K-Line Tilt is a Predictor of Postoperative Kyphotic Deformity After Laminoplasty for Cervical Myelopathy Caused by Ossification of the Posterior Longitudinal Ligament

Abstract

Study Design: Retrospective single-center study. Objectives: K-line is a decision-making tool to determine the appropriate surgical procedures for patients with cervical ossification of the posterior longitudinal ligament (C-OPLL). Laminoplasty (LAMP) is one of the standard surgical procedures indicated on the basis of K-line measurements (+: OPLL does not cross the K-line). We investigated the impact of K-line tilt, a radiographic parameter of cervical sagittal balance measured using the K-line, on surgical outcomes after LAMP. Methods: The study included 62 consecutive patients with K-line (+) C-OPLL who underwent LAMP. The following preoperative and postoperative radiographic measurements were evaluated: (1) the K-line, (2) K-line tilt (an angle between the K-line and vertical line), (3) center of gravity of the head –C7 sagittal vertical axis, (4) C2–C7 lordotic angle, (5) C7 slope, and (6) C2–C7 range of motion. Clinical results were evaluated using the Japanese Orthopedic Association scoring system for cervical myelopathy (C-JOA score). Results: All the patients had non-kyphotic cervical alignment (CL ≥ 0°) preoperatively; however, kyphotic deformity (CL < 0°) was observed in 6 patients (9.7%) postoperatively. The recovery rate of the C-JOA scores was poor in the kyphotic deformity (+) group (7.8%) than in the kyphotic deformity (−) group (47.5%). The K-line tilt was identified to be a preoperative risk factor in the multivariate analysis, and the cutoff K-line tilt for predicting the postoperative kyphotic deformity was 20°. Conclusions: LAMP is not suitable for K-line (+) C-OPLL patients with K-line tilts >20°.

Analysis between preoperative cervical radiographic parameters represented by the K-line tilt and the short-term prognosis of laminoplasty for posterior longitudinal ligament ossification: A retrospective study

“…This is similar to previous findings. Kim ( 11 ) and Sakai ( 14 ) have also confirmed a linear relationship between C2–C7 SVA and K-line tilt. Furthermore, Tang ( 22 ) found a significant positive linear correlation between C2–C7 SVA and NDI score (Neck disability index, an index to assess cervical pain and disability that can be used to assess surgical prognosis).…”

“…Rao ( 13 ) found that the greater the preoperative K-line tilt, the greater the probability of developing postoperative cervical kyphosis change and postoperative neck pain. Sakai ( 14 ) found that preoperative K-line tilt >20° was a risk factor for cervical kyphosis change after cervical LAMP. In our study, according to the regression equation established by the postoperative JOA score and the preoperative K-line tilt, the larger the K-line tilt, the lower the postoperative JOA score.…”

“…Patients with LAMP-treated OPLL tend to have postoperative kyphosis change which means poor postoperative prognosis ( 14 ). This study had no kyphosis change patient at 1 year after surgery in both the high and low JOA score groups; however, kyphosis change patients was observed at a longer follow-up.…”

“…Here is a case of a kyphosis change patient ( Figure 6 ), it is hypothesized that the postoperative imbalance in the anterior-posterior muscles tension balance of the cervical spine led to the kyphosis change. In previous studies, Sakai ( 14 ) and Lee ( 27 ) discovered that a large preoperative K-line tilt is a risk factor for cervical kyphosis change in LAMP treated cervical OPLL. They concluded that a higher K-line tilt meant that the patient's head center of gravity was farther from the midline, and this exacerbated the rate and degree of kyphosis change.…”

“…Kim ( 11 ) introduced the K-line tilt in 2018, and it is a derivative form of K-line, defined as an angle between the K-line and the plumb line of the horizon. Combined with the findings of subsequent studies ( 12 – 14 ), K-line tilt can be used as a new preoperative cervical radiographic parameter to predict cervical spine surgery prognosis.…”