The centralization phenomenon: Its role in the assessment and management of low back pain

One of the most common and perplexing problems faced by the primary care physician is the clinical management of the patient with low back pain. Roughly 60% of individuals in the population will experience low back pain in their lives,[1] yet this condition is poorly understood and often poorly managed, despite growing evidence that demonstrates the value of the physical examination in low back pain management.

Perhaps the main difficulty associated with low back disorders is making a meaningful diagnosis. In most cases this is either difficult or impossible. The Quebec Task Force Report lists 21 terms used to describe low back disorders and the lack of consistency in their application.[2] The authors of the report conclude that these diagnostic determinations are “the fundamental source of error,” and propose a new classification system based, in part, on symptom location. Although this leads to greater uniformity of sorting, it does not solve the problem of clinical management. Diagnostic imaging, particularly by MRI, gives great anatomical detail but is often diagnostically unreliable because of high rates of false-positive and false-negative findings.[3-6]

Without an appropriate diagnosis, selecting a treatment becomes guesswork. Deyo[7] describes the history of the treatment of low back pain as consisting of a succession of fads, each initially practised with widespread enthusiasm then discarded. The Occupational Health Guidelines for the Management of Low Back Pain at Work[8] and many other clinical guidelines catalogue the lack of demonstrated efficacy of many commonly used therapies.

There is now considerable evidence that a large part of the solution lies in the clinical evaluation. A curious contrast exists between the assessment of a peripheral joint problem and that of a spinal joint. In the former case, the clinician is likely to gather information from the following sources:

• Patient’s history of onset.
• Factors that aggravate or relieve symptoms.
• A physical examination, which includes stressing the joint thoroughly in all directions.

All this information is rightly considered essential in making a diagnosis. In the case of spinal joints, this procedure is poorly understood by many clinicians and is therefore rarely followed; consequently, clinical management is somewhat arbitrary.

Many clinicians have expressed the opinion that information obtained from patients regarding their pain response to movements and positions is “too subjective” and is thus suspect. In fact, many studies have documented just the opposite: the strong reliability of measuring the patient’s pain response to clinical tests.[9-12] The straight leg raising test and the coughing test that can elicit the concordant pain of sciatica are just two examples of pain response tests commonly used by physicians when assessing spinal disorders. In contrast, many of the so-called objective tests—for example, X-rays and CT and MRI scans—have proven of little value in evaluating spinal pain because of high rates of false-positive and false-negative findings.[4,6,13-15]

Studies over the last 15 years have shown that the low-tech physical examination can reveal useful information that makes effective management possible for large numbers of patients. Many of these studies, some of which are discussed here, refer to the phenomenon of pain “centralization” and its helpfulness to doctors in their clinical decision making.

Centralization

In 1981, physiotherapist Robin McKenzie[16] described the phenomenon of centralization, which occurs when referred pain moves from a distal to a more proximal location. This can be observed when a patient bends backward and forward during a clinical examination.

For example, a patient presenting with pain referred into the calf may report that the calf pain abolishes after bending backward into full extension a few times. Often, further movements in the same direction will lead to the pain migrating even closer to the spine. When the test movements have been completed, the distal pain remains abolished.

Based on his many years of clinical observation of patients with low back pain, McKenzie claimed that this phenomenon was a reliable indicator of a good clinical outcome. By contrast, he noticed that where pain failed to centralize or moved more distally—to become “peripheralized”—the clinical outcome was consistently poorer. Subsequent published peer-reviewed studies of centralization confirm this claim.[17-26]

The first of these studies, published in 1990 by Donelson and colleague[25] was a retrospective analysis of patients seen at an orthopaedic outpatient clinic with complaints of low back and referred pain. Those patients in whom centralization was demonstrated during the initial assessment were in the great majority (more than 80%) and typically went on to an excellent outcome, while those few who did not centralize tended to fare poorly. The small number who eventually required disc surgery were all “noncentralizers” at the time of their initial assessment.

Subsequently, 10 additional peer-reviewed studies have reported on the high frequency with which centralization occurs, both in the acute and chronic low back pain populations. In acute low back pain populations, Werneke[24] reported centralization in 77% of patients, Sufka in 83%,[21] and Karas in 73%.[20] Long’s 1995[22] and Donelson’s 1997[19] studies assessed patients with chronic low back pain and still found that 47% and 49%, respectively, centralized. Five of these studies also measured outcome and all found a superior response in patients who exhibited centralization in their initial evaluation and poor outcomes in noncentralizers.[20-22,24,26] Furthermore, Werneke[26] also reported that centralization was a more reliable indicator of recovery than psychosocial factors that had previously been considered by many as the best indicators of recovery.

A 1997 paper by Donelson and colleague[19] compared the findings of the McKenzie evaluation with discography findings in 62 chronic lumbar pain patients. They noted that the physical examination was able to reliably differentiate discogenic from nondiscogenic pain and also distinguish a competent from an incompetent annulus. Kopp’s study[27] demonstrated that even patients with neurological deficit may centralize if given the appropriate movements.

The assessment

The examination portion of the assessment measures a patient’s symptomatic response to repeated end-range movements performed in both standing and lying positions. The movements of flexion and extension are used most often, as they are typically the most revealing. However, some patients require testing with lateral trunk movements. In any case, two points need particular emphasis:

• Movements should be taken as closely as possible to end-range in order to maximize symptomatic changes.
• Movements must be repeated at least 10 or 12 times, as pain may change with repeated testing. During the movements, pain may initially increase before gradually centralizing and reducing in intensity or abolishing. Centralization and pain reduction may not occur until several movements have been performed. Conversely, movements that initially appear to decrease pain may, when repeated, cause symptoms to worsen or peripheralize.

A typical assessment proceeds as follows. The patient’s baseline symptom locations are recorded first in the standing position, with particular emphasis being placed on the most distal symptoms. The patient is asked to bend forward as far as possible and then return to the starting position. The examiner notes any loss or abnormal quality of the movement and records any effect that movement has had on the patient’s symptoms. This process is repeated 10 to 12 times and, at the conclusion, the patient is asked to report any lasting change in location or intensity of symptoms. Standing extension is assessed in a similar manner. Because symptom response may vary depending on whether the tests are done in a standing or a lying position, both positions should be used. Recumbent flexion is tested by having the patient repeatedly bend the knees up and hug them toward the chest. Lumbar extension is produced by having the patient push the shoulders up off the bed from a prone position. Pain responses to each of these test directions are recorded.

At the conclusion of the assessment, the examiner will have information about which movements increase or decrease reported symptoms and whether centralization or peripheralization is occurring. When centralization does occur, it is normally related to a single direction of testing only.

Management decisions based on assessment

Typically, if movement in one direction produces centralization, further movement in this favorable direction results in the abolition of the patient’s midline symptoms. McKenzie[16] has described the treatment and management of patients in this centralizing category with direction-specific end-range exercises. The value of basing the choice of therapeutic exercise on movements producing centralization was demonstrated in a study by Long,[28] who randomly assigned patients whose symptoms centralized into three exercise treatment groups. The first group performed exercises in the same direction as the movements that produced centralization. The second group performed exercises in the direction opposite to the movement that had centralized their symptoms. The third group acted as a control by doing nonspecific exercises. The group exercising in the direction that matched their centralization movement showed a significantly greater improvement in all outcome measures compared with the other two groups; no patient in this group experienced a worsening of symptoms. The group exercising in the direction opposite to their centralizing movement had more subjects whose symptoms worsened than improved.

But what of those patients whose symptoms worsen distally (i.e., peripheralize)? The Donelson study of 1997[19] demonstrated that those patients whose symptoms only peripheralized usually had discogram findings that showed a leaking or incompetent annulus. This type of patient is not likely to improve in the short-term and indeed may be a candidate for surgery. Patients exhibiting only partial or gradual centralization may need more time to respond or they may require further evaluation.

There are considerable benefits to categorizing patients with low back and radiating pain as “responders” (centralizers) or “nonresponders” (noncentralizers). X-rays and other more expensive imaging techniques are not required with the large subset of responders and need only be used on the nonresponders, saving valuable health care dollars. Rapid responders can be taught the necessary self-treatment exercises and posture strategies to bring about their own recovery, lessening their dependency on our overburdened medical system.

Researchers currently conduct studies that provide the same intervention to all back pain sufferers as though they all had the same underlying problem. There is sufficient evidence to suggest that centralizers form a distinct subgroup in the nonspecific low back pain category. They have shown superior outcome rates when compared with noncentralizers. Future studies should assess the efficacy of various interventions on these two distinct subgroups. This approach offers the prospect of real progress in the management of low back pain by:

• Identifying those who can benefit from an inexpensive exercise program. 
• Ending the fruitless search for one intervention to manage all low back pain problems, which has dominated randomized controlled studies in recent years.

Conclusion

A low-tech clinical examination using the patient’s symptomatic response to active lumbar test movements can provide the primary care physician with an effective early sorting tool for differentiating the responder with highly prevalent and rapidly reversible mechanical problems from those nonresponders with more complex causes. With this early differentiation guiding both diagnostic and treatment decision making, patients can be provided with earlier and more effective treatments and avoid unnecessary interventions.

Competing interests
Mr Davies receives fees for making presentations and conducting courses on the assessment and treatment of spinal and extremity joint problems for the McKenzie Institute International, an education and research organization.

C.L. Davies, C.M. Blackwood, MD

Mr Davies is a physiotherapist actively involved in clinical practice in the Lower Mainland at a number of sites and who travels internationally lecturing on the McKenzie approach to spinal clinical entities. Dr Blackwood practises family medicine in Mission, BC.