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A Descriptive Study of the Centralization Phenomenon

A Descriptive Study of the Centralization Phenomenon A Prospective Analysis Mark Werneke, MS, PT, Dip. MDT,* Dennis L. Hart, PhD, PT, and David Cook, BS, RN SPINE Volume 24, Number 7, pp ,
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A Descriptive Study of the Centralization Phenomenon A Prospective Analysis Mark Werneke, MS, PT, Dip. MDT,* Dennis L. Hart, PhD, PT, and David Cook, BS, RN SPINE Volume 24, Number 7, pp , Lippincott Williams & Wilkins, Inc. Study Design. Occurrence and treatment responses associated with the centralization phenomenon were analyzed prospectively in 289 patients with acute neck and back pain with or without referred spinal symptoms. Objectives. To document symptom changes to mechanical assessment during initial evaluation and during consecutive visits. Using standard operational definitions, patients were categorized reliably into three inclusive and mutually exclusive pain pattern groups: centralization, noncentralization, and partial reduction. It was hypothesized that the occurrence of centralization would be less than previously reported and that the centralization group would have better treatment results. Summary of Background Data. Centralization has been reported to occur with high frequency during mechanical assessments of patients with acute spinal syndromes. When centralization is observed, a favorable treatment result is expected. Because centralization has not been defined consistently in the literature, the true prevalence and treatment responses associated with centralization have not been confirmed. Methods. Consecutive patients with neck or back pain syndromes and referred to outpatient physical therapy services were categorized into three pain pattern groups by experienced therapists trained in the McKenzie system. Changes in distal pain location were scored and documented before and after each visit. Maximal pain intensity over 24 hours, perceived functional status, and number of treatment visits were compared between groups. Results. Patients could be categorized reliably according to movement signs and symptoms. The centralization pain pattern group had significantly fewer visits than the other two groups (P 0.001). Pain intensity rating and perceived function were different between the centralization and noncentralization groups (P 0.001). There was no difference in treatment response between the centralization and partial-reduction groups (P 0.306). Prevalence of patients assigned to the three groups was 30.8% in the centralization group, 23.2% in noncentralization, and 46% in the partial-reduction group. Conclusion. Categorization by changes in pain location to mechanical assessment and treatment allowed identification of patients with improved treatment outcomes and facilitated planning of conservative treatment From *NovaCare at Southern Ocean Center For Health, Forked River, New Jersey, Focus On Therapeutic Outcomes, Great Falls, Virginia, and Automotive Motors at Thomasville, Thomasville, North Carolina. Data collected from the Office of American Rehabilitation Services, High Point, and the Office of Employee Health Clinic of Automotive Motors at Thomasville, Thomasville, North Carolina. Data Analyzed at the Office of Focus On Therapeutic Outcomes, Inc., Great Falls, Virginia. Acknowledgment date: February 3, First revision date: May 13, Acceptance date: August 18, Device status category: 1. of patients with acute spinal pain syndromes. If a proximal change in pain location is not observed by the seventh treatment visit, the results of this study support additional medical evaluation for physical or nonphysical factors that could be delaying quick resolution of the acute episode. [Key words: acute spinal pain, centralization, pain location, pain patterns] Spine 1999;24: Centralization is a clinical phenomenon observed during mechanical assessment of patients with pain in the neck or back. The centralization phenomenon (CP), as originally described by McKenzie, 17 was defined as a rapid change in the location of pain from a distal or peripheral location to a more proximal or central position. The CP could be observed in patients even if the pain was localized and spread only to the buttock. 4 In addition, the pain pattern would remain better, e.g., reduction in midline, lateral, or distal pain would not reappear if the movements or positions found to centralize symptoms were repeated or sustained while other movements were temporarily avoided. 5,16,17,28 The key and essential component to understanding centralization is this rapid response to changes in pain location as a result of clinically directed movement and positioning techniques. 7 If the appropriate mechanical procedure is not applied, then centralization will not be observed. 5,28 Medical interest in the CP has increased over the past decade because of the reported high frequency in the clinic, predictive value in identifying patients who will respond satisfactorily to conservative rehabilitation efforts, and usefulness in guiding treatment planning. 4,5,7,14,22 Although the concept of centralization appears to be straightforward, the definition of centralization as described by McKenzie 16,17 has not been consistently applied nor documented in the literature. 3,4,7,8,12,24 In addition to inconsistencies in the definition of the CP, previous research has focused primarily on this phenomenon occurring during the initial evaluation period only. Therefore, it is not clear from the literature if 1) centralization had to be noted during one or all visits, 2) referred symptoms needed to be completely or partially reduced; and 3) patients who showed no change in the location of pain during the initial evaluation period could be categorized accurately into a noncentralization group. Monitoring changes in pain location during not only the initial evaluation but also subsequent visits appears to be important in differentiating CP from variable patterns of reductions or abolition of pain from natural history alone. 676 Centralization Phenomenon Werneke et al 677 There is a general lack of evidence to substantiate the prognostic value of centralization for patients with acute spinal syndromes. Karas et al 12 found that patients who had centralized symptoms had a significant increase in return to work at 6 months compared with patients whose symptoms did not centralize. A mix of patients with acute and chronic pain was studied, and demographics concerning acuity were not discussed. Sufka et al 24 reported that patients who had complete centralization had a significant improvement in subjective functional scores compared with those who did not have complete centralization. Generalizability of their results are difficult because of the small number of patients with acute pain (N 15) studied. In a retrospective analysis, Donelson et al 7 reported that referred symptoms to the buttock, thigh, or leg in 89% of the patients with acute pain centralized during mechanical assessment. Of this centralization group, 91% had excellent outcomes resulting in complete relief of pain and restoration to function. It is not known from this study if complete and partial centralization are equally predictive of favorable outcomes, or if patients who do not have symptoms that centralize on any visit yet who demonstrate a partial reduction in pain location over time have satisfactory outcomes. The authors of the current study are unaware of any other studies in which the clinical and predictive usefulness of the CP has been investigated specifically for patients with acute neck or back pain syndromes. Previous literature has not clearly distinguished the prognostic value of the CP from what is expected with natural history. This raises the question of CP as an important predictor of a favorable response to conservative care in the acute episode compared with the natural history of acute low back or neck pain. With no consistent definition of centralization, comparing occurrence and treatment outcomes related to the CP across different clinical trials is problematic. Therefore, the purposes of this prospective study were 1) to standardize the operational definition of CP; 2) to determine the occurrence of the CP as defined in this study in a large cohort of patients with acute neck and back pain syndromes; 3) to quantify the reliability of categorizing all patients into three pain pattern groups, i.e., centralization, noncentralization, or a partial-reduction group; and 4) to determine if there is a difference between pain pattern groups in clinical outcomes from physical therapy (visits, pain intensity, and function). The authors tested the following hypotheses: 1) the occurrence of the centralization pain pattern will be substantially less then the occurrence of CP previously reported; 2) the three pain pattern groups can be reliably distinguished; and 3) the centralization pain pattern group will have better outcomes than those of the other two pain pattern groups. Methods To evaluate CP, the authors of this study propose that Mc- Kenzie s 17 original operational definition for the CP be standardized. Patients were categorized into one of three groups based on the following operational definitions. Centralization Group: 1. A clinically induced change in location of pain/symptoms referred from the spine moves from the most distal position toward the cervical or lumbar midline. Note: For patients with only central or midline pain, the midline pain must cease during the initial visit. 2. The change in pain location or abolition of midline pain must remain better (e.g., the lateral or distal pain does not reappear) as a result of mechanical movements/positions. 3. The change in pain location initially observed on the first visit must continue its proximal movement on subsequent trials until all symptoms are abolished. Note: Midline pain must remain abolished on subsequent visits. Noncentralization Group: 1. No changes in the location of pain occur, or 2. Location of pain changes from a central to a more distal location throughout all treatment visits. Partial Reduction Group: 1. Location of pain changes from a more distal to a more central location during each visit without a progressive movement in initial pain location toward the midline at consecutive visits, or 2. No change in pain location occurs during any one visit, but the patient has a gradual decrease in pain location over subsequent visits. For patients to be categorized as centralizers, all of the criteria listed for centralizers must be met. The definitions emphasize the importance of rapid changes in pain location (not pain intensity) and progressive improvement in pain location, and the changes are induced clinically and controlled by specific movement/positioning techniques. Subjects. The patient sample consisted of 351 consecutive adult patients who met the following admission criteria: years of age, diagnosed with neck or low back pain syndromes with or without referred symptoms, referred by a physician for conservative treatment, and having symptoms of less than 6 weeks duration. The patients were referred to one of two independent medical centers for physical therapy services between January 1996 and June Before referral to physical therapy services, all patients received appropriate medical diagnostic triage, medical reassurance, medications, and temporary work restrictions if deemed necessary by the primary physician. In addition, the majority of the patients were on workers compensation and unable to resume full duty tasks. If there were no improvements, i.e., if the patient was unable to return to full duty or if significant pain persisted at the physician s follow-up evaluation and conservative management was still indicated, patients were referred to physical therapy. Patients were excluded if they 1) reported spinal pain or work loss because of spinal pain within 6 months before this episode, 2) had poor English proficiency or were unable to complete intake questionnaires independently, 3) had a history 678 Spine Volume 24 Number Table 1. Patient Characteristics at Initial Evaluation Characteristic Male Female n Age (yrs) Spinal type Cervical (%) Lumbar (%) Symptom location Midline (%) Shoulder or buttock (%) Leg or arm (%) Duration of Symptoms (days) Payer Type Worker s Compensation (%) Automobile insurance (%) Other commercial (%) Medicare/Medicaid (%) 0 0 Current working status Full duty, full time (%) Full duty, part time (%) Light duty, full time (%) Light duty, part time (%) Not working (%) Physical demand level of job Sedentary (%) Light (%) Medium (%) Heavy (%) Very heavy (%) of spinal surgery, 4) were pregnant. or 5) refused to sign a consent form to participate in the study. A total of 51 patients did not meet the admission criteria or refused to participate. A total of 300 patients consented to participate. Eleven patients dropped out after the initial physical therapy evaluation and were excluded, leaving 289 patients (Table 1). Of these patients, 22.8% reported cervical symptoms and 77.2% reported low back pain. The average duration of symptoms before the initial physical therapy evaluation was 13 days. The majority of the patients (71.6%) were receiving workers compensation benefits. Eighty-seven percent were not working or were working at modified duty, and only 13% were working full duty full-time during the treatments. Of the patients remaining in the study, 80% of the men and 53% of the women had medium or heavier physical job demand duties. Physical Therapists. Five physical therapists participated in the study. Three physical therapists had years of clinical experience, and the other two therapists had 5 7 years of experience. All therapists were trained in the McKenzie evaluation and treatment methods. Three physical therapists were diplomats attaining the highest level of training by the McKenzie Institute, and two therapists who completed the basic A D courses received their credentials from the Institute. Patients were assigned to a therapist by the front-desk clerical staff member who was blinded to the methods of the study. The only criterion for assigning patients was the therapist s current patient caseload. Procedure. At the initial physical therapy consultation, each patient was asked to complete a body diagram, a pain intensity scale, and an Oswestry 9 or Neck 27 Disability Index questionnaire. Final Oswestry or Neck Disability Index questionnaires were completed by each patient immediately after the patient s discharge visit. The clerical staff member, again blinded to the administration and outcomes of the study, administered the questionnaires. The body diagram was used to record the location of the patient s pain before and after the initial evaluation and before and after each treatment visit. Each patient was instructed by the clerical staff member in a standardized manner to shade in all areas on the diagram where he or she was experiencing pain and referred symptoms when appropriate. After completing the intake questionnaires and forms, all patients received a mechanical evaluation following McKenzie s 16,17 assessment methods by one of the five physical therapists. Each patient was treated by the evaluating therapist. Subsequent treatment visits were scheduled by the clerical staff; hour intervals were recommended between visits. Exercises and manual techniques, if needed, were implemented according to the different pain responses from repeated end-range movement tests and/or positioning techniques observed during the objective examination. The movement(s) associated with pain centralization identified the direction of exercises for the patient (i.e., directional preference of exercise). Exercises performed in a specific direction were used during treatment with the goal of facilitating CP while avoiding movement patterns associated with exacerbation of symptoms. For example, if lumbar extension movements centralized pain, exercises that moved the patient toward lumbar extension and manual procedures that produced lumbar extension forces were selected as management techniques to control symptoms. Flexion movements and forces would be avoided temporarily in these patients. Different movements, positions, and/or forces were used on other patients depending on the findings of the initial evaluation. If centralization of pain was not observed and a directional preference for exercise was not found, an individualized active rehabilitation plan was developed for the patient by the treating therapist. This plan emphasized return to function, while activities that specifically peripheralized their pain were avoided. All patients received the same educational approach: empower the patient to become actively involved in his or her own recovery to reduce fear of physical activity and movement intolerance. Therapeutic modalities (e.g., ice or heat) were provided on a limited basis at the discretion of the therapist. Modalities were used to facilitate educational efforts and to enhance the patient s response to active treatment. Specific treatments varied according to the needs of each patient. The present project is a descriptive study of the CP, and, therefore, no attempt was made to standardize care beyond the above guidelines. After the patients completed each body diagram, the therapists coded the most distal pain location using a clear overlay template (Figure 1). This template and the scoring technique documenting the pain location has been described previously. 5,14 The cervical scoring grid used in this study has been recommended by Donelson (MW, personal communication, 1995), but has not yet been published. The location of the most distal pain site, shaded by the patient on the body diagram before the clinical examination and before each treatment visit, was defined as the PRE Pain Location Score (PRE PLS). After the examination and after each treatment visit, another body diagram was administered using the same standardized instructions. Using the same procedure as above, the most distal pain site was coded by the therapist (POST PSL). The coded pain location scores (0 6) were recorded on a Pain Pattern Spreadsheet (Figure 2). In this way, the operational definitions of the three patient groups could be quantified for analysis. Centralization Phenomenon Werneke et al 679 calculated as an effect size score. 13,23 The effect size score is calculated by subtracting the pain intensity at the initial evaluation from that at discharge, and dividing this result by the standard deviation of the pain intensity rating at initial evaluation for the group of patients. In this way, the absolute change in pain intensity score was reduced to a standardized score in standard deviation units. The suggested interpretation rating of effect size scores was followed in this study, in which 0.2 to 0.4 is small, 0.5 to 0.7 is moderate, and equal to or greater than 0.8 is large. 2 In this way, the variance of the initial evaluation scores is used to normalize the absolute change scores from initial evaluation to discharge. The effect size score was used as the data point for the analyses. As the patients improved, i.e., their pain intensity ratings decreased, the effect size scores became negative. Negative effect size scores represent reduction in pain intensity over the treatment period. Figure 1. Overlay body template. To test the inter-rater reliability for therapists to code the location of the most distal pain on the body diagrams using the Donelson et al 5 and Long 14 techniques, three therapists independently scored 30 different pain diagrams. Pain diagrams were chosen randomly by the clerical staff member. Pain diagrams were selected at random by the clerical staff member until 15 patients with neck pain syndromes and 15 patients with low back syndromes were identified and approximately 50% of each group had referred versus central pain locations. Each therapist was blinded to the scores from the other raters. One therapist (MW) reviewed the Pain Pattern Spreadsheets at discharge to categorize each patient into the centralization, noncentralization, or partial-reduc
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