OPLL: Disease Entity, Incidence, Literature Search, and Prognosis

Abstract

Ossifi cation of the posterior longitudinal ligament (OPLL) is a hyperostotic condition of the spine associated with severe neurological defi cit [1–5]. The disease was fi rst reported more than a century and a half ago [6]. OPLL was previously considered specifi c to Asian peoples [7] and did not attract attention in Europe or the United States. However, because of reports that this disease occurs in Caucasians [8–14] and that about half of the patients with diffuse idiopathic skeletal hyperostosis (DISH), which is well known in Europe and the United States, had OPLL, this disease has come to be recognized as a subtype of DISH [15,16]. Resnick et al. [15] reported DISH to be a common disorder characterized by bone proliferation in axial and extraaxial sites. The most characteristic abnormalities in this condition are ligamentous calcifi cation and ossifi cation along the vertebral body [16]. Changes in extraspinal locations are also frequent, including ligament and tendon calcifi cation and ossifi cation, paraarticular osteophytes, and bony excrescence at sites of ligament and tendon attachment to bone. In their study of a group of 74 patients with DISH, 37 (50%) patients had concomitant OPLL on cervical radiographs [17]. Whereas DISH is a fairly common disease among the general population of Caucasians more than 50 years of age, its frequent association with OPLL suggests that OPLL itself cannot be a rare disease in Caucasians. In 1992, Epstein proposed a new concept for OPLL. Epstein examined computed tomography (CT) scans of the cervical spine in Caucasians and noted hypertrophy of the posterior longitudinal ligament with punctuate calcifi cation. This fi nding was described as ossifi cation of the posterior longitudinal ligament in evolution (OEV) [18]. Epstein emphasized that the prevalence of OPLL among Caucasians with cervical myelopathy has recently increased from 2% to 25% [19]. All epidemiological surveys of OPLL by Japanese researchers were conducted using plain radiography of the cervical spine for OPLL diagnosis. Most Japanese researchers did not include OEV in the OPLL survey. There is controversy between Japanese and North American researchers regarding the defi nition of OPLL.