Lumbar Fusion With Polyetheretherketone Rods Use for Patients With Degenerative Disease

PEEK is thought to have several advantages when compared with titanium. These advantages include more physiologic load sharing and reduction in stress shielding, improved durability, reduced risk of failure in osteoporotic bone, less wear debris, no change in bone forming environment, and imaging radiolucency.^4,9 Spinal PEEK cages have been reported to allow more uniform radiation dose distribution compared with metal constructs, an advantage that also may pertain to PEEK rods.¹⁰ Disadvantages of PEEK rods include an inability to detect rod breakage easily, lack of data on the use in more than minimally unstable clinical situations, and greater expense, although this was not the authors’ observation.^3,4,11

Importantly, it has been reported that PEEK rods permit a greater range of motion in all planes when compared with titanium rods.⁹ Polyetheretherketone rods unload the bone screw interface and increased the anterior column load to a more physiologic 75% when compared with titanium rods.^6,9 However, in another biomechanical study that compared titanium rods, PEEK rods, and a dynamic stabilization device, it was reported that anterior load sharing was 55%, 59%, and 75%, respectively.¹² This indicated that PEEK rods are closer to metal rods than truly dynamic devices for anterior load sharing. The endurance limit of a PEEK rod construct was similar to that of clinically useful metal systems.⁹ PEEK rods resulted in no increase in postfatigue motion compared with titanium rods in a biomechanical model.¹³ Intradiscal pressures at PEEK instrumented segments were similar to uninstrumented segments and greater than those with titanium rod constructs.¹⁴ Intradiscal pressures at adjacent segments were highest with dynamic devices, intermediate with semirigid rods, and lowest with rigid constructs; however, stress values at adjacent segments were lower in PEEK than titanium constructs in any direction of motion.^15,16

Fusion Rates

The use of PEEK rods in lumbar fusion has been reported previously.^3,4,17,18 However, these studies featured small sample sizes, short follow up times, and contradictory results.⁴ Of 8 outcome reports found in a systematic review, 2 studies reported on procedures designed to create nonfusion outcomes (a third similar trial from 2013 was not included in the systematic review), and 1 study reported only on the condition of PEEK rods removed at subsequent surgery.^3,19-21 Reported fusion rates varied from 86 to 100%.

In 42 patients with PEEK rod fusions who were followed for a mean of 31.4 months, 5 patients required adjacent segment surgery and 3 patients were treated for interbody cage migration and nonunion.¹⁷ Radiographic fusion rate was 86%. These authors concluded that PEEK rod fusion results were similar to those of other constructs, but not better, or perhaps worse than, metal rods.

Other studies have reported better results with PEEK.^{11,18,19,22-24} Highsmith and colleagues reported on 3 successful example cases of the use of PEEK rods.¹¹ De Iure and colleagues reported on 30 cases up to 5 levels (mean, 2.9) using autograft bone, with a mean follow up of 18 months.²³ Results were reported as satisfactory. Three patients had radiographic nonunions, 1 of which required revision for asymptomatic screw loosening at the cranial end of the construct. Qi and colleagues, reported on 20 patients with PEEK rods compared to 21 patients with titanium alloy rods.²⁴ Both groups had similar clinical outcomes, structural parameters, and 100% fusion rates. Athanasakopoulos and colleagues reported on 52 patients with up to 3 level fusions followed for a mean of 3 years.²² There were significant improvements in PROs: at 1 year 96% had radiographic union. Two patients had screw breakage, 1 of whom required revision to a metal rod construct. Colangeli and colleagues reported on 12 patients treated with PEEK rods compared with 12 who were treated with a dynamic system.¹⁸ They reported significant improvements, no complications, and 100% fusion at 6 months. Huang and colleagues reported on 38 patients intended to undergo a nonfusion procedure with 2 years of follow up.¹⁹ They reported good outcomes and 1 case of screw loosening. As no fusion was intended, no fusion outcomes were reported. All these studies suggested that longer follow up and more patients would be needed to assess the role of PEEK rods in lumbar fusion.³

Our results show a radiographic fusion rate of 86.4% and a radiographic nonunion rate of 9.9% in patients followed for at least 12 months. There was no clinical need for revision fusion at the index level. In our retrospective review, patients had high levels of smoking, DM, depression, immunosuppression, and obesity, which may negatively influence radiographic fusion rates when compared with other studies with 100% reported fusion rates. There was no instance of construct breakage or screw breakout, indicating that PEEK rods may allow enough flexibility to avoid construct failure under stress as in a fall.