Purpose: In patients with carpal tunnel syndrome (CTS), a proximal stimulus can sometimes evoke typical symptoms. Explanations for this phenomenon include local disturbance of arterial circulation, stimulation of trigger points, and the double crush syndrome (DCS). The aim of this study was to investigate the value of these hypotheses with a new provocation test performed on the infraspinatus muscle (infraspinatus test [IsT]) in a multiple-blind, controlled study.
Methods: Thirty-four subjects were recruited, tested with IsT, and measured with nerve conduction velocity (NCV). Additionally, the Tinel sign (TS) was examined. The McNemar test was used to compare the IsT and NCV with the subjects' symptoms. The Fisher exact test was used to correlate IsT and symptoms.
Results: In the McNemar test, IsT showed no significant difference to the NCV (P = 0.18, sensitivity: 69.7%, specificity: 87.1%) regarding the subjects' symptoms (P = 0.2888, sensitivity 80.6%, specificity 93.9%). The Fisher exact test proved the significance of the IsT with regard to symptoms (P < 0.0001).
Conclusions: Pressure exerted on a certain point of the infraspinatus muscle has significant diagnostic power and may be a valuable clinical test in everyday practice. We discuss the arguments for and against a new, latent trigger point and whether other mechanisms may play a role.