Introduction: Cervical laminoplasty (LAMP) is a standard surgical procedure for patients with cervical myelopathy caused by ossification of the posterior longitudinal ligament (C‐OPLL). However, it is well known that LAMP is not suitable for patients with massive OPLL lesions or cervical kyphotic alignments. Moreover, one of the important complications following LAMP is postoperative kyphotic deformity, which prevents posterior spinal cord shift and leads to postoperative residual anterior compression of the spinal cord. While the K‐line, which can evaluate OPLL size and cervical alignment in one parameter, is a good clinical tool for making decisions about surgical procedures, it cannot predict the postoperative kyphotic deformity following LAMP. Recently, it was reported that preoperative cervical sagittal imbalance is a predictive factor for postoperative kyphotic deformity following LAMP. We proposed the ‘K‐line tilt’, a novel radiographic parameter of cervical sagittal balance, and hypothesized that it may influence the occurrence of postoperative kyphotic deformity following LAMP.
Materials and Methods: The study included a total of 38 consecutive patients (27 male, 11 female; mean age 65.4 years) who underwent LAMP for C‐OPLL at our hospital from 2008 and completed at least 1 year of follow‐up. We performed LAMP only for patients with slight OPLL lesions and without cervical kyphotic alignment. The average follow‐up period was 3.1 years. We defined the K‐line tilt as an angle between the K‐line, which connects the midpoints of the spinal canal at C2 and C7, and the vertical line (Figure 1). Cervical lateral X‐ray images taken in the neutral standing position were evaluated preoperatively and at the final follow‐up visit. Radiographic measurements included the following: (1) K‐line (2) K‐line tilt, (3) CGH‐C7 SVA, (4) CL (C2–7 lordotic angle) and (5) C7 slope. Clinical results were evaluated using the Japanese Orthopedic Association scoring system for cervical myelopathy (C‐JOA score).
Results: The K‐line tilt was strongly correlated with the CGH‐C7 SVA preoperatively (R = 0.842) and postoperatively (R = 0.845). Preoperatively, all 38 patients had non‐kyphotic cervical alignment and K‐line ( + ); however, kyphotic deformity (CL < ‐5°) was observed in 5 patients and K‐line (‐) in 6 patients at the final follow‐up. We compared preoperative factors between the kyphotic deformity group (5 cases) and the non‐kyphotic deformity group (33 cases). Preoperative K‐line tilt was significantly different (P < 0.01), but age, the CL and the C7 slope were similar between the two groups. The recovery rates of the C‐JOA scores at the final follow‐up in the kyphotic deformity group were worse than those in the nonkyphotic deformity group (14.1% vs. 46.6%: P < 0.05). K‐line tilt was determined to be a preoperative risk factor using multivariate analysis (P = 0.014, OR = 1.366). The cutoff value by ROC analysis was a K‐line tilt of 20°, which was associated with 80.0% sensitivity and 93.9% specificity, for predicting kyphotic deformity.
Conclusion: K‐line tilt is a predictive factor for postoperative kyphotic deformity after LAMP for C‐OPLL patients, and LAMP is not suitable for patients with a K‐line tilt ≥ 20°, even in cases with normal preoperative alignment and slight OPLL lesions.