IWTC in Portland, USA 2006

The Importance of an Early Positive Change in Neck Function in Predicting Improvement Following a Tailored Cervical Strengthening Program for Chronic Neck Pain. Dr Lauren Harding Osteopath M.H.Sc. (Osteo) B.Sc.(Clin.Sc.) B.App.Sc.(H.Mvt.)

Background  There is increasing research that supports the efficacy of muscular strengthening in neck rehabilitation programs.  The role of strengthening for chronic neck pain is still not clear from systematic reviews.  Clinically, neck strengthening is often prescribed by manual therapists for chronic neck pain  However is appears only 50% of patients respond to cervical strengthening (Keating et al 2005).  Useful to be able to predict those that will respond to the intervention.  Just as important to be able to select out those unlikely to respond.

Neck Pain and Neck Weakness – An Association?  Several studies have reported an association between neck pain and neck muscle weakness.  Ylinen et al (2004) demonstrated that pain and maximal strength were inversely related – Pain prevents full effort during strength tests and hence prevents the production of maximal force.  Prushansky et al (2004) report that male and female whiplash victims suffered cervical strength reductions of about 80% and 90% respectively. – Fear avoidance behaviour in these patients resulting in a reduction of maximal force.

Fear Avoidance  Vlaeyen et al (2000) postulate that ‘confrontation’ and ‘avoidance’ are the two extremes.  ‘Confrontation’ = reduction of fear over time.  ‘Avoidance’ = maintenance or exacerbation of fear.  Fear Avoidance may play a role in: – poor muscular performance – de-conditioning

Exercise Interventions for Chronic Neck Pain  Verhagen et al (2004) concluded that active interventions tended to be more effective than passive interventions.  Gross et al (2004) concluded that mobilization and manipulation techniques are only effective when combined with exercise.

How Many People Respond to Exercise Therapy?  Keating et al (2005) investigated three RCTs to determine the percentage of people that changed on the NDI by more than the MCID in response to exercise therapy.  Three RCTs were Brontfort et al (2001), Korthals-de Bos et al (2003) and Ylinen et al (2003).  Stratford et al (1999) propose MCID for NDI of 7/50 points (14%).  Authors argue that approximately 50% of people benefit from exercise therapy.

Where to from here?  Prescribing neck strengthening for everyone presenting with neck pain is likely to prove ineffective for 50% of those seeking care.  Clinicians often see patients achieve significant functional improvements in response to neck strengthening programs.  Challenge is in identifying those people likely and unlikely to benefit from any treatment intervention.  How long should a person persist with an exercise routine before the probability of response is unacceptably low?

Aim  To determine the efficacy of early change in NDI scores for predicting people who are likely to respond or not respond to an exercise program.  Hypothesis: The probability of responding to a course of neck strengthening treatment is greater in those that respond in the first 3 weeks.

Methods  Between 2000 and 2003, three hundred and nine (309) patients were referred to a Clinic in Australia for treatment of chronic neck pain.  Two hundred and forty one started treatment (241).  Reasons for not starting treatment included:  Personal reasons (n = 53) – time, funds, location  Aggravated symptoms after initial evaluation (n = 6)  Did not meet inclusion criteria (n = 4)  Not approved for treatment from third party payer (n = 2)  Waiting on legal proceedings (n = 1)  Referred to interstate Centers (n = 1)  Advised against the program by a doctor (n = 1)

Methods  Twenty seven (27) patients dropped out before first re-evaluation: – Personal reasons (n = 12) – Flared symptoms (n = 5) – Dissatisfaction with results (n = 8) – Unknown (n = 2)  Two hundred and fourteen (214) completed > than a 3 week strengthening program.

Equipment  Multi-Cervical Unit (BTE Technologies Inc.) “MCU”  Used to measure maximal isometric strength of flexors, extensors and lateral flexors in: – in neutral – 25° rotation left and right – 45° rotation left and right  Excellent reliability in isometric strength measurement with ICCs ranging from 0.92 – 0.99 (Chui et al 2002).

Exclusion Criteria  Unable to initiate 3 lbs (1.36kgs) of force for isometric testing.  Flare-up post-evaluation that lasted for longer than 36 hours.  Significant exacerbation of peripheral symptoms.

The Initial Evaluation  History and duration of complaint  Age  Gender  Compensation status (Private or Compensable)  Neck Disability Index  VBI screening  Evaluated on the MCU for Maximal Isometric Strength

Maximal isometric strength testing  Participants were allowed familiarization  “Push as hard and as fast as you can”  Hold maximal isometric contraction for 3 seconds.  3 trials with 10 second rest period between trials  Trials were averaged to obtain maximal isometric strength in lbs.  Trials were repeated if an effort was not within COV of 15%.

Treatment Program  The exercise program was designed to achieve strength scores comparable to isometric strength measurements of 100 healthy subjects (Jordan et al 1995).  Initial resistance = 25-40% of the maximum isometric score achieved during testing  2-3 times per week  30 minute supervised session  3 sets of 10 repetitions for each of 6-8 exercises  Participants were re-evaluated for strength and NDI scores after every 9 sessions until discharge.

Length of Program  Time period between initial and final evaluation dependent upon: – How quickly a person responded to therapy – How long the person took to complete each 9 sessions

Responders  The MCID (minimum clinically important difference) for the NDI is 7 points (Stratford 1999).  Participants were considered responders if their NDI scores had changed by 7 points or more, or as non-responders if the NDI score did not change by 7 points or more.

Analysis of Data  Linear Regression analysis was used to study the relationship between final NDI scores and 3 week NDI change scores.  Odd ratios were used to describe the relationship between 3 week and discharge NDI scores.  Other analyses included positive and negative predictive scores, and sensitivity and specificity. Unable to report all due to time restraints.

Demographics  80/115 were female (70%)  Average age - 41 years (SD 12)  67 private (58%); 48 compensable (42%)  Median duration of symptoms – 60 months (inter-quartile range 19 – 120)  Median initial NDI scores – 18 points (36%) (inter-quartile range 14 – 25 points)  Median length of treatment – 10 weeks (inter- quartile range 7 – 14 weeks)

Results of Regression Analysis  A positive change in the 3 week NDI score explained 47% of the variance in the final NDI positive change (F = 97.36; p = 0.00).  Significant association between 3 week and discharge NDI scores (r = 0.69; p = 0.00)

Regression Line of Best Fit

Contingency Table Improved Not Total at Final Improved at Final Improved 41 3 44 at 3 weeks Not 25 46 71 Improved at 3 Weeks Total 66 (57%) 49 115

Results of Odds Ratio Analysis  Odds ratio = 25.15 (95% confidence interval 7.07 – 89.49)  If a patient demonstrated a positive improvement after 3 weeks of therapy, then the patient has a 25 x greater (25.15) odds of responding overall to the course of neck strengthening therapy.

Possible Mechanisms of Effect  Fear Avoidance Model – Fear avoidance has been proposed to play a role in “de-conditioning” (Vlaeyen 2000). – Neck strengthening pushes these patients into the confrontation extreme of the fear avoidance model which can result in a reduction in fear and therefore a reduction in self perceived disability.  Increase in muscle fibre size (hypertrophy)  Motor Skill Acquisition – CNS harnesses existing resources to perform activities more efficiently.  Changes in co-activation of antagonists

Early Change to Strengthening  Hypertrophy does not occur until after 3 weeks  Sub-group of patients (35.7%) who respond favorably in the first 3 weeks  Change is likely motor skill acquisition

Later Change to Strengthening  Combination of motor skill acquisition and muscle hypertrophy?  Additionally there may have been changes in the co-activation of the antagonists  Hakkinen et al (1998) demonstrated that progressive strength training leads to significant decreases in the co-activation of the antagonists recorded during maximal isometric action.

Role of Further Strengthening in Early Responders  Why continue with strengthening in the early responders?  Average additional improvement is only 2 NDI points.  Still a role for continued strengthening in early responders for protective/maintenance effects rather than discharging patients after 3 weeks.  Six month or two year follow up would be useful to compare outcome differences between early responders discharged at 3 weeks and early responders discharged at 6 or 9 weeks.  Collected but not yet analyzed.

Future Research Directions  Use of EMG and MVC to further study the mechanism of effect for early and late responders  Could more specifically define the contributions of motor skill acquisition and muscle hypertrophy  Investigate other factors that may have contributed to a reduction in self perceived disability – Fear avoidance questionnaires – Joint ROM – Measure both agonists and antagonists via EMG

Future Research Directions  Six month follow up comparing the outcomes of early responders discharged after 3 weeks and early responders who continued for further therapy  Predictor variables for late responders (n = 25)  Correlate increase in strength with a decrease in self perceived disability (functional questionnaire such as NDI)

Implications for Clinicians, Patients and Third Party Payers  Neck strengthening programs do not provide hypertrophy benefits alone.  Clinicians can provide a probability for response based on early change (as early as 3 weeks). – For responders, this can aid in further third party approval or encourage patients to continue for the protective or maintenance effects (based on the clinical premise that further rehabilitation will improve longer term outcome). – For non-responders at 3 weeks, clinicians can provide patients with a probability for longer term change and the patient, clinician or third party can decide if the odds warrant continued investment in the program.

Acknowledgements  BTE Technologies, Colorado www.btetech.com  Melbourne Whiplash Centre www.whiplashcentre.com  Professor Jenny Keating, Monash University, Melbourne, AUSTRALIA.

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IWTC in Portland, USA 2006

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