[Effect of Modic changes on fusion rate and cage subsidence after transforaminal lumbar interbody fusion]

Objective: To investigate the effects of Modic changes on the fusion rate and cage subsidence after transforaminal lumbar interbody fusion (TLIF). Methods: From January 2015 to January 2018, a total of 186 patients with degenerative lumbar disease who received lumbar instrumentation fusion and monosegmental TLIF with single polyetheretherketone (PEEK) cage in Nanjing Drum Tower Hospital were retrospectively reviewed. Patients with Modic changes at the level where the cage was placed were enrolled as Modic group, and the remaining were assigned into non-Modic group. Disk height, lumbar lordosis and segmental lordosis of the level with TLIF were measured based on the preoperative, postoperative and latest follow-up lateral radiograph. The fusion rate and cage subsidence (more than 2 mm on either endplate) were recorded based on CT scan at the latest follow-up. The Oswestry disability index (ODI) and visual analogue scale (VAS) of pain was used to evaluate the clinical outcome. The data were compared with paired t test between the two groups. Results: In this study, there were 70 males and 116 females with an average age of (55±13) years. There were 99 patients in the Modic group (25 with type 1, 66 with type 2, 8 with type 3), and 87 patients in the non-Modic group. There was no significant difference between Modic group and non-Modic group in demographics and postoperative radiographs. The patients were followed-up for (19±4) months (13 to 48 months). All patients achieved grade 1 or 2 fusion. Cage subsidence was detected in 34 patients (18.3%, 34/186). The incidence of subsidence in Modic group (24.2%, 24/99) was significantly higher than that in non-Modic group (11.5%, 10/87) (χ(2)=5.038, P<0.05), and the incidence of subsidence in type Ⅰ (28.0%, 7/25) and type Ⅱ (24.2%, 16/66) were higher than that in non-Modic group (11.5%, 10/87). There was no significant difference in ODI and VAS between Modic group and non-Modic group before and after the operation and at the latest follow-up (t=0.397-1.568, all P>0.05). Conclusion: Preoperative Modic changes have no impact on fusion rate after transforaminal lumbar interbody fusion, but both type Ⅰ and Ⅱ Modic changes do increase the risk of cage subsidence.