Introduction: We developed a three-dimensional image analysis method to evaluate ossification of the posterior longitudinal ligament (OPLL) of the cervical spine, including volumetric changes over time. Using this method, we identified the rate and risk factors associated with ossification progression. In this study, we extended an initial cross-sectional analysis (based on two volume measurements) into a longitudinal study by incorporating a third measurement. Both non-surgical and surgical groups were included.
Methods: A total of 64 patients who were followed at our hospital and affiliated facilities between 2005 and 2020 were included. The non-surgical group (N group) consisted of 15 patients (7 males, 8 females), with a mean age of 62 years (range: 30-73 years). The laminoplasty group (LP group) included 28 patients (20 males, 8 females), with a mean age of 65 years (range: 44-79 years). The posterior fusion group (F group) consisted of 21 patients (15 males, 6 females), with a mean age of 62 years (range: 49-85 years). Image analysis was conducted three times for each patient, with intervals of more than one year between measurements, to measure the volume of ossification and the annual rate of increase among the three groups.
Results: Ossification volumes for the N group were 1,818 mm3, 1,917 mm3, and 1,989 mm3 at the first, second, and third measurements, respectively. For the LP group, volumes were 2,802 mm3, 2,971 mm3, and 3,152 mm3. In the F group, the values were 2,436 mm3, 2,552 mm3, and 2,634 mm3. All groups showed a significant increase in ossification volume over time (all p < 0.01), except between the second and third measurements in the F group.
The mean annual rate of increase was 4.0% in the N group, 6.6% in the LP group, and 2.2% in the F group. There was a trend towards a lower progression rate in the F group (p = 0.06). Changes in the annual rate of increase from the first to the second and second to the third measurements was 4.5% and 3.5% in the N group, 6.5% and 6.6% in the LP group, and 2.7% and 1.6% in the F group, respectively, with only group F showing a significant decline over time (p < 0.05).
Conclusions: The annual progression rate of OPLL followed the order: F group < N group < LP group, corresponding to approximate annual increases of 2%, 4%, and 6%, respectively. Notably, only the F group showed a decline in the annual progression rate over time, suggesting that instrumented posterior fusion may help suppress the progression of OPLL.
