.29,0.57) (0.26,0.56) (0.11,0.43) (0.13,0.45) (0.25,0.55) (0.15,0.47) (0.14,0.46) (0.15,0.47) (0.06,0.39) (0.02,0.35) (0.02,0.35) (− 0.07,0.28) (− 0.30,0.05) (− 0.31,0.04) (− 0.21,0.14) (− 0.14,0.21) (− 0.37,−0.04) (− 0.27,0.08) (− 0.31,0.04) (− 0.21,0.14) (− 0.30,0.05) SLS = single limb support. r represents the Pearson correlation coefficient between gait parameters and the outcome measures. P values for all correlations are significant and P b 0.05. Correlations between SLS and the outcomes were greater than all other correlations. No significant correlations were found between the left and right toe out angles and the measured outcomes. a These outcomes did not have a normal distribution and were examined using a Spearman's rank correlation coefficient. 34 A. Elbaz et al. / The Knee 19 (2012) 32–35 3. Results The correlations between the gait parameters (SLS, cadence, and left and right toe out angles) and WOMAC-pain, WOMAC-function and the eight sub-categories of the SF-36 are summarized in Table 1. The results for the partial linear correlation tests adjusted for age and BMI were similar to the non-adjusted values (data not shown). Moderate significant correlations were found between WOMAC-pain and WOMACfunction and SF-36 pain and physical functioning sub-categories and the SLS phase. Figs. 1 and 2 present the correlation between WOMAC pain and WOMAC function over SLS. All other gait parameters aside toe out angle showed significant correlations with the questionnaire results. All these correlations were lower than the correlations between SLS and the questionnaires. The patients were divided into five SLS quintiles in order to further evaluate and clarify the correlations between SLS and the questionnaire outcomes. The quintiles were divided as follows: Q1 = b33% (N = 25, mean age 72 (SD 10.4) years, mean body mass index 35 (SD 6.0)); Q2 = 33% b SLS ≤ 35.5% (N = 26, mean age 66 (SD 11.2) years, mean body mass index 33 (SD 5.9)); Q3 = 35.5% b SLS ≤ 37% (N = 25, mean age 65 (SD 10.0) years, mean body mass index 33 (SD 5.2)); Q4 = 37% b SLS ≤ 38.5% (N = 24, mean age 64 (SD 8.7) years, mean body mass index 31 (SD 6.4)); and Q5 = SLS N 38.5% (N = 25, mean age 61 (SD 12.9) years, mean body mass index 27 (SD 3.0)). Significant differences were found between SLS quintiles in age and BMI (one-way ANOVA test, P b 0.01) (data not shown). Overall, the means of the WOMAC-pain and WOMAC-function scores decreased gradually over the SLS quintiles from the first to the fifth quintile (Table 2), and the means of the SF-36 sub-category scores (Table 3) and the means of the gait parameter values increased gradually over these quintiles (Table 4). 4. Discussion We hypothesized that the SLS parameter of a gait analysis would reflect KOA symptoms and functional condition as evaluated by selfevaluation questionnaires. In order to examine the role of SLS, the range of SLS values was divided into quintiles that potentially represent 5 stages of severity. The data distribution of pain and function and the distribution of the gait parameters over these quintiles supported our hypothesis. Lower SLS values corresponded significantly with worse KOA symptoms of pain, function and quality of life as measured by self-evaluation questionnaires. A significant increase in KOA functional severity was also seen in objective evaluations of functional performance as measured by the velocity and step length parameters of the gait analysis. This was demonstrated in the distribution of these parameters over the SLS quintiles. A question left open by this study is whether SLS is better than gait velocity or step length at predicting KOA symptomatic severity. Gait velocity and step length are part of the gait velocity equation: Velocity = Step length × Cadence. The findings of a previous study of ours give preliminary answers to this question at least in regard to gait velocity. Our findings showed that walking in two different gait velocities did not correspond with significant differences in SLS of patients with KOA [15]. It may be assumed, therefore that SLS is more Fig. 2. Scatter plot comparing single limb support and WOMAC function in Knee OA. stable and less controllable by patients with KOA, as opposed to gait velocity, which constantly changes in response to fatigue, times of the day, decisions of patient and many more factors. The results of this study are reflective of the findings of similar studies. As in our study, other researchers have found that patients change their gait in response to OA in either the hip or knee [16]. Previous studies have also shown that patients with KOA specifically have a shorter SLS phase, shorter step length and slower gait velocity compared to healthy individuals [1,8,9]. The findings of these studies and ours suggest that SLS may reflect a patient's ability to bear loads on a limb with KOA. A patient with severe pain and dysfunction is expected to decrease loads from the affected limb by decreasing SLS phase. This may help explain why our results showed a strong association between SLS and knee OA symptomatic severity (pain and function). This study had some limitations. The study design enabled a first and basic understanding of SLS as a parameter that can help evaluate the level of functional severity of patients with KOA. The study results showed that SLS correlates with the level of pain, function and quality of life of patients with KOA. We did not however measure this correlation over a period of time. Future studies should compare the changes in SLS with the changes in self-evaluation questionnaires and in radiographic grading over specified amounts of time in order to determine the true predictive value of SLS scores. In conclusion, we have found that single limb support increases consistently with improvements in pain and function in patients with KOA. The results suggest that a gait analysis would be a good addition to an analysis of KOA. We recommend that healthcare workers use the quintiles implemented in this study as an assistive tool for the Table 2 WOMAC-pain, WOMAC-function and WOMAC-stiffness distribution in the SLS quintiles. Results are presented as mean (SD) [95% confidence interval]. SLS quintile (% of gait cycle) WOMAC-pain (0–10 cm) Q1 (b 33%) 6.3 (1.81) [5.6–7.1] Q2 (33%–35.5%) 4.7 (2.1) [3.8–5.6] Q3 (35.5%–37%) 5.0 (2.6) [4.0–6.1] Q4 (37%–38.5%) 3.0 (2.2) [2.1–4.0] Q5 (N 38.5%) 2.7 (2.1) [1.8–3.6] P-for-trend over quintiles: P b 0.01 Fig. 1. Scatter plot comparing single limb support and WOMAC pain in Knee OA. SLS = single limb support; Q = quintile. WOMAC-function (0–10 cm) WOMAC-stiffness (0–10 cm) 6.6 (2.0) 5.1 (2.0) 4.8 (2.8) 3.0 (2.4) 2.6 (2.5) 6.0 4.7 4.4 3.3 2.2 [5.8–7.4] [4.3–5.9] [3.6–5.9] [2.0–4.1] [1.6–3.6] (3.1) (2.9) (3.2) (3.1) (2.9) [4.8–7.3] [3.6–5.9] [3.1–5.7] [2.0–5.6] [1.1–3.4] 35 A. Elbaz et al. / The Knee 19 (2012) 32–35 Table 3 SF-36 health survey sub-categories distribution over the SLS quintiles. Results are presented as mean (SD) [95% confidence interval]. SLS (% of gait cycle) Physical function (0–100) Q1 (b 33%) 23.6 Q2 (33%–35.5%) 40.8 Q3 (35.5%–37%) 53.0 Q4 (37%–38.5%) 56.9 Q5 (N 38.5%) 58.4 P over quintiles: P b 0.01a SLS (% of gait cycle) (15.0) (18.1) (27.4) (24.3) (23.7) [17.4–29.8] [33.4–48.1] [41.7–64.3] [46.6–67.1] [48.6–68.2] Emotional well being (0–100) Q1 (b 33%) 62.2 Q2 (33%–35.5%) 65.2 Q3 (35.5%–37%) 68.8 Q4 (37%–38.5%) 79.8 Q5 (N 38.5%) 76.2 P over quintiles: P b 0.01b (18.9) (17.7) (19.4) (14.8) (15.3) [54.5–70.0] [58.1–72.4] [60.8–76.8] [73.5–86.0] [69.9–82.5] Role limitation due to physical health (0–100) Role limitation due to emotional problems (0–100) Energy/fatigue (0–100) 24.0 33.7 56.0 53.1 69.0 44.0 53.8 66.0 72.2 84.0 43.0 51.7 53.8 66.7 62.6 (26.5) [13.1–34.9] (41.8) [16.8–50.5] (37.0) [40.7–71.3] (42.5) [35.2–71.1] (39.1) [52.9–85.1] (39.3) (42.2) (42.1) (42.5) (27.4) Social functioning (0–100) Pain (0–100) 63.0 66.8 77.0 84.9 76.5 25.3 37.0 53.1 56.3 60.6 (24.6) [52.8–73.2] (26.4) [56.1–77.5] (25.2) [66.6–87.4] (24.4) [74.6–95.2] (23.5) [66.8–86.2] (20.1) (21.5) (24.8) (29.2) (18.7) [27.8–60.2] [36.8–70.9] [48.6–83.4] [54.3–90.2] [72.7–95.3] (20.2) (22.8) (24.3) (17.9) (17.5) [34.7–51.3] [42.5–60.9] [43.8–63.8] [59.1–74.2] [55.4–69.8] General health (0–100) [17.0–33.6] [28.3–45.7] [42.9–63.3] [43.9–68.6] [52.9–68.3] 48.5 57.1 58.3 63.5 66.0 (15.9) (17.2) (17.7) (12.8) (16.2) [41.9–55.1] [50.1–64.0] [51.0–65.6] [58.1–67.0] [59.3–72.7] SLS = single limb support; Q = quintile. a The Kruskal–Wallis test was used to evaluate differences between groups in the role limitation due to physical health and role limitation due to emotional problems subcategories of the SF-36 quality of life health survey because they were nonparametric. Other variables were evaluated using one-way ANOVA tests. b The Kruskal–Wallis test was used to evaluate differences between groups in the social functioning subcategory of the SF-36 quality of life health survey because it was nonparametric. Other variables were evaluated using one-way ANOVA tests. Table 4 Gait velocity and step length distribution in the SLS quintiles. Results are presented as mean (SD). SLS (% of gait cycle) Velocity (cm/s) Q1 (b 33%) 63.8 (15.5) Q2 (33%–35.5%) 85.8 (15.5) Q3 (35.5%–37%) 101.6 (13.9) Q4 (37%–38.5%) 106.1 (14.8) Q5 (N 38.5%) 115.1 (11.6) P-for-trend over quintiles: P b 0.01 Left step length (cm) Right step length (cm) 41.1 50.2 56.1 56.9 60.3 42.1 50.6 55.6 58.2 60.9 (8.0) (5.5) (6.4) (6.9) (5.8) (8.1) (5.4) (7.0) (6.3) (6.0) SLS = single limb support; Q = quintile. assessment of KOA functional severity. 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