Shoulder functional assessments in persons with chronic ... - IOS Press

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Work 38 (2011) 169–180 DOI 10.3233/WOR-2011-1119 IOS Press

Shoulder functional assessments in persons with chronic neck/shoulder pain and healthy subjects: Reliability and effects of movement repetition Karen V. Lomond∗ and Julie N. Côté McGill University Currie Gymnasium, Montreal, Quebec, Canada

Received 15 June 2009 Accepted 22 August 2009

Abstract. Objective: Obtaining reliable functional capacity measures from injured workers is an essential part of the return to work (RTW) process. The present study compares shoulder functional outcomes between healthy individuals and others with neck/shoulder pain, assesses reliability and examines the influence of repetitive movements on shoulder function. Methods: Subjects performed trials of flexion and abduction active range of motion (ROM), and cumulative power output (PO) in a pushing/pulling task on the Baltimore Therapeutic Equipment Simulator II in two consecutive sessions. Tasks were assessed before and after performing a repetitive arm task, during which heart rate (HR) was recorded, until scoring 8 on the Borg CR-10 scale or on a 11-point numeric rating scale (NRS) for pain. Participants: Persons with chronic neck/shoulder pain (intensity > 3/10 for > 3 months) (n = 16) and an age- and sex-matched control group (n = 16). Results: Functional shoulder measures demonstrated strong inter-session reliability, except PO in the pain group. Average repetitive task duration was shorter in the pain group (4 min vs. 7 min). Conclusions: The protocol detected both pain- and time-related impairments, with HR and PO being sensitive to movement duration and ROM to pain. Keywords: Chronic neck/shoulder pain, functional capacity evaluation, test-retest reliability, fatigue, repetitive movements

1. Introduction Work-related musculoskeletal disorders (WMSD) of the upper limb represent an important proportion of workers compensation claims, lost time and health care costs [1]. Health interventions aimed at minimizing lost time and ensuring safe and prompt return to work (RTW) have been developed to combat the complex

∗ Address

for correspondence: Karen V. Lomond, McGill University Currie Gymnasium, 475 Pine Avenue West, Montreal, Quebec, H2W 1S4, Canada. Tel.: +1 450 688 9550 ext. 4827; Fax: +1 514 298 4186; E-mail: [email protected].

nature, common occurrence and high costs associated with chronic WMSD [2]. Many have described the complexities of RTW, and have identified evaluation of an individual’s ability to perform their work tasks as an important part of the RTW trajectory [3]. A variety of assessment tools, termed functional capacity evaluations (FCE), have been developed to facilitate this process. FCE are standardized clinical tests aimed at qualifying a worker’s ability to safely perform work-related activities by relating their physical capacity with actual job task requirements [3]. Decisions regarding employment status (e.g. benefit suspension or claim clo-

1051-9815/11/$27.50  2011 – IOS Press and the authors. All rights reserved

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K.V. Lomond and J.N. Côté / Shoulder functional assessments in persons with chronic neck/shoulder pain and healthy subjects

sure) are often directly linked to the results of the FCE; consequently, their outcomes have important financial implications for patients, employers, insurers, and society [3,4]. As such, FCEs must: accurately and reliably measure the desired performance outcomes; hold discriminative power for given diagnoses; and allow direct relation of these outcomes to valid real-world situations [5,6]. The Baltimore Therapeutic Equipment Work Simuc Baltimore, MD) is an lator II (Sim-II) (BTE-Tech , FCE tool commonly used to measure upper limb function [7–14]. The system consists of a software-based controller interface, a position adjustable exercise head with resistance control, and a set of interchangeable attachments to simulate a variety of work tasks. The Sim-II records a variety of functional outcome measures (e.g. peak force, time, and cumulative power output) in either static or dynamic mode. The Sim-II has been the focus of several investigations, which have notably focused on its reliability and validity. Generally, this instrument demonstrates good test-retest reliability in the static mode; however, only a limited number of the Sim-II’s 22 attachments have been tested [14–18]. Investigations into Sim-II dynamic protocols have focused primarily on the protocol’s validity and tend to yield more variable results. Some authors have reported strong correlations between physiological measures recorded during real and simulated manual materials handling (MMH) tasks [9], while others have reported that simulated tasks tended to elicit lower metabolic responses than actual tasks [9–11]. Despite the equivocal findings about its reliability and validity, the SimII offers some notable advantages in FCE as it simulates actual job tasks in a controlled environment, providing objective outcome measures that can be related to work performance. Moreover, its flexibility allows users to target specific risk factors for work injury in their assessment protocols (e.g. for neck/shoulder pain or performing tasks at or above shoulder height); thus, the Sim-II has been a popular means of assessing patient functional abilities during MMH tasks (e.g. lifting/lowering, pushing/pulling) [7–10]. Several authors have established guidelines for the safe performance of MMH tasks e.g. [19,20]; however, task performance can be mediated by individual factors such as the presence of pain and/or fatigue. Pain, whether experimentally induced, musculoskeletal, or stemming from systemic disease, has been shown to alter some aspects of movement (e.g. movement speed) [21,22]. For instance, shoulder pain has been shown to be associated with reductions in active shoul-

der abduction and flexion ROM [23,24] and whole body movement adaptations in multi-joint tasks [22,25]. Together, this suggests that assessing work tasks in persons with pain in terms of traditional outcome measures (e.g. isometric force production) may not be sufficient, and that other functional indicators (e.g. movement speed or power output) may be recommended to ensure comprehensive assessment of one’s functional capacity. Several authors have also described inherently higher variability in functional outcome measures in persons with chronic pain [26–28], suggesting that assessing the reliability of outcome measures in healthy groups only may not be sufficient to adequately represent physical behaviour of clinical populations. Moreover, epidemiological evidence suggests that many upper limb WMSD risk factors are related to the inherent characteristics of the task [29]. In particular, tasks that are highly repetitive and occur at or above shoulder height have been linked to the development of chronic neck/shoulder pain [29,30]. The effects of these task characteristics are often exacerbated in the presence of muscular fatigue. The effects of fatigue on functional capacity include reductions in maximal isometric force and power output [31]. Moreover, repetitive motion-induced fatigue causes adaptations in movement strategies [32,33], which appear unique in persons with chronic neck shoulder pain [25]. Consequently, clinician should be aware that prior movements may impact functional outcome measures differently between patients and healthy persons. Thus, it is important to assess reliability of measures in both groups before and after performing repetitive arm movements. To date, the Sim-II has demonstrated some success in differentiating between patient groups [12]; however, it appears unable to distinguish between groups with similar pathologies (e.g. fibromyalgia and rheumatoid arthritis [13]). While this lends some support to the use of Sim-II in FCE, the ability of Sim-II protocols to detect chronic musculoskeletal pain or muscular fatigue remains unknown. As such, this paper describes a study that was undertaken to quantify key functional outcomes relevant to the workplace and likely affected by chronic neck/shoulder pain. The purposes of this study were to (1) compare objective shoulder functional measures between subjects with chronic neck/shoulder pain and healthy subjects; (2) evaluate the test-retest properties of shoulder functional measures in subjects of both groups, and; (3) examine the influence of a repetitive reaching task (RRT) on shoulder function in subjects of both groups.


2. Methods 2.1. Participants Sixteen subjects with chronic neck/shoulder pain (7 males, 9 females; mean age ± SD = 40.1 ± 12.1 years) were recruited through a rehabilitation program of the institution and advertisements in local newspapers to participate in this study. Inclusion in the pain group required that subjects be diagnosed with chronic neck and/or shoulder pain interfering with their work and/or activities of daily living. Pain level inclusion criteria were expressed in intensity (i.e. greater than 3 on an 11-point numeric rating scale (NRS)) and duration (i.e. longer than 3 consecutive months within the last year) and were verified in a telephone interview. Additionally, subjects had to have sought medical attention (e.g. family physician, physiatrist, physical therapist, etc.) for their pain during the last twelve months. Subjects were excluded from the study if they had: a concomitant medical condition that would interfere with performance of the experimental tasks or render them contraindicated; been diagnosed with shoulder capsulitis or paralysis of the dominant arm; received a pain-relieving steroid injection or supra-ulnar nerve block during the month preceding their participation; suffered from head or neck trauma or a concussion in the previous six months; been involved in litigation with regard to their injury. Sixteen healthy subjects (7 males, 9 females; mean age ± SD = 39.7 ± 13.2 years) were recruited through research center staff and social networks to constitute the control group. Inclusion in the control group required that subjects have no history of neck/shoulder pain within the previous year. All subjects in the healthy group were matched to the neck/shoulder injured group on the basis of age, gender, and hand dominance. All subjects in the study signed informed consent forms approved by the Research Ethics Board of the Centre for Interdisciplinary Research in Rehabilitation (CRIR) of Greater Montreal and refrained from beginning any new exercise or treatment programs during their participation in the study.

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horizontal plane at shoulder level. These tasks were chosen as they represent movements commonly impeded in persons with chronic neck/shoulder pain and MMH tasks associated with incidence of neck/shoulder WMSD [34,35]. This part of the protocol was repeated in a second testing session, scheduled a minimum of 48 hours later. During one of the two sessions (randomly assigned), after the initial ROM and PO recordings, subjects stood with feet shoulder width apart and performed the fatiguing activity which was a repetitive reaching task (RRT). Subjects reached back and forth between two targets, which consisted of cylindrical touch sensors (QT110IS, Quantum Research Group Ltd., Hampshire, UK; response time: 130ms), fixed at 30 and 100% of arm length, at shoulder height in front of the subjects’ midline. A mesh barrier was placed immediately beneath the elbow joint’s horizontal trajectory to ensure that the arm remained in the horizontal plane at shoulder height. Subjects were first asked to reach back and forth between the targets as quickly as possible for ten seconds to assess maximal reach speed. Then, subjects were to reach from one target to the other at a rate of one movement per second (1 Hz) until they were asked to stop. Auditory feedback from the touch sensors and a metronome was used to guide movement rhythm. Subjects rated their self-perceived task difficulty (Borg CR-10 scale, [36]) and pain in the neck/shoulder region on the NRS during the final 30 seconds of every minute of reaching, while heart rate (HR) was recorded with a Polar s610 Heart Rate Monitor (Polar Electro, Kempele, Finland) throughout the RRT. Subjects continuously performed the RRT until the 1 Hz rhythm could not be maintained, or they reached a score of eight on either the Borg CR-10 or NRS scales [25,32]. Subjects were unaware of these stoppage criteria. Data from the first and last minute of the RRT (RRTi and RRTt , respectively) were retained for analysis. Following completion of the RRT, subjects immediately performed one post-fatigue PO trial, three abduction ROM trials, and three flexion ROM trials.

2.2. Experimental protocol

3. Data acquisition

The protocol consisted of performing a series of shoulder functional tasks before and after a fatiguing activity. Functional tasks consisted of active shoulder range of motion (ROM) in both flexion and abduction and cumulative power output (PO) accumulated over 10s during a repetitive pushing/pulling task in a

The shoulder functional assessment protocol was conducted using the Sim-II (Simulator-IITM, BTE c Baltimore, MD, USA, serial number: Technologies , 1113ST, sampling frequency ≈10 Hz) with a custommodified version of the large crank handle (#802) tool, consisting of a 23 inch long section of 11/4 inch box

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Fig. 1. Experimental set-up of Sim-II for each of the following tasks: A) shoulder flexion range of motion; B) shoulder abduction range of motion, and; C) cumulative power output (where the arrow indicates movement direction).

steel. The far end of the tool was fitted with a round handle placed parallel to the Sim-II’s axis of rotation to allow for force application during the various tasks. A removable Velcro strap was used to secure the subject’s arm to the attachment (Fig. 1A). For all tasks performed with the Sim-II, subjects were seated on a chair which was secured to the floor and had their upper trunk secured to the backrest via adjustable straps. To avoid inducing pain early on in the protocol, Sim-II tasks performed before the RRT were performed in the following order: flexion ROM, abduction ROM, PO. 3.1. Flexion and abduction ROM Shoulder flexion ROM was assessed with subjects seated such that the axis of shoulder flexion rotation (i.e. through the head of the humerus at the acromion process of the scapula) was aligned with the Sim-II’s axis of rotation (Fig. 1A). The attachment was aligned along the lateral side of the longitudinal axis of the humerus. Initially, the arm rested at the subjects’ side.

Subjects were instructed to “rotate their arm as far up and back as comfortably possible, and then return to the starting position”. To assess shoulder ROM in abduction, subjects sat with their backs to the Sim-II, such that the axis of abduction rotation (i.e. on the anterior portion of the acromion process of the scapula through the center of the head of the humerus) was aligned with the Sim-II’s axis of rotation (Fig. 1B). The attachment was aligned along the posterior, longitudinal axis of the humerus. From the same starting position as for flexion ROM, instructions were: “raise the arm to the side as high as comfortably possible, and then return to the starting position”. For all shoulder ROM tasks, subjects completed three consecutive trials, with 10 to 30s between trials and two minutes between tasks. 3.2. PO Following approximately five minutes of rest, subjects performed a dynamic pushing and pulling task in which PO was recorded over a 10s sample. The


Sim-II’s axis of rotation was adjusted perpendicular to the floor (Fig. 1C). Subjects grasped the handle of the attachment in a power grip while a mesh barrier was placed beneath their elbow to ensure that the arm was kept in the horizontal plane at shoulder level (Fig. 1C). To determine the resistive force used during this task, subjects initially performed three maximal voluntary pushing effort (MVPE) trials in the position described above, with the attachment of the Sim-II locked into position with elbow angle ≈ 120◦ . The instructions were to “push forward as hard as possible”, in a ramp up and hold effort of approximately 3s, with two minutes of rest between trials. Following a rest period, the unit was unlocked such that the attachment was free to rotate in the transverse plane, with a resistance of 50% of the peak MVPE force in the clockwise and counterclockwise rotations (Fig. 1 C). Subjects were instructed to “push and pull the handle back and forth as fast as comfortably possible for ten seconds”, while receiving verbal encouragement. Subjects completed three trials with two minutes of rest between each. 3.3. Assessments of pain and exertion Prior to the experiment, subjects in the pain group reported their pain and disability in the neck/shoulder region on the day of the experiment on the Shoulder Pain and Disability Index (SPADI) and Neck Disability Index (NDI). The SPADI and NDI have demonstrated reliability and validity in assessing pain and disability constructs [37,38]. Subjects in the pain group were also asked to periodically rate their pain (in the neck/shoulder region) throughout the protocol on an 11point NRS, where 0 indicates “no pain” and 10 indicates “worst imaginable pain”. This method is commonly used to assess pain in a variety of clinical groups and has demonstrated strong reliability and validity [39]. NRS scores were recorded immediately prior to beginning the protocol (NRSBaseline ), immediately following the final PO trial (NRSP O ), and during the first and last minute of the RRT (NRSRRT i and NRSRRT t , respectively). The Borg CR-10 scale, which was used to assess self-perceived exertion during the RRT, has been used previously to infer repetitive-motion induced fatigue in upper limb movements [25,32]. 4. Data analysis 4.1. Baseline shoulder functional measures Rotation of the Sim-II’s exercise head and PO were obtained from the Sim-II software after each trial.

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Shoulder ROM in flexion and abduction was measured as the difference between the maximum and minimum angular positions of the exercise head during each trial, with the mean of the three trials retained for analyses. Peak PO across the initial three trials and the single PO trial collected after the RRT were also retained for analyses. Maximal reaching speed was calculated as the average speed (reaches per second) over the ten second sample. Descriptive statistics (mean ± SD) were calculated for each group, for each outcome measure during each session. Group demographic data and mean maximal reaching speed were compared using independent ttests (p < 0.05 considered significant). Shoulder functional parameters from each session were analyzed using two-way repeated measures ANOVA, where conditions of Session (day 1 and day 2) and Group (Control and Pain) were treated as independent factors. Significant Session x Group interactions were assessed by Tukey’s post-hoc comparisons (p < 0.05). To examine the within-session relationships between pain and disability with functional measures, Spearman correlations were calculated between SPADI, NDI and NRS scores and functional outcomes measured from the pain group. Unless otherwise indicated, all statistical analyses were conducted with Statistica 7.0 (Statsoft Inc., Tulsa, OK). 4.2. Test-retest reliability Test-retest reliability of the baseline shoulder functional tasks was assessed by Intraclass Correlation Coefficients (ICC). The model ICC(2,1) was used to assess reliability of outcome measures with a single value per session (i.e. PO, NRS scores), while the model ICC(2,3) was used to assess outcome measures with scores averaged over multiple trials (i.e. flexion and abduction ROM) [40]. Spearmen ranked order correlation coefficients (ρ) were also calculated between and within sessions to facilitate comparisons with the literature e.g. [9,41]. Standard error of the measurement (SEM) values were calculated as estimates of the error associated with each group on each outcome [40]. SEM was also used to calculate the minimal detectable change for the 90th percentile confidence interval (MDC90 ) [42]. MDC90 reflects the minimum amount of change in a measurement that is not likely to be due to chance variation in the measurement. Strengths of reliability measures for each group were interpreted using Portney and Watkins’ [40] classification scheme, while ICC val-

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K.V. Lomond and J.N. Côté / Shoulder functional assessments in persons with chronic neck/shoulder pain and healthy subjects Table 1 Subject demographics

Age (years) Height (cm) Weight (kg) Time Between Session (days) Time to Task Termination (s) Maximal Reach Speed (Hz) Pain Intensity (/10) Pain Duration (years) SPADI (%) NDI (%)

PAINa (mean ± std) 40.1 ± 12.1 167.0 ± 10.5 67.9 ± 11.6 9.5 ± 7.1 243 ± 145 2.9 ± 0.4 5.2 ± 1.5 4.4 ± 3.5 29.0 ± 13.2 20.0 ± 14.0

CTRLb (mean ± std) 39.7 ± 13.2 170.5 ± 9.0 78.1 ± 19.3 12.5 ± 7.0 447 ± 179 3.8 ± 0.8 − − − −

Group (p values) ns ns ns ns 0.001 < 0.001 − − − −

a Pain

group; group; ns = not significant; Note: See text for description of additional abbreviations. b Control

ues were calculated using a website recognized by the scientific research community (http://sip.medizin.uniulm.de/informatik/projekte/Odds/icc.html). 4.3. Effects of the RRT Group means of shoulder functional measures were calculated for trials immediately before and after the RRT; while group means for HR, rating of perceived exertion (Borg CR-10), and NRS for pain were computed for each subject’s RRTi and RRTt . These outcome measures were analyzed using a two-way repeated measures ANOVA, where conditions of Time (RRTi and RRTt ) and Group (Control and Pain) were treated as independent factors. Significant Time x Group interactions were assessed by Tukey’s post-hoc comparisons (p < 0.05). Independent t-tests were used to compare the duration of the reaching task between groups.

5. Results 5.1. Participant demographics Mean time between testing sessions was 9.5 (± 7.1) and 12.5 (± 7.0) days for the pain and control groups, respectively, with no significant difference between groups. At screening, subjects in the pain group reported pain ranging in intensity from 3 to 7.5/10 (mean 5.2 ± 1.5/10) on the NRS for durations ranging from 1 to 15 years (mean 4.4 ± 3.5 years). At the time of testing, all subjects were participating in their usual daily activities, including work and school.

5.2. Baseline shoulder functional measures: Group effects The ANOVA Session x Group indicated a significant interaction for abduction ROM (Table 2). Tukey posthoc analysis revealed that the control group had greater abduction ROM (196.8 ± 19.1◦) in session 1 than the pain group (143.5 ± 50.2◦ , F (2, 30) = 5.84, p = 0.01). However, there was a significant increase in abduction ROM between sessions 1 and 2 in the pain group only (mean increase, 21.9, F (2, 30) = 5.84), such that there was no difference between groups in session 2 (Table 2). Flexion ROM demonstrated a significant main group effect (F (2, 30) = 7.47), with the control group showing larger ROM (210.2 ± 24.3◦) than the pain group (175.5 ± 37.3◦ ). There were no significant differences in PO between sessions or groups. T-test analysis revealed that maximal reach speed was significantly faster (t (22) = 3.20) in the control group (3.8 ± 0.8 Hz) compared to the pain group (2.9 ± 0.4 Hz) (Table 1). Within session Spearman correlations indicate weak relationships between pain (i.e. NDI, SPADI, and NRS) and shoulder functional measures in both sessions, except for session two abduction ROM which was moderately correlated with both NDI and NRSP O (ρ = 0.52 and 0.54, respectively). 5.3. Reliability of baseline shoulder functional and pain measures Between testing sessions, there were no significant differences in most pain and disability scores, except a significant decrease in NDI scores (Table 2). The ICC, SEM, and MDC90 scores for each group on each measure are presented in Table 3. Within the pain group,


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Table 2 Mean pain and disability scores (pain group) and shoulder function measures (pain and control groups) Group SPADIc (%) PAINf NDId (%) PAIN NRSeBaseline (/10) PAIN NRSP O (/10) PAIN FLEXh (◦ ) CTRLg FLEX (◦ ) PAIN ABDi (◦ ) CTRL ABD (◦ ) PAIN POj (W) CTRL PO (W) PAIN

Session 1 (mean ± SD) 30.0 ± 13.4 23.0 ± 13.7 3.0 ± 1.9 4.1 ± 2.2 209.2 ± 26.0 173.2 ± 38.7 196.8 ± 19.1 143.5 ± 50.2 39.8 ± 27.0 34.4 ± 44.2

Session 2 (mean ± SD) 27.7 ± 11.5 18.7 ± 12.5 2.3 ± 2.3 4.2 ± 2.3 211.3 ± 23.3 184.8 ± 36.1 201.8 ± 19.4 165.4 ± 38.2 42.7 ± 29.8 45.7 ± 37.9

Session Group Session × Tukey post-hoc (p values) (p values) group (p values) (within group) nsa − − − 0.03a − − − nsa − − − nsa − − − nsb 0.008b nsb − − < 0.001b < 0.001b 0.02b nsb < 0.001b nsb nsb nsb −

a Student’s

independent t-test analysis; measures ANOVA analysis; c Shoulder Pain and Disability Index; d Neck Disability Index; e Numerical Rating Scale; f Pain group; g Control group; h Flexion range of motion; i Abduction range of motion; j Cumulative power output; ns = Not significant. b Repeated

Table 3 Test-retest reliability of outcome measures

Questionnaires NRS Pain Scores BTE Functional Measures

SPADI % g NDI %h NRSBaseline (/10)i NRSP O (/10) FLEX (◦ )j ABD (◦ )k PO (W)l

Spearman ρa CTRLe PAINf − 0.78 − 0.80 − 0.61 − 0.56 0.90 0.81 0.70 0.79 0.97 0.37

ICCb CTRL PAIN − 0.74 − 0.82 − 0.69 − 0.59 0.95 0.92 0.85 0.87 0.94 0.53

SEMc CTRL PAIN − 6.89 − 5.84 − 1.05 − 1.30 4.72 14.76 6.06 24.35 7.52 30.25

MDCd 90 CTRL PAIN − 16.08 − 13.63 − 2.44 − 3.03 11.01 34.44 14.15 56.81 17.54 70.59

a Spearman’s

rho co-efficient; correlation co-efficient; c Standard error of the measurement; d Minimally detectable change (90th percentile of the population); e Control group; f Pain group; g Shoulder Pain and Disability Index; h Neck Disability Index; i Numerical rating scale for pain; j Flexion range of motion; k Abduction range of motion; l Cumulative power output. b Intraclass

Spearman correlation coefficients (ρ) of questionnaire and NRS scores between testing sessions were moderate to high, ranging from 0.56 to 0.80. Both questionnaire measures were highly correlated (ρ = 0.78 and 0.80 for SPADI and NDI, respectively) and demonstrated high ICC values (0.74 and 0.85, for SPADI and NDI, respectively) across both testing sessions. Mean SEM and MDC90 values were 5.6 ± 2.1% and 13.0 ± 4.9%, for the SPADI and NDI, respectively. NRS pain scores taken at the same point in the protocol (i.e. NRSBaseline and NRSP O ) were slightly more

variable from one day to the other, with only moderate correlations between sessions, ranging from ρ = 0.57 to 0.61 and ICC = 0.53 to 0.69. Mean SEM values were low at 1.3 ± 0.3/10, ranging from 1.1 to 1.5/10. Mean MDC90 values were 3.1 ± 0.7/10, ranging from 2.4 to 3.5/10. NRSBaseline ratings consistently demonstrated the highest correlation coefficient and ICC and the lowest SEM and MDC90 values. Spearman’s ρ coefficients of shoulder functional measures were good to excellent in the control group, ranging from 0.70 to 0.97; similarly, ICCs in this group

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were good to excellent, ranging from 0.85 to 0.95. The pain group demonstrated similar Spearman’s ρ values and ICCs in both ROM tasks, rating good to excellent on both measures; however, PO values showed poor reliability (ρ and ICC, 0.37 and 0.53, respectively). Both SEM and MDC90 measures were higher in the pain group (range = 14.76 to 30.25 and 34.44 to 70.59, respectively) than in the control group (range = 4.72 to 7.52 and 11.01 to 17.54, respectively), although in both groups, the PO task demonstrated the largest SEM and MDC90 values. 5.4. RRT effects Average time to task termination was significantly shorter for the pain group (4.1 ± 2.4 min) than the control group (7.5 ± 3.0 min; t (30) = 3.55, p = 0.001). The analysis of scores for perceived exertion (Borg CR10) and pain (NRS) showed Time x Group interaction effects (F (2, 30) = 7.38, p = 0.01; and F (2, 30) = 10.51, p = 0.003, respectively) (Table 4). Post-hoc analyses revealed that both Borg and NRS scores increased significantly from RRTi to RRTt within each group (p < 0.0002). NRS scores were also significantly higher in the pain group at RRTi than the control group (p < 0.006), though there were no significant differences in either Borg or NRS scores at RRTt . Although no Time x Group interaction effects were observed for either variable, HR and PO showed an overall main effect of time as HR increased and PO decreased as a result of performing the RRT (Table 4). No significant Group x Time interaction effects were observed for either ROM variable, although as noted previously there was a significant group effect.

6. Discussion 6.1. Baseline shoulder functional measures: Group effects The first purpose of this study was to compare shoulder functional measures between healthy subjects to those of people with chronic neck/shoulder pain. In accordance with previous results, there were differences in ROM between the pain and control groups. Possible reasons for this are discussed below. Together, our data suggest some limitations in shoulder ROM in the pain group, which is likely to affect their functional abilities. Mean ROM values in abduction and flexion for the control group tended to be greater than those reported

in the literature [43–47]. This may be due to the seated posture used in our experimental protocol, as many goniometric protocols opt to measure shoulder ROM in the supine position to minimize scapular movement e.g. [48]. Subjects in the present study were secured to a high-backed chair with Velcro straps to limit upper trunk movement; however this may not have been sufficient to completely stabilize the scapula. Mean ROM in abduction and flexion for the pain group in this study also tended to be higher than those reported in other studies of shoulder pathology [44,49,50]. However, this is likely due to differences in patient group characteristics as well as other methodological issues (see above). In our study, the ability of subjects with pain to perform at the same level as the control group varied by task. For instance, pain subjects had significantly slower maximal reaching speed than the control group, in accordance with previous work e.g. [21]. However, our results show no significant differences in PO between groups or testing sessions, suggesting that subjects with pain are able to perform that task as effectively as the control group, although this absence of group difference may be due to the high within-group variability in the PO data, and overall poor reliability of measures on this task especially in the pain group (see below). 6.2. Reliability of baseline shoulder functional and pain measures The second purpose of the study was to evaluate the test-retest properties of the shoulder functional assessment protocol in both groups. The Sim-II’s psychometric properties have been investigated previously, with protocols demonstrating moderate to good criterion validity with several attachments [5,6], especially in the static mode [16,17,41]. However, several authors expressed concerns about reliability of measures in the dynamic testing mode [15–18,51], which was used throughout the present protocol. Fess [16,17] described two distinct phases within the dynamic mode, termed the pre-inertia stage and the rotational stage. While the rotational stage (beyond 20◦ per movement arc) appears somewhat stable, in the pre-inertia stage (6◦ –20◦ of movement arc) if the applied force is not sufficient to overcome rotational inertia the Sim-II may not accurately record the torque. Fess [16,17] also referred to occasional “surges” occurring in this stage that increased recorded values by 30 to 50%. Despite this, studies using this testing mode have not cited concerns regarding the consistency of the unit’s resistance


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Table 4 Statistical analysis of heart rate, perceived exertion, pain and shoulder function pre-/post-RRT

Borge (/10) NRSf (/10) HRg (bpm) FLEXh (◦ ) ABDi (◦ ) POj (W)

Group

RRTai

RRTb t

CTRLc PAINd CTRL PAIN CTRL PAIN CTRL PAIN CTRL PAIN CTRL PAIN

0.6 ± 0.7 2.3 ± 1.8 0.3 ± 0.6 2.9 ± 2.1 89.3 ± 6.4 83.9 ± 10.7 212.4 ± 24.5 178.5 ± 39.0 200.6 ± 20.4 153.0 ± 53.1 42.1 ± 27.2 38.7 ± 40.0

6.5 ± 2.1 5.9 ± 2.0 6.8 ± 2.4 6.7 ± 1.7 97.3 ± 9.1 88.9 ± 12.9 213.8 ± 34.2 181.7 ± 47.0 203.9 ± 20.3 155.3 ± 55.3 35.1 ± 24.8 33.4 ± 33.8

Time (p values) < 0.001

Group (p values) ns

Time × group (p values) 0.01

< 0.001

0.02

0.003

< 0.001

ns

ns

ns

0.01

ns

ns

0.001

ns

< 0.001

ns

ns

Tukey post-hoc (within group) < 0.001 < 0.001 < 0.001 < 0.001 − − − − − − −

a First

30 s of the repetitive reaching task; 30 s of the repetitive reaching task; c Control group; d Pain group; e Borg CR-10 Scale; f Numerical rating scale for pain; g Mean heart rate; h Flexion range of motion; i Abduction range of motion; j Cumulative power output; ns = Not significant. b Last

torque, with some reporting moderate validity (r = 0.52 to 0.92) of Work Simulator measurements compared to real task demands [9]. In our study, functional measures demonstrated good to excellent reliability in both groups (ICC ranging from 0.85 to 0.95), with the exception of the pain group’s PO task (ICC = 0.53). Robust ICCs from ROM tasks were likely due to large angular displacements inherent to the tasks, which place the task in the more stable rotational stage of the movement arc [16,17]. In the PO task, subjects were free to choose the degree of angular displacement of the tool, yet all performed the task with 45 to 55◦ of rotation, which also falls within the “reliable range” of operation; thus it appears that the lower reliability of the PO task was not related to inherent error within the Sim-II unit. These poor test-retest characteristics are more likely related to within-group variability, with the range of individual subject PO being larger in the pain group than the control group over both testing sessions. In fact, the pain group consistently demonstrated SEM and MDC90 values almost double those of the control group in all three shoulder functional tasks. Several authors have described similar variability among groups of subjects with chronic pain performing functional tasks [26–28], which may be due to variability in baseline pain and disability levels among subjects within pain groups, such as is the case in the present study (see Table 1). Typically,

shoulder ROM demonstrates strong inter-session reliability in persons with chronic pain [52–54]; therefore, the inter-session changes in abduction ROM observed here may correspond with between-session changes in pain level or functional status of the pain subjects. Although no significant changes occurred in NRS or SPADI scores between sessions, NDI scores did decrease significantly, remaining in the mild disability classification [55]. This 4.3% reduction suggests improved neck function between sessions; however, it is less than the MDC90 calculated here (13.6%) (Table 2) or reported by the questionnaire’s authors (10.0%) [55]. Nevertheless some association may exist between shoulder abduction ROM and neck disability characteristics, as evidenced by the significant moderate correlation between these measures during session two. Finally, improvements in some functional outcome of pain patients may also be linked with reduced fear of effort and/or movement from one experimental session to the next, which has been demonstrated to occur in another reliability study involving people with neck pain [56]. 6.3. RRT effects The third purpose of this study was to examine the influence of a repetitive movement task on shoulder function in subjects with chronic neck/shoulder pain and healthy controls. Increases in perceived exertion,

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pain, mean HR, and decreased PO all suggest that the RRT successfully induced fatigue in both groups, while significant increases in both Borg CR-10 and NRS pain scores for the neck/shoulder region across both groups suggest that fatigue was localized to this region. Decreased PO values after RRTt also indicated that shoulder function was impaired by the RRT task. This is consistent with other studies of tasks performed at or above shoulder height, which have found the shoulder elevators to be most sensitive to fatigue induced by repetitive arm tasks [29,32]. Average time to task termination in the control group (7.4 ± 3.0 min) was similar to that observed in a group of healthy young adults performing the same reaching task (7.9 ± 4.0 min) in a previous study [32] and in a study using a sustained 90◦ bilateral shoulder abduction task (6.4 ± 2.7 min) [57]. Subjects with chronic pain were not able to perform the task as long (4.1 ± 2.4 min). Impaired endurance in the pain group is not likely related to their limited shoulder ROM as mean values (154.5 and 179.0◦, in abduction and flexion, respectively) were well above the 90◦ of abduction and 90◦ of flexion required to perform the RRT. Several studies of chronic pain patients also reported decreased endurance times, which were related to fundamental differences in muscular response to the experimental tasks [58–61]. These findings are also consistent with clinical studies that have demonstrated strength reductions in persons with chronic neck pain compared to healthy controls [62]. In our study, neither group displayed any reduction in active flexion of abduction ROM after performing the RRT, this despite the subjects with pain having higher pain ratings to start the task. This suggests that ROM measures are robust indicators of shoulder pain symptoms, independently from the presence of fatigue. Conversely, the PO was not sensitive enough to discriminate between subjects with and without chronic pain; however a main effect of time on PO, combined with parallel increases in perceptions of task difficulty (i.e. Borg-CR10) in both groups, suggests that this measure shows some promise as a measure of fatigue state, particularly in healthy subjects. Finally, a simple task to assess peak movement speed, such as the maximal reach speed task, may also be used to detect pain status, as it was able to successfully discriminate between groups in our study. 7. Conclusions FCE are an integral part of the RTW process, and can objectively define functional standards that closely

match a worker’s actual job tasks. From our protocol, it appears that the Sim-II’s shoulder ROM measurements are able to discriminate between persons with and without chronic neck/shoulder pain and are sufficiently reliable for clinical practice. The variability within the pain group was too large to allow reliable estimates of PO; however, despite these limitations, the PO task appears useful as an indicator of fatigue. Taken together this does not imply that the Sim-II is without merit in FCE. Its flexibility of task design and objective, quantitative data measurement regarding patients’ abilities are worthy components towards accurate FCE. Careful design and application of testing protocols (e.g. close monitoring of pain status, multiple dynamic trials, etc) should allow clinicians to overcome many of the limitations identified here to be able to accurately assess shoulder function in persons with chronic neck/shoulder pain. In the absence of expensive testing apparatus like the Sim-II, it appears that movement speed and endurance time can be used as indicators of various aspects of patient function.

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