Complex Adult Spine and Scoliosis Surgeries using 4.5 mm Molybdenum-Rhenium (MoRe®) Rods: 2-year follow-up Multicenter Retrospective Review

Introduction: The rate of rod fractures at 1-year follow-up with 5.5mm Ti and CoCr rods is approximately 9% and increases to approximately 22% with the addition of PSO or SPO osteotomies. Rod fractures have significant morbidities for patients including pain, loss of deformity correction and physiological stress of potential revision surgery. In laboratory testing, Molybdenum-47.5 Rhenium (MoRe®) rods have demonstrated superior yield strength, stiffness and fatigue endurance limits when compared to Ti-6Al-4V and CoCr. At stresses that result in early rod fracture for Titanium and CoCr (100 ksi), MoRe rods survive out to over 10M cycles.

Methods: Retrospective review 159 consecutive patients from 10 independent surgical facilities undergoing multilevel complex surgical procedures with 4.5 mm MoRe rods. Inclusion criteria: ≥ 4 levels posterior instrumentation, ≥ 18 years of age, 2 years or longer radiographic and clinical follow-up.

Results: One hundred and fifty-nine (159) consecutive patients from ten different medical centers that had spinal surgery from August 2019 until April 2022 met the inclusion criteria. Patients’ mean age 63 ±11.8 years; 50% were women; 31% were smokers; 19% diabetic with a mean body mass index (BMI) 30 ±7.3. Mean number of levels fused 5.9 ±2.7; 22.6% (4 levels), 64.2% (5-9 levels) and 13.2% (10 levels or greater). Approximately half thoracolumbar(27.7%), thoracolumbar to pelvis (24.5%) and approximately half (47.2%)lumbar-sacral. Thirty-eight patients (38/24%) had a pedicle subtraction osteotomy (PSO) and 59/39% patients had a Smith Peterson Osteotomy (SPO). All cases were done with molybdenum-rhenium 4.5mm diameter rods. There were no RFs reported in the 159 cases (0/159; 0.0%) at a mean follow-up of 22.36 months [range 12.23–44.93 months; 1 yr: 94 (59.1%), 2 yrs or >: 65 (40.9%)].

Conclusion : At similar rod diameters, a MoRe rod has significantly higher yield strength and fatigue endurance compared to Titanium and CoCr rods. Because of the performance of the MoRe alloy, it is now possible to use smaller, lower profile spine constructs including smaller diameter rods (4.5mm MoRe rods) in multilevel complex spine surgery without sacrificing mechanical performance.