A 7-year minimum follow-up of the M6-L total disk replacement for low back pain with radiculopathy in young railway employees: a retrospective single-center study

To report our minimum 7-year clinical and radiographic outcomes, as well as complications of the M6-L disk prostheses in railway workers with lumbar disk herniation (LDH) causing low back pain with radiculopathy. 97 cases underwent total disk replacement (TDR) using the M6-L disk prostheses between 2012 and 2017. Of those, 88.6% had surpassed the minimum 7-year follow-up and were included in the retrospective single-center study. Clinical and radiological data were obtained preoperatively, at 1-year and 106 (90;139) months post-operatively. Factors associated with delayed or failure return to work were identified. 90.7% had a successful outcome, as defined by the FDA. The average range of motion (ROM) of the operated, upper and lower adjacent segments increased significantly at the final follow-up. Intra-operatively, a vena cava tear occurred in 3 patients. Four cases of retrograde ejaculation were observed. At the last follow-up, 3 patients complained of low back pain (VAS > 50 mm), leg pain (VAS > 20 mm) and the ODI > 20 points. There were no cases that required revision surgery due to implant failure. No patient had symptomatic adjacent segment degeneration requiring reoperation. Heterotopic ossification was detected in 35/86 (40.7%) operative segments. At the last follow-up period, 87.2% patients went back to their original work, and 9.3% patients changed jobs, with 3.5% patients unable to return to work. Factors associated with delayed or failure return to work were: age over 40 years, body mass index over 30 kg/m 2 , presence of concomitant pathology, ASA III grade, daily use of painkillers, preoperative heavy-very heavy workload, preoperative segmental ROM at index level 4° and less, less than 15-point improvement in ODI. This study suggests that lumbar TDR using M6-L disk prostheses is a safe and effective treatment for low back pain with radiculopathy caused by LDH at a minimum 7 years postoperatively. We found that the prosthesis retained its functionality in the long-term postoperative period and was associated with good clinical and radiological results with a minimal incidence of complications. The study represents the largest cohort of patients to date with long-term M6-L disc prostheses use status.