The cutoff value of ossification of posterior longitudinal ligament (OPLL) for early diagnosis of myelopathy using somatosensory evoked potential in cervical OPLL patients.

STUDY
DESIGN: Retrospective study.
OBJECTIVES: The objective of this study was to find out whether ossification of posterior longitudinal ligament (OPLL) characteristics, including size, shape and subtype, can be used to diagnose myelopathy using somatosensory evoked potential (SEP) in cervical OPLL patients.
SETTING: Yonsei University College of Medicine, Seoul, Korea.
METHODS: We retrospectively reviewed the medical records of 153 cervical OPLL patients who underwent SEP study. OPLL anterior-posterior (AP) diameter, area and involved longitudinal vertebral level were measured. OPLL was classified into subtypes according to longitudinal continuity and shape. Correlation analysis and receiver operating curve were used.
RESULTS: Tibial SEP latency was significantly correlated with OPLL AP diameter (P=0.001), diameter occupying ratio (P=0.019), area (P=0.007), area occupying ratio (P=0.008), involved longitudinal vertebral level (P=0.028) and space available for the spinal cord (P=0.019). The cutoff values that were diagnostic for SEP prolongation suggesting myelopathy were 4.91 mm for OPLL AP diameter, 6.02 mm for space available for the spinal cord, 44.5% for diameter occupying ratio, 63.4 mm2 for area, 36.1% for area occupying ratio and level 2 for the involved longitudinal vertebral level.
CONCLUSIONS: Our results revealed that tibial SEP latency was significantly correlated with OPLL size and suggested cutoff values of OPLL diameter (4.91 mm, 44.5%) and area (63.4 mm2, 36.1%) for early diagnosis of myelopathy. These results can help to establish treatment plans.