Referred pain pattern of the abductor pollicis brevis muscle and its possible mechanism

Objectives: The purpose of this study is to reveal the referred pain patterns of abductor pollcis brevis [APB] muscle and propose the possible mechanism for such patterns. Methods: Sixty-four arms of 32 healthy normal adult asymptomatic subjects were studied. Muscle pain was induced with injection of 0.2 ml of six percent hypertonic saline into the APB muscle under ultrasonographic guidance. Subjects drew in their pain areas on a pain diagram, and this drawing was transferred into the Pain Chart System® for analysis. Results: Two main referred pain patterns were observed. The most common pattern [70.3 percent], Pattern 1, localized pain around thenar area and dorsal first web space and extended proximally to the distal one-third of the forearm along the radial aspect and distally to the lateral side of second finger tip in a third of the arms. The second main pattern [23.4 percent], Pattern 2, localized pain around the thenar area and the distal part of palmaris longus muscle and the pain around medial epicondyle was also reported in a third of the arms. Conclusions: These referred pain patterns cannot be explained by peripheral or central nervous system interaction. They may be explained by the anatomical relationship of APB with the accessory slip of APB and first dorsal interosseous muscle in Pattern 1, and the palmaris longus in Pattern 2. Thus, the anatomical relationship may be alternative explanation of the referred pain.