#335 The Kappa Line - A Predictor of Neurologic Outcome after Cervical Laminoplasty

General Session: Cervical Motion Preservation

Presented by: D. Lee

Author(s):

D.-H. Lee (1)
H. Kim (2)
H.S. Lee (1)
H. Noh (1)
N.-H. Kim (1)
C. Hwang (1)
S.K. Cho (3)

(1) Asan Medical Center, University of Ulsan College of Medicine, Orthopedic Surgery, Seoul, Korea, Republic of
(2) Seoul National University College of Medicine, Seoul, Korea, Republic of
(3) Mount Sinai School of Medicine, Orthopaedics, New York, NY, USA

Abstract

Introduction: Kyphotic alignment and large hill-type mass are two major risk factors of poor surgical outcome following laminoplasty in cervical myelopathy patients with ossification of posterior longitudinal ligament (OPLL). The K-line (a straight line connecting the midpoints of the spinal canal at C2 and C7 on the lateral radiograph) has been introduced previously to incorporate those two factors simultaneously. However, one of its limitations is it could not be applied to patients who need ≤ 4-level laminoplasty as it was designed for total en bloc laminoplasty of five segments from C3 to C7. In the present study, we introduce the kappa line (a modification of the K-line) and evaluated its value as a predictor of postoperative neurologic recovery and residual spinal cord compression in patients who underwent ≤ 4-level laminoplasty.

Methods: The kappa line was defined as a straight line connecting the midpoints of spinal canal at 1-level above and 1-level below the decompressed segments on the plain lateral radiograph in neutral position (Figure 1). Fifty-one consecutive patients who underwent ≤4-level laminoplasty for OPLL with minimum 2-year follow-up were divided into kappa (+) and kappa (-) groups. Kappa (+) meant the OPLL mass did not pass the kappa line, while kappa (-) meant OPLL had grown posteriorly beyond the kappa line. The patients were also divided into K (+) and K (-) according to the original definition of the K-line. To investigate the correlation of the OPLL size and the cervical alignment with the kappa line, the thickness and the occupying ratio of OPLL on the preoperative CT and the cervical lordosis on the plain lateral radiograph were compared between kappa (+) and (-) groups. In addition, we compared the recovery rate of Japanese Orthopaedic Association (JOA) score and the severity of spinal cord compression based on 6 grade classification system on the postoperative MRI between the subgroups according to both the K-line and the kappa line criteria to evaluate which scheme was more efficient in predicting surgical outcome.

Results: The kappa (-) group had significantly thicker masses (6.3 mm vs. 4.3 mm, p=0.004), higher occupying ratio (54.0% vs. 38.2%, p=0.003), and smaller cervical lordosis (12.1º vs. 18.5º, p=0.004) than the kappa (+) group. The JOA recovery rate following laminoplasty was lower (43.7 % vs. 74.5%, p=0.018) (Figure 2) and the postoperative cord compression was more severe (1.9 vs. 0.9, p=0.004) in the kappa (-) than in the kappa (+) group. However, there were no significant differences between K (+) and K (-) groups in terms of those neurologic and radiographic outcomes.

Conclusion: The kappa line correlated well with OPLL size and cervical alignment. Also, it could predict neurologic recovery and remaining cord compression following ≤4-level laminoplasty more correctly than the K-line. The kappa line could be utilized as a simple method to determine the laminoplasty level for cervical myelopathy patients with OPLL.

Figure 1

Figure 2