Linköping University Medical Dissertations No. 1523 Neck muscle function in individuals with persistent pain and disability after whiplash injury Gunnel Peterson Department of Medical and Health Sciences Linköping University, Sweden Linköping 2016 Gunnel Peterson, 2016 Cover illustration: Emilia Norström Illustration in the thesis: Emilia Norström Published articles have been reprinted with the permission of the copyright holder. Printed in Sweden by LiU-Tryck, Linköping, Sweden, 2016 ISBN 978-91-7685-747-2 ISSN 0345-0082 To my family Att vara smart är att göra något bra. Och är man inte så smart så är det bra att fråga. Albin 4 år Contents CONTENTS ABSTRACT ..................................................................................................... 1 LIST OF PAPERS .......................................................................................... 3 ABBREVIATIONS ......................................................................................... 4 DEFINITIONS .............................................................................................. 5 BACKGROUND............................................................................................. 7 Biomechanics of the cervical spine in whiplash-associated disorders . 7 Diagnosis in WAD ..................................................................................... 8 Ultrasound measurement of skeletal muscle ........................................ 9 Motor control and muscle function ..................................................... 10 Neck muscle function ............................................................................... 11 Muscle adaption to pain ........................................................................13 The biopsychosocial model of pain ......................................................... 13 Treatment of persistent whiplash-associated disorders ..................... 14 Exercises and behavioral approaches in WAD ....................................... 14 Exercise regimens in WAD ...................................................................... 15 The individual perspective on treatment ................................................. 15 Rationale of the thesis ........................................................................... 17 AIMS OF THE THESIS ............................................................................... 18 General aim .......................................................................................... 18 Specific aims ......................................................................................... 18 METHODS .................................................................................................. 19 Study design ......................................................................................... 19 Study population .................................................................................. 20 Participants, study A ............................................................................... 21 Participants study B ................................................................................ 23 Ethical consideration .............................................................................. 25 Data collections .................................................................................... 26 Contents Study A ..................................................................................................... 26 Study B ..................................................................................................... 28 Interventions study A ............................................................................31 Statistical analyses ............................................................................... 35 Group comparison ................................................................................... 35 Correlation and linear regression of deformation and deformation rate ........................................................................................................... 36 Outliers .................................................................................................... 36 Multivariate statistics .............................................................................. 37 RESULTS .................................................................................................... 39 The effect of three different exercise interventions on neck muscle endurance test, pain intensity, kinesiophobia, exercise compliance and patient satisfaction (Paper I) ........................................................ 39 Dorsal Neck Muscle Endurance .............................................................. 39 Ventral Neck Muscle Endurance ............................................................. 39 Neck pain intensity .................................................................................. 39 Kinesiophobia .......................................................................................... 42 Patient satisfaction and exercise compliance ......................................... 42 Mechanical neck muscle function, deformation and deformation rate (Papers II, III and IV) .......................................................................... 42 Comparisons between the WAD and control group in deformation ....... 42 Comparison between the WAD and control groups in deformation rate .......................................................................................................... .45 Neck muscle interactions in individuals with persistent WAD and healthy controls .................................................................................................... 51 Differences in ventral neck muscle function after three months neck- specific exercises compared to waiting-list ......................................... 57 DISCUSSION .............................................................................................. 59 Main findings........................................................................................ 59 Discussion of the results ...................................................................... 59 The effect of three different exercise interventions on neck muscle endurance and pain intensity .................................................................. 59 The effect of three exercise interventions on kinesiophobia, exercise compliance and patient satisfaction ........................................................ 61 Mechanical neck muscle function, deformation and deformation rate ... 62 Contents Neck muscle interactions in individuals with persistent WAD and healthy controls .................................................................................................... 63 Methodological considerations ............................................................ 65 Generalization of the results ................................................................... 65 The effect of three exercise interventions on neck muscle endurance and pain .......................................................................................................... 65 Validity and limitations of ultrasound ..................................................... 67 Gender differences .................................................................................. 69 CONCLUSION ............................................................................................. 71 CLINICAL IMPLICATIONS ....................................................................... 72 FUTURE RESEARCH ................................................................................. 73 SUMMARY IN SWEDISH .......................................................................... 74 ACKNOWLEDGEMENTS .......................................................................... 76 REFERENCES ............................................................................................ 79 Abstract ABSTRACT Background: Neck pain and disability are common after whiplash injury. One year after the accident up to 50 % still have symptoms called whiplash associated disorders (WAD). Despite decades of research the cause of persistent pain and disability are largely unknown and effective treatment and diagnostic tools are lacking. Altered neck muscle function may cause pain and disability, and real-time non-invasive methods that investigate both superficial and deep neck muscle function need to be evaluated. Aim: The general aim of the work presented in this thesis was to investigate mechanical neck muscle function and evaluate effects of three different exercise interventions related to neck muscle function in individuals with persistent pain and disability after whiplash injury. Method: The thesis comprised two studies, reported in four papers. Study A was a prospective randomized controlled trial with 216 participants. The effects of three exercise interventions; neck-specific exercises, neck- specific exercises with behavioral approach and prescription of physical activity were evaluated. Neck muscle endurance, perceived pain following testing, kinesiophobia and satisfaction with treatment were compared between the three groups (paper I). Study B was an experimental case- control study with participants consecutively recruited from the randomized controlled trial. Deformation and deformation rates in the neck muscles were investigated with real-time ultrasound imaging during ten repetitive arm elevations (paper II-IV). To investigate ventral neck muscles,