World Neurosurgery article about benefits of Karma® posterior fixation system

Metal-Free Cortico-Pedicular Device for Supplemental Fixation in Lumbar Interbody Fusion

Nunley et. al. Metal-free Cortico-pedicular Device for Supplemental Fixation in Lumbar Interbody Fusion, World Neurosurgery, Apr. 2023


Pedicle screw fixation is a commonly utilized adjunct for lumbar interbody fusion, yet risks include screw malposition, pullout, loosening, neurovascular injury, and stress transfers leading to adjacent segment degeneration. This report describes the preclinical and initial clinical results of a minimally invasive, metal-free cortico-pedicular fixation device used for supplemental posterior fixation in lumbar interbody fusion.


Safety of arcuate tunnel creation was evaluated in cadaveric lumbar (L1–S1) specimens. A finite element analysis study evaluated clinical stability of the device to pedicular screw-rod fixation at L4–L5. Preliminary clinical results were assessed by analysis of Manufacturer and User Facility Device Experience database complications, and 6-month outcomes in 13 patients treated with the device.


Among 35 curved drill holes in 5 lumbar specimens, no breaches of the anterior cortex were identified. The mean minimum distance from the anterior surface of the hole to the spinal canal ranged from 5.1 mm at L1–L2 to 9.8 mm at L5–S1. In the finite element analysis study, the polyetheretherketone strap provided comparable clinical stability and reduced anterior stress shielding compared to the conventional screw-rod construct. The Manufacturer and User Facility Device Experience database identified 1 device fracture with no clinical sequelae among 227 procedures. Initial clinical experience showed a 53% decrease in pain severity (P = 0.009), a 50% decrease in Oswestry Disability Index (P < 0.001), and no device-related complications.


Cortico-pedicular fixation is a safe and reproducible procedure that may address limitations of pedicle screw fixation. Longer term clinical data in large clinical studies are recommended to confirm these promising early results.