How does the ossification area of the posterior longitudinal ligament thicken following cervical laminoplasty?

Study Design. Retrospective case series. Objective. To investigate the progression of the thickness of the ossification area over time following cervical laminoplasty. Summary of Background Data. Cervical laminoplasty has become the standard technique for the treatment of patients with myelopathy due to ossification of the posterior longitudinal ligament (OPLL). However, OPLL is a progressive disease, and an increase in the area of ossification following laminoplasty affects the surgical results. To date, complete analysis of the thickness of OPLL progression has not been undertaken because changes in the ossification thickness are minor compared with those of the longitudinal axis. Methods. Fifty-five patients who were available for serial radiographs more than 5 years after cervical laminoplasty were included. The extent of ossification thickness was assessed using lateral radiographs of the cervical spine and computer software. The neurologic evaluation was graded using the Japanese Orthopedic Association score (JOA score). The associations between the progression of OPLL and the clinical and radiologic data were analyzed. We also evaluated the progression of the thickness of the ossification area over time following surgery. Results. Twelve patients (21.8%) had progression in the OPLL thickness. Progression was marked in younger patients with the mixed or continuous types of OPLL. C3 involvement was also common in the patients with the OPLL progression. The progression of OPLL thickness was not directly related to the score-based recovery rate. The progression of OPLL was frequently observed at C2, C3, and C4 levels. Progression in OPLL thickness was detected in 42.1% of C2 ossifications, 13.3% of C3, 11.9% of C4, 4.1% of C5, 5.5% of C6, and 6.6% of C7. Conclusion. Young patients with continuous or mixed-type OPLL and C3 involvement of ossification had a risk for progression in OPLL thickness following surgery. As the increased thickness of ossified lesions directly causes the narrowing of the spinal canal, it is important to pay attention to these risk factors and the increase in ossification before and after cervical laminoplasty in the surgical treatment of patients with OPLL.