Influence of contoured versus straight rod on clinical outcomes and sagittal parameters in minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) at L4/5 level-more than 5 years follow-up

Minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) is among the most commonly performed surgical procedure to treat lumbar degenerative disorders. In open TLIF procedure, usually rods were contoured to restore normal lumbar sagittal alignment. However, in MIS-TLIF procedure, contoured rods sometimes were easier to rotate and harder to be locked at the satisfactory position due to instrumentation design and limited exposure. Thus, straight rods had been used in single-level MIS-TLIF in our institution. However, the effect of rod contouring on sagittal parameters and clinical outcomes remains unclear. In the present study, we aim to evaluate the effects of single-segment MIS-TLIF with contoured versus straight rods on sagittal parameters and clinical outcomes. A retrospective review of MIS-TLIF at L4/5 was performed between 2009 and 2013 in our hospital. Seventy-six cases were divided into contoured rod group (CR group, n = 35) and straight rod group (SR group, n = 41). Clinical outcomes and radiographic measurements at five years’ follow-up were evaluated by visual analog score (VAS), Oswestry disability index (ODI) and Japanese Orthopaedic Association (JOA) score, spino-pelvic parameters, disc height and fused segment angle. Fusion rate and cage subsidence were also measured. Preoperative VAS, JOA, ODI and radiographic parameters were comparable between two groups. The average follow-up was 63.72 ± 3.86 months. VAS, JOA and ODI were significantly improved at 5-year follow-up in both groups, and there were no significant differences between two groups(P > 0.05). Fused segment angle (FSA) was greater in CR group than SR group (P = 0.024), while the other radiographic parameters were not significantly different(P > 0.05). Rod process, fusion rate and cage subsidence were not risk factors of post-surgical malalignment, patients with pre-surgical sagittal imbalance was more prone to show post-surgical malalignment (P < 0.05). Both CR and SR groups acquired satisfactory clinical results. Although contoured rods had better fused segment angle, contoured or straight rods at single L4/5 level had little effect on global spino-pelvic parameters and clinical outcomes in a 5-year follow-up.