Deep cross-friction pressure with a finger or an elbow in the proximal gluteal region causes a sciaticlike pain along the side of the thigh and the leg as a clinical presence of referred pain (RP) in patients with nonspecific low back pain (LBP). This study investigated the reliability and discriminative ability of experimentally provoked RP as a result of deep cross-friction with the aid of a Fischer algometer. The new clinical examination method measures the provoked RP threshold resulting in an outcome, expressed in kg/cm2.Methods
Forty two patients with subacute LBP (3 to 12 wk) participated in a prospective clinical trial. The outcome was assessed by means of the standard (perpendicular) pressure pain thresholds (PPT) measured with the aid of a Fischer algometer on both sides of the gluteus medius, the provoked RP pain thresholds (PPT-RP) at the location of the medial superior cluneal nerve, the Oswestry Disability Index , and the McGill Pain Questionnaire. The diagnostic criteria for the clinical presence of RP were determined by the patient on the pain chart drawings of the McGill Pain Questionnaire. The criteria for provoked RP were determined by means of PPT-RP with the aid of a Fischer algometer until the patient pointed out the RP zone in the thigh and/or the leg.Results
The interobserver reliability was sufficient for both sides with and without RP (intraclass correlation coefficient>0.97). The test-retest performed independently of the observers ranking, showed a perfect reliability of the PPT-RP measurements (intraclass correlation coefficient>0.98). The PPT-RP at the level of the medial superior cluneal nerve in the subgroup with a clinical presence of RP (N=20) was significantly higher (3.5 kg/cm2) than in the subgroup patients without RP (N=22). The correlation between the factor RP and the PPT-RP was high (R=0.91, P<0.001). The clinically important difference between provoked and clinical presence of RP was found to be higher or lower than 5.6 kg/cm2. The standard PPT measurement of the gluteus medius revealed no significant differences between the subgroups with and without RP.Conclusions
This clinical study support the reliability and discriminative ability of a new method of experimentally provoked RP, using deep cross-friction pressure with the aid of a Fischer algometer in patients with LBP. The experimentally “provoked referred pain threshold” (PPT-RP) values lower than 6 kg/cm2 correspond clinically with the presence of a referred muscle pain area in the thigh and/or the leg. Further studies of a similar kind are nevertheless needed to confirm those conclusions and to assess the responsiveness of the provoked RP measurements in different treatment follow-up periods.