Physiotherapy for osteoarthritis of the knee

391 Pages·2012·3.8 MB·English

Physiotherapy for osteoarthritis of the knee:
Predictors of outcome at one year

Cathy Chapple

A thesis for the degree of
Doctor of Philosophy
At the University of Otago, Dunedin,
New Zealand

26 September 2011
Abstract
Background: Knee osteoarthritis (OA) is a prevalent disease which
contributes to significant pain and disability in older individuals. There is
increasing evidence that physiotherapy, in the form of exercise or manual therapy,
is an effective intervention. However, not all knee OA patients will benefit from
physiotherapy treatment, and there are numerous other treatment options.
Matching effective interventions to individuals who are most likely to benefit is
desirable.
Aim: To identify predictors of successful response to physiotherapy
treatment, evaluated at one year, for individuals with knee OA.
Methods: This observational cohort study was nested within a randomised
controlled trial investigating effectiveness of physiotherapy for individuals with
lower limb OA. Selection of variables for a standardised baseline assessment was
informed by a systematic review identifying predictors of knee OA progression,
and an inter-rater reliability study. A scale was developed to provide a valid and
reliable method for assessing irritability, a potential predictor of outcome.
Participants received physiotherapy including exercise and manual therapy.
Outcome was evaluated at nine weeks and one year using the Western Ontario
and McMaster osteoarthritis index (WOMAC) and global rating of change (GRC)
transition scale; with response determined using OMERACT-OARSI (Clinical
Trials Response Criteria Initiative and Outcome Measures in Rheumatology/
Osteoarthritis Research Society International) responder criteria. Nine week
response was investigated as an additional predictor of successful outcome.
Data Analysis: Pre-test probability of success was the number of participants
with a successful response following physiotherapy treatment, divided by the
total number of participants in the treatment cohort.
ii
Baseline variables with a univariate association with one year outcome
(p<0.2), were entered into multivariate logistic regression with backward
elimination, to identify a set of variables (p < 0.1) that predicted successful
outcome at one year. Accuracy statistics were used to calculate post-test
probability of success for different numbers of retained predictors. A novel
approach used post-estimation analysis to identify named combinations of
variables, and associated probability of success.
Results: Pre-test probability of success was 35%. Six predictors of success
were identified: posterior knee pain, disturbed sleep, absence of knee injury,
instability, symptom duration (> 5 years), and female sex. The optimal model,
with at least four out of six predictors, increased post-test probability of success to
66%. Presence of less than three out of six predictors decreased post-test
probability of success to 11%. Using the post-estimation test, a five variable model
(posterior knee pain, disturbed sleep, absence of knee injury, instability, and
female sex), gave an 87% probability of success.
Data from the usual care control group did not fit the model, providing some
evidence that variables were predictors of treatment response rather than natural
progression of knee OA.
Nine week response gave an inferior prediction of probability of success at
one year (52%), but combined with baseline predictors produced an optimal
model of at least five out of seven predictors, with a post-test probability of 86%.
Conclusion: It is possible to use baseline variables, with or without nine
week response, to predict physiotherapy treatment response at one year, for
patients with knee OA. These findings represent the derivation stage of a clinical
prediction rule which requires validation in future research.

iii
Acknowledgements

My thanks and appreciation goes to my supervisory team, Professor Helen
Nicholson, Professor G. David Baxter, and Dr J Haxby Abbott. I’m amazed and
grateful for the time and effort you have put towards the production of this
thesis.
Haxby, thanks for providing me with the opportunity and convincing me I
could do it.
Helen, for always keeping your eye on the end game, and dragging me back
on track whenever I veered off course, thank-you.
Dave, thanks for encouraging and supporting me throughout (was it carrot
or was it stick?)
Special thanks to my two fellow PhD/MOA colleagues, Lexie and Dan, for
generously sharing your time and knowledge. It was great to share the journey,
and I couldn’t have done it without you!
Thank-you Dr Jose Garcia, for revealing the mysteries of biomedical
statistics, and helping me with the analysis.
Thanks Emma Tumilty for countless things, and for always doing them with
a smile.
Thanks to Dr Marina Moss and the other MOA clinical trial administrators,
Andrew Sullivan, Helen Ingrams, and Bob Matthews. Your professionalism and
hard work was much appreciated, as well as your time and support for me.
Brigid Ryan, thanks for being a complete star!
Thank-you to everyone involved with the MOA trial: co-investigators,
physiotherapists and all the participants. Without all your hard work and time I
wouldn’t have had a study! It is much appreciated.
ii
Thanks also to Sinead Lodge and the staff in the School of Physiotherapy
Clinics, for keeping me grounded in the real world of clinical practice, and for lots
of words of encouragement and support. Special thanks to Sue Kennedy (my
unofficial supervisor!).
Thanks to the Staff and postgraduate students at the School of
Physiotherapy; so many of you have helped me at different times. It’s been great
to be part of the physiotherapy PhD community, there’s nothing like going
through it together, and I wish you all luck for completing your studies.
Thank-you to all my physiotherapy friends and colleagues, especially those
from Dunedin Hospital. Thanks for your support and for believing that I could
do it.
Thanks to all my friends in New Zealand and England for your help,
encouragement and support; for not telling me too often I was mad, for excusing
me from all sorts of things, for picking up the kids or keeping them occupied, and
for all the numerous ways you have helped me to keep all the balls in the air!
Thanks especially to Mum and Dad and the rest of my family, for always
encouraging me to pursue my goals, and having faith in me to achieve them.
A huge, massive, enormous thank-you to my two boys, Matt and Robbie, for
sharing Mum with this PhD thing (even though it has “only got eight chapters”);
for trying hard to let me study, for putting up with me not always being there,
and for reminding me what’s really important!
And finally, thank-you Mike for everything…
iii
Table of Contents
1. Introduction __________________________________________________ 1
2. Systematic review of prognostic studies: variables that predict
progression of knee osteoarthritis ___________________________________ 11
2.1. Introduction ____________________________________________________ 11
2.2. Methods _______________________________________________________ 12
2.2.1. Search and identification of studies __________________________________ 12
2.2.2. Assessment of bias ________________________________________________ 15
2.2.3. Data extraction ___________________________________________________ 18
2.2.4. Synthesis of evidence ______________________________________________ 18
2.3. Results ________________________________________________________ 19
2.3.1. Search results ____________________________________________________ 19
2.3.2. Study details _____________________________________________________ 19
2.3.3. Assessment of Bias ________________________________________________ 20
2.3.4. Synthesis of evidence ______________________________________________ 23
2.3.5. Sensitivity analysis ________________________________________________ 34
2.4. Discussion _____________________________________________________ 35
2.4.1. Comparison with previous research _________________________________ 36
2.4.2. Study limitations _________________________________________________ 38
2.4.3. Implications for future research _____________________________________ 40
2.4.4. Summary ________________________________________________________ 41
2.5. Implications for selection of baseline variables as potential predictors of
treatment response for patients with knee OA ____________________________ 41
3. The concept of irritability and development of the i-score ________ 43
3.1. Overview ______________________________________________________ 43
3.2. Concept of irritability ___________________________________________ 43
3.3. Scale development and testing ___________________________________ 45
iv
3.3.1. Item selection ____________________________________________________ 45
3.3.2. Scaling of responses _______________________________________________ 45
3.3.3. Conversion of items to a scale ______________________________________ 46
3.3.4. Testing psychometric properties ____________________________________ 46
3.4. Methods _______________________________________________________ 48
3.4.1. Existing method for assessment of irritability _________________________ 48
3.4.2. Development of scale for assessment of irritability _____________________ 48
3.4.3. Testing psychometric properties of the i-score ________________________ 50
3.4.4. Recruitment ______________________________________________________ 53
3.4.5. Data analysis _____________________________________________________ 54
3.5. Results ________________________________________________________ 55
3.6. Discussion _____________________________________________________ 64
3.6.1. Previous research _________________________________________________ 64
3.6.2. Strengths ________________________________________________________ 64
3.6.3. Limitations_______________________________________________________ 66
3.6.4. Future research ___________________________________________________ 67
3.6.5. Implications for use of the i-score ___________________________________ 68
3.7. Conclusions ____________________________________________________ 69
4. Inter rater reliability of baseline measures ______________________ 70
4.1. Introduction ____________________________________________________ 70
4.2. Methods _______________________________________________________ 71
4.2.1. Literature review _________________________________________________ 71
4.2.2. Investigation of inter-rater reliability for clinical tests __________________ 72
4.2.3. Data analysis _____________________________________________________ 73
4.3. Results ________________________________________________________ 75
4.3.1. Literature review _________________________________________________ 75
4.3.2. Physical examination – investigation of inter-rater reliability of clinical
measures ________________________________________________________ 92
4.4. Discussion ____________________________________________________ 102
v
4.4.1. Limitations and implications for future research ______________________ 103
4.5. Conclusion ____________________________________________________ 106
5. Study to identify predictors of outcome: Methods ______________ 107
5.1. Chapter overview ______________________________________________ 107
5.2. Study design __________________________________________________ 108
5.2.1. Study setting ____________________________________________________ 109
5.2.2. Participants _____________________________________________________ 110
5.2.3. Assessors _______________________________________________________ 113
5.3. Baseline assessment ____________________________________________ 113
5.3.1. Patient history ___________________________________________________ 114
5.3.2. Clinical features and physical examination __________________________ 117
5.4. Overview of trial procedure _____________________________________ 124
5.4.1. Randomisation __________________________________________________ 124
5.4.2. Standardised treatment ___________________________________________ 124
5.4.3. Follow-up assessments ___________________________________________ 125
5.5. Outcome measures _____________________________________________ 126
5.6. Response Criteria ______________________________________________ 127
5.7. Data management and preparation ______________________________ 128
5.7.1. Management of missing data ______________________________________ 128
5.7.2. Management of incomplete data due to surgical intervention __________ 130
5.7.3. Screening of baseline variables for analysis __________________________ 131
5.7.4. Cut-points in data ________________________________________________ 132
5.8. Data analysis __________________________________________________ 133
5.8.1. Overview of analysis _____________________________________________ 133
5.8.2. Univariate analysis _______________________________________________ 135
5.8.3. Multivariate analysis _____________________________________________ 135
5.8.4. Confounders ____________________________________________________ 136
5.8.5. Combinations of predictor variables and post-test probability __________ 136
5.8.6. Secondary analyses ______________________________________________ 138
vi
6. Study to identify predictors of outcome: Results ________________ 142
6.1. Overview _____________________________________________________ 142
6.2. Characteristics of knee OA cohort from the clinical trial ____________ 142
6.3. Dropouts, missing data and surgical participants __________________ 147
6.4. Baseline variables for prognostic study ___________________________ 149
6.4.1. Screening of baseline variables _____________________________________ 149
6.4.2. Creation of cut-points in data ______________________________________ 156
6.5. Predictors of success at one year for participants with knee OA following
physiotherapy intervention _____________________________________ 157
6.5.1. Successful outcome at one year ____________________________________ 157
6.5.2. Univariate analysis identifying baseline variables associated with success at
one year ________________________________________________________ 158
6.5.3. Multivariate analysis identifying baseline variables associated with success at
one year ________________________________________________________ 159
6.5.4. Stratified analysis ________________________________________________ 161
6.5.5. Clusters of predictor variables, and post-test probability of success at one
year ____________________________________________________________ 162
6.5.6. Secondary analyses ______________________________________________ 170
6.5.7. Sensitivity Analyses ______________________________________________ 181
7. Study to identify predictors of outcome: discussion _____________ 197
7.1. Chapter overview ______________________________________________ 197
7.2. Predicting success with physiotherapy for patients with knee OA ___ 197
7.2.1. Posterior knee pain _______________________________________________ 198
7.2.2. Absence of previous knee injury ___________________________________ 200
7.2.3. Disturbed sleep __________________________________________________ 202
7.2.4. Instability _______________________________________________________ 203
7.2.5. Sex _____________________________________________________________ 204
7.2.6. Symptom duration ( > 5 years) _____________________________________ 206
7.2.7. Hip external rotator muscle strength ________________________________ 208
vii
7.2.8. Irritability _______________________________________________________ 209
7.3. Variables not identified as predictors ____________________________ 210
7.4. Secondary analyses ____________________________________________ 214
7.4.1. Do identified variables predict response to physiotherapy intervention
or natural progression over one year? ____________________________ 214
7.4.2. Nine week response as predictor of one year outcome _________________ 215
7.4.3. Predictors of poor outcome at one year______________________________ 218
7.5. Sensitivity analyses ____________________________________________ 218
7.6. Comparison with previous findings _____________________________ 220
7.7. Strengths and limitations _______________________________________ 221
7.7.1. Strengths _______________________________________________________ 221
7.7.2. Limitations______________________________________________________ 223
7.8. Summary _____________________________________________________ 228
7.8.1. Clinical implications _____________________________________________ 228
7.8.2. Research implications ____________________________________________ 230
8. Predictors of outcome following physiotherapy for individuals with
knee osteoarthritis: Conclusions _________________________________ 234
8.1. Summary of major findings of prognostic study ___________________ 234
8.2. Summary of major findings of supplementary studies _____________ 237
8.2.1. Systematic review identifying predictors of progression in patients with
knee OA ________________________________________________________ 237
8.2.2. The concept of irritability and development of the i-score ______________ 238
8.2.3. Inter-rater reliability of clinical tests used to evaluate patients with knee OA
________________________________________________________________ 239
8.3. Strengths and limitations _______________________________________ 240
8.4. Research implications __________________________________________ 241
8.5. Clinical implications ___________________________________________ 243
viii