P143. Efficacy of multi-rod constructs: comparison of two different 4-rod and 3-rod configurations in adult spinal deformity patients with long fusions to the sacrum

Abstract

BACKGROUND CONTEXT Rod constructs in adult spinal deformity (ASD) surgery can be variable and modular, in many revision surgeries the new instrumentation is connected to the previous implants for extension of fusion or for junctional failure. Previous studies recently reported a lower rate of rod fractures and nonunion with the addition of extra rods and multi-rod constructs across 3CO site and complex spinal reconstructions. The high rate of rod failures in ASD lead to the adoption of various multi-rod constructs. The effect of rod configuration on the rate of implant failure in multi-rod constructs is unknown. Currently, no classification system exits to describe the different multi-rod constructs to allow comparison of rod configurations across data bases. There is no agreement on the terms used to describe multi-rod constructs. PURPOSE We present a new classification system that allows accurate description of various multi-rod constructs used in spine deformity in terms of rod configuration and density. Rod configurations in 110 ASD patients after long PSF to the sacrum with 4-rod and 3-rod constructs were classified according to the new classification system. Four-rod and 3-rod constructs were divided into two groups based on rod configuration: accessory rod group and satellite rod group. We compared rod failure rate (RF) between the two different groups, accessory vs satellite, to determine the effect or rod configuration on the rod fracture rate. STUDY DESIGN/SETTING Retrospective review of institutional database of ASD patients who underwent PSF to the sacrum with the use of multi-rod constructs, 3-rod and 4-rod constructs. The multi-rod constructs were classified according the new system based on the rod configurations (RC) of the additional rods. PATIENT SAMPLE ASD patients who underwent PSF to the sacrum with the use of multi-rod constructs, 3-rod and 4-rod constructs. OUTCOME MEASURES Radiographic evidence of rod failure, either unilateral or bilateral on follow up radiographs. METHODS Our institutional database of 526 ASD patients fused to sacrum was reviewed, 110 patients with multi-rod constructs were identified and divided into 4-rod or 3-rod constructs. Within the 4-rod or 3-rod groups, constructs were classified according to the rod configuration into either accessory group (A-group) with additional accessory rods or satellite group (S-group) with additional satellite rods. Accessory rods were defined as additional rods connected to the main construct but not attached to any anchors. Satellite rods were defined as shorter additional rods attached to screws or hooks, and either connected or not connected to the main construct. Most of the satellite rods were midline rod with hooks. Accessory and satellite rod configurations for 4-rod and 3-rod constructs were compared for fractures either unilateral or bilateral after a minimum of 2-year follow up. RESULTS The 4-rod constructs included 15 satellite (S-group) and 18 accessory (A-group) rod configurations. Average BMI and % primary to revision surgeries in both groups was not different p=0.38. Rod diameter (5.5 vs 6.35) in both groups was not different p=0.28. Median levels fused in S-group were 15 (13-17) vs A-group 12 (10-15) p=0.11. Interbody fusion was not different, S-group 12 (80%), A-group 15 (83%), p=0.81. Rod failures in S-group occurred in 2 (13.3%) vs 4 (22.2%) in A-group, p=0.47. Duration of time from surgery to rod failure was 27 months in the S-group compared to 14.5 months in A-group. The 3-rod constructs included 42 satellite and 29 accessory rod configurations. Average BMI was not different (p=0.83), the S-group had more revision cases 38 (90.5%) vs 17 (58.6%) for A-group p=0.03. In S-group 14 (33.3%) patients were 5.5 rods, 27 (64.3%) had 6.35 rods vs A-group: 26 (89.6%) 5.5 rods and 3(10.34%) had 6.35 rods, p=0.01. Median levels fused was not different between both groups, but A-group had more interbody fusions performed 12 (41.4%) vs 4 (9.52%) p=0.03. Rod failures in S-group were 7 (16.7%) vs 15 (51.7%) in the A-group, p=0.01. Duration of time from surgery to rod failure in satellite group was 41 months vs accessory group 31 months. CONCLUSIONS Multi-rod constructs with different rod configurations were compared using a new classification system, 4-rod constructs showed no difference in rate of rod failures. In the 3-rod constructs group, accessory rod configurations had more rod failures compared to satellite rod configurations. The multi-rod construct classification system is helpful in comparing different rod configurations in terms of implant complications. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.