Radiological risk factors for progression of ossification of posterior longitudinal ligament following laminoplasty

Background Context Research shows the progression of ossification of the posterior longitudinal ligament (OPLL) following decompressive surgery for cervical myelopathy, particularly in cases presenting with continuous or mixed radiographic types. To date, no study has investigated OPLL progression within each motion segment. Purpose To evaluate progression of cervical OPLL in each motion segment using a novel system of classification, and to identify risk factors for OPLL progression following laminoplasty. Study Design/Setting Retrospective case series. Patient Sample This study included 34 patients (86 segments) with cervical myelopathy secondary to OPLL. Outcome Measures Clinical and radiological data (plain radiographs and computed tomography [CT]) were obtained. Methods Clinical data from 34 patients (86 segments) with cervical myelopathy secondary to OPLL were evaluated retrospectively. All subjects had undergone laminoplasty at a single center. Sagittal reconstructive CT images were used to measure OPLL thickness in each segment. Ossified masses were classified into four types according to the degree of disc space involvement: type 1 (no involvement); type 2 (involving disc space but not crossing); type 3 (crossing disc space but not fused); and type 4 (complete bridging). Range of motion (ROM) for each segment was measured using dynamic radiographs. Statistical analyses were performed to determine the degree of OPLL progression according to the four disc space involvement types and ROM. Results Mean OPLL progression was significantly higher in types 2 (1.3 mm) and 3 (1.5 mm) than in type 1 (0.5 mm) (p 2 mm) was more frequent in types 2 (8 of 29) and 3 (7 of 16) than in types 1 (1 of 35) or 4 (0 of 6) (p=.002). In types 2 or 3, ROM>5° was correlated with severe OPLL progression (52% vs. 8%; p=.035). Conclusions Type 2 or 3 disc involvement and segmental ROM>5° were risk factors for OPLL progression. Classification of cervical OPLL according to disc involvement may help predict OPLL progression following laminoplasty. Close follow-up is warranted in cases of type 2 or 3 with greater segmental motion.