Can K-Line Predict the Clinical Outcome of Anterior Controllable Antedisplacement and Fusion Surgery for Cervical Myelopathy Caused by Multisegmental Ossification of the Posterior Longitudinal Ligament?

Objective: To analyze the correlation between the K-line-based classification of patients with ossification of the posterior longitudinal ligament (OPLL) and their outcome after anterior controllable antedisplacement and fusion (ACAF) surgery.

Methods: A series of 24 patients with multisegmental OPLL were enrolled. All patients underwent ACAF surgery. First, the patients were classified into 2 groups according to their K-line classification. Then, we separated the patients into subgroups according to their OPLL thickness. The Japanese Orthopaedic Association scores before and 6 months after surgery were studied, and the recovery rate (RR) was calculated. The preoperative and postoperative radiologic parameters were also investigated.

Results: Clinical and radiographic assessments showed no significant correlation between the K-line-based classification of patients with OPLL and their outcome of ACAF surgery (P > 0.05). When the OPLL was ≤6 mm thick, K-line-based classification groups had a similar change of occupation ratio and RR (P > 0.05). However, when the OPLL was >6 mm thick, the mean RR was 61.8% ± 14.0% in the K-line (+) group and 78.3% ± 9.7% in the K-line (-) group (P < 0.05), and the mean was 16.0% ± 4.2% in the K-line (+) group and 28.0% ± 7.1% in the K-line (-) group (P < 0.05).

Conclusions: This study shows that K-line can predict the clinical outcome of ACAF surgery for multisegmental OPLL in a different way from posterior decompression surgery. When the OPLL was thin, the outcome was satisfactory and there was no correlation with K-line-based classification of patients with OPLL. When the OPLL was >6 mm thick, the K-line (-) group patients had a better outcome than did K-line (+) group patients.