Accepted Manuscript Clinic-based assessment of weight bearing asymmetry during squatting in people with anterior cruciate ligament reconstruction using Nintendo Wii Balance Boards Ross A. Clark, PhD Brooke Howells, BPhysio Julian Feller, MD Tim Whitehead, MD Kate E. Webster, PhD PII:
S0003-9993(14)00186-5
DOI:
10.1016/j.apmr.2014.02.024
Reference:
YAPMR 55765
To appear in:
ARCHIVES OF PHYSICAL MEDICINE AND REHABILITATION
Received Date: 27 January 2014 Revised Date:
26 February 2014
Accepted Date: 26 February 2014
Please cite this article as: Clark RA, Howells B, Feller J, Whitehead T, Webster KE, Clinic-based assessment of weight bearing asymmetry during squatting in people with anterior cruciate ligament reconstruction using Nintendo Wii Balance Boards, ARCHIVES OF PHYSICAL MEDICINE AND REHABILITATION (2014), doi: 10.1016/j.apmr.2014.02.024. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Running Head: Squat Asymmetry after ACL Reconstruction
Clinic-based assessment of weight bearing asymmetry during
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squatting in people with anterior cruciate ligament reconstruction using Nintendo Wii Balance Boards
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Ross A. Clark (PhD)1, Brooke Howells (BPhysio)2, Julian Feller (MD)3, Tim Whitehead (MD)3, Kate E. Webster (PhD)2
School of Exercise Science, Australian Catholic University, Melbourne, Australia 2
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Musculoskeletal Research Centre, La Trobe University, Melbourne, Australia 3
OrthoSport Victoria, Epworth HealthCare, Richmond, Australia
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Study Performed: OrthoSport Victoria, Epworth HealthCare, Richmond, Australia Submission Type: Original Article Acknowledgements: None
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Conflict of Interest: None
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Corresponding Author: Dr Ross A. Clark
School of Exercise Science Faculty of Health Sciences Level 1, Daniel Mannix Building Australian Catholic University Fitzroy, Victoria, 3065 Australia Email: [email protected] Tel:+61 431737609
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Clinic-based assessment of weight bearing asymmetry during squatting in people with
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anterior cruciate ligament reconstruction using Nintendo Wii Balance Boards
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ABSTRACT
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Objective: To use low-cost Nintendo Wii Balance Boards to assess WBA in people who
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have undergone anterior cruciate ligament reconstruction (ACLR), and to compare their
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results with a matched control group.
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Design: Quantitative clinical study using a cross-sectional design.
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Setting: Orthopaedic clinic of a private hospital
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Participants: Eighty-two participants (41 ACLR). The ACLR participants (age: 26.0+9.8yrs;
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current Cincinnati sports activity level: 75.3+19.8) performed testing in conjunction with
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their routine 6 or 12 month clinical follow-up, and the control group were matched for age,
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height, body mass and physical activity level.
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Interventions: Participants performed double-limb squats while standing on two Nintendo
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Wii Balance Boards – one under each foot.
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Main Outcome Measures: The WBA variables mean mass difference as a percentage of
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body mass, time favoring a single limb by >5% body mass, absolute symmetry index and
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symmetry index relative to the operated or matched control limb were derived. Mann-
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Whitney U tests were performed to assess between group differences.
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Results: Significant (p < 0.05) increases in asymmetry in the ACLR group were found for all
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outcome measures except symmetry index relative to the operated limb.
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ACCEPTED MANUSCRIPT Conclusions: In summary, people who have undergone an ACLR are likely to possess WBA
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during squats, and this can be assessed using low-cost Nintendo Wii Balance Boards in a
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clinical setting. Interestingly, the observed asymmetry was not specific to the surgical limb.
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Future research is needed to assess the relationship between WBA early in the rehabilitation
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process and long-term outcomes.
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Key words: force; kinetic; osteoarthritis; injury; knee
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List of abbreviations: weight bearing asymmetry (WBA); anterior cruciate ligament
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reconstruction (ACLR); mean mass difference as a percentage of body mass (MMD); time
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favouring a single limb by >5% body mass (TFSL); symmetry index (ASI); Nintendo Wii
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Balance Boards (WBB)
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INTRODUCTION
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Assessing the forces distributed through each limb during dynamic movements could provide
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important information with respect to loading asymmetries.3 For example, in the short term a
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weight bearing asymmetry (WBA) in favour of reducing load on the surgical limb has been
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observed post anterior cruciate ligament reconstruction (ACLR).4, 5 While this is logical, and
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potentially beneficial in the very early stages of post-operative rehabilitation to reduce load
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through a new graft ligament, this may be deleterious to outcomes if maintained over the
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long-term. Previous evidence indicates that asymmetries in loading patterns have been
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associated with increased risk of re-injury of the surgically reconstructed ACL.2 Additionally,
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chronic loading asymmetry could reduce bone mineral density 6 which in turn may hasten the
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development of post-surgical knee osteoarthritis.3 Previous evidence also suggests that a
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ACCEPTED MANUSCRIPT reduction in the load through the cartilage may alter its makeup, reducing its quality which in
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turn will speed up degradation once a return to sport occurs.3, 7 These negative implications of
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WBA make its assessment and correction of potentially great importance for optimising
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rehabilitation and return to sport outcomes.
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Subjective assessment of WBA is often performed by either the patient or clinician, however
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in other clinical populations such as stroke this has been shown to have little relationship to
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actual WBA.8 Consequently, instrumenting movements such as the two legged squat using
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multiple force plates 5, 9 or insole foot pressure analysis systems 10 has been used to identify
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WBA. These assessments require expensive equipment (typically >$20 000 per force plate or
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insole sensor system) that is often restricted to research laboratories, and which is often
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unwieldy and difficult to transport, and hence their inclusion into ACL rehabilitation
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protocols and regular clinical assessment is limited. However, recent evidence indicates that
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low cost, widely available Nintendo Wii Balance Boards provide accurate force data,11 and
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can be used with customised software to assess WBA during squatting.12 This system has
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been used to examine WBA in healthy and athletic populations,13 however no previous
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studies have examined its use in a clinical population such as ACLR patients. Therefore, the
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aim of this study is to examine whether a WBA exists in ACLR patients who are attending
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their regular post-surgery clinical assessment when compared to matched control participants
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using this low-cost system. We hypothesised that a significant WBA would exist in this
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population, that this asymmetry would be a result of reducing load through the operated limb,
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and that the asymmetry would be reduced with greater time post-surgery.
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METHODS
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ACCEPTED MANUSCRIPT Two groups of 41 participants (14 females in each) were recruited into this study, one
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consisting of people who had undergone an uncomplicated primary ACLR with a four strand
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hamstring autograft and the other a matched control group (Table 1). These participant
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numbers were based on sample size calculations for obtaining a moderate effect size,14 which
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required a minimum 68 participants (34 per group with ß = 0.2, α = 0.05). Ethics approval
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was obtained from the Faculty Human Ethics Committee and all participants provided written
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consent prior to participation.
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ACLR participants were recruited from the private practices of two experienced knee
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surgeons at their scheduled 6 or 12 month post-surgery follow-up, however we did not
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enforce time-based study exclusion criteria. As such, there was a diverse range of time since
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surgery, with clusters around the 6 and 12 month time points as shown in Figure 1. Exclusion
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criteria were: (1) previous or concurrent posterior or collateral cruciate ligament injury, (2)
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history of visual, vestibular or neurological disorders, (3) use of ototoxic medications (e.g.
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chemotherapeutic agents such as methotrexate) likely to influence the postural control system
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within the previous six months, (4) greater than two years between ACL injury and ACLR,
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(5) history of lower limb, neck or back injury in the previous six weeks significantly affecting
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activity, and (6) inability to squat to a sufficient depth (with or without pain) to undertake the
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assessment.
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All participants underwent an arthroscopically assisted ACLR using a hamstring tendon graft.
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Discharge from hospital was on the first postoperative day. Every patient undertook a
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postoperative rehabilitation protocol that encouraged immediate full knee extension and the
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restoration of quadriceps function as soon as possible, with particular emphasis placed on
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restoring vastus medialis function. Neither attendance nor location of the program was
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enforced. Weight bearing was allowed on an as-tolerated basis from the first postoperative
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day, and no braces or splints were used. Most patients were full weight bearing by two to
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three weeks, riding a stationary bicycle by four weeks and running by three to four months.
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Sports-specific drills were introduced from the four month time point.
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The control group consisted of university staff and students recruited via advertisement, and
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recreational athletes recruited via sporting clubs. Control participants had no history of ACL injury or surgery, and no lower limb injury within the previous six months that required
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surgery or restricted participation in activities of daily living for greater than two weeks.
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Other exclusion criteria were the same as for the ACLR group. Each ACLR participant was
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individually matched with a control participant by age (+4 years), gender, physical activity
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level (by use of the Cincinnati Sports Activity Scale15) and limb dominance. The dominant
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limb was defined as the limb used to kick a ball.
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The data collection and analysis protocol utilized in this study is similar to that of previous
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work.12, 13 Briefly, two Nintendo Wii Balance Boards (WBB) were used to evaluate the
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symmetry of weight distribution during squatting tasks, a system with reliability reported
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previously.12 At testing commencement the participant was asked to stand behind the WBB in
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a relaxed bipedal stance position, and the boards were positioned with the longitudinal and
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mediolateral axes aligned to the respective axes of their feet. Six practice squats standing
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behind the WBB were performed to validate the correct inter-board width and, where
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necessary, to adjust this position to ensure a comfortable squatting position. Data were
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acquired from the WBB via a Bluetooth connection, and were sampled at 40 Hz and filtered
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during post-processing using an eighth order Butterworth filter with a low pass cut-off
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frequency of 12 Hz. Prior to data collection each board was calibrated using a previously
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ACCEPTED MANUSCRIPT described technique of applying multiple loads to each board and creating a scale and offset
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factor. This consists of applying loads ranging from 0 to 45kg on each of the four sensors
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individually and using a regression equation to convert the raw sensor data into force values.
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Once this is complete, these loads are applied to the center of the WBB and a regression
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equation is created based on the sum of the force signals from the four sensors and the known
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loads.16 During this calibration process the calculated forces were required to be within a +4N
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threshold, which was chosen because it equates to error of less than 0.5% of the expected
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body mass of the participants.
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The testing protocol involved performing squatting without visual feedback. The participant
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completed six squats at a tempo of one repetition per six seconds, which was relayed audibly
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to the subject using a low frequency, low volume tone which was built into the data
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collection software. Feedback was provided at three second intervals, representative of the
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top and bottom of the squat movement. The participants were asked to squat to 900 knee
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flexion, which was monitored subjectively by the researcher during practice trials with
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feedback provided to ensure the correct depth would be reached during data collection. The
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loading condition during the squats consisted of body mass only, and was chosen based on
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the finding of Flanagan and Salem 17 that increasing the load had minimal influence on the
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magnitude of WBA. This allowed for a low-risk, simple and easy to administer test of WBA
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during squatting to be performed in a clinical setting, without the need for gym equipment or
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the time taken to implement either one repetition maximum or percentage bodyweight related
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loading schemes.
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ACCEPTED MANUSCRIPT Similar to previous work 13 we calculated the WBA measures mean mass difference as a
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percentage of bodyweight (MMD), time favoring a single limb by greater than 5% of body
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mass (TFSL) and the absolute symmetry index (SI). MMD provides a measure of the overall
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WBA, and is simply the difference between limbs, regardless of which side was favored,
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throughout the entire trial relative to the person’s body mass. This was calculated by
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obtaining the root mean square difference between limbs for each testing sample, assessing
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the average of this difference throughout the trial and then normalizing this value to body
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mass. TFSL reflects the time spent outside of the typical “healthy” level of asymmetry during
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each trial, which was deemed +5% of bodyweight based on previous research.18, 19 The TFSL
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was assessed by dividing the time spent outside this threshold by the total testing time, and
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multiplying this number by 100. Higher values indicate a greater amount of time favoring a
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single limb. The absolute symmetry index (SI) was also calculated based on previous work,18,
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divided by half of the subject’s body mass and multiplied by 100 to express it as a
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percentage. The SI differs from the MMD in that it is limb specific. For example, if someone
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tends to overcorrect their perceived asymmetry, resulting in them favoring one leg during one
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repetition but the other leg during the next repetition, their SI score would be quite low (an
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equal mean load through each limb) but their MMD would be high (their mean between limb
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difference is quite large). An additional measure, relative SI, was calculated to express the
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asymmetry relative to the operated limb, with a positive value indicative of increased load
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through the non-operated limb. This variable was calculated for the matched limb of the
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individually matched control subjects to allow comparison between the ACLR and control
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groups on this measure. All analysis was performed during post-processing using custom
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LabVIEW software.
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and is simply the absolute difference in mass distributed through the right and left limb
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ACCEPTED MANUSCRIPT Statistical analysis for each outcome measure consisted of assessment of normality using
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Shapiro-Wilk analysis, which revealed data to be not normally distributed. Consequently, to
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assess the relationship between time since surgery and the WBA outcome measures
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Spearman’s correlation analysis was performed. Mann-Whitney U tests were then performed
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to compare the ACLR and control groups for each of the WBA variables. All analyses were
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performed using SPSS Version 20, with a 2-sided alpha level set at 0.05. Notched boxplots
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were created using the online statistical site wessa.net.
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RESULTS
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No significant correlations were observed between time since surgery and any of the WBA
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outcome measures (Table 2: Spearman’s rho range = 0.003 to -0.279, p range = 0.077 to
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0.983). As expected due to the matching of the subjects, no significant differences were
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observed between the ACLR and control groups for age, height, body mass or current sports
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activity levels (Table 1). Significant differences were observed between the two groups for
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three of the WBA outcome measures, as shown in Figure 2. The MMD, TFSL, and absolute
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symmetry index were all higher in the ACLR group, indicating greater asymmetry when
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compared to the control group. Although the mean relative symmetry index indicated that
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overall the ACLR group preferentially loaded their non-operated limb, the index value was
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small and not significantly different from the control group.
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DISCUSSION
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No previous studies have assessed WBA during the two-legged squat in ACLR patients using
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Nintendo Wii Balance Boards. We found significant (p2 years post-
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surgery. However, we observed only a weak and non-significant relationship between time
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since surgery and favouring the non-operated limb, so this comparison between studies may
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be valid. Future work should examine why the non-operated limb is not favoured. This could
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include assessing the relationship that WBA has with strength imbalances and postural
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control impairments, which are known to occur in people who have undergone ACLR. 22-24
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Study Limitations
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Our combined ACLR group were recruited at various stages of the rehabilitation process
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post-surgery as part of their routine clinical assessments, and not at specific time points with
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set time thresholds for inclusion. This resulted in an inability to perform inter-group 6 and 12
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month post-surgery comparisons, but did provide the advantage of allowing increased subject
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numbers in the study. In support of this recruitment protocol, the lack of association between
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time since surgery and any WBA variable indicates that an inter-group comparison would not
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have found significant differences. Our results are also likely to have been stronger if we
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collected data in a group who were just beginning to perform dynamic dual-limbed exercises,
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for example in the initial months post-surgery, or if the task was made more difficult by
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modifying the tempo, loading and/or depth of the movement. This study also examined
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performance such as strength deficits or balance impairment. Future research should examine
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how strength and balance deficits influence WBA during dynamic movements, and whether
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improvements in these factors reduce WBA. Additionally, this study was cross-sectional in
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nature, and therefore inferences cannot be made about how useful the WBA information is in
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a clinical setting. For example, if feedback is given to the patient that they are asymmetrical -
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can they correct themselves in a way that has beneficial long-term outcomes? With respect to
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the rehabilitation program, we did not control this and therefore cannot make inferences
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about whether a structured early post-surgery program reduced asymmetry. Finally, although
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the system in this study provides kinetic information, it is not capable of collecting
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information related to joint angles. However, to maintain a low-cost, clinically feasible
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system it could be integrated with motion capture equipment such as the Microsoft Kinect 25
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to create an assessment tool which provides both kinetic and kinematic descriptors of
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movement.
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CONCLUSION
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In conclusion, WBA exists in people who have undergone an ACLR during body weight
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squats. This asymmetry can be recorded in a clinical setting using low-cost WBB. Future
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research is needed to assess the relationship between WBA early in the rehabilitation process
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and long-term outcomes, and the optimal methods of providing feedback of WBA in this
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population.
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18. Robinson RO, Herzog W, Nigg BM. Use of force platform variables to quantify the effects of chiropractic manipulation on gait symmetry. J Manipulative Physiol Ther 1987;10(4):172-6. 19. Herzog W, Nigg BM, Read LJ, Olsson EWA. Asymmetries in ground reaction force patterns in normal human gait. Med Sci Sports Exerc 1989;21(1):110-4. 20. Copay AG, Subach BR, Glassman SD, Polly Jr DW, Schuler TC. Understanding the minimum clinically important difference: a review of concepts and methods. The Spine Journal 2007;7(5):541-6. 21. Castanharo R, Da Luz BS, Bitar AC, D'Elia CO, Castropil W, Duarte M. Males still have limb asymmetries in multijoint movement tasks more than 2 years following anterior cruciate ligament reconstruction. J Orthop Sci 2011;16(5):531-5. 22. Howells B, Clark R, Ardern C, Bryant AL, Feller J, Whitehead T et al. Postural control and the influence of a secondary task in people with anterior cruciate ligament reconstructed knees. Br J Sports Med 2013; - in press. 23. Hoffman M, Schrader J, Koceja D. An Investigation of Postural Control in Postoperative Anterior Cruciate Ligament Reconstruction Patients. Journal of Athletic Training 1999;34(2):130-6. 24. Xergia SA, Pappas E, Zampeli F, Georgiou S, Georgoulis AD. Asymmetries in functional hop tests, lower extremity kinematics, and isokinetic strength persist 6 to 9 months following anterior cruciate ligament reconstruction. J Orthop Sports Phys Ther 2013;43(3):154-62. 25. Clark RA, Pua YH, Fortin K, Ritchie C, Webster KE, Denehy L et al. Validity of the Microsoft Kinect for assessment of postural control. Gait Posture 2012;36(3):372-7.
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LIST OF TABLES
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TABLE 1. Comparison of the anterior cruciate ligament reconstruction (ACLR) and control participants.
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TABLE 2. Correlations between days since surgery and weight bearing asymmetry outcome measures.
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LIST OF FIGURES
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FIGURE 1. Time since surgery for subjects attending their scheduled 6 and 12 month postsurgery follow-up session.
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FIGURE 2. Notched boxplot between group comparison of mean mass difference as a percentage of bodyweight (Mean Mass Difference), time favoring a single limb by greater than 5% of body mass (Time Favoring Single Limb), symmetry relative to the operated or control matched limb (Relative Symmetry Index) and absolute asymmetry irrespective of operated limb (Absolute Symmetry Index) for the anterior cruciate ligament reconstruction and control subjects. The values for median, 75th and 25th percentiles are provided for each group and variable next to each plot. A notched box plot can be interpreted similar to a standard box plot, with the addition of the 95% confidence interval which is represented by the position either side of the median at which the notch ends. If the lower notch of one group does not overlap with the upper notch of the other group this provides visual evidence of a statistically significant between-group difference. * significant difference between groups (p
S0003-9993(14)00186-5
DOI:
10.1016/j.apmr.2014.02.024
Reference:
YAPMR 55765
To appear in:
ARCHIVES OF PHYSICAL MEDICINE AND REHABILITATION
Received Date: 27 January 2014 Revised Date:
26 February 2014
Accepted Date: 26 February 2014
Please cite this article as: Clark RA, Howells B, Feller J, Whitehead T, Webster KE, Clinic-based assessment of weight bearing asymmetry during squatting in people with anterior cruciate ligament reconstruction using Nintendo Wii Balance Boards, ARCHIVES OF PHYSICAL MEDICINE AND REHABILITATION (2014), doi: 10.1016/j.apmr.2014.02.024. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Running Head: Squat Asymmetry after ACL Reconstruction
Clinic-based assessment of weight bearing asymmetry during
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squatting in people with anterior cruciate ligament reconstruction using Nintendo Wii Balance Boards
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Ross A. Clark (PhD)1, Brooke Howells (BPhysio)2, Julian Feller (MD)3, Tim Whitehead (MD)3, Kate E. Webster (PhD)2
School of Exercise Science, Australian Catholic University, Melbourne, Australia 2
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Musculoskeletal Research Centre, La Trobe University, Melbourne, Australia 3
OrthoSport Victoria, Epworth HealthCare, Richmond, Australia
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Study Performed: OrthoSport Victoria, Epworth HealthCare, Richmond, Australia Submission Type: Original Article Acknowledgements: None
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Conflict of Interest: None
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Corresponding Author: Dr Ross A. Clark
School of Exercise Science Faculty of Health Sciences Level 1, Daniel Mannix Building Australian Catholic University Fitzroy, Victoria, 3065 Australia Email: [email protected] Tel:+61 431737609
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Clinic-based assessment of weight bearing asymmetry during squatting in people with
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anterior cruciate ligament reconstruction using Nintendo Wii Balance Boards
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ABSTRACT
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Objective: To use low-cost Nintendo Wii Balance Boards to assess WBA in people who
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have undergone anterior cruciate ligament reconstruction (ACLR), and to compare their
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results with a matched control group.
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Design: Quantitative clinical study using a cross-sectional design.
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Setting: Orthopaedic clinic of a private hospital
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Participants: Eighty-two participants (41 ACLR). The ACLR participants (age: 26.0+9.8yrs;
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current Cincinnati sports activity level: 75.3+19.8) performed testing in conjunction with
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their routine 6 or 12 month clinical follow-up, and the control group were matched for age,
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height, body mass and physical activity level.
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Interventions: Participants performed double-limb squats while standing on two Nintendo
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Wii Balance Boards – one under each foot.
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Main Outcome Measures: The WBA variables mean mass difference as a percentage of
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body mass, time favoring a single limb by >5% body mass, absolute symmetry index and
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symmetry index relative to the operated or matched control limb were derived. Mann-
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Whitney U tests were performed to assess between group differences.
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Results: Significant (p < 0.05) increases in asymmetry in the ACLR group were found for all
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outcome measures except symmetry index relative to the operated limb.
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ACCEPTED MANUSCRIPT Conclusions: In summary, people who have undergone an ACLR are likely to possess WBA
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during squats, and this can be assessed using low-cost Nintendo Wii Balance Boards in a
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clinical setting. Interestingly, the observed asymmetry was not specific to the surgical limb.
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Future research is needed to assess the relationship between WBA early in the rehabilitation
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process and long-term outcomes.
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Key words: force; kinetic; osteoarthritis; injury; knee
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List of abbreviations: weight bearing asymmetry (WBA); anterior cruciate ligament
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reconstruction (ACLR); mean mass difference as a percentage of body mass (MMD); time
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favouring a single limb by >5% body mass (TFSL); symmetry index (ASI); Nintendo Wii
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Balance Boards (WBB)
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INTRODUCTION
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Assessing the forces distributed through each limb during dynamic movements could provide
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important information with respect to loading asymmetries.3 For example, in the short term a
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weight bearing asymmetry (WBA) in favour of reducing load on the surgical limb has been
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observed post anterior cruciate ligament reconstruction (ACLR).4, 5 While this is logical, and
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potentially beneficial in the very early stages of post-operative rehabilitation to reduce load
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through a new graft ligament, this may be deleterious to outcomes if maintained over the
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long-term. Previous evidence indicates that asymmetries in loading patterns have been
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associated with increased risk of re-injury of the surgically reconstructed ACL.2 Additionally,
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chronic loading asymmetry could reduce bone mineral density 6 which in turn may hasten the
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development of post-surgical knee osteoarthritis.3 Previous evidence also suggests that a
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turn will speed up degradation once a return to sport occurs.3, 7 These negative implications of
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WBA make its assessment and correction of potentially great importance for optimising
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rehabilitation and return to sport outcomes.
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Subjective assessment of WBA is often performed by either the patient or clinician, however
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in other clinical populations such as stroke this has been shown to have little relationship to
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actual WBA.8 Consequently, instrumenting movements such as the two legged squat using
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multiple force plates 5, 9 or insole foot pressure analysis systems 10 has been used to identify
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WBA. These assessments require expensive equipment (typically >$20 000 per force plate or
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insole sensor system) that is often restricted to research laboratories, and which is often
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unwieldy and difficult to transport, and hence their inclusion into ACL rehabilitation
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protocols and regular clinical assessment is limited. However, recent evidence indicates that
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low cost, widely available Nintendo Wii Balance Boards provide accurate force data,11 and
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can be used with customised software to assess WBA during squatting.12 This system has
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been used to examine WBA in healthy and athletic populations,13 however no previous
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studies have examined its use in a clinical population such as ACLR patients. Therefore, the
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aim of this study is to examine whether a WBA exists in ACLR patients who are attending
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their regular post-surgery clinical assessment when compared to matched control participants
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using this low-cost system. We hypothesised that a significant WBA would exist in this
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population, that this asymmetry would be a result of reducing load through the operated limb,
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and that the asymmetry would be reduced with greater time post-surgery.
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METHODS
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ACCEPTED MANUSCRIPT Two groups of 41 participants (14 females in each) were recruited into this study, one
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consisting of people who had undergone an uncomplicated primary ACLR with a four strand
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hamstring autograft and the other a matched control group (Table 1). These participant
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numbers were based on sample size calculations for obtaining a moderate effect size,14 which
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required a minimum 68 participants (34 per group with ß = 0.2, α = 0.05). Ethics approval
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was obtained from the Faculty Human Ethics Committee and all participants provided written
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consent prior to participation.
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ACLR participants were recruited from the private practices of two experienced knee
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surgeons at their scheduled 6 or 12 month post-surgery follow-up, however we did not
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enforce time-based study exclusion criteria. As such, there was a diverse range of time since
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surgery, with clusters around the 6 and 12 month time points as shown in Figure 1. Exclusion
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criteria were: (1) previous or concurrent posterior or collateral cruciate ligament injury, (2)
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history of visual, vestibular or neurological disorders, (3) use of ototoxic medications (e.g.
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chemotherapeutic agents such as methotrexate) likely to influence the postural control system
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within the previous six months, (4) greater than two years between ACL injury and ACLR,
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(5) history of lower limb, neck or back injury in the previous six weeks significantly affecting
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activity, and (6) inability to squat to a sufficient depth (with or without pain) to undertake the
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assessment.
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All participants underwent an arthroscopically assisted ACLR using a hamstring tendon graft.
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Discharge from hospital was on the first postoperative day. Every patient undertook a
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postoperative rehabilitation protocol that encouraged immediate full knee extension and the
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restoration of quadriceps function as soon as possible, with particular emphasis placed on
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restoring vastus medialis function. Neither attendance nor location of the program was
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enforced. Weight bearing was allowed on an as-tolerated basis from the first postoperative
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day, and no braces or splints were used. Most patients were full weight bearing by two to
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three weeks, riding a stationary bicycle by four weeks and running by three to four months.
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Sports-specific drills were introduced from the four month time point.
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The control group consisted of university staff and students recruited via advertisement, and
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recreational athletes recruited via sporting clubs. Control participants had no history of ACL injury or surgery, and no lower limb injury within the previous six months that required
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surgery or restricted participation in activities of daily living for greater than two weeks.
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Other exclusion criteria were the same as for the ACLR group. Each ACLR participant was
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individually matched with a control participant by age (+4 years), gender, physical activity
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level (by use of the Cincinnati Sports Activity Scale15) and limb dominance. The dominant
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limb was defined as the limb used to kick a ball.
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The data collection and analysis protocol utilized in this study is similar to that of previous
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work.12, 13 Briefly, two Nintendo Wii Balance Boards (WBB) were used to evaluate the
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symmetry of weight distribution during squatting tasks, a system with reliability reported
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previously.12 At testing commencement the participant was asked to stand behind the WBB in
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a relaxed bipedal stance position, and the boards were positioned with the longitudinal and
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mediolateral axes aligned to the respective axes of their feet. Six practice squats standing
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behind the WBB were performed to validate the correct inter-board width and, where
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necessary, to adjust this position to ensure a comfortable squatting position. Data were
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acquired from the WBB via a Bluetooth connection, and were sampled at 40 Hz and filtered
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during post-processing using an eighth order Butterworth filter with a low pass cut-off
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frequency of 12 Hz. Prior to data collection each board was calibrated using a previously
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factor. This consists of applying loads ranging from 0 to 45kg on each of the four sensors
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individually and using a regression equation to convert the raw sensor data into force values.
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Once this is complete, these loads are applied to the center of the WBB and a regression
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equation is created based on the sum of the force signals from the four sensors and the known
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loads.16 During this calibration process the calculated forces were required to be within a +4N
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threshold, which was chosen because it equates to error of less than 0.5% of the expected
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body mass of the participants.
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The testing protocol involved performing squatting without visual feedback. The participant
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completed six squats at a tempo of one repetition per six seconds, which was relayed audibly
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to the subject using a low frequency, low volume tone which was built into the data
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collection software. Feedback was provided at three second intervals, representative of the
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top and bottom of the squat movement. The participants were asked to squat to 900 knee
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flexion, which was monitored subjectively by the researcher during practice trials with
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feedback provided to ensure the correct depth would be reached during data collection. The
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loading condition during the squats consisted of body mass only, and was chosen based on
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the finding of Flanagan and Salem 17 that increasing the load had minimal influence on the
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magnitude of WBA. This allowed for a low-risk, simple and easy to administer test of WBA
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during squatting to be performed in a clinical setting, without the need for gym equipment or
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the time taken to implement either one repetition maximum or percentage bodyweight related
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loading schemes.
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ACCEPTED MANUSCRIPT Similar to previous work 13 we calculated the WBA measures mean mass difference as a
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percentage of bodyweight (MMD), time favoring a single limb by greater than 5% of body
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mass (TFSL) and the absolute symmetry index (SI). MMD provides a measure of the overall
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WBA, and is simply the difference between limbs, regardless of which side was favored,
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throughout the entire trial relative to the person’s body mass. This was calculated by
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obtaining the root mean square difference between limbs for each testing sample, assessing
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the average of this difference throughout the trial and then normalizing this value to body
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mass. TFSL reflects the time spent outside of the typical “healthy” level of asymmetry during
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each trial, which was deemed +5% of bodyweight based on previous research.18, 19 The TFSL
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was assessed by dividing the time spent outside this threshold by the total testing time, and
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multiplying this number by 100. Higher values indicate a greater amount of time favoring a
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single limb. The absolute symmetry index (SI) was also calculated based on previous work,18,
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divided by half of the subject’s body mass and multiplied by 100 to express it as a
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percentage. The SI differs from the MMD in that it is limb specific. For example, if someone
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tends to overcorrect their perceived asymmetry, resulting in them favoring one leg during one
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repetition but the other leg during the next repetition, their SI score would be quite low (an
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equal mean load through each limb) but their MMD would be high (their mean between limb
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difference is quite large). An additional measure, relative SI, was calculated to express the
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asymmetry relative to the operated limb, with a positive value indicative of increased load
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through the non-operated limb. This variable was calculated for the matched limb of the
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individually matched control subjects to allow comparison between the ACLR and control
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groups on this measure. All analysis was performed during post-processing using custom
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LabVIEW software.
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and is simply the absolute difference in mass distributed through the right and left limb
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ACCEPTED MANUSCRIPT Statistical analysis for each outcome measure consisted of assessment of normality using
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Shapiro-Wilk analysis, which revealed data to be not normally distributed. Consequently, to
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assess the relationship between time since surgery and the WBA outcome measures
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Spearman’s correlation analysis was performed. Mann-Whitney U tests were then performed
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to compare the ACLR and control groups for each of the WBA variables. All analyses were
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performed using SPSS Version 20, with a 2-sided alpha level set at 0.05. Notched boxplots
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were created using the online statistical site wessa.net.
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RESULTS
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No significant correlations were observed between time since surgery and any of the WBA
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outcome measures (Table 2: Spearman’s rho range = 0.003 to -0.279, p range = 0.077 to
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0.983). As expected due to the matching of the subjects, no significant differences were
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observed between the ACLR and control groups for age, height, body mass or current sports
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activity levels (Table 1). Significant differences were observed between the two groups for
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three of the WBA outcome measures, as shown in Figure 2. The MMD, TFSL, and absolute
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symmetry index were all higher in the ACLR group, indicating greater asymmetry when
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compared to the control group. Although the mean relative symmetry index indicated that
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overall the ACLR group preferentially loaded their non-operated limb, the index value was
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small and not significantly different from the control group.
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DISCUSSION
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No previous studies have assessed WBA during the two-legged squat in ACLR patients using
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Nintendo Wii Balance Boards. We found significant (p2 years post-
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surgery. However, we observed only a weak and non-significant relationship between time
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since surgery and favouring the non-operated limb, so this comparison between studies may
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be valid. Future work should examine why the non-operated limb is not favoured. This could
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include assessing the relationship that WBA has with strength imbalances and postural
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control impairments, which are known to occur in people who have undergone ACLR. 22-24
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Study Limitations
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Our combined ACLR group were recruited at various stages of the rehabilitation process
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post-surgery as part of their routine clinical assessments, and not at specific time points with
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set time thresholds for inclusion. This resulted in an inability to perform inter-group 6 and 12
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month post-surgery comparisons, but did provide the advantage of allowing increased subject
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numbers in the study. In support of this recruitment protocol, the lack of association between
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time since surgery and any WBA variable indicates that an inter-group comparison would not
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have found significant differences. Our results are also likely to have been stronger if we
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collected data in a group who were just beginning to perform dynamic dual-limbed exercises,
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for example in the initial months post-surgery, or if the task was made more difficult by
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modifying the tempo, loading and/or depth of the movement. This study also examined
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performance such as strength deficits or balance impairment. Future research should examine
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how strength and balance deficits influence WBA during dynamic movements, and whether
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improvements in these factors reduce WBA. Additionally, this study was cross-sectional in
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nature, and therefore inferences cannot be made about how useful the WBA information is in
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a clinical setting. For example, if feedback is given to the patient that they are asymmetrical -
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can they correct themselves in a way that has beneficial long-term outcomes? With respect to
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the rehabilitation program, we did not control this and therefore cannot make inferences
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about whether a structured early post-surgery program reduced asymmetry. Finally, although
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the system in this study provides kinetic information, it is not capable of collecting
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information related to joint angles. However, to maintain a low-cost, clinically feasible
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system it could be integrated with motion capture equipment such as the Microsoft Kinect 25
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to create an assessment tool which provides both kinetic and kinematic descriptors of
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movement.
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CONCLUSION
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In conclusion, WBA exists in people who have undergone an ACLR during body weight
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squats. This asymmetry can be recorded in a clinical setting using low-cost WBB. Future
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research is needed to assess the relationship between WBA early in the rehabilitation process
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and long-term outcomes, and the optimal methods of providing feedback of WBA in this
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population.
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ACCEPTED MANUSCRIPT REFERENCES
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18. Robinson RO, Herzog W, Nigg BM. Use of force platform variables to quantify the effects of chiropractic manipulation on gait symmetry. J Manipulative Physiol Ther 1987;10(4):172-6. 19. Herzog W, Nigg BM, Read LJ, Olsson EWA. Asymmetries in ground reaction force patterns in normal human gait. Med Sci Sports Exerc 1989;21(1):110-4. 20. Copay AG, Subach BR, Glassman SD, Polly Jr DW, Schuler TC. Understanding the minimum clinically important difference: a review of concepts and methods. The Spine Journal 2007;7(5):541-6. 21. Castanharo R, Da Luz BS, Bitar AC, D'Elia CO, Castropil W, Duarte M. Males still have limb asymmetries in multijoint movement tasks more than 2 years following anterior cruciate ligament reconstruction. J Orthop Sci 2011;16(5):531-5. 22. Howells B, Clark R, Ardern C, Bryant AL, Feller J, Whitehead T et al. Postural control and the influence of a secondary task in people with anterior cruciate ligament reconstructed knees. Br J Sports Med 2013; - in press. 23. Hoffman M, Schrader J, Koceja D. An Investigation of Postural Control in Postoperative Anterior Cruciate Ligament Reconstruction Patients. Journal of Athletic Training 1999;34(2):130-6. 24. Xergia SA, Pappas E, Zampeli F, Georgiou S, Georgoulis AD. Asymmetries in functional hop tests, lower extremity kinematics, and isokinetic strength persist 6 to 9 months following anterior cruciate ligament reconstruction. J Orthop Sports Phys Ther 2013;43(3):154-62. 25. Clark RA, Pua YH, Fortin K, Ritchie C, Webster KE, Denehy L et al. Validity of the Microsoft Kinect for assessment of postural control. Gait Posture 2012;36(3):372-7.
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LIST OF TABLES
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TABLE 1. Comparison of the anterior cruciate ligament reconstruction (ACLR) and control participants.
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TABLE 2. Correlations between days since surgery and weight bearing asymmetry outcome measures.
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LIST OF FIGURES
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FIGURE 1. Time since surgery for subjects attending their scheduled 6 and 12 month postsurgery follow-up session.
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FIGURE 2. Notched boxplot between group comparison of mean mass difference as a percentage of bodyweight (Mean Mass Difference), time favoring a single limb by greater than 5% of body mass (Time Favoring Single Limb), symmetry relative to the operated or control matched limb (Relative Symmetry Index) and absolute asymmetry irrespective of operated limb (Absolute Symmetry Index) for the anterior cruciate ligament reconstruction and control subjects. The values for median, 75th and 25th percentiles are provided for each group and variable next to each plot. A notched box plot can be interpreted similar to a standard box plot, with the addition of the 95% confidence interval which is represented by the position either side of the median at which the notch ends. If the lower notch of one group does not overlap with the upper notch of the other group this provides visual evidence of a statistically significant between-group difference. * significant difference between groups (p
