Study Design. A retrospective cohort study. 

Objective. The aim of this study was to identify the risk factors for acute progression of myelopathic symptoms (PMS) associated with ossification of the posterior longitudinal ligament (OPLL) after minor trauma and to compare the prognosis between an acute PMS group and a chronic PMS group. 

Summary of Background Data. Although the prevalence of OPLL among patients with cervical myelopathy is high, few studies have been published regarding the risk factors for acute PMS associated with OPLL after minor trauma. 

Methods. Patients with OPLL who had histories of minor trauma and had undergone surgery were divided according to clinical course into an acute (within 48hours, n=38) and a chronic PMS group (n=32). The type of trauma and the clinical and radiologic characteristics were compared. The clinical outcomes were also compared at admission and at 1 and 2 years postoperatively. 

Results. The types of trauma were significantly different between the two groups (P<0.05). Univariate analysis revealed that older age, a narrower space available for the cord, and a higher rate of stenosis in the spinal canal were associated with acute PMS after minor trauma (P=0.014, 0.020, and 0.006, respectively). However, the rate of stenosis in the spinal canal was the only risk factor that was identified in a multivariate analysis (P=0.023; odds ratio, 0.872; 95% confidence interval, 0.774-0.982). The Japanese Orthopedic Association scores at the initial visit and at postoperative years 1 and 2 were significantly lower in the acute PMS group than in the chronic PMS group (P<0.001, P<0.001, and P<0.001, respectively). 

Conclusion. One risk factor for acute PMS in patients with OPLL after minor trauma is a higher rate of stenosis of the spinal canal. Patients with acute PMS exhibited unfavorable neurologic outcomes. Preventive surgical treatment may be recommended for patients with significant OPLL with mild cervical myelopathy.