Custom Made (PMMA) Intervertebral Spacer in TLIF Preliminary Results of a Prospective Randomized Trial

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Introduction The use of bone cement in orthopedic surgery has been quite current for many years. In spine surgery, it has been used first for replacing defects after corpectomy. Then, vertebroplasty and kyphoplasty got used worldwide. Sporadically, some surgeons used cement to refill the intervertebral space after discectomy, combined with dorsal stabilization and fusion. Most recently in our institution, we started to perform routinely percutaneous cement discoplasty, for elderly patients. We also use PMMA as a spacer in TLIF. In a previous retrospective analysis, we reviewed results with this kind of surgeries. The aim of this study was to validate the use of custom-made PMMA spacer in TLIF with a high level of evidence in a randomized, prospective study. Patients and Methods In our study, we planned to collect 100 consecutive patients to whom we perform one level TLIF in the lumbar spine. The patients are randomized in three groups by the GraphPad QuickCalcs software. Group A is standard TLIF with PEEK spacer positioned in the anterior part of the intervertebral space. Group B is standard TLIF with PMMA spacer placed in the anterior part of the intervertebral space. Group C is standard TLIF with PMMA spacer positioned in the posterior part of the intervertebral space. Patients between the age of 18 and 65 years were included. Patients with a high-grade spondylolisthesis, metabolic bone disease, spinal infection, cancer, and severe scoliosis (Cobb over 30 degrees) were excluded. We evaluate the clinical results with standard questioners. Radiological evaluation focuses on bony fusion, loosening of any instrument implanted (PMMA spacer or screws), osteolysis around the cement, subsidence, changes in segmental, and overall lordosis according to the position of the spacer. Results Until today, 40 patients have a minimum of 1-year follow-up. We present these early results. On CT scan 6 months after surgery, we could observe completed fusion in 78.5% of the operated segments. The fusion rate was higher in the PMMA spacer groups (B + C), but the difference is not significant. We found six subsidence (15%), from four was in the PEEK spacer group (A) meaning, that the subsidence rate was significantly higher in this group. We found radiolucent zone around the implant (loosening) in only two cases (5%), one in the group A and one in group B. The overall clinical result was very good in 61%, good in 28%, and poor in 11% of the cases without significant difference between the groups. Conclusion With this preliminary results, we can estimate that the use of custom-made PMMA spacer in TLIF even in younger population provides good results noninferior to preformed PEEK spacer, and it even has some following advantages on preformed cages: (1) It fits better to irregularity of the end plates than preformed spacers, which can correlate with the difference in subsidence rate. (2) It requires smaller annular window to implant.