Is high T-1 slope a significant risk factor for developing interlaminar bony fusion after cervical laminoplasty? A...

OBJECTIVE Several investigators have reported the occurrence of interlaminar bony fusion after cervical laminoplasty, which is reportedly associated with reduced postoperative cervical range of motion (ROM). However, to the authors' knowledge, no previous study has investigated the characteristics of patients who were likely to develop interlaminar bony fusion after cervical laminoplasty. Therefore, the objective of this study was to investigate the risk factors for interlaminar bony fusion in patients with cervical spondylotic myelopathy (CSM) following cervical laminoplasty and to investigate the effect of interlaminar bony fusion on surgical outcomes. METHODS The authors retrospectively reviewed data from 92 patients with CSM (63 men and 29 women) after cervical laminoplasty. The presence of interlaminar bony fusion was evaluated by functional radiographs 2 years after surgery. The patients were divided into 2 groups according to the presence of postoperative interlaminar bony fusion: a fusion group (at least 1 new postoperative interlaminar bony fusion) and a nonfusion group (no new interlaminar bony fusion). Potential risk factors for postoperative interlaminar bony fusion were assessed, including diabetes mellitus, smoking status, whether the C-2 lamina was included in the surgical treatment, C2-7 Cobb angle in each cervical position, preoperative cervical ROM, and T-1 slope. The differences in each variable were compared between the fusion and nonfusion groups. Thereafter, multivariate logistic regression analysis was performed to identify the risk factors for postoperative interlaminar bony fusion. For surgical outcomes, the recovery rate based on Japanese Orthopaedic Association scores and the reduction rate of cervical ROM were evaluated 2 years after surgery. RESULTS Interlaminar bony fusion was observed in 60 cases, 52 of which were observed at the C2-3 level. Patients in the fusion group were significantly older, had a significantly larger C2-7 angle in flexion, and had a significantly lower preoperative cervical ROM than those in the nonfusion group. A high T-1 slope was significantly more frequent in the fusion group. Multivariate analysis revealed that the significant risk factors for postoperative interlaminar bony fusion were high T-1 slope (odds ratio 4.81; p = 0.0015) and older age (odds ratio 1.05; p = 0.025). The Japanese Orthopaedic Association recovery rate in patients with interlaminar bony fusion did not differ significantly from those without bony fusion (45% vs 48%; p = 0.73). However, patients with bony fusion showed significantly reduced postoperative cervical ROM compared with those without bony fusion (50% vs 25%; p < 0.001). CONCLUSIONS High T-1 slope and older age were significant risk factors for developing interlaminar bony fusion after cervical laminoplasty in patients with CSM. Interlaminar bony fusion was associated with reduced postoperative cervical ROM, but it did not affect neurological outcomes.