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A study of the inter-rater reliability of a test battery for use in patients after total hip replacement

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A study of the inter-rater reliability of a test battery for use in patients after total hip replacement
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    http://cre.sagepub.com/  Clinical Rehabilitation  http://cre.sagepub.com/content/early/2014/05/20/0269215514534088The online version of this article can be found at: DOI: 10.1177/0269215514534088 published online 21 May 2014 Clin Rehabil  Lone Ramer Mikkelsen, Søren Mikkelsen, Kjeld Søballe, Inger Mechlenburg and Annemette Krintel Petersen replacementA study of the inter-rater reliability of a test battery for use in patients after total hip  Published by:  http://www.sagepublications.com  can be found at: Clinical Rehabilitation  Additional services and information for http://cre.sagepub.com/cgi/alerts Email Alerts: http://cre.sagepub.com/subscriptions Subscriptions:  http://www.sagepub.com/journalsReprints.nav Reprints:  http://www.sagepub.com/journalsPermissions.nav Permissions:  What is This? - May 21, 2014OnlineFirst Version of Record >> by guest on May 22, 2014cre.sagepub.comDownloaded from by guest on May 22, 2014cre.sagepub.comDownloaded from   Clinical Rehabilitation 1  –10© The Author(s) 2014Reprints and permissions: sagepub.co.uk/journalsPermissions.navDOI: 10.1177/0269215514534088cre.sagepub.com CLINICALREHABILITATION A study of the inter-rater reliability of a test battery for use in patients after total hip replacement Lone Ramer Mikkelsen 1 , Søren Mikkelsen 1 , Kjeld Søballe 2 , Inger Mechlenburg 2  and Annemette Krintel Petersen 3 AbstractObjective: To assess the within-day inter-rater reliability of a test battery of functional performance, muscle strength and leg extension power on total hip replacement patients. Design: A test–retest design was used. Setting: Orthopaedic department at a Regional Hospital in Denmark. Subjects: Two convenience samples of 20 total hip replacement patients were included. Intervention: The tests were performed three months after total hip replacement. Two raters performed test and re-test, with two hours rest in-between. Main measures: The test battery included: sit-to-stand performance, 20-metre maximum walking speed, stair climb performance, isometric muscle strength (hip abduction/flexion), and leg extension power. Absolute reliability was assessed with Bland Altman plots, standard error of measurement (SEM), and minimal detectable change. Relative reliability was assessed with intra-class correlation coefficient. Results: Systematic differences between testers were seen in tests of walking speed (0.32 seconds p  = 0.03) and stair climb performance (0.18 seconds p  = 0.003). In per cent of the grand mean, the standard error of measurement was 3%–10%, indicating the measurement error on a group level, and the minimal detectable change was 10%–27%, indicating the measurement error on an individual level. The intra-class correlation coefficients were above 0.80 in all tests (range 0.83–0.95). Conclusions: The tests showed acceptable relative and absolute inter-rater reliability on a group level, but not on an individual level (except from test of walking speed and stair climb performance). Systematic differences between testers were considered clinically irrelevant (0.3 and 0.2 seconds). Keywords Arthroplasty, measurement error, muscle strength, reliability, walking Received: 13 January 2014; accepted: 12 April 2014 1 Interdisciplinary Research Unit, Silkeborg Regional Hospital, Silkeborg, Denmark  2 Department of Orthopaedic Surgery, Aarhus University Hospital, Aarhus, Denmark  3 Department of Physiotherapy- and Occupational Therapy, Aarhus University Hospital, Denmark  534088 CRE 0010.1177/0269215514534088Clinical Rehabilitation Mikkelsen etal. research-article   2014  Article Corresponding author: Lone Ramer Mikkelsen, Interdisciplinary Research Unit, Elective Surgery Centre, Silkeborg Regional Hospital, Falkevej 1-3, Silkeborg 8600, Denmark. Email: lonemike@rm.dk   by guest on May 22, 2014cre.sagepub.comDownloaded from   2 Clinical Rehabilitation Introduction Total hip replacement is offered to patients with end-stage osteoarthritis to reduce their pain and improve their function. 1  Although it is generally a successful procedure, both acute and long-term deficits in muscle strength and functional perfor-mance have been documented. 2–4  No clear evi-dence exists to support the effect of rehabilitation interventions aimed at reducing these deficits. 5  Reliable, objective performance measures are needed in rehabilitation research and to ensure  proper clinical evaluation of therapeutic outcomes. To appraise the efforts of current rehabilitation research devoted to intensive strength training after total hip replacement 6,7  it is essential to measure changes in muscle strength and lower-extremity  power as well as functional performance.Previous studies of the reliability of muscle strength and performance tests have focused on  patients with osteoarthritis. 8–12  To our knowledge, no previous studies have aimed specifically at eval-uating the reliability of functional performance tests after total hip replacement.The aim of this study is to assess the inter-rater reliability of a proposed test battery that includes four lower-extremity performance tests, two iso-metric muscle strength tests, and one test of leg extension power in total hip replacement patients three months after surgery. Furthermore, the aim is to determine which is the more reliable of two commonly used sit-to-stand tests in total hip replacement patients: five repetitions sit-to-stand or 30 seconds sit-to-stand. Methods Eligible patients were contacted before their sched-uled three-month postoperative outpatient visit at the hospital (convenience sample). They were given written and verbal information; and if they were willing to participate in the study, the tests were performed on the day of their hospital visit. Inclusion criteria were: 55–80 years of age and pri-mary, unilateral total hip replacement surgery at Silkeborg Regional Hospital, Denmark, three months before testing. Exclusion criteria were: neurological diseases, inability to read or speak Danish, cognitive problems/dementia or major  postoperative complications (e.g. infection, frac-ture, or hip dislocation). The study was conducted in accordance with the Declaration of Helsinki II and approved by the Central Denmark Region Committee on Biomedical Research Ethics (M-20090231).All patients were tested twice on the same day  by two physiotherapists (rater A and B) with a two-hour break between the tests. The test bat-tery was divided into two for this reliability study to reduce the impact of fatigue owing to perfor-mance of all tests twice on the same day. Thus, we performed the reliability study on two patient samples. The physiotherapists underwent train-ing and pilot testing of the standardised test pro-cedures before the study was initiated. Each  patient was randomized to whichever physiother-apist performed the initial testing. Sealed enve-lopes were used for randomization to rater A or rater B as the first tester (1:1). During the second test, the rater was blinded to the results of the  previous test. Sample 1 performed test–retest of each of the following tests: five repetitions sit-to-stand, 30 seconds sit-to-stand, stair-climb test and isometric strength test in hip abduction and flexion. Sample 2 performed the leg extension  power test using the Leg Extensor Power Rig and a 20 metre walk test. Measurements Five repetitions sit-to-stand  The test is a part of the Osteoarthritis Initiative 13  and it is often used in patients with osteoarthritis and after total hip replacement. 14–16  Patients were seated on a standard chair (seat height: 44 cm) with their arms crossed over the chest and the back touching the back rest. They were instructed to rise to a fully extended position and to sit again, five times as quickly as possible. The better of two tri-als, with 30 seconds rest in-between, measured to the nearest 0.01 second was used as the data point. If the patient was unable to rise from the chair five times, the test could not be completed.  by guest on May 22, 2014cre.sagepub.comDownloaded from    Mikkelsen et al. 3 30 seconds sit-to-stand  The 30 seconds sit-to-stand test is widely used in  patients with osteoarthritis and after total joint replacement. 17–21  The chair and the starting posi-tion were as described above. The patient was instructed to perform as many rises as possible in 30 seconds. The physiotherapist counted the rises out loud and stopped the patient after 30 seconds. The number of rises to a fully extended position was used as the data point. If a single rise was impossible, the score was 0. The better of two tri-als, with 30 seconds rest in-between, was used as the data point. 20 metre walking test The test is a part of the Osteoarthritis Initiative 13  and is used in recent studies on patients with hip and knee osteoarthritis. 14,15  Patients started in a standing position behind the starting line and walked 20 metre as fast as possible towards a cone two metres beyond the end-point line. This proce-dure measures acceleration, but not deceleration. The better of two trials, with 30 seconds rest in- between, measured to the nearest 0.01 seconds, was used as the data point. Stair-climb test Stair-climbing performance has been suggested and used when measuring functional performance in hip osteoarthritis patients 12,22  and after total hip replacement. 16,23,24  Participants were instructed to ascend nine steps (16.5 cm high) as fast as possible without using the handrail. The better of two trials, with 30 seconds rest in-between, measured to the nearest 0.01 seconds, was used as the data point. Leg extensor power  Leg extension power is highly correlated with functional performance and the risk of falling 17,25–27  and it has been used in hip osteoarthritis patients, 8  and after total hip and knee replacement. 15,17,18  The  Nottingham Power Rig (University of Nottingham Mechanical Engineering Unit, UK) was used to measure leg extension power that was expressed as the product of force and velocity in a single-leg simultaneous hip and knee extension. Patients were seated with their arms crossed, the operated leg  placed on the footplate, and the other foot resting on the floor. They were asked to push the pedal down as hard and fast as possible; we used a sound file with the verbal command to avoid that the voice and the accentuation of the tester would affect the test performance. The power was recorded for each push (30 seconds rest between trials) until they reached a plateau defined as two successive measurements below the highest meas-urement. A minimum of six trials to minimise learning effect, and a maximum of 12 trials to min-imise fatigue, were obtained and the highest meas-urement in watt was used as the data point. Isometric strength test in hip abduction and flexion Isometric hip strength was tested with the hand-held dynamometer, Power Track II Commander (JTECH Medical, Salt Lake City, UT, USA). Hand-held dynamometer testing of lower extremity mus-cle strength is suggested as a valid measurement for evaluating orthopaedic patients, 28  and it is applied in osteoarthritis patients 10  and after total  joint replacement surgery. 17,29  We used standard-ised test procedures as described by Thorborg et al. 30  Additionally, we used a sound file with the verbal command to avoid that the voice and the accentuation of the tester would affect the test per-formance. The test consisted of a five-second iso-metric maximum voluntary contraction against the dynamometer. The test was repeated with a 30-sec-ond rest in-between until a plateau was reached, which was defined as two successive measure-ments below the highest. A minimum of four tests were required to minimise the learning effect and a maximum of 10 to minimise fatigue. The highest score, measured in Newtons, was used as the data  point.Hip abduction was measured in a supine posi-tion with the participants stabilising themselves with their hands holding on to the sides of the table. 30  The participant pressed as hard as possible by guest on May 22, 2014cre.sagepub.comDownloaded from   4 Clinical Rehabilitation towards the dynamometer placed 5 cm proximal to the lateral malleolus with the hip in neutral posi-tion. Hip flexion was measured in a sitting position with the hip at 90° of flexion and the participant holding on to the sides of the table with both hands. The resistance was applied 5 cm proximal to the  proximal edge of the patella against hip flexion. Sample size We defined an intra-class correlation coefficient (ICC) level >0.8 to be satisfactory. Often 0.7 is defined as acceptable, 31  but owing to expected var-iability in the scores, we decided on this more con-servative cut-off level. With two raters, acceptable ICCs of 0.8, and a 95% CI (confidence interval) of ±0.2, a sample size of 13 subjects is required. 32  To decrease the uncertainty of the results and to increase generalisability, we decided to include 20 subjects for each sample. Statistics Statistically significant differences in test results  between the two trials were analysed with paired t  -tests as data were normally distributed. In accord-ance with published guidelines for reporting relia- bility and agreement studies, reliability was investigated in terms of test–retest reliability and measurement error. 33  The agreement between the tests was examined by a Bland Altman plots. 33  Identification of the mean difference with 95% CI and limits of agreement were included in the plots. The standard error of measurement (SEM), which represents the typical error in a single measure-ment, 34  was calculated by the equation SD/ √ 2. The minimal detectable change defined as the measure of statistically significant change between two measurements, 34  was calculated by the equation 1.96 × √ 2 × SEM. For a statistically significant change between two observations to be detected, the change must be at least the minimal detectable change. SEM and minimal detectable change (MDC) are presented in actual units, but they are also expressed as a percentage of the mean of the two test sessions (grand mean), making compari-sons between tests and studies easier. 35  The relative reliability was calculated using the ICC model 2.1. The ICC is a ratio of the variance between subjects over the total variance. The ICC 2.1 is a fixed model addressing both systematic and random error. 36  The significance level was 0.05. A STATA 12.1 (StataCorp, College Station, TX) software  package was used for data analysis. Results Two samples, each consisting of 20 subjects, were included in the period November 2010–May 2011. Of 87 eligible total hip replacement patients, 44 (51%) refused to participate in the study, the major-ity owing to lack of time on the scheduled day. Three  patients withdrew consent to participate before com-mencement of the tests, leaving 40 patients (20 in each sample) that completed the study. Patient char-acteristics concerning the two samples are presented in Table 1. One patient in Sample 1 was not able to complete the last test (stair-climb test) in the second test session owing to fatigue; thus, 19 participants are included in the analysis on stair-climb test. Otherwise there was no missing data.As seen in Table 2, there were systematic differ-ences between the test results from rater A and B concerning the 20 metre walk test (0.32 seconds,  p  = 0.03) and stair-climb test (0.18 seconds  p  = 0.003). In the remaining tests, no significant differences Table 1.  Patient characteristics in two samples of patients three months after total hip replacement.Sample 1 ( n  = 20)Sample 2 ( n  = 20)Sex, men/women11/911/9Age, mean ±SD66.2 ± 8.268.4 ± 5.1BMI, mean ±SD (kg/m 2 )27.8 ± 4.128.0 ± 3.1THR side, right/left12/812/8 BMI: body mass index; THR: total hip replacement.  by guest on May 22, 2014cre.sagepub.comDownloaded from 
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