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
M.H.Sc. (Osteo) B.Sc.(Clin.Sc.) B.App.Sc.(H.Mvt.)
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
Just as important to be able to select out those unlikely
Neck Pain and Neck Weakness – An
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%
– Fear avoidance behaviour in these patients resulting
in a reduction of maximal force.
Vlaeyen et al (2000) postulate that
‘confrontation’ and ‘avoidance’ are the two
‘Confrontation’ = reduction of fear over time.
‘Avoidance’ = maintenance or exacerbation of
Fear Avoidance may play a role in:
– poor muscular performance
Exercise Interventions for Chronic
Verhagen et al (2004) concluded that active
interventions tended to be more effective than
Gross et al (2004) concluded that mobilization
and manipulation techniques are only effective
when combined with exercise.
How Many People Respond to
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
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
Challenge is in identifying those people likely
and unlikely to benefit from any treatment
How long should a person persist with an
exercise routine before the probability of
response is unacceptably low?
To determine the efficacy of early change
in NDI scores for predicting people who
are likely to respond or not respond to an
Hypothesis: The probability of responding
to a course of neck strengthening
treatment is greater in those that respond
in the first 3 weeks.
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)
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
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
measurement with ICCs
ranging from 0.92 – 0.99
(Chui et al 2002).
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
The Initial Evaluation
History and duration of complaint
Compensation status (Private or Compensable)
Neck Disability Index
Evaluated on the MCU for Maximal Isometric
Maximal isometric strength testing
Participants were allowed familiarization
“Push as hard and as fast as you can”
Hold maximal isometric contraction for 3
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%.
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
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
Other analyses included positive and negative
predictive scores, and sensitivity and specificity.
Unable to report all due to time restraints.
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)
Improved Not Total
at Final Improved
Improved 41 3 44
at 3 weeks
Not 25 46 71
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
Changes in co-activation of antagonists
Early Change to Strengthening
Hypertrophy does not occur until after 3
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
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
Why continue with strengthening in the early
Average additional improvement is only 2 NDI
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
Could more specifically define the contributions
of motor skill acquisition and muscle
Investigate other factors that may have
contributed to a reduction in self perceived
– 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
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.
BTE Technologies, Colorado
Melbourne Whiplash Centre
Professor Jenny Keating, Monash
University, Melbourne, AUSTRALIA.
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