|Study||Sample and Characteristics||Non-OPLL Factors Assessed||OPLL Factors Assessed||Main Outcome Measure|
|Chen et al.21 (2014)|
|Choi et al.22 (2005)|
|Iwasaki et al.23 (2002)|
|Iwasaki et al.7 (2007)|
|Kim et al.24 (2015)|
|Ogawa et al.25 (2005)|
|Uchida et al.26 (2005)|
↵* JOA = Japanese Orthopaedic Association score, BMI = body mass index, SCEP = spinal cord evoked potentials.
↵† Evaluated on axial CT scan.
↵‡ The Hida double-layer sign was investigated to indicate dural ossification.
↵§ (Area of OPLL/area of the spinal canal) × 100%; evaluated on axial CT scan.
↵# Continuous, segmental, mixed, or circumscribed/localized.
↵** Evaluated on lateral radiographs or CT scans.
↵†† Recovery rate = (postoperative JOA score − preoperative JOA score)/(17 − preoperative JOA score) × 100%.