Incidence and clinical impact of vertebral endplate changes after limited lumbar microdiscectomy and implantation of a bone-anchored annular closure device

Abstract

Background: An annular closure device (ACD) could potentially prevent recurrent herniation by blocking larger annular defects after limited microdiscectomy (LMD). The purpose of this study was to analyze the incidence of endplate changes (EPC) and outcome after LMD with additional implantation of an ACD to prevent reherniation.

Methods: This analysis includes data from a) RCT study-arm of patients undergoing LMD with ACD implantation and b) additional patients undergoing ACD implantation at our institution. Clinical findings (VAS, ODI), radiological outcome (reherniation, implant integrity, volume of EPC) and risk factors for EPC were assessed.

Results: Seventy-two patients (37 men, 47 ± 11.63yo) underwent LMD and ACD implantation between 2013-2016. A total of 71 (99%) patients presented with some degree of EPC during the follow-up period (14.67 ± 4.77 months). In the multivariate regression analysis, localization of the anchor was the only significant predictor of EPC (p = 0.038). The largest EPC measured 4.2 cm³. Reherniation was documented in 17 (24%) patients (symptomatic: n = 10; asymptomatic: n = 7). Six (8.3%) patients with symptomatic reherniation underwent rediscectomy. Implant failure was documented in 19 (26.4%) patients including anchor head breakage (n = 1, 1.3%), dislocation of the whole device (n = 5, 6.9%), and mesh dislocation into the spinal canal (n = 13, 18%). Mesh subsidence within the EPC was documented in 15 (20.8%) patients. Seven (9.7%) patients underwent explantation of the entire, or parts of the device.

Conclusion: Clinical improvement after LMD and ACD implantation was proven in our study. High incidence and volume of EPC did not correlate with clinical outcome. The ACD might prevent disc reherniation despite implant failure rates. Mechanical friction of the polymer mesh with the endplate is most likely the cause of EPC after ACD.

Keywords: Annular closure device; Barricaid®; Disc herniation; Endplate changes; Polymer mesh; Reherniation.

Fig. 1

Demonstration of the nomenclature of upper and lower endplate changes in relation to the vertebra. a ACD anchor implanted in the inferior endplate of L4 with EPC in the upper endplate of L5. b ACD anchor in the superior endplate of L5 with EPC in the lower EP of L4. EPC Endplate changes, EP Endplate

Fig. 2

Multiple examples of patients with EPC and the volume measurement technique using Elements software (Brainlab®, Munich, Germany)

Fig. 3

Median EPC volume with interquartile range (25%—75% quartiles) of all patients at the lower and upper endplate, log(10) scale. p = 0.006

Fig. 4

Median lower and upper EPC volumes with interquartile range (25%—75% quartiles), split out for the two anchor locations superior and inferior, log(10) scale. p = 0.002

Fig. 5

Case report of a patient that underwent LMD and ACD implantation at L4/5 level due to disc herniation. a Preoperative baseline CT: No EPC visible. b One-year follow-up: EPC (0.57 cm³) appear at the lower EP of L4. c 2-year follow-up: EPC (1.15 cm³) progressed at lower EP of L4. d 3-year follow-up: EPC (2.46 cm³) accelerated to a grade 3, with polymer mesh subsidence into lower EP of L4

Fig. 6

Several types of device failure are shown. a Dislocation of the whole device posterior into spinal canal. Patient underwent rediscectomy and ACD removal. b Device material failure: fracture of the titanium anchor-head and dislocation toward spinal canal. Rediscectomy and anchor head and mesh removal was performed. c Posterior dislocation of polymer mesh into spinal canal. A LMD and mesh removal was performed during revision surgery. d Intraoperative picture of removed ACD device. e Radiological appearance of mesh subsidence into EPC and vertebra osteolysis. Clinically asymptomatic finding, no reoperation necessary to-date. f ACD failure: symptomatic recurrent disc herniation at the index level leading to a reoperation with LMD only

Fig. 7

Clinical outcome a + b Regarding right and left leg pain VAS, a significant postoperative improvement could be shown. c Mean low back pain VAS improved significantly after surgery. d Significant improvement of mean postoperative ODI

Fig. 8

Assignment of our study cohort according to Pfirrmann classification. The majority intervertebral discs were classified as grade III before and after surgery

Fig. 9

Assessment of endplate changes according to Modic classification in the current study patients. The amount of patients having Modic changes and specifically Type 1 Modic changes, increased after surgery. Number of Type 2 Modic changes was stable, and no Type 3 Modic changes were seen