Radiographic fusion rate after implantation of facet bone dowels

Abstract

Background context: Achieving a posterolateral fusion in conjunction with performing decompressive laminectomies can prevent recurrence of stenosis or worsening of spondylolisthesis. Facet bone dowels have been introduced and marketed as a less invasive alternative to pedicle screws. Surgeons have been placing them during lumbar laminectomy surgery and coding for intervertebral biomechanical device and posterolateral fusion. These bone dowels have also been placed percutaneously in outpatient surgery centers and pain clinics for facet-mediated back pain.

Purpose: To describe fusion outcomes in patients who underwent facet bone dowel placement.

Study design/setting: Retrospective analysis of a single center's experience.

Patient sample: Ninety-six patients comprise the entire cohort of patients who underwent facet bone dowel implantation at our institution with adequate postoperative imaging to determine fusion status.

Outcome measures: Fusion rates as determined on postoperative computed tomography (CT) scans and dynamic lumbar X-rays if CT is not available.

Methods: Threaded facet bone dowels in this study were placed according to the manufacturer's recommended methods. The bone dowels were placed after open exploration of the facet complex or percutaneously through a tubular retractor on the contralateral side from a microdiscectomy or synovial cyst resection. The most recent available postoperative imaging was reviewed to determine fusion status.

Results: Of 96 patients in our series, 6 (6.3%) had a fusion seen on CT and 4 did not exhibit any movement on dynamic lumbar X-rays for a total fusion rate of 10.4% (10/96). Eighty-six (89.6%) patients were shown on imaging to not have a solid fusion either by visualizing a patent facet joint on CT or measurable movement between the flexion and the extension lumbar X-rays.

Conclusions: This article is mainly intended to question whether the implantation of facet bone dowels can produce a solid fusion radiographically. In our experience, the placement of facet bone dowels does not equal the time, skill, or attention to detail that is necessary for a posterolateral lumbar arthrodesis, and our follow-up radiographic studies clearly demonstrate an inadequate fusion rate.

Keywords: Bone dowel; Facet bone dowel; Facet fusion; Posterolateral fusion; Spinal fusion; Threaded bone dowel.