Early clinical results with the cortical bone trajectory pedicle screw fixation of the lumbar spine, used for the surgical treatment of the degenerative spondylolisthesis

Abstract

Introduction: Low bone mineral density in patients undergoing lumbar spinal surgery with screws is an especially difficult challenge because poor bone quality can severely compromise themaximum achievable purchase of the screws. Wide posterior approaches to the lumbarspine, exposing lateral to the facet joints and onto transverse processes causes an additional degree of muscular damage and blood loss not present with a simple laminectomy. A cortical bone trajectory (CBT) of the pediclescrewhas been proposed as an alternative to prevent screw pullout and decrease the morbidity Associated with the wide posterior approach to the spine. The CBT screw follows a lateral path in the transverse plane and caudocephalad path in the sagittal plane. This technique has been advocated because it is reportedly less invasive, improves screw−bone purchase and reduces neurovascular injury. Materials and methods: Between January 2016 and March 2016, seven patients (2 men and 5 women) underwent transforaminal lumbar interbody fusion (TLIF) using the cortical bone trajectory instead of traditional pediclescrew fixation for degenerative spondylolisthesis of the lumbar spine. The cortical screws where placed with the assistance of the BrainLab Curve navigation systemand the Siemens Artis Zee multi-purpose system. Results: The average patient age was 63,5 years (range 55 – 72 years). Prior to surgery, all patients underwent MRI, CT and DEXA scans. Low vertebral bone mineral density (osteoporosis and osteopenia)was found in three cases. The L3 to S1 levels where instrumented. For the L3 and L4 pedicles, we used 5,5x35 mm polyaxial screws, for L5 - 6,5x35 mm screws. For S1 we used a different trajectory of the screw, oriented to engage with the high-density bone by penetrating the S1 superior endplate. This insertion technique allowed a larger 7,5 x 40 mm screw to be used, thus increasing the stability of the instrumentation construct. We obtained good postoperative results in all seven cases. Considerable improvement in both back and leg pain was achieved. In terms of complications, one case of pedicle fracture at the insertion site on the facetectomy side occurred. No dural tear, superior facet violation or screw misplacement where encountered. The mean operation time, radiation exposure and blood loss was significantly less than in the traditional lumbar fusion surgery. Conclusion: We present early clinical results of a new technique that appeared to have a better fixation profile in laboratory testing. The CBT represents a good alternative option to obtain fixation for the lumbar spine, even in case of low bone quality.