INTRODUCTION: Ossification of the posterior longitudinal ligament (OPLL) is a progressive disease, and it has been reported that an increased area of ossification affects the surgical results in the long‐term follow‐up after laminoplasty. The previous report clarified that the progression of OPLL is common in younger patients with continuous or mixed types of ossification. However, it is uncertain how the ossification area progresses after laminoplasty. The purpose of the present study was to investigate the progression course of OPLL after cervical laminoplasty.
METHODS: Fifty‐five patients who had available serial radiographs over 10 years after surgery were included. Radiographs of the cervical spine were taken before and after the operation (6 months, 1 year, 3 years, 5 years, and over 10 years). The extent of ossification in the longitudinal axis was assessed on lateral radiographs with a software which measures the progression of OPLL (OPLL Draw Version 2J; Array Corporation). Progression of OPLL was defined as an increased ossification of more than 2 mm in the longitudinal extent at the point of final follow‐up (progression group). The relationship between the progression of OPLL and the following items were analyzed: 1) age of patients at the time of operation, 2) sex, 3) the type of OPLL, 4) the existence of barsony, 5) the existence of ossification of the anterior longitudinal ligament (OALL), 6) the existence of ossification at C3 level, 7) alignment of the cervical spine, and 8) existence of overlapping OPLL. We also analyzed how the ossification progressed with time after surgery. We analyzed the peak speed for the progression of OPLL.
RESULTS: Forty‐one (74.5%) had progression of OPLL after laminoplasty. 1) Comparison of the clinical features between the groups with and without progression of ossification; The average age of the progression group (53.9 years old) was significantly younger than that of the non‐progression group. Progression of OPLL was marked in the patients with ossification at C3 level, compared to the patients without it. There was no consistent relationship between the progression of OPLL and the other items. 2) How dose the ossification in OPLL progress after cervical lminoplasty?; The patients were divided into three groups. Group 1 is characterized by patients in their 40’s with continuous or mixed type. These patients showed slow progression at the beginning, then the progression became fast. Group 2 is characterized by patients of over 50 with continuous or mixed type. These patients showed rapid progression at the beginning and then the progression became slow. The inclination of the simple regression for the OPLL progression in Group 1 is significantly higher than in Group 2 (p = 0.0001). Most of the patients with segmental type were included in Group 3. These patients showed no or slight progression of OPLL.
CONCLUSIONS: Our findings suggested that the progression pattern could be classified into three groups. Based on these results, we speculated that the progression of OPLL becomes slow as the patient get ages. These findings should be important for the management of patients with OPLL after surgery.
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