Background: Ossification of the posterior longitudinal
ligament often causes compressive myelopathy. Ossification is a
progressive disease, and it has been reported that the area of ossification
increases after decompressive surgery. However, it is uncertain
how the progression of ossification affects the long-term
outcome after cervical laminoplasty. This study was performed to
clarify the relationship between the progression of ossification
of the posterior longitudinal ligament and the clinical results
following en bloc cervical laminoplasty.
Methods: Forty-five patients who were followed
for more than ten years after laminoplasty participated in this
study. Radiographs and tomograms of the cervical spine of each patient
were made before and after the operation and at the time of the
latest follow-up. The extent of ossification in the longitudinal
and sagittal axes was evaluated. Neurological function was graded
with use of the Japanese Orthopaedic Association scoring system.
The relationship between the progression of ossification and the
score-based rate of recovery was analyzed.
Results: Thirty-three (73%) of the patients
had progression of ossification of the posterior longitudinal ligament
after laminoplasty. Progression was frequent in patients with the
mixed type of ossification and in those with the continuous type,
whereas it was rare in patients with the segmental type. The patients
with progression of the ossification were significantly younger
than those without progression (p = 0.018). The Japanese
Orthopaedic Association score improved rapidly within one year and continued
to improve up to five years after surgery. The score tended to decrease
thereafter. For thirteen patients, the score had worsened at the
time of the latest follow-up. Three patients had neurological deterioration following
an increase in the thickness of the ossification.
Conclusions: Progression of ossification of the
posterior longitudinal ligament was often observed during the long-term
follow-up period after laminoplasty. Young patients with mixed and
continuous types of ossification had the greatest risk for progression.
Preventive measures, such as the use of a wider laminar opening
during the laminoplasty, should be considered for patients who are
at risk for progression of ossification.