Immediate effects of inhibitive distraction on active range of cervical flexion in patients with neck pain
From: J Man Manip Ther. 2007;15(2):82-92
Neck pain as well as headaches with a proposed neck related etiology or contribution are highly prevalent disorders. Doug lass and Bope reported a point-prevalence for neck pain in the general population of 9%. They further noted a 1 month, 6 month, and lifetime prevalence of 10%, 54%, and 66%, respectively. In a cross-sectional population survey, investigators found an 18% prevalence for chronic neck pain greater than months’ duration. Headache types associated with cervical spine dysfunction include tension type and cervicogenic headache, occipital neuralgia, and to a lesser extent migraine headaches. Tension type headache affects two-thirds of men and over 80% of women in developed countries. For the general population, the prevalence of cervicogenic headache varies between 0.4% and 2.5%; in those with chronic headaches, prevalence may be as high as 15% to 20%.
Neck pain and headache are not only highly prevalent but also frequent reasons for patients to seek medical or physical therapy care. In the United States, neck pain accounts for almost 1% of all primary care physician visits, and cervical spine diagnoses were the reason for referral in 16% of 1,258 outpatient physical therapy patients, second only to lumbar spine related diagnoses, which accounted for 19% of referrals. No data are available on the prevalence of headache as a cause for physical therapy management; however, an investigator reported headache as co-morbidity in 22% of 2,433 patients presenting for outpatient physical and occupational therapy, and headaches are reportedly the leading cause for visits to a neurologist.
Physical therapists place a diagnostic emphasis on identifying impairments that may be amenable to management with interventions within their scope of practice. In this context, impairments are defined as any loss or abnormality of body structure or of a physiological or psychological function. Studies have shown a strong correlation between neck pain and restricted cervical flexion-extension mobility, and limited motion may be the most relevant impairment associated with neck pain and headache of a proposed cervical etiology. An investigator attributed cervical hypomobility to either a voluntary or reflexogenic muscular restraint caused by pain or a purely mechanical restraint caused by degeneration of the joint surfaces and ligaments. Corresponding to said degenerative process, investigators described a fibrotic process in connective tissue, whereby it shrinks progressively, caused by arthrokinematic dysfunction, poor posture, overuse, habit patterns, or structural or movement imbalances. They further suggested that in many cases the surrounding musculature maintains a hypertonic recruitment pattern long after the inducing injury has healed, potentially immobilizing joints by the surrounding muscle hypertonicity.
Myofascial trigger points in the cervical muscles constitute another potentially relevant muscle dysfunction leading to limited cervical spine mobility. These are defined as hyperirritable spots in skeletal muscle with a potential to give rise to characteristic referred pain, motor dysfunction, and autonomic phenomena. Motor aspects of myofascial trigger points may include disturbed motor function, muscle weakness as a result of motor inhibition, and most importantly in the context of this study—muscle stiffness and restricted range of motion. Trigger points in the head and neck region have been implicated in the reported headache and central sensitization in patients with tension type headache. Their referral patterns correspond to the pain characteristics and distribution reported by patients with cervicogenic headache, occipital neuralgia, and migraine headache. Studies have reported significantly greater numbers of active myofascial trigger points in the suboccipital muscles of patients with tension type headache and in patients with migraine headache when compared to asymptomatic controls. Motor effects of these suboccipital myofascial trigger points in the sense of muscle shortening may explain the increased forward head posture and decreased cervical active range of motion reported in patients with chronic tension type headache or migraine headache as compared to asymptomatic controls.
Relevant to the management of patients with neck pain and headache, Paris has described a technique called inhibitive
distraction in which the therapist uses the fingertips of both hands to exert a sustained ventrocranial force on the occiput just caudal to the superior nuchal line. He proposed that this technique might inhibit the muscles inserting into the nuchal line and that it could be used to apply a distraction to the cervical spine structures. Paris did not claim this technique as his own, instead ascribing its origin to cranial osteopathy. Indeed, this technique has been described within various manual medicine disciplines under various names such as cranial base release, suboccipital release, and trigger point pressure release. The proposed effects are mainly neurophysiological, perhaps circulatory, and mildly mechanical.
Within the context of this study, the relevant suggested effects of inhibitive distraction on the cervical spine involve inhibition of local and general posterior muscle tone, inactivation of suboccipital muscle trigger points, and gentle joint mobilization. These effects are all hypothesized to result in an increase in cervical flexion active range of motion. Therefore, the purpose of this pilot study was to examine the immediate effects of inhibitive distraction on active range of motion into cervical flexion in patients with neck pain with or without concomitant headache. The main objective was to show whether, when used alone in a single treatment session, this intervention would signifi cantly increase cervical flexion active range of motion. A secondary objective of this study was to see whether patient subgroups could be identified that might benefit more from inhibitive distraction by studying variables such as age, pain intensity, presence
of headache, or pre-intervention active range of motion and by looking at patients’ ability to identify pre to post intervention changes in their ability to actively move through a range of motion.
For both the experimental and the placebo intervention, the patient was asked to rest supine on the treatment table. The experimental inhibitive distraction intervention had the therapist place the fingertips onto the suboccipital musculotendinous structures just caudal to the superior nuchal line and induce a sustained force in a ventrocranial direction, thus exerting compressive forces as well as a distraction to the cervical and suboccipital structures. The pressure applied to achieve muscle inhibition during treatment was applied slowly, maintained, and then released slowly; it was applied perpendicular to the longitudinal axis of the muscles and tendons involved. The amount of applied pressure was adjusted to just less than that which would excite the muscle further, and as the therapist maintained the pressure and the patient’s muscles relaxed, ideally the pressure was applied at an increasingly deeper level. Good palpatory awareness is important for correct execution of inhibitive distraction, as excessive pressure will have the opposite effect by causing irritation and an undesired increase in muscle tone. In other words, the amount of pressure applied was individualized according to therapist perception of the patient’s tolerance as reflected by muscle response. This muscle response was constantly monitored and thus, the amount of pressure could change during the administration of this intervention. Thus, the force applied varied anywhere from light pressure and no distraction forces applied with the weight of the subject’s head partially supported by the therapist’s thenar eminences, to the full weight of the subject’s head resting on the therapist’s fingertips and distraction applied. The inhibitive distraction intervention was applied for 3 to 3.5 minutes.
Those in the control group rested their heads in the palms of the clinician for the same duration to mimic the treatment position as much as possible. In this way, these subjects received the effects of touch, warmth, and rest, without the actual proposed mechanical effects of the experimental inhibitive distraction intervention.
Although equally affecting both groups, an important issue that needs to be addressed concerns the observed variability of change in active range of motion. In this study, the amount of change in active cervical flexion over all varied greatly, regardless of whether the patient received the pressure treatment or the placebo treatment, and ranged from a decrease of 10° to an increase of 16°. A large variability in cervical active range of motion has been reported for both asymptomatic and symptomatic subjects, measured with an electro-goniometer and an electromagnetic tracking system. Alteration in proprioceptive sensibility is a dysfunction recognized in patients with cervical pain, and Rheault et al suggested that a “guarding” effect at the end of active range of motion may be a characteristic of patients with neck dysfunction. Both proprioceptive dysfunction and end-range guarding may have led to the great degree of variability between measurements observed in the symptomatic subjects participating in this study, in spite of our efforts to minimize measurement errors. It is possible that the observed variability “washed out” the small pre to post intervention changes observed in this study, and we have to consider that active range of motion measurements may not be an appropriate outcome measure to study the effects of inhibitive distraction and other manual interventions. Alternatively, variability could possibly be decreased by selection criteria that result in a more homogenous patient population.
As noted above, we were not able to identify subgroups more likely to benefit from inhibitive distraction however, a trend for the greatest post-intervention changes was found in those subjects in the experimental group, who complained of headaches, indicated lower levels of pain, had less pre-intervention active range of motion, and had suffered discomfort for greater than 6 months. These subjects may have had symptoms that were more likely to respond to a muscle inhibitory treatment or they may have tolerated the treatment better due to a more chronic state and lower levels of pain, or both. In this study, a number of the patients in the experimental group did not tolerate the full application of inhibitive distraction and received only gentle pressure not dissimilar from the placebo intervention. Consequently, a sufficient mechanical and/or neurophysiological effect was probably not obtained and statistical significance of between group differences was likely affected. Future studies and possibly clinical application of this technique should likely limit selection criteria to reflect the trend for greater improvement in chronic patients with headaches, lower pain levels, and less active range of motion.
The results of the present study suggest that applying sustained pressure to the sub-occipital region does not result in improved cervical flexion active range of motion. The results do not, however, exclude the occurrence of potential short-lived neurophysiological inhibitory effects, as these were not directly measured. Studies on the effects of tendon pressure on muscle activity have found that although excitability of the motor neurons supplying the muscles decreased, this effect lasted only as long as the stimulus was present. If immediate short-lived inhibitory effects are, in fact, achieved, sustained pressure treatment may be suitable as a preparatory treatment for soft-tissue or joint manipulation, which should take place immediately after the application of the inhibitory pressure. This may have implications for future study with inhibitory distraction as part of a pragmatic physical therapy intervention and for its use in clinical practice. Our results, however, show no indication that any effects due to the sustained pressure alone are maintained long enough to be beneficial to the patient, e.g., for self-stretching or range of motion exercises after the pressure is released.
A final consideration is that the inhibitory distraction technique may have a local rather than the proposed regional effect, i.e., that its effect is limited to the suboccipital muscles. If this is the case, the expected changes in active range of motion may be limited to cranio-cervical motion and might not be captured with a general cervical flexion active range of motion measurement.
This pilot study researched the immediate effects of inhibitive distraction on cervical flexion active range of motion in patients with neck pain with or without associated headache. It also attempted to identify potential subgroups more amenable to this technique based on subject age, pain intensity, presence of headache, or preintervention active range of motion. The results did not show a statistically significant advantage of inhibitive distraction over the placebo treatment. We were also unable to identify potential subgroups more likely to respond to inhibitive distraction, although a trend emerged for greater improvement in chronic patients with headaches, lower pain levels, and less active range of motion.
A large variability in active range of motion and intervention response contributed to the low power observed in the present study. Future studies should use selection criteria that are likely to produce a more homogenous study population by including only patients with symptoms of greater than 6 months’ duration, headaches, lower pain levels, and more restricted preintervention active range of motion. To allow for inferences with regard to the predictive validity of subject age with regard to outcome, older subjects will need to be recruited. Future studies may compare the effects of inhibitive distraction on patients with cervicogenic versus tension type headache, or as part of a pragmatic program to be directly followed by other manual interventions. If active range of motion measurements are selected as outcome measures, perhaps cranio-cervical rather than general cervical flexion measurements should be considered.
The limitations in this pilot study do not allow us to make inferences either way; inhibitive distraction may or may not have an immediate effect on cervical flexion active range of motion. The trend for greater effect noted in chronic patients with headaches, lower pain levels, and less active range of motion, in their opinion, warrant further study into this technique and continued—albeit more discerning—use of this technique in clinical practice.
