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O031 Repeatability of the Oxford Foot Model in hemiplegic cerebral palsy
Abstracts of the 17th Annual Meeting of ESMAC, Oral Presentations / Gait & Posture 28S (2008) S1–S48 coloured + clear area). For all measurements the total variability was similar to or better than that when using the conventional gait model.
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than the conventional model suggesting that good results might also be achieved by less experienced assessors. References [1] [2] [3] [4] [5] [6] [7] [8]
Lu & O’Connor J. J Biomech 1999; 32: 129–134. Charlton et al. Gait Posture 2004; 20: 213−21. Reinbolt et al. J Biomech 2005; 38: 621−6. Leardini et al. J Biomech 1999; 32: 99–103. Schwartz & Rozumalski J Biomech 2005; 38: 107−16. Camomilla et al. J Biomech 2006; 39: 1096–106. Noonan et al. J Pediatr Orthoped 2003; 23: 279−87. Gorton et al. Gait Posture 2008 In press.
O031 Repeatability of the Oxford Foot Model in hemiplegic cerebral palsy J. Stebbins1 , A. Zavatsky2 , N. Thompson1 , T. Theologis1 . 1 Oxford Gait Laboratory, Nuffield Orthopaedic Centre; 2 Engineering Science, Oxford University, UK
Figure 1.
Figure 2. Discussion: The new model performs very well particularly in relation to the within or between assessor variability which is around 2º or less across all variables. This presents excellent performance when compared with earlier studies of repeatability using the conventional gait model at a range of different centres [7,8]. Use of functional calibration techniques suggest that many of the variables will be less sensitive to assessor expertise
Summary: Repeatability of multi-segment foot kinematics was measured for the first time in a pathological condition. Children with hemiplegic cerebral palsy (CP) were found to have similar repeatability to healthy children. Conclusions: The Oxford Foot Model (OFM) has been designed to be adaptable in its application to measure different types of foot deformity. The results of this study show that it provides repeatable results in children with hemiplegic CP and associated foot deformity. To be distinguished from measurement artefact, changes in foot kinematics, as a result of intervention or as natural progression over time, must be greater than the repeatability reported here. Introduction: The OFM is a multi-segment, kinematic model that has been developed to assess dynamic motion of the foot. It has previously been assessed for repeatability in healthy populations (both adults and children) [1,2]. In order to determine the efficacy of the model for detecting foot deformity, it is important to know repeatability in pathological conditions. The aim of this study was to assess repeatability in children with hemiplegic CP. Patients/Materials and Methods: Sixteen children with hemiplegic CP were assessed (mean age 9.6 years, range 6−14 years; 11 male, 5 female; 9 left side and 7 right side affected). Fifteen healthy children (mean age 9.5 years, range 6−14 years; 10 female and 5 male) were also assessed. Data for the OFM [1] was collected during level walking using a 12 camera Vicon 612 system. Each child was measured on 3 occasions. Markers were applied, and data collected and processed by a single tester. A repeated measures of ANOVA was run, and the within-subject standard deviations calculated for each of 15 clinically relevant, kinematic variables (Figure 1). Results: Within-subject standard deviations were similar for the healthy and CP groups of children. In the transverse plane, the CP group tended to have lower variability than the healthy group. Maximum dorsiflexion in both stance and swing was more variable in the CP group than the healthy group. Overall, range of motion at the hindfoot and forefoot were less variable than maximum values. Discussion: In order to distinguish real change from measurement artefact, it is important to know the inherent repeatability of the measurement system. The results of this study show the variability in multi-segment foot kinematics from day to day in a pathological
S22
Abstracts of the 17th Annual Meeting of ESMAC, Oral Presentations / Gait & Posture 28S (2008) S1–S48
population. For a change in kinematics to be deemed important clinically, the difference in measured values between visits would need to exceed the repeatability values reported here.
Figure 1. References [1] Stebbins, J et al. (2006). Repeatability of a model for measuring foot kinematics in children. Gait & Posture, 23, 401−10. [2] Carson, M et al. (2001). Kinematic analysis of a multi-segment foot model for research and clinical applications: A repeatability analysis. J Biomech 34, 1299–307.
of 10 healthy children was used for reference (3 boys, 7 girls). Oxygen cost was assessed during a 5-minute walking test at a self-preferred, comfortable speed by means of a portable gasanalysis system (VmaxST). The measurements were repeated 2 times within a 4- to 6-week interval. Reliability was analyzed based on the following steps: (i) Standard Error of Measurement (SEM) values with regard to net oxygen cost data (J/kg/m) were calculated for the different GMFCS levels (Fig. 1), (ii) absolute subject differences between the 2 repeated measurements were plotted against the respective subject means, and (iii) Kendell’s t correlation coefficients were also calculated. If, from these pre-analyses, it was shown that heteroscedasticity was present, i.e. if a positive correlation was observed, then a logarithmic transformation of the data was done [4]. Results: Reliability analysis of net oxygen cost data showed increasing SEM values with increasing scores on the GMFCS (Figure 1). Furthermore, a positive, significant correlation (t = 0.280) between the absolute differences and the subject means was found, indicating that heteroscedasticity was present. Having taken the logarithms of these data, the correlation reduced numerically (t = 0.145).
O032 Variability of oxygen cost measurements is dependent on GMFCS level M.A. Brehm, V. Scholtes, A. Dallmeijer, J. Harlaar. Department of Rehabilitation Medicine, VU University Medical Center, The Netherlands Summary: This study assessed whether the variability of oxygen cost measurements in children with CP is dependent on the GMFCS level (range: I-III). Conclusions: Reliability levels of oxygen cost measurements are proportional to the mean. This so called heteroscedastic error can be avoided when the data is log transformed before reliability indices are calculated. In this way, reliability analysis and subsequent treatment decision-making can be carried out, being valid for all GMFCS levels. Introduction: In recent clinical gait studies, attention for optimizing the reliability of oxygen cost measurements in children with CP has markedly been increased [1,2]. Based on proposed optimization techniques, applied in small groups of mildly involved children (mainly GMFCS I), reliability is generally reported to be good [2,3]. Yet, whether these results warrant generalization to other GMFCS levels is uncertain, as these studies also indicate that variability of oxygen cost measurements might vary more, as GMFCS levels, and therewith, mean oxygen cost values, increase. If the variability is to increase with increasing mean cost values, the data is said to be heteroscedastic [4]. In such case, a different approach to reliability analysis would be needed. The purpose of this study was to assess whether the variability of oxygen cost measurements in children with CP is dependent on the magnitude of the mean, as classified by GMFCS level (range: I-III). Patients/Materials and Methods: Oxygen cost data was collected in 33 children with CP, with varying GMFCS levels (19 boys, 14 girls; GMFCS level I [n = 16], II [n = 7], III [n = 10]). A group
Figure 1. Variability of net oxygen cost increases with GMFCS level. Discussion: Although heteroscedasticity of oxygen cost data has never been examined, legitimate concerns have been expressed in the past [3]. These concerns were confirmed by the results of the present study, showing that variability of oxygen cost was proportional to the mean. This is in line with Nevill & Atkinson [4], who provided evidence that when assessing variability of outcome measures recorded on a ratio scale, heteroscedastic errors seem to be the norm. As such, it seems imperative that gait reliability studies in heterogeneous groups of children with CP always include an examination on how variability relates to the magnitude of the measurement mean. When, from such pre-analysis, heteroscedasticity is shown to be present, than the use of the log transformation is advocated. References [1] [2] [3] [4]
Schwartz 2007, Gait Posture 26: 494–500. Brehm et al 2008, Gait Posture 27(2): 196–201. Keefer et al 2005, Gait Posture 21: 80−4. Nevill & Atkinson 1997, Br J Sports Med 31: 314−8.
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than the conventional model suggesting that good results might also be achieved by less experienced assessors. References [1] [2] [3] [4] [5] [6] [7] [8]
Lu & O’Connor J. J Biomech 1999; 32: 129–134. Charlton et al. Gait Posture 2004; 20: 213−21. Reinbolt et al. J Biomech 2005; 38: 621−6. Leardini et al. J Biomech 1999; 32: 99–103. Schwartz & Rozumalski J Biomech 2005; 38: 107−16. Camomilla et al. J Biomech 2006; 39: 1096–106. Noonan et al. J Pediatr Orthoped 2003; 23: 279−87. Gorton et al. Gait Posture 2008 In press.
O031 Repeatability of the Oxford Foot Model in hemiplegic cerebral palsy J. Stebbins1 , A. Zavatsky2 , N. Thompson1 , T. Theologis1 . 1 Oxford Gait Laboratory, Nuffield Orthopaedic Centre; 2 Engineering Science, Oxford University, UK
Figure 1.
Figure 2. Discussion: The new model performs very well particularly in relation to the within or between assessor variability which is around 2º or less across all variables. This presents excellent performance when compared with earlier studies of repeatability using the conventional gait model at a range of different centres [7,8]. Use of functional calibration techniques suggest that many of the variables will be less sensitive to assessor expertise
Summary: Repeatability of multi-segment foot kinematics was measured for the first time in a pathological condition. Children with hemiplegic cerebral palsy (CP) were found to have similar repeatability to healthy children. Conclusions: The Oxford Foot Model (OFM) has been designed to be adaptable in its application to measure different types of foot deformity. The results of this study show that it provides repeatable results in children with hemiplegic CP and associated foot deformity. To be distinguished from measurement artefact, changes in foot kinematics, as a result of intervention or as natural progression over time, must be greater than the repeatability reported here. Introduction: The OFM is a multi-segment, kinematic model that has been developed to assess dynamic motion of the foot. It has previously been assessed for repeatability in healthy populations (both adults and children) [1,2]. In order to determine the efficacy of the model for detecting foot deformity, it is important to know repeatability in pathological conditions. The aim of this study was to assess repeatability in children with hemiplegic CP. Patients/Materials and Methods: Sixteen children with hemiplegic CP were assessed (mean age 9.6 years, range 6−14 years; 11 male, 5 female; 9 left side and 7 right side affected). Fifteen healthy children (mean age 9.5 years, range 6−14 years; 10 female and 5 male) were also assessed. Data for the OFM [1] was collected during level walking using a 12 camera Vicon 612 system. Each child was measured on 3 occasions. Markers were applied, and data collected and processed by a single tester. A repeated measures of ANOVA was run, and the within-subject standard deviations calculated for each of 15 clinically relevant, kinematic variables (Figure 1). Results: Within-subject standard deviations were similar for the healthy and CP groups of children. In the transverse plane, the CP group tended to have lower variability than the healthy group. Maximum dorsiflexion in both stance and swing was more variable in the CP group than the healthy group. Overall, range of motion at the hindfoot and forefoot were less variable than maximum values. Discussion: In order to distinguish real change from measurement artefact, it is important to know the inherent repeatability of the measurement system. The results of this study show the variability in multi-segment foot kinematics from day to day in a pathological
S22
Abstracts of the 17th Annual Meeting of ESMAC, Oral Presentations / Gait & Posture 28S (2008) S1–S48
population. For a change in kinematics to be deemed important clinically, the difference in measured values between visits would need to exceed the repeatability values reported here.
Figure 1. References [1] Stebbins, J et al. (2006). Repeatability of a model for measuring foot kinematics in children. Gait & Posture, 23, 401−10. [2] Carson, M et al. (2001). Kinematic analysis of a multi-segment foot model for research and clinical applications: A repeatability analysis. J Biomech 34, 1299–307.
of 10 healthy children was used for reference (3 boys, 7 girls). Oxygen cost was assessed during a 5-minute walking test at a self-preferred, comfortable speed by means of a portable gasanalysis system (VmaxST). The measurements were repeated 2 times within a 4- to 6-week interval. Reliability was analyzed based on the following steps: (i) Standard Error of Measurement (SEM) values with regard to net oxygen cost data (J/kg/m) were calculated for the different GMFCS levels (Fig. 1), (ii) absolute subject differences between the 2 repeated measurements were plotted against the respective subject means, and (iii) Kendell’s t correlation coefficients were also calculated. If, from these pre-analyses, it was shown that heteroscedasticity was present, i.e. if a positive correlation was observed, then a logarithmic transformation of the data was done [4]. Results: Reliability analysis of net oxygen cost data showed increasing SEM values with increasing scores on the GMFCS (Figure 1). Furthermore, a positive, significant correlation (t = 0.280) between the absolute differences and the subject means was found, indicating that heteroscedasticity was present. Having taken the logarithms of these data, the correlation reduced numerically (t = 0.145).
O032 Variability of oxygen cost measurements is dependent on GMFCS level M.A. Brehm, V. Scholtes, A. Dallmeijer, J. Harlaar. Department of Rehabilitation Medicine, VU University Medical Center, The Netherlands Summary: This study assessed whether the variability of oxygen cost measurements in children with CP is dependent on the GMFCS level (range: I-III). Conclusions: Reliability levels of oxygen cost measurements are proportional to the mean. This so called heteroscedastic error can be avoided when the data is log transformed before reliability indices are calculated. In this way, reliability analysis and subsequent treatment decision-making can be carried out, being valid for all GMFCS levels. Introduction: In recent clinical gait studies, attention for optimizing the reliability of oxygen cost measurements in children with CP has markedly been increased [1,2]. Based on proposed optimization techniques, applied in small groups of mildly involved children (mainly GMFCS I), reliability is generally reported to be good [2,3]. Yet, whether these results warrant generalization to other GMFCS levels is uncertain, as these studies also indicate that variability of oxygen cost measurements might vary more, as GMFCS levels, and therewith, mean oxygen cost values, increase. If the variability is to increase with increasing mean cost values, the data is said to be heteroscedastic [4]. In such case, a different approach to reliability analysis would be needed. The purpose of this study was to assess whether the variability of oxygen cost measurements in children with CP is dependent on the magnitude of the mean, as classified by GMFCS level (range: I-III). Patients/Materials and Methods: Oxygen cost data was collected in 33 children with CP, with varying GMFCS levels (19 boys, 14 girls; GMFCS level I [n = 16], II [n = 7], III [n = 10]). A group
Figure 1. Variability of net oxygen cost increases with GMFCS level. Discussion: Although heteroscedasticity of oxygen cost data has never been examined, legitimate concerns have been expressed in the past [3]. These concerns were confirmed by the results of the present study, showing that variability of oxygen cost was proportional to the mean. This is in line with Nevill & Atkinson [4], who provided evidence that when assessing variability of outcome measures recorded on a ratio scale, heteroscedastic errors seem to be the norm. As such, it seems imperative that gait reliability studies in heterogeneous groups of children with CP always include an examination on how variability relates to the magnitude of the measurement mean. When, from such pre-analysis, heteroscedasticity is shown to be present, than the use of the log transformation is advocated. References [1] [2] [3] [4]
Schwartz 2007, Gait Posture 26: 494–500. Brehm et al 2008, Gait Posture 27(2): 196–201. Keefer et al 2005, Gait Posture 21: 80−4. Nevill & Atkinson 1997, Br J Sports Med 31: 314−8.