Jacques Forestier's vanished bowstring sign in ankylosing spondylitis: a call to test its validity and possible relation to spinal myofascial hypertonicity.

Jacques Forestier's bowstring sign (signe de la "corde de l'arc") in ankylosing spondylitis (AS) was described by him in his 1951 book (French). In free lateral bending, the early AS patient has palpably firm, contracted dorsolumbar muscles on the concave side, opposite to the findings in normals. Forestier described this sign as a common and characteristic finding in AS. Perplexingly, the sign is essentially unknown in the rheumatologic field. A single report (Polish) on electromyographic (EMG) findings in AS and control subjects documented the electromotor component of the bowstring sign as well as its diagnostic utility in early AS patients. In this paper, the literature on EMG studies in series of AS patients is reviewed as well as kinesiologic EMG studies of normals in lateral bending. Paravertebral and other muscle pathology in AS was reviewed in relation to the EMG findings. Critical, controlled assessment of Forestier's bowstring sign and biomechanical investigations of the dorsolumbar muscles in AS promise to offer new insights into the early physiopathogenesis of this unique disease.