The aim of this study was to: 1) Identify the prevalence of types of pain response to repeated movements and guided positioning in patients with sciatica. 2) To examine the possible association between baseline pain responses and the treatment outcome and baseline type of disc lesion.

Methods: This is a secondary analysis of data from a prospective randomized controlled trial investigating conservative treatment in patients suffering from sciatica.

Inclusion/Exclusion criteria:
Inclusion: 1) 18-65 years of age, 2) had radicular pain of dermatomal distribution to the knee or below in one or both legs, 3) leg pain greater than or equal to three on a 1-10 point scale at first visit, 4) duration of sciatica between two weeks and one year.
Exclusion: 1) Cauda Equina Syndrome, 2) pending worker's litigation, 3) previous back surgery, 4) spinal tumors, 5) pregnancy, 6) first language other than Danish, 7) inability to follow the rehabilitation protocol due to concomitant disease such as depression or heart failure.

Centralization procedures: The examiner was a physiotherapist with 10 years of clinical experience, but no formal McKenzie training. A Diplomate from the McKenzie Institute provided training in centralization and the use of standardized examination procedures to the baseline examiner and the treating therapist.

The definition of centralization used in this study was: the phenomenon by which distal limb pain emanation from the spine is immediately or eventually abolished in response to the deliberate application of loading strategies. Such loading causes reduction, then abolition of peripheral pain that appears to progressively retreat in a proximal direction. A mechanical evaluation was used to classify individual patients pain as displaying centralization, peripheralization. For those displaying centralization, sub-categories were determined.

Abolition centralization: the most distal pain was abolished and pain was recorded more proximally on the second pain drawing then on the first. Reduction centralization: the pain was located at the same distal location, but with reduced intensity.

Unstable centralization: the pain was reduced or abolished during the repeated movement testing or positioning but after resuming a weight-bearing position for one minute, the pain intensity level returned to the pre-testing intensity. Lumbar MRI was performed immediately after the baseline examination. The following classification terms were used: normal bulging, focal protrusion, broad-based protrusion, extrusion and sequestration. The intra and inter-tester reliability for this classification system is high, with kappa values of .78 and .68. 165 patients were available for data collection.

Demographics: The mean age of the participants was 45 (37-52), with 48% being women. Sum score of positive SLR, sensory and motor deficits and asymmetric reflexes in LE was: 0 =1%, 1 = 4%, 2 = 30%, 3 = 43%, 4 = 22%. The mean Roland Morris Disability Questionnaire score was 15.5 (11-18). Prevalence of types of pain response to repeated movement and positioning. 84.8% of people had one of the three types of centralization: 25.5% had abolition centralization, 43.6% reduction centralization, and 15.8% an unstable centralization. 15.2% were non-centralizers, 7.9% showed no effect for repeated movements or sustained positions. No patient worsened or developed further neurological deficit.

Prevalence of types of disc lesions in the participants was: sequestered discs 6%, extruded discs 31%, broad-based disc bulge 9%, focal disc protrusion 38%, disc bulge 18% and normal discs 8%. Association of types of pain response with MRI findings. 83.7% of the people with normal discs or discs with bulge and an intact inter-discal pressure were able to centralize. The patients with extruded and sequestered discs with certain lack of intra-discal pressure had the highest centralization level of all at 93.5%. Overall both the centralization groups and the peripheralization groups improved, the no effect group made the least improvements in all outcome measures.

This study has shown that even though the disc model may not fully explain centralization, nonetheless it occurs. Since MDT clinicians do not rely on pathoanatomical diagnosis, this is really not surprising and of no real concern. As a McKenzie faculty may say, Don't put the theoretical cart in front of the clinical horse. As a clinician, we rely on pain patterns and mechanical as well as symptomatic change. The patient population in this study had considerable current leg pain at baseline and 65% had 3 or 4 out of 4 positive root compression signs. 84.8% were able to centralize there pain. The worst prognosis was with the no effect or no change group. This is not surprising, as a clinician one of the worst outcomes is no better, no worse, having a patient who peripheralizes after one assessment needs further mechanical diagnosis, as Werneke has demonstrated, some centralizers are not identified until subsequent treatment sessions are undertaken. This may explain why some peripheralizers did well in the study. Overall, it is further validation that the crux of Mechanical Diagnosis and Therapy is in actually evaluating the patient mechanically and not relying on the diagnostic label put upon the patient.

Centralisation