Pressure Threshold for Referred Pain by Compression on the Trigger Point and Adjacent Areas

Abstract

Objective: This study is designed to investigate the amount of pressure on a myofascial pain trigger point [TrP] sufficient to initiate referred pain. Methods: Sensitive spots in palpable taut bands of extensor digitorum communis muscles in Group 1 subjects with latent TrPs [no spontaneous pain but tender] and in Group 2 patients with active TrPs [with spontaneous pain] were studied. A pressure algometer was used to measure the threshold of the pressure sufficient to induce local pain, referred pain and intolerable pain for each subject. The TrP [site A], a non-TrP location [site B] in the same taut band, and a control site in "normal" muscle tissue free of taut bands [site C] were measured. Results: It was found that the referred pain could be elicited with a higher incidence at site A [46.8% for a latent TrP; 100% for an active TrP] than at site B [36.2% for a latent TrP; 100% for an active TrP] than at site C [23.4% for a latent TrP; 68.0% for an active TrP]. For either a latent TrP or an active TrP, the mean pressure threshold to elicit a referred pain from site B was higher than from site A, but lower than from site C. For the same site, the pressure required to elicit referred pain was higher for a latent TrP than for an active TrP. There is a linear relationship between the pain threshold and the pressure threshold required to induce referred pain. The difference between pain threshold and referred pain threshold was less in an active TrP than in a latent one. In those cases when no referred pain could be elicited before reaching tolerance, the referred pain threshold was either higher than the threshold of pain tolerance or was absent at that site. Conclusion: It is concluded that a referred pain pattern can be induced more easily by compressing an active TrP than by compressing a less active or a latent one. The fact that the difference between pain threshold nd referred pain threshold is much less in an active TrP than in a latent TrP may be another useful sign to distinguish them clinically. Referred pain was reliably elicited by compression of an active TrP is adequate pressure was applied, but could not always be elicited by compression of a latent TrP. A similar referred pain could also be elicited by compressing sites near a TrP is enough pressure was applied. Therefore, referred pain is an appropriate sign to indicate an active TrP, but is not a reliable sign for the identification of a latent myofascial TrP.

KEYWORDS:

• Myofascial pain syndrome
• Pain threshold
• Referred pain
• Trigger Point