- Email: [email protected]
Early development of the Standing-start 180° Turn Test
Physiotherapy 91 (2005) 6–13
Early development of the Standing-start 180◦ Turn Test Emma Stacka,b,∗ , Ann Ashburna a
Movement Disorders Group, School of Health Professions and Rehabilitation Sciences, University of Southampton, Southampton, UK Rehabilitation Research Unit, Southampton General Hospital, Mailpoint 886, E Level, Tremona Road, Southampton SO166YD, UK
b
Abstract Objectives To design and validate a new video-based tool for quantifying turning during gait in people with Parkinson’s Disease. Dysfunctional turning is common in Parkinson’s Disease but most existing measurement tools are inadequate for this group, lack validity and are laboratorybased. Design Descriptors of turning were identified and the new tool, the Standing-start 180◦ Turn Test (SS-180), was derived from a short-list. Criterion validity was tested using Cartesian Optoelectronic Dynamic Anthropometry (CODA) as the criterion measure, and intra-rater and inter-rater reliability were tested. Participants Thirty-two healthy adults (aged 21–83 years) and eight people with Parkinson’s Disease (aged 69–85 years). Results Seventy descriptors were identified and 20 were short-listed and combined to form four items: Turning Steps, Turn Time, Turn Type and Turn Quality. Time measurements from video and CODA agreed within 0.5 s on 95% of occasions in healthy adults and within 20% of each other in people with Parkinson’s Disease; there was 92% agreement on Turning Steps and 84% agreement on Turn Type. Intra-rater reliability was 100% for Turning Steps, Turn Type and Turn Quality; mean Turn Time difference 0.1 s (95% limits of agreement −0.3 to 0.1 s). Inter-rater reliability was 80% for Turning Steps, 100% for Turn Type and 90% for Turn Quality; mean Turn Time difference 0.0 s (95% limits of agreement −0.4 to 0.5 s). Conclusions The video-based SS-180 was developed for measurement in Parkinson’s Disease. Preliminary studies suggest that the simple turn test compares well with a laboratory-based criterion measure, and that reliability exceeds similar existing observational analysis tools. © 2004 Chartered Society of Physiotherapy. Published by Elsevier Ltd. All rights reserved. Keywords: Turning; Parkinson’s Disease; SS-180; Validity; Reliability
Background A loss of continuity and/or stability when attempting to turn is common in Parkinson’s Disease. Several Parkinson’sDisease-specific scales require an assessment of turning ‘readiness’ [1], ‘regularity’ [2], ‘effort’ [3] or ‘difficulty’ [4]. Turning is associated with freezing [5] and falling [6–8], and also with hip fracture [9], if the Parkinsonian faller’s protective reactions are compromised so that the impact to the femur is not dissipated [10–13]. Mobility deficits and frequent falls may lead to a referral to physiotherapy but turning has been poorly described in comparison with straight forward gait, so there is no standard protocol by which a therapist can assess an individual’s ability to turn. Most assessments of turning, if made at all, are based on informal observation, perhaps dur∗
Corresponding author. E-mail address: [email protected] (E. Stack).
ing a mobility assessment such as the Timed Up and Go Test [14]. There is little available information to suggest what a therapist might record following such an assessment or how the findings might guide management. Turning remains inadequately understood. Most research has involved small samples of young, healthy volunteers [15–21]. The emphasis has been on counting steps and/or timing turning [22–24]. Some measures require a judgement as to whether a turn is normal or not (e.g. Tinetti et al. [25]), but there is insufficient research to define what constitutes normality and such guesswork is unnecessary if one describes instead an observed turn [26–28]. Existing measures are inadequate; most lack validity [25,28,29] and tend to be laboratory based, sketchy and prescriptive. As people with Parkinson’s Disease show ‘poor correspondence between behaviour in real life and performance in the laboratory’ [12], laboratorybased research is largely unsuitable, e.g. turning when cued or on a walkway or force plate (e.g. Morris et al. [16])
0031-9406/$ – see front matter © 2004 Chartered Society of Physiotherapy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.physio.2004.07.003
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reveals little about normal timing or foot placement. A more comprehensive tool is required that is more than a record of steps and time, usable in the research, clinical and domestic environments and does not restrict how someone turns. A video-based tool would be appropriate as acceptable reliability has been reported [30,31]. Turning from a standing start when ready would not impose or even restrict the choice of: (1) turn initiation speed or direction, (2) foot placement or (3) the area covered while turning; criticisms, that can be levelled at more prescriptive protocols [28,29]. Standing-start turns (i.e. from standing to walking via turning) have greater ecological validity than walking 180◦ turns or on-the-spot turns, being part of the normal repertoire of everyday activities that challenge balance [32]. Whilst walking 180◦ turns or on-the-spot turns have been widely studied, these actions are rarely performed in the real world. Standingstart turns, on the other hand, are used frequently during functional tasks, e.g. turning to walk away from a sink after washing or doing the washing up, from a post box or post-office counter, or with something selected from a cupboard or off a shelf. Laboratory-based research investigations have largely addressed the transition from walking to turning but are inappropriate for people with Parkinson’s Disease, as terminating straight forward gait to manage the transition into turning is an added complication. The protocol for a standing-start turn is entirely novel. The purposes of this study were to design a tool that would facilitate the assessment and recording of how people turn, and promote better understanding of dysfunctional turning in Parkinson’s Disease, validate it against a gold standard and test reliability. The study was conducted in two phases: in Phase 1, descriptors of turning were identified and shortlisted, and the new tool was derived; and in Phase 2, criterion validity, intra-rater reliability and inter-rater reliability were tested. Phase 1: generation of items and tool design Methods The first step in designing the new tool was to identify descriptors of turning (i.e. terms applied to turning, components of turning or the ability to turn) for possible incorporation into the Standing-start 180◦ Turn Test (SS-180) as variables (e.g. ‘head rotation’) or features of the protocol (e.g. ‘assistance’). Five sources were searched to provide a range of perspectives on turning: the literature, existing video recordings, six movement researchers, four physiotherapists working with elderly in-patients and people with Parkinson’s Disease who had difficulty turning. • The literature was searched for measures of turning or that mentioned turning. • The lead researcher made observations from video on how 25 people with and without Parkinson’s Disease turned during the Timed Up and Go Test [14].
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• Researchers debated which components of turning could be assessed from video. • Before and after watching 12 video recordings, therapists were asked what they assess when observing patients with difficulty turning. • Descriptors were extracted from verbatim descriptions of difficulty turning by people with Parkinson’s Disease [10,27]. The next step was to reduce the descriptors to a manageable short-list from which to draft the SS-180. To produce the short-list, six researchers experienced in movement analysis were asked individually to indicate which third of the descriptors they considered to be the most important aspects of turning and which third they considered could best be assessed from video. Each researcher was given a form containing three columns; the descriptors were listed in the first column, while columns two and three consisted of tick boxes for ‘important’ and ‘measurable’, respectively. When all six researchers had indicated which descriptors they considered to be most important and measurable from video, a descriptor was short-listed if it had been considered to be important by half of the researchers and measurable by the majority. The final step was to draft the new tool. Decisions were made as to whether each short-listed descriptor should be combined with another or form a distinct item on the SS180, and whether criterion validity and reliability could be tested. Results Seventy descriptors of turning were identified (Table 1): of the 70, 28 were considered to be important by half of the researchers who voted and 31 were considered to be measurable from video by the majority of the researchers, but only 20 descriptors met both short-listing criteria. The 20 short-listed descriptors were combined to form: • • • • • • • •
Turning Steps (Descriptors 23 and 41) Turn Type (12, 28 and 40) Ground Clearance (33, 42, 49 and 68) Continuity (21 and 62) Turn Time (27 and 47) Independence (38 and 52) Stability (3, 15 and 39) Posture (35)
Five of these items (Independence, Ground Clearance, Stability, Continuity and Posture) were grouped to form a composite measure of Turn Quality. The other short-listed descriptor (50: Turns Both Ways) was incorporated into the protocol: participants would turn once in each direction, with a mean score calculated for Turning Steps, Turn Time and Turn Quality (see Appendix A). The SS-180 protocol is as follows (see Fig. 1):
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1. Adopt starting position: subjects are shown the position of a video camera (the target): they then stand approximately 2–3 m from the target, facing away from it. 2. Perform direction-unspecified turn: subjects are instructed ‘When you are ready, please walk towards the target’. The assessor notes the direction in which the subjects turn. Subjects return to the starting position and are told in which direction they had turned during the directionunspecified turn. 3. Perform direction-specified turn: they are asked to repeat the procedure and are instructed ‘Making a point of going round the other way this time, when you are ready, please walk towards the target’.
Table 1 Descriptors identified (20 short-listed descriptors highlighted)
Phase 2: validity and reliability testing
From video review 30. Stability 31. Fluency 32. Base width
33. Ground clearance 34. Arm swing 35. Posture
36. Head rotation 37. Number of steps
From researchers 38. Use of support
40. Turn Type 41. Number of steps
42. Reduced heel strike 43. Use of space
49. Heel strike 50. Turns both ways 51. Continuity
54. Balance reactions 55. Step length 56. Needs assistance
52. Can turn 53. Foot movement
57. Foot positions 58. Weight transference
63. Decreased initiation 64. Foot clearance 65. Speed of turning
67. Maintains balance 68. Feet get tangled 69. Feet moved
66. Takes several steps
70. Loss of balance
Methods With multiple items to be rated during turning (Steps, Time, Type and Quality), video recording overcomes some of the problems associated with naked eye evaluation [33]. Videos can be viewed repeatedly so that one item can be rated per playback, and they facilitate reliability testing within and between raters. Although, with one exception [34], the existing observational assessments of turning have not been validated against an external criterion measure, two preliminary investigations were conducted during the development of the SS-180 to evaluate how video-based analysis compared with a laboratory-based gold standard. Toro et al. [33] described criterion validity as the ‘highest level of tool validity’ and defined it as ‘the degree to which the assessment made using the tool reflects actual events’. The Cartesian Optoelectronic Dynamic Anthropometry (CODA) motion analysis system (Charnwood Dynamics, Leicester, UK) was chosen as the criterion measure because it is an accurate way of recording movement [35] that does
From literature 1. Turning is difficult 2. Turns effortlessly 3. Unsteadiness as turns 4. Turns regularly 5. Turns readily 6. Turn Time slowing 7. Ability to turn 8. Turns very slowly 9. Initiation of turning 10. Clumsy
39. Apparent instability From physiotherapists 44. Trunk rotation 45. Turning circle 46. Posture and head rotation 47. Time taken 48. Arm swing From people with PD 59. Attention 60. Environment 61. Fearful when turning 62. Freezes or feet stick
11. Effort of turning 12. Steps backwards 13. Pivots when turning 14. Steps in an arc 15. Grabs, staggers or holds 16. Step continuity 17. Sideways or back steps 18. Unsteadiness 19. Turns normally
21. Continuous with walking 22. Can look behind 23. Number of steps 24. Weight-shifts well 25. Needs supervision 26. Able to turn safely 27. Speed of turning 28. Festinant steps 29. Moves forwards
20. Staggering
PD, Parkinson’s Disease.
Fig. 1. Example of a standing-start turn (toward type turn to the left): (A) starting position, (B) completion of first Turning Step, onset of second, and (C) completion of second Turning Step, onset of first straight forward step towards target.
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not hinder the way in which the subject moves. The system uses active markers that are tracked (200 times per second in these studies) during movement by a scanner unit linked to a computer. The markers (attached to matchbox-sized battery packs) are attached quickly and easily to the subject using double-sided tape. Turning Steps, Turn Time and Turn Type could be validated against CODA because identical parameters could be measured from video and the criterion measure, but Turn Quality could not be validated in this way during the development of the SS-180: while two of the constituent items (Ground Clearance and Continuity) could be validated against CODA, Independence, Stability and Posture need to be validated against an external criterion based on expert opinion or consensus. At this early stage in test development, it was inappropriate to consider any opinion ‘expert’. The video recordings used in this phase of the study were drawn from those collected during an investigation into how people with and without Parkinson’s Disease turn [36]. Participants completed the SS-180 in a laboratory, while their turns were recorded by video and CODA. The camera and scanner were stacked in the position of the target towards which participants walked during the test. Four CODA markers were attached to the participants’ footwear, on the midline of each heel and over each great toe (Fig. 2). Testing criterion validity To test the validity of measuring Turning Steps and Turn Type from video, a set of 20 videos was selected from the records available. The lead researcher rated the CODA output (Fig. 3), counting a Turning Step if the markers from one foot were repositioned while the markers from the other remained on the floor, until the markers indicated the onset of the first straight forward step towards the target. Turn Type was ascertained from the movement of the markers, i.e. the definition of Turn Type that best matched the magnitude and direction of each Turning Step was selected. To minimise bias, an independent researcher, trained on a different set of records, rated Turning Steps and Turn Type from video us-
Fig. 2. Placement of CODA markers on one foot.
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Fig. 3. Example of CODA output (a Toward Type Turn of 1.3 s). (i) The onset of the first Turning Step (at ↑ (a)), 1.5 s after the subject was instructed to begin the test ‘when ready’ (at which point, both heel markers were 16 cm behind the ‘origin’ set for CODA); the completion of the first Turning Step (at ↑ (b)), 0.5 s later, by which point the right heel marker had advanced 30 cm towards the target and the onset of the second and final Turning Step (at ↑ (c)), 0.9 s into the test (at this point, both heel markers were lost from the scanner’s view, as the subject was now facing the target and the scanner was recording toe markers). (ii) The cyclical movement of toe markers towards the target, characteristic of straight forward gait. The completion of the final Turning Step is shown (at ↑ (a)) at 2.8 s and 80 cm behind the CODA origin (i.e. a Turn Time of 1.3 s, covering 64 cm of the distance to the target) and the initiation of the first straight forward step. The completion of the first straight forward step is shown (at ↑ (b)), a step of approximately 1 m in length.
ing the guidelines. The strength of agreement between video and CODA was estimated using the Kappa measure (k), as recommended by Altman [37], interpreted as per Landis and Koch [38]. To test the validity of Turn Time, 10 more videos were selected from the records available. Turning was timed from the CODA output (showing marker movement) from the onset of the first Turning Step to the onset of the first straight forward step toward the target (see Fig. 3). Turning was timed from video as per the rating guidelines. The strength of agreement between video and CODA was estimated using the method for continuous data [39] in which the difference between measures is plotted against their mean, with the mean ± 2 standard deviations defining the 95% limits of agreement, i.e. agreement in most cases.
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Testing reliability To test reliability, 10 more videos were selected from the records available. To establish the reliability with which the lead researcher rated the video-based SS-180, she rated the turns (Rating A-1) then repeated the procedure 1 week later (Rating A-2): Ratings A-1 and A-2 were compared. Another trained researcher rated the same turns (Rating B) to establish the reliability with which she and the lead researcher rated the test: Ratings A-1 and B were compared. Again, the agreement between ratings was estimated using the method recommended by Bland and Altman [39].
0.1 s (±0.1), 95% limits of agreement −0.3 to 0.1 s (Table 2). Inter-rater reliability was also acceptable. There was good agreement on Turning Steps (80%; kw = 0.70), with a one-step discrepancy on just two turns. There was 100% agreement on Turn Type and very good agreement on Turn Quality (90%; k = 0.82), with a one-point discrepancy on just one turn. The mean difference in Turn Times was 0.0 s (±0.2), 95% limits of agreement −0.4 to 0.5 s (Table 2).
Results
The lack of an appropriate measure with which to evaluate turning and communicate the findings made it necessary to develop the SS-180, which it is envisaged will facilitate research on dysfunctional turning in Parkinson’s Disease. The simple test provides a comprehensive assessment of turning and is already in use. Results are meaningful and easily communicated: compare ‘incremental turns in both directions, an average of five steps in 2.6 s, less than maximal quality’ with ‘turning appears normal’ or ‘on a five-point scale, scores two’. As people with Parkinson’s Disease often report that turning in one direction is particularly difficult, an assessment of turning in only one freely-chosen direction is likely to be an assessment of turning the preferred way. If only one turn is assessed, a subject assessed on two occasions may turn in different directions, making the results difficult to compare. Protocols that impose one direction of turning on subjects, often the case with laboratory set-ups, are equally difficult to interpret, as some subjects will have turned in their preferred direction while others will not. One advantage of the SS-180 is that subjects must turn both ways before a mean is recorded for Turning Steps, Turn Time and Turn Quality. As yet, there is no accepted terminology for turning (the equivalent of ‘the gait cycle’) so there is no consensus as to what constitutes a turning step, e.g. Simpson et al. [29] counted attempts to shift the body weight, successful or not, with alternate feet. They did not report their reliability and neither did Lipsitz et al. [23] who counted steps and timed turning. With the SS-180, we achieved much better inter-rater reliability using the standard protocol for turn analysis than in an earlier study in which we used less-structured movement analysis [26]. Following preliminary investigations, our Turning Step and Turn Time definitions appear robust. Counting steps from video was a valid and reliable approximation of the count made using CODA. Timing from video generated results consistent with the literature. Thigpen et al. [28] reported similar inter-rater agreement for counting turning steps and timing turning from video (k = 0.67 and 0.90, respectively). This was, however, after repeated testing on the same set of videos and the categorisation of continuous data. Others have reported intra-class correlation coefficients (ICCs) of 0.8 [30] and 0.95 [31], respectively, when timing turning from video. Our Turn Type definitions appeared robust: the structured protocol and/or detailed rating guidelines may have con-
Criterion validity The Turning Steps and Turn Type sample consisted of 20 people aged from 27 to 83 years: a faulty CODA marker meant that one record (two turns) could not be analysed. A weighted Kappa (kw ) was calculated for the Turning Step count: initial comparison revealed moderate agreement (71%; kw = 0.57), with a one-step discrepancy on 11 turns. Repeating the ratings using a modified Turning Step definition improved agreement and revealed very good agreement (92%; kw = 0.86), with a one-step discrepancy on just three turns. Comparing Turn Types rated from CODA and video revealed good agreement (84%; k = 0.78). The Turn Time sample consisted of five people with Parkinson’s Disease and five without, aged from 28 to 85 years. Video and CODA agreed well in healthy adults: mean Turn Time difference 0.0 s (±0.2), 95% limits of agreement −0.5 to 0.5 s. The difference increased with the mean in Parkinson’s Disease, so considering the differences as proportions, a CODA timing would be likely to lie within 20% of a video timing. Reliability The reliability sample consisted of three people with mild to moderate Parkinson’s Disease and seven without, aged from 21 to 85 years. Intra-rater reliability was acceptable: 100% agreement between the ratings of Turning Steps, Turn Type and Turn Quality; mean difference in Turn Times of Table 2 Reliability results—time (seconds) Subject 1 2 3 4 5 6 7 8 9 10 Mean
Rating A-1 Rating A-2 Difference to A-1 1.4 1.2 −0.2 1.1 1.0 −0.1 1.5 1.4 −0.1 1.4 1.0 −0.4 1.3 1.2 −0.1 1.6 1.5 −0.1 1.7 1.7 0.0 1.8 1.8 0.0 2.5 2.3 −0.2 6.9 6.8 −0.1 0.1 (±0.1)
Rating B Difference to A-1 1.5 0.1 1.2 0.1 1.3 −0.2 1.7 0.3 1.2 −0.1 1.5 −0.1 1.3 −0.4 2.1 0.3 2.6 0.1 7.1 0.2 0.0 (±0.2)
Discussion
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tributed to our achieving better inter-rater reliability than in earlier studies [26,28]. Hase and Stein [17] found that the turn type deployed during walking turns (either a ‘spin turn’ or a ‘step turn’) was dependent on the leg leading when the cue to turn was given. The SS-180 gives a free choice of leg with which to take the first turning step; by not imposing the choice on the subject, the test may promote a more natural turn than do other protocols. Turn Quality demonstrated acceptable reliability and compares favourably with published agreement on ‘stability’ (k = 0.76), and ‘the use of support’ (k = 0.91) [26] and ‘staggering’ (k = 0.71) [28]. Future studies are required to externally validate the video analysis of Turn Quality in its entirety. Being video based, the SS-180 is usable in environments other than the laboratory if there is sufficient space between the subject and his or her target. In too confined a space, the subject may need, or feel the need, to turn on-the-spot and then walk towards the target. The test was designed to discourage such a contrived manoeuvre: the instructions omit the word ‘turn’ in an attempt to focus the subject on walking to the target, rather than providing an auditory cue to turn. The preliminary studies encompassed a range of participants but were small for two reasons. Firstly, different sub-sets of video recordings were used for training and in each study; using the whole set each time would have given misleading estimates of agreement if assessors became too familiar with the data, introducing bias. Secondly, as the studies were completed early in the tool’s development and were laboratory based, it was not appropriate to recruit a large number of people with Parkinson’s Disease: experience has shown that they find travel to the laboratory daunting and that their performances are a poor reflection of real life. Importantly, if the studies had revealed that the videobased SS-180 lacked validity or reliability, immediate refinements could have been made. Instead, the encouraging early findings suggest that the test is workable and provide a starting point for its further development, testing and refinement. The SS-180 has already been used for research purposes with a large number of people with Parkinson’s Disease in their homes [36], the purpose for which it was developed, and evidence supporting the tool’s construct validity is emerging. The SS-180 would benefit from abbreviation before it is suitable for routine clinical application. Even so, we recommend that the standing-start protocol supersedes the walking or on-the-spot turns commonly assessed informally in current clinical settings.
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Conclusions The SS-180 overcomes many of the disadvantages of existing measures of turning. It is ecologically valid, usable in a range of environments (being video based) and simple to complete, and it provides a comprehensive assessment of turning 180◦ in both directions: the results are meaningful and easy to communicate. Findings suggest that the SS-180 is valid and reliable; further study is required to validate Turn Quality, which was not appropriate for validation against a laboratory-based criterion. The small preliminary investigations into validity and reliability were integral parts of early development and require repetition during the test’s further development. The SS-180 is suitable for research purposes and we recommend the standing-start protocol for use in the informal assessment of turning that is commonly attempted clinically.
Key messages • The SS-180 is a simple yet comprehensive test of turning in each direction, measuring Turning Steps, Turn Time, Turn Type and Turn Quality. • Video-based analysis of the SS-180 generates valid findings comparable to those from an external criterion measure, with acceptable reliability. • The SS-180 is suitable for research purposes, being ecologically valid and deployable in a range of environments.
Ethical approval Southampton and South West Hampshire Joint Research Ethics Committee and The North and Mid Hampshire Local Research Ethics Committee.
Acknowledgements Funding: Research Training Fellowship (RDF 081) from the NHS South East Region.
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Appendix A The SS-180 scoring form and rating guidelines
Enter data in the highlighted boxes following the Rating Guidelines, one observation of the video recording per item rated. Rate the direction-unspecified (DU) turn and the direction-specified (DS) turn, and then calculate mean scores for Turning Steps, Turn Time and Turn Quality (i.e. [DU + DS]/2).
SS-180 Rating Guidelines Turning Steps (foot movements rotating subject through 180◦ to face target). Count each foot movement during turning. Do not count first walking step (i.e. first step to target, predominantly unidirectional from toe-off). Turn Time (time from initiation to completion of Turning Steps). Start watch when first Turning Step begins. Stop watch when last Turning Step complete. Record mean of five timings. Turn Type. Choose which definition best fits turn observed. Toward: 2 Turning Steps. Initiated with same foot as direction of turn. Direct advance to target; negligible lateral deviation. Pivotal: 2–3 Turning Steps. Initial step wider than it is long, followed by wide second step. Lateral: 2–3 Turning Steps. Initiated with foot opposite to direction of turn. Incremental: Turning on-the-spot before advancing to target. Delayed Onset: 4+ Turning Steps. Initial steps with each foot make negligible advance to target or in changing direction. Turn Quality. For each question, if answer is ‘yes’ score 0; if answer is ‘no’ score 1. Independence: Did subject require external support, walking aid or help (physical or verbal) from another person?
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Ground Clearance: Did both feet clear ground and each other throughout turn except when pivoting to change direction during one Turning Step? Continuity: Was there a pause during turning or after turning before advancing towards target? Posture: Did subject become clearly more flexed during turn than when they began test; did they lower their height? Stability: Did subject appear unstable or at risk of falling when turning; did they or an attendant make any saving reactions? References [1] Lieberman A. Parkinson’s Disease: a clinical review. Am J Med Sci 1974;267:66–80. [2] Yahr M, Duvoisin R, Schear M. Treatment of parkinsonism with levodopa. Arch Neurol 1969;21:343–54. [3] Webster D. Critical analysis of the disability in Parkinson’s Disease. Mod Treat 1968;5:257. [4] Canter G, De la Torre R, Mier M. A method for evaluating disability in patients with Parkinson’s Disease. J Nerv Ment Dis 1961;133:143–7. [5] Giladi N, McMahon D, Przedborski S. Motor blocks in Parkinson’s Disease. Neurology 1992;42:333–9. [6] Bloem B, van Vugt J, Beckley D. Postural instability and falls in Parkinson’s Disease. Adv Neurol 2001;87:209–23. [7] Charlett A, Weller C, Purkiss A, Dobbs S, Dobbs R. Breadth of base whilst walking: effect of ageing and parkinsonism. Age Ageing 1998;27:49–54. [8] Nieuwboer A, De Weerdt W, Dom R, Lesaffre E. A frequency and correlation analysis of motor deficits in Parkinson patients. Disab Rehabil 1998;20:142–50. [9] Cummings S, Nevitt M. A hypothesis: the causes of hip fractures. J Geront 1989;44:M107–11. [10] Stack E, Ashburn A. Fall-events described by people with Parkinson’s Disease: implications for clinical interviewing and the research agenda. Physiol Res Int 1999;4:190–200. [11] Tinetti M. Prevention of falls and fall injuries in elderly people: a research agenda. Prev Med 1994;23:756–62. [12] Yekutiel M. Patients fall records as an aid to designing and assessing therapy in parkinsonism. Disab Rehabil 1993;15:189–93. [13] Johnell O, Melton L, Atkinson E, O’Fallon W, Kurland L. Fracture risk in patients with parkinsonism: a population-based study in Olmstead County, Minnesota. Age Ageing 1992;21:32–8. [14] Podsiadlo D, Richardson S. The timed up and go: a test of basic functional mobility for frail elderly persons. J Am Geriatr Soc 1991;39:142–8. [15] Imai T, Moore S, Raphan T, Cohen B. Interaction of the body, head and eyes during walking and turning. Exp Brain Res 2001;136:1–18. [16] Morris M, Huxham F, McGinley J, Dodd K, Iansek R. The biomechanics and motor control of gait in Parkinson’s Disease. Clin Biomech 2001;16:459–70. [17] Hase K, Stein R. Turning strategies during human walking. J Neurophysiol 1999;81:2914–22. [18] Patla A, Adkin A, Ballard T. Online steering: co-ordination and control of body centre of mass, head and body reorientation. Exp Brain Res 1999;129:629–34. [19] Grasso R, Prevost P, Ivanenko Y, Berthoz A. Eye-head co-ordination for the steering of locomotion in humans: an anticipatory synergy. Neurosci Lett 1998;253:115–8. [20] Grasso R, Assaiante C, Prevost P, Berthoz A. Development of anticipatory orienting strategies during locomotor tasks in children. Neurosci Biobehav Rev 1998;22:533–9.
[21] Grasso R, Glasauer S, Takei Y, Berthoz A. The predictive brain: anticipatory control of head direction for the steering of locomotion. NeuroReport 1996;7:1170–4. [22] Imms F, Edholm O. Studies of gait and mobility in the elderly. Age Ageing 1981;10:147–56. [23] Lipsitz L, Jonsson P, Kelley M, Koestner J. Causes and correlates of recurrent falls in ambulatory frail elderly. J Geront 1991;46:M114–22. [24] Schenkman M, Shipp K, Chandler J, Studenski S, Kuchibhatla M. Relationships between mobility of axial structures and physical performance. Phys Ther 1996;76:276–85. [25] Tinetti M. Performance-orientated assessment of mobility problems in elderly patients. J Am Geriatr Soc 1986;34:119–26. [26] Stack E, Jupp K, Ashburn A. Developing methods to evaluate how people with Parkinson’s Disease turn 180◦ : an activity frequently associated with falls. Disab Rehabil 2004;26:478–84. [27] Ashburn A, Stack E, Jupp K. Movement strategies used by people with Parkinson’s Disease during activities associated with falls. Final Report to the Sir Jules Thorn Charitable Trust, UK; 2001. [28] Thigpen M, Light K, Creel G, Flynn S. Turning difficulty characteristics of adults aged 65 years or older. Phys Ther 2000;80:1174– 87. [29] Simpson J, Worsfold C, Reilly E, Nye N. A standard procedure for using TURN180: testing dynamic postural stability among elderly people. Physiotherapy 2002;88:342–53. [30] Schenkman M, Cutson T, Kuchibhatla M, Chandler J, Pieper C. Reliability of impairment and physical performance measures for persons with Parkinson’s Disease. Phys Ther 1997;77:19–27. [31] Suteerawattanon M, Protas E. Reliability of outcome measures in individuals with Parkinson’s Disease. Physio Theor Pract 2000;16:211–8. [32] Patla A, Frank J, Winter D. Balance control in the elderly: implications for clinical assessment and rehabilitation. Can J Pub Health 1992;83:S29–33. [33] Toro B, Nester C, Farren P. A review of observational gait assessment in clinical practice. Physio Theor Pract 2003;19:137–49. [34] Berg K, Wood-Dauphinee S, Williams J, Maki B. Measuring balance in the elderly: validation of an instrument. Can J Pub Health 1992;83:S7–11. [35] Mitchelson D. Proceedings of the First World Congress of Biomedics-Imaged-based Motion Analysis, vol. 1356, 1990. p. 26–37. [36] Stack E. Movements used during turning and factors influencing the way in which people with Parkinson’s Disease turn. Ph.D. Thesis, University of Southampton; 2003. [37] Altman D. Practical statistics for medical research. London: Chapman & Hall; 1991 [chapter 14]. [38] Landis J, Koch G. The measurement of observer agreement for categorical data. Biometrics 1977;33:159–74. [39] Bland J, Altman D. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986;I: 307–10.
Early development of the Standing-start 180◦ Turn Test Emma Stacka,b,∗ , Ann Ashburna a
Movement Disorders Group, School of Health Professions and Rehabilitation Sciences, University of Southampton, Southampton, UK Rehabilitation Research Unit, Southampton General Hospital, Mailpoint 886, E Level, Tremona Road, Southampton SO166YD, UK
b
Abstract Objectives To design and validate a new video-based tool for quantifying turning during gait in people with Parkinson’s Disease. Dysfunctional turning is common in Parkinson’s Disease but most existing measurement tools are inadequate for this group, lack validity and are laboratorybased. Design Descriptors of turning were identified and the new tool, the Standing-start 180◦ Turn Test (SS-180), was derived from a short-list. Criterion validity was tested using Cartesian Optoelectronic Dynamic Anthropometry (CODA) as the criterion measure, and intra-rater and inter-rater reliability were tested. Participants Thirty-two healthy adults (aged 21–83 years) and eight people with Parkinson’s Disease (aged 69–85 years). Results Seventy descriptors were identified and 20 were short-listed and combined to form four items: Turning Steps, Turn Time, Turn Type and Turn Quality. Time measurements from video and CODA agreed within 0.5 s on 95% of occasions in healthy adults and within 20% of each other in people with Parkinson’s Disease; there was 92% agreement on Turning Steps and 84% agreement on Turn Type. Intra-rater reliability was 100% for Turning Steps, Turn Type and Turn Quality; mean Turn Time difference 0.1 s (95% limits of agreement −0.3 to 0.1 s). Inter-rater reliability was 80% for Turning Steps, 100% for Turn Type and 90% for Turn Quality; mean Turn Time difference 0.0 s (95% limits of agreement −0.4 to 0.5 s). Conclusions The video-based SS-180 was developed for measurement in Parkinson’s Disease. Preliminary studies suggest that the simple turn test compares well with a laboratory-based criterion measure, and that reliability exceeds similar existing observational analysis tools. © 2004 Chartered Society of Physiotherapy. Published by Elsevier Ltd. All rights reserved. Keywords: Turning; Parkinson’s Disease; SS-180; Validity; Reliability
Background A loss of continuity and/or stability when attempting to turn is common in Parkinson’s Disease. Several Parkinson’sDisease-specific scales require an assessment of turning ‘readiness’ [1], ‘regularity’ [2], ‘effort’ [3] or ‘difficulty’ [4]. Turning is associated with freezing [5] and falling [6–8], and also with hip fracture [9], if the Parkinsonian faller’s protective reactions are compromised so that the impact to the femur is not dissipated [10–13]. Mobility deficits and frequent falls may lead to a referral to physiotherapy but turning has been poorly described in comparison with straight forward gait, so there is no standard protocol by which a therapist can assess an individual’s ability to turn. Most assessments of turning, if made at all, are based on informal observation, perhaps dur∗
Corresponding author. E-mail address: [email protected] (E. Stack).
ing a mobility assessment such as the Timed Up and Go Test [14]. There is little available information to suggest what a therapist might record following such an assessment or how the findings might guide management. Turning remains inadequately understood. Most research has involved small samples of young, healthy volunteers [15–21]. The emphasis has been on counting steps and/or timing turning [22–24]. Some measures require a judgement as to whether a turn is normal or not (e.g. Tinetti et al. [25]), but there is insufficient research to define what constitutes normality and such guesswork is unnecessary if one describes instead an observed turn [26–28]. Existing measures are inadequate; most lack validity [25,28,29] and tend to be laboratory based, sketchy and prescriptive. As people with Parkinson’s Disease show ‘poor correspondence between behaviour in real life and performance in the laboratory’ [12], laboratorybased research is largely unsuitable, e.g. turning when cued or on a walkway or force plate (e.g. Morris et al. [16])
0031-9406/$ – see front matter © 2004 Chartered Society of Physiotherapy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.physio.2004.07.003
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reveals little about normal timing or foot placement. A more comprehensive tool is required that is more than a record of steps and time, usable in the research, clinical and domestic environments and does not restrict how someone turns. A video-based tool would be appropriate as acceptable reliability has been reported [30,31]. Turning from a standing start when ready would not impose or even restrict the choice of: (1) turn initiation speed or direction, (2) foot placement or (3) the area covered while turning; criticisms, that can be levelled at more prescriptive protocols [28,29]. Standing-start turns (i.e. from standing to walking via turning) have greater ecological validity than walking 180◦ turns or on-the-spot turns, being part of the normal repertoire of everyday activities that challenge balance [32]. Whilst walking 180◦ turns or on-the-spot turns have been widely studied, these actions are rarely performed in the real world. Standingstart turns, on the other hand, are used frequently during functional tasks, e.g. turning to walk away from a sink after washing or doing the washing up, from a post box or post-office counter, or with something selected from a cupboard or off a shelf. Laboratory-based research investigations have largely addressed the transition from walking to turning but are inappropriate for people with Parkinson’s Disease, as terminating straight forward gait to manage the transition into turning is an added complication. The protocol for a standing-start turn is entirely novel. The purposes of this study were to design a tool that would facilitate the assessment and recording of how people turn, and promote better understanding of dysfunctional turning in Parkinson’s Disease, validate it against a gold standard and test reliability. The study was conducted in two phases: in Phase 1, descriptors of turning were identified and shortlisted, and the new tool was derived; and in Phase 2, criterion validity, intra-rater reliability and inter-rater reliability were tested. Phase 1: generation of items and tool design Methods The first step in designing the new tool was to identify descriptors of turning (i.e. terms applied to turning, components of turning or the ability to turn) for possible incorporation into the Standing-start 180◦ Turn Test (SS-180) as variables (e.g. ‘head rotation’) or features of the protocol (e.g. ‘assistance’). Five sources were searched to provide a range of perspectives on turning: the literature, existing video recordings, six movement researchers, four physiotherapists working with elderly in-patients and people with Parkinson’s Disease who had difficulty turning. • The literature was searched for measures of turning or that mentioned turning. • The lead researcher made observations from video on how 25 people with and without Parkinson’s Disease turned during the Timed Up and Go Test [14].
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• Researchers debated which components of turning could be assessed from video. • Before and after watching 12 video recordings, therapists were asked what they assess when observing patients with difficulty turning. • Descriptors were extracted from verbatim descriptions of difficulty turning by people with Parkinson’s Disease [10,27]. The next step was to reduce the descriptors to a manageable short-list from which to draft the SS-180. To produce the short-list, six researchers experienced in movement analysis were asked individually to indicate which third of the descriptors they considered to be the most important aspects of turning and which third they considered could best be assessed from video. Each researcher was given a form containing three columns; the descriptors were listed in the first column, while columns two and three consisted of tick boxes for ‘important’ and ‘measurable’, respectively. When all six researchers had indicated which descriptors they considered to be most important and measurable from video, a descriptor was short-listed if it had been considered to be important by half of the researchers and measurable by the majority. The final step was to draft the new tool. Decisions were made as to whether each short-listed descriptor should be combined with another or form a distinct item on the SS180, and whether criterion validity and reliability could be tested. Results Seventy descriptors of turning were identified (Table 1): of the 70, 28 were considered to be important by half of the researchers who voted and 31 were considered to be measurable from video by the majority of the researchers, but only 20 descriptors met both short-listing criteria. The 20 short-listed descriptors were combined to form: • • • • • • • •
Turning Steps (Descriptors 23 and 41) Turn Type (12, 28 and 40) Ground Clearance (33, 42, 49 and 68) Continuity (21 and 62) Turn Time (27 and 47) Independence (38 and 52) Stability (3, 15 and 39) Posture (35)
Five of these items (Independence, Ground Clearance, Stability, Continuity and Posture) were grouped to form a composite measure of Turn Quality. The other short-listed descriptor (50: Turns Both Ways) was incorporated into the protocol: participants would turn once in each direction, with a mean score calculated for Turning Steps, Turn Time and Turn Quality (see Appendix A). The SS-180 protocol is as follows (see Fig. 1):
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1. Adopt starting position: subjects are shown the position of a video camera (the target): they then stand approximately 2–3 m from the target, facing away from it. 2. Perform direction-unspecified turn: subjects are instructed ‘When you are ready, please walk towards the target’. The assessor notes the direction in which the subjects turn. Subjects return to the starting position and are told in which direction they had turned during the directionunspecified turn. 3. Perform direction-specified turn: they are asked to repeat the procedure and are instructed ‘Making a point of going round the other way this time, when you are ready, please walk towards the target’.
Table 1 Descriptors identified (20 short-listed descriptors highlighted)
Phase 2: validity and reliability testing
From video review 30. Stability 31. Fluency 32. Base width
33. Ground clearance 34. Arm swing 35. Posture
36. Head rotation 37. Number of steps
From researchers 38. Use of support
40. Turn Type 41. Number of steps
42. Reduced heel strike 43. Use of space
49. Heel strike 50. Turns both ways 51. Continuity
54. Balance reactions 55. Step length 56. Needs assistance
52. Can turn 53. Foot movement
57. Foot positions 58. Weight transference
63. Decreased initiation 64. Foot clearance 65. Speed of turning
67. Maintains balance 68. Feet get tangled 69. Feet moved
66. Takes several steps
70. Loss of balance
Methods With multiple items to be rated during turning (Steps, Time, Type and Quality), video recording overcomes some of the problems associated with naked eye evaluation [33]. Videos can be viewed repeatedly so that one item can be rated per playback, and they facilitate reliability testing within and between raters. Although, with one exception [34], the existing observational assessments of turning have not been validated against an external criterion measure, two preliminary investigations were conducted during the development of the SS-180 to evaluate how video-based analysis compared with a laboratory-based gold standard. Toro et al. [33] described criterion validity as the ‘highest level of tool validity’ and defined it as ‘the degree to which the assessment made using the tool reflects actual events’. The Cartesian Optoelectronic Dynamic Anthropometry (CODA) motion analysis system (Charnwood Dynamics, Leicester, UK) was chosen as the criterion measure because it is an accurate way of recording movement [35] that does
From literature 1. Turning is difficult 2. Turns effortlessly 3. Unsteadiness as turns 4. Turns regularly 5. Turns readily 6. Turn Time slowing 7. Ability to turn 8. Turns very slowly 9. Initiation of turning 10. Clumsy
39. Apparent instability From physiotherapists 44. Trunk rotation 45. Turning circle 46. Posture and head rotation 47. Time taken 48. Arm swing From people with PD 59. Attention 60. Environment 61. Fearful when turning 62. Freezes or feet stick
11. Effort of turning 12. Steps backwards 13. Pivots when turning 14. Steps in an arc 15. Grabs, staggers or holds 16. Step continuity 17. Sideways or back steps 18. Unsteadiness 19. Turns normally
21. Continuous with walking 22. Can look behind 23. Number of steps 24. Weight-shifts well 25. Needs supervision 26. Able to turn safely 27. Speed of turning 28. Festinant steps 29. Moves forwards
20. Staggering
PD, Parkinson’s Disease.
Fig. 1. Example of a standing-start turn (toward type turn to the left): (A) starting position, (B) completion of first Turning Step, onset of second, and (C) completion of second Turning Step, onset of first straight forward step towards target.
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not hinder the way in which the subject moves. The system uses active markers that are tracked (200 times per second in these studies) during movement by a scanner unit linked to a computer. The markers (attached to matchbox-sized battery packs) are attached quickly and easily to the subject using double-sided tape. Turning Steps, Turn Time and Turn Type could be validated against CODA because identical parameters could be measured from video and the criterion measure, but Turn Quality could not be validated in this way during the development of the SS-180: while two of the constituent items (Ground Clearance and Continuity) could be validated against CODA, Independence, Stability and Posture need to be validated against an external criterion based on expert opinion or consensus. At this early stage in test development, it was inappropriate to consider any opinion ‘expert’. The video recordings used in this phase of the study were drawn from those collected during an investigation into how people with and without Parkinson’s Disease turn [36]. Participants completed the SS-180 in a laboratory, while their turns were recorded by video and CODA. The camera and scanner were stacked in the position of the target towards which participants walked during the test. Four CODA markers were attached to the participants’ footwear, on the midline of each heel and over each great toe (Fig. 2). Testing criterion validity To test the validity of measuring Turning Steps and Turn Type from video, a set of 20 videos was selected from the records available. The lead researcher rated the CODA output (Fig. 3), counting a Turning Step if the markers from one foot were repositioned while the markers from the other remained on the floor, until the markers indicated the onset of the first straight forward step towards the target. Turn Type was ascertained from the movement of the markers, i.e. the definition of Turn Type that best matched the magnitude and direction of each Turning Step was selected. To minimise bias, an independent researcher, trained on a different set of records, rated Turning Steps and Turn Type from video us-
Fig. 2. Placement of CODA markers on one foot.
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Fig. 3. Example of CODA output (a Toward Type Turn of 1.3 s). (i) The onset of the first Turning Step (at ↑ (a)), 1.5 s after the subject was instructed to begin the test ‘when ready’ (at which point, both heel markers were 16 cm behind the ‘origin’ set for CODA); the completion of the first Turning Step (at ↑ (b)), 0.5 s later, by which point the right heel marker had advanced 30 cm towards the target and the onset of the second and final Turning Step (at ↑ (c)), 0.9 s into the test (at this point, both heel markers were lost from the scanner’s view, as the subject was now facing the target and the scanner was recording toe markers). (ii) The cyclical movement of toe markers towards the target, characteristic of straight forward gait. The completion of the final Turning Step is shown (at ↑ (a)) at 2.8 s and 80 cm behind the CODA origin (i.e. a Turn Time of 1.3 s, covering 64 cm of the distance to the target) and the initiation of the first straight forward step. The completion of the first straight forward step is shown (at ↑ (b)), a step of approximately 1 m in length.
ing the guidelines. The strength of agreement between video and CODA was estimated using the Kappa measure (k), as recommended by Altman [37], interpreted as per Landis and Koch [38]. To test the validity of Turn Time, 10 more videos were selected from the records available. Turning was timed from the CODA output (showing marker movement) from the onset of the first Turning Step to the onset of the first straight forward step toward the target (see Fig. 3). Turning was timed from video as per the rating guidelines. The strength of agreement between video and CODA was estimated using the method for continuous data [39] in which the difference between measures is plotted against their mean, with the mean ± 2 standard deviations defining the 95% limits of agreement, i.e. agreement in most cases.
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Testing reliability To test reliability, 10 more videos were selected from the records available. To establish the reliability with which the lead researcher rated the video-based SS-180, she rated the turns (Rating A-1) then repeated the procedure 1 week later (Rating A-2): Ratings A-1 and A-2 were compared. Another trained researcher rated the same turns (Rating B) to establish the reliability with which she and the lead researcher rated the test: Ratings A-1 and B were compared. Again, the agreement between ratings was estimated using the method recommended by Bland and Altman [39].
0.1 s (±0.1), 95% limits of agreement −0.3 to 0.1 s (Table 2). Inter-rater reliability was also acceptable. There was good agreement on Turning Steps (80%; kw = 0.70), with a one-step discrepancy on just two turns. There was 100% agreement on Turn Type and very good agreement on Turn Quality (90%; k = 0.82), with a one-point discrepancy on just one turn. The mean difference in Turn Times was 0.0 s (±0.2), 95% limits of agreement −0.4 to 0.5 s (Table 2).
Results
The lack of an appropriate measure with which to evaluate turning and communicate the findings made it necessary to develop the SS-180, which it is envisaged will facilitate research on dysfunctional turning in Parkinson’s Disease. The simple test provides a comprehensive assessment of turning and is already in use. Results are meaningful and easily communicated: compare ‘incremental turns in both directions, an average of five steps in 2.6 s, less than maximal quality’ with ‘turning appears normal’ or ‘on a five-point scale, scores two’. As people with Parkinson’s Disease often report that turning in one direction is particularly difficult, an assessment of turning in only one freely-chosen direction is likely to be an assessment of turning the preferred way. If only one turn is assessed, a subject assessed on two occasions may turn in different directions, making the results difficult to compare. Protocols that impose one direction of turning on subjects, often the case with laboratory set-ups, are equally difficult to interpret, as some subjects will have turned in their preferred direction while others will not. One advantage of the SS-180 is that subjects must turn both ways before a mean is recorded for Turning Steps, Turn Time and Turn Quality. As yet, there is no accepted terminology for turning (the equivalent of ‘the gait cycle’) so there is no consensus as to what constitutes a turning step, e.g. Simpson et al. [29] counted attempts to shift the body weight, successful or not, with alternate feet. They did not report their reliability and neither did Lipsitz et al. [23] who counted steps and timed turning. With the SS-180, we achieved much better inter-rater reliability using the standard protocol for turn analysis than in an earlier study in which we used less-structured movement analysis [26]. Following preliminary investigations, our Turning Step and Turn Time definitions appear robust. Counting steps from video was a valid and reliable approximation of the count made using CODA. Timing from video generated results consistent with the literature. Thigpen et al. [28] reported similar inter-rater agreement for counting turning steps and timing turning from video (k = 0.67 and 0.90, respectively). This was, however, after repeated testing on the same set of videos and the categorisation of continuous data. Others have reported intra-class correlation coefficients (ICCs) of 0.8 [30] and 0.95 [31], respectively, when timing turning from video. Our Turn Type definitions appeared robust: the structured protocol and/or detailed rating guidelines may have con-
Criterion validity The Turning Steps and Turn Type sample consisted of 20 people aged from 27 to 83 years: a faulty CODA marker meant that one record (two turns) could not be analysed. A weighted Kappa (kw ) was calculated for the Turning Step count: initial comparison revealed moderate agreement (71%; kw = 0.57), with a one-step discrepancy on 11 turns. Repeating the ratings using a modified Turning Step definition improved agreement and revealed very good agreement (92%; kw = 0.86), with a one-step discrepancy on just three turns. Comparing Turn Types rated from CODA and video revealed good agreement (84%; k = 0.78). The Turn Time sample consisted of five people with Parkinson’s Disease and five without, aged from 28 to 85 years. Video and CODA agreed well in healthy adults: mean Turn Time difference 0.0 s (±0.2), 95% limits of agreement −0.5 to 0.5 s. The difference increased with the mean in Parkinson’s Disease, so considering the differences as proportions, a CODA timing would be likely to lie within 20% of a video timing. Reliability The reliability sample consisted of three people with mild to moderate Parkinson’s Disease and seven without, aged from 21 to 85 years. Intra-rater reliability was acceptable: 100% agreement between the ratings of Turning Steps, Turn Type and Turn Quality; mean difference in Turn Times of Table 2 Reliability results—time (seconds) Subject 1 2 3 4 5 6 7 8 9 10 Mean
Rating A-1 Rating A-2 Difference to A-1 1.4 1.2 −0.2 1.1 1.0 −0.1 1.5 1.4 −0.1 1.4 1.0 −0.4 1.3 1.2 −0.1 1.6 1.5 −0.1 1.7 1.7 0.0 1.8 1.8 0.0 2.5 2.3 −0.2 6.9 6.8 −0.1 0.1 (±0.1)
Rating B Difference to A-1 1.5 0.1 1.2 0.1 1.3 −0.2 1.7 0.3 1.2 −0.1 1.5 −0.1 1.3 −0.4 2.1 0.3 2.6 0.1 7.1 0.2 0.0 (±0.2)
Discussion
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tributed to our achieving better inter-rater reliability than in earlier studies [26,28]. Hase and Stein [17] found that the turn type deployed during walking turns (either a ‘spin turn’ or a ‘step turn’) was dependent on the leg leading when the cue to turn was given. The SS-180 gives a free choice of leg with which to take the first turning step; by not imposing the choice on the subject, the test may promote a more natural turn than do other protocols. Turn Quality demonstrated acceptable reliability and compares favourably with published agreement on ‘stability’ (k = 0.76), and ‘the use of support’ (k = 0.91) [26] and ‘staggering’ (k = 0.71) [28]. Future studies are required to externally validate the video analysis of Turn Quality in its entirety. Being video based, the SS-180 is usable in environments other than the laboratory if there is sufficient space between the subject and his or her target. In too confined a space, the subject may need, or feel the need, to turn on-the-spot and then walk towards the target. The test was designed to discourage such a contrived manoeuvre: the instructions omit the word ‘turn’ in an attempt to focus the subject on walking to the target, rather than providing an auditory cue to turn. The preliminary studies encompassed a range of participants but were small for two reasons. Firstly, different sub-sets of video recordings were used for training and in each study; using the whole set each time would have given misleading estimates of agreement if assessors became too familiar with the data, introducing bias. Secondly, as the studies were completed early in the tool’s development and were laboratory based, it was not appropriate to recruit a large number of people with Parkinson’s Disease: experience has shown that they find travel to the laboratory daunting and that their performances are a poor reflection of real life. Importantly, if the studies had revealed that the videobased SS-180 lacked validity or reliability, immediate refinements could have been made. Instead, the encouraging early findings suggest that the test is workable and provide a starting point for its further development, testing and refinement. The SS-180 has already been used for research purposes with a large number of people with Parkinson’s Disease in their homes [36], the purpose for which it was developed, and evidence supporting the tool’s construct validity is emerging. The SS-180 would benefit from abbreviation before it is suitable for routine clinical application. Even so, we recommend that the standing-start protocol supersedes the walking or on-the-spot turns commonly assessed informally in current clinical settings.
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Conclusions The SS-180 overcomes many of the disadvantages of existing measures of turning. It is ecologically valid, usable in a range of environments (being video based) and simple to complete, and it provides a comprehensive assessment of turning 180◦ in both directions: the results are meaningful and easy to communicate. Findings suggest that the SS-180 is valid and reliable; further study is required to validate Turn Quality, which was not appropriate for validation against a laboratory-based criterion. The small preliminary investigations into validity and reliability were integral parts of early development and require repetition during the test’s further development. The SS-180 is suitable for research purposes and we recommend the standing-start protocol for use in the informal assessment of turning that is commonly attempted clinically.
Key messages • The SS-180 is a simple yet comprehensive test of turning in each direction, measuring Turning Steps, Turn Time, Turn Type and Turn Quality. • Video-based analysis of the SS-180 generates valid findings comparable to those from an external criterion measure, with acceptable reliability. • The SS-180 is suitable for research purposes, being ecologically valid and deployable in a range of environments.
Ethical approval Southampton and South West Hampshire Joint Research Ethics Committee and The North and Mid Hampshire Local Research Ethics Committee.
Acknowledgements Funding: Research Training Fellowship (RDF 081) from the NHS South East Region.
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Appendix A The SS-180 scoring form and rating guidelines
Enter data in the highlighted boxes following the Rating Guidelines, one observation of the video recording per item rated. Rate the direction-unspecified (DU) turn and the direction-specified (DS) turn, and then calculate mean scores for Turning Steps, Turn Time and Turn Quality (i.e. [DU + DS]/2).
SS-180 Rating Guidelines Turning Steps (foot movements rotating subject through 180◦ to face target). Count each foot movement during turning. Do not count first walking step (i.e. first step to target, predominantly unidirectional from toe-off). Turn Time (time from initiation to completion of Turning Steps). Start watch when first Turning Step begins. Stop watch when last Turning Step complete. Record mean of five timings. Turn Type. Choose which definition best fits turn observed. Toward: 2 Turning Steps. Initiated with same foot as direction of turn. Direct advance to target; negligible lateral deviation. Pivotal: 2–3 Turning Steps. Initial step wider than it is long, followed by wide second step. Lateral: 2–3 Turning Steps. Initiated with foot opposite to direction of turn. Incremental: Turning on-the-spot before advancing to target. Delayed Onset: 4+ Turning Steps. Initial steps with each foot make negligible advance to target or in changing direction. Turn Quality. For each question, if answer is ‘yes’ score 0; if answer is ‘no’ score 1. Independence: Did subject require external support, walking aid or help (physical or verbal) from another person?
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Ground Clearance: Did both feet clear ground and each other throughout turn except when pivoting to change direction during one Turning Step? Continuity: Was there a pause during turning or after turning before advancing towards target? Posture: Did subject become clearly more flexed during turn than when they began test; did they lower their height? Stability: Did subject appear unstable or at risk of falling when turning; did they or an attendant make any saving reactions? References [1] Lieberman A. Parkinson’s Disease: a clinical review. Am J Med Sci 1974;267:66–80. [2] Yahr M, Duvoisin R, Schear M. Treatment of parkinsonism with levodopa. Arch Neurol 1969;21:343–54. [3] Webster D. Critical analysis of the disability in Parkinson’s Disease. Mod Treat 1968;5:257. [4] Canter G, De la Torre R, Mier M. A method for evaluating disability in patients with Parkinson’s Disease. J Nerv Ment Dis 1961;133:143–7. [5] Giladi N, McMahon D, Przedborski S. Motor blocks in Parkinson’s Disease. Neurology 1992;42:333–9. [6] Bloem B, van Vugt J, Beckley D. Postural instability and falls in Parkinson’s Disease. Adv Neurol 2001;87:209–23. [7] Charlett A, Weller C, Purkiss A, Dobbs S, Dobbs R. Breadth of base whilst walking: effect of ageing and parkinsonism. Age Ageing 1998;27:49–54. [8] Nieuwboer A, De Weerdt W, Dom R, Lesaffre E. A frequency and correlation analysis of motor deficits in Parkinson patients. Disab Rehabil 1998;20:142–50. [9] Cummings S, Nevitt M. A hypothesis: the causes of hip fractures. J Geront 1989;44:M107–11. [10] Stack E, Ashburn A. Fall-events described by people with Parkinson’s Disease: implications for clinical interviewing and the research agenda. Physiol Res Int 1999;4:190–200. [11] Tinetti M. Prevention of falls and fall injuries in elderly people: a research agenda. Prev Med 1994;23:756–62. [12] Yekutiel M. Patients fall records as an aid to designing and assessing therapy in parkinsonism. Disab Rehabil 1993;15:189–93. [13] Johnell O, Melton L, Atkinson E, O’Fallon W, Kurland L. Fracture risk in patients with parkinsonism: a population-based study in Olmstead County, Minnesota. Age Ageing 1992;21:32–8. [14] Podsiadlo D, Richardson S. The timed up and go: a test of basic functional mobility for frail elderly persons. J Am Geriatr Soc 1991;39:142–8. [15] Imai T, Moore S, Raphan T, Cohen B. Interaction of the body, head and eyes during walking and turning. Exp Brain Res 2001;136:1–18. [16] Morris M, Huxham F, McGinley J, Dodd K, Iansek R. The biomechanics and motor control of gait in Parkinson’s Disease. Clin Biomech 2001;16:459–70. [17] Hase K, Stein R. Turning strategies during human walking. J Neurophysiol 1999;81:2914–22. [18] Patla A, Adkin A, Ballard T. Online steering: co-ordination and control of body centre of mass, head and body reorientation. Exp Brain Res 1999;129:629–34. [19] Grasso R, Prevost P, Ivanenko Y, Berthoz A. Eye-head co-ordination for the steering of locomotion in humans: an anticipatory synergy. Neurosci Lett 1998;253:115–8. [20] Grasso R, Assaiante C, Prevost P, Berthoz A. Development of anticipatory orienting strategies during locomotor tasks in children. Neurosci Biobehav Rev 1998;22:533–9.
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