Weakness of the neck extensors, possible causes and relation to adolescent idiopathic cervical kyphosis

Cervical kyphosis may be congenital, or occur as a result of laminectomy, post-traumatic deformity, infection, neuromuscular disorders such as muscular dystrophies, motor neuron disorders such as amyotrophic lateral sclerosis, tumor, and inflammation such as ankylosing spondylitis. Furthermore, adolescent idiopathic cervical kyphosis was defined as cervical kyphotic deformity of adolescent patient without any cause such as those previously described. As no standard values for “cervical kyphosis” could be found in the literature, many reported studies only report a subjective classification, “kyphotic, straight or lordotic”. But this method had proven to be unreliable. Grob et al. defined “straight” for the global curvature as +4° to −4°, and lordotic and kyphotic as <−4° and >+4°, respectively. The etiology and pathogenesis of adolescent idiopathic cervical kyphosis remain little understood. Weakness of the neck extensors can result in “dropped head syndrome”, a rare disorder characterized by weakness of neck extensor muscles causing an inability to extend the neck and resulting in a chin-on-chest deformity. The purpose of this paper is to propose a possible mechanical cause leading to the kyphotic deformity. We hypothesize that weakness of the neck extensors could be the initiating factor for adolescent idiopathic cervical kyphosis.