The lexicon of multirod constructs in adult spinal deformity: a concise description of when, why, and how

The use of multirod constructs in the setting of adult spinal deformity (ASD) began to prevent rod fracture and pseudarthrosis near the site of pedicle subtraction osteotomies (PSOs) and 3-column osteotomies (3COs). However, there has been unclear and inconsistent nomenclature, both clinically and in the literature, for the various techniques of supplemental rod implantation. In this review the authors aim to provide the first succinct lexicon of multirod constructs available for the treatment of ASD, providing a universal nomenclature and definition for each type of supplementary rod. The primary rod of ASD constructs is the longest rod that typically spans from the bottom of the construct to the upper instrumented vertebrae. The secondary rod is shorter than the primary rod, but is connected directly to pedicle screws, albeit fewer of them, and connects to the primary rod via lateral connectors or cross-linkers. Satellite rods are a 4-rod technique in which 2 rods span only the site of a 3CO via pedicle screws at the levels above and below, and are not connected to the primary rod (hence the term “satellite”). Accessory rods are connected to the primary rods via side connectors and buttress the primary rod in areas of high rod strain, such as at a 3CO or the lumbosacral junction. Delta rods span the site of a 3CO, typically a PSO, and are not contoured to the newly restored lordosis of the spine, thus buttressing the primary rod above and below a 3CO. The kickstand rod itself functions as an additional means of restoring coronal balance and is secured to a newly placed iliac screw on the side of truncal shift and connected to the primary rod; distracting against the kickstand then helps to correct the concavity of a coronal curve. The use of multirod constructs has dramatically increased over the last several years in parallel with the increasing prevalence of ASD correction surgery. However, ambiguity persists both clinically and in the literature regarding the nomenclature of each supplemental rod. This nomenclature of supplemental rods should help unify the lexicon of multirod constructs and generalize their usage in a variety of scientific and clinical scenarios.

Characteristics and Risk Factors of Rod Fracture Following Adult Spinal Deformity Surgery: A Systematic Review and Meta-Analysis

Objective: The aim of study is to investigate the features and risk factors of rod fracture (RF) following adult spinal deformity (ASD) surgery.Methods: We searched the PubMed, Embase, Web of Science, and Cochrane Library databases to identify relevant studies. Patient’s data including age, sex, body mass index (BMI), previous spine surgery, pedicle subtraction osteotomy (PSO), interbody fusion, fusion to the pelvis, smoking history, preoperative sagittal vertical axis (SVA), preoperative pelvic tilt (PT), preoperative pelvic incidence minus lumbar lordosis, preoperative thoracic kyphosis (TK), and change in the SVA were documented. Comparable factors were evaluated using odds ratio (OR) and weighted mean difference (WMD) with 95% confidence interval (CI).Results: Seven studies were included. The overall incidence of RF following ASD surgery was 12%. Advanced age (WMD, 2.8; 95% CI, 1.01–4.59; p < 0.002), higher BMI (WMD, 1.98; 95% CI, 0.65–3.31; p = 0.004), previous spine surgery (OR, 1.47; 95% CI, 1.05–2.04; p = 0.02), PSO (OR, 2.28; 95% CI, 1.62–3.19; p < 0.0001), a larger preoperative PT (WMD, 6.17; 95% CI, 3.55–8.97; p < 0.00001), and a larger preoperative TK (WMD, 5.19; 95% CI, 1.41–8.98; p = 0.007) were identified as risk factors for incidence of RF.Conclusion: The incidence of RF in patients following ASD surgery was 12%. Advanced age, higher BMI, previous spine surgery, and PSO were significantly associated with an increased occurrence of RF. A larger preoperative PT and TK were also identified as risk factors for occurrence of RF following ASD surgery.

Incidence of Chronic Periscapular Pain After Adult Thoracolumbar Deformity Correction and Impact on Outcomes

Objective: Extension of the posterior upper-most instrumented vertebra (UIV) into the upper thoracic (UT) spine allows for greater deformity correction and reduced incidence of proximal junction kyphosis (PJK) in adult spinal deformity (ASD) patients. However, it may be associated with chronic postoperative scapular pain (POSP). The goal of this study was to assess the relationship between UT UIV and persistent POSP, describe the pain, and assess its impact on patient disability.Methods: ASD patients who underwent multilevel posterior fusion were retrospectively identified then administered a survey regarding scapular pain and the Oswestry Disability Index (ODI), by telephone. Univariate and multivariate analysis were utilized.Results: A total of 74 ASD patients were included in the study: 37 patients with chronic POSP and 37 without scapular pain. The mean age was 70.5 years, and 63.9% were women. There were no significant differences in clinical characteristics, including mechanical complications (PJK, pseudarthrosis, and rod fracture) or reoperation between groups. Patients with persistent POSP were more likely to have a UT than a lower thoracic UIV (p = 0.018). UT UIV was independently associated with chronic POSP on multivariate analysis (p = 0.022). ODI score was significantly higher in patients with scapular pain (p = 0.001). Chronic POSP (p = 0.001) and prior spine surgery (p = 0.037) were independently associated with ODI on multivariate analysis.Conclusion: A UT UIV is independently associated with increased odds of chronic POSP, and this pain is associated with significant increases in patient disability. It is a significant clinical problem despite solid radiographic fusion and the absence of PJK.

Multiple-rod constructs and use of bone morphogenetic protein–2 in relation to lower rod fracture rates in 141 patients with adult spinal deformity who underwent lumbar pedicle subtraction osteotomy

OBJECTIVE The purpose of this study was to compare rod fracture (RF) rates among three types of rod constructs (RCs) following lumbar pedicle subtraction osteotomy (PSO) for adult spinal deformity (ASD). METHODS A retrospective review of consecutive patients with adult spinal deformity who were treated with lumbar PSO between 2007 and 2017 was performed. The minimum follow-up was 2 years. Three RCs were compared: standard (2 main rods), satellite (2 main rods with satellite rod), and nested (2 main rods and 2 short rods spanning osteotomy). Outcomes examined included RF rate, time to RF, pseudarthrosis, and reoperation. Multivariate analysis was used. RESULTS A total of 141 patients were included 55 with standard, 23 with satellite, and 63 with nested RCs. The mean age was 65.2 years and 34.8% of patients were male. Radiographic preoperative and postoperative results were as follows: sagittal vertical axis (11.0 vs 3.9 cm), lumbar lordosis (28.5° vs 57.1°), pelvic tilt (30.6° vs 21.0°), pelvic incidence (61.5° vs 60.0°), distance between central sacral vertical line and C7 plumb line (2.2 vs 1.5 cm), and scoliosis (18.9° vs 11.3°). The average time to RF was 12.4 months. Overall RF, bilateral RF, pseudarthrosis, and reoperation rates were 22.7%, 5.0%, 20.6%, and 17.7%, respectively. Standard RCs had a significantly higher RF (36.4% vs 13.0% vs 14.3%, p = 0.008), bilateral RF (35.0% vs 0.0% vs 0.0%, p = 0.021), pseudarthrosis (34.5% vs 8.7% vs 12.7%, p = 0.004), and reoperation (30.9% vs 4.3% vs 11.1%, p = 0.004) rates. Satellite RCs (OR 0.21, p = 0.015), nested RCs (OR 0.24, p = 0.003), and bone morphogenetic protein–2 (OR 0.28, p = 0.005) were independently associated with lower odds of RF. CONCLUSIONS Use of multiple rods in the satellite RC and nested RC groups was associated with lower rates of RF, pseudarthrosis, and reoperations following lumbar PSO. Bone morphogenetic protein–2 was associated with a reduction in RF rate as well.