ABSTRACT
BACKGROUND: Lumbar decompression can result in postsurgical instability and spondylolisthesis in patients with lumbar spinal stenosis (LSS). While pedicle screw (PS) constructs improve stability and support fusion, their use can lead to adjacent level degeneration due to rigidity and resultant overload of anatomical structures. The FFX device is a facet spacer designed to be a less invasive alternative for obtaining fusion compared with PS. OBJECTIVE: The present study aimed to compare biomechanical performance of the FFX device to different lumbar spine procedures using the finite element (FE) method. STUDY DESIGN: Comparative biomechanical study by FE method. METHODS: An FE model for the lumbar spine was developed and validated to assess vertebral displacement and stress variations in the facet joints and discs following surgery. Modeled scenarios included a healthy spine as a reference model, laminectomy (LAM), and prior to/following L4-L5 fusion for LAM + FFX and LAM + PS. RESULTS: LAM increased displacement compared with the healthy spine and both instrumented spine procedures. Facet joint stress at adjacent levels for LAM + PS was significantly higher than with LAM + FFX prior to fusion (+13.5% for L3-L4; +15.7% for L5-S1). Adjacent level disc stress at L5-S1 was 7.7% higher for LAM + PS vs LAM + FFX. Adjacent level facet joint and disc stresses for LAM + FFX were equivalent to LAM + PS once fusion occurred. CONCLUSIONS: Instrumented spine fixation prevents the risk of lumbar instability associated with LAM alone. Compared with PS, the FFX device is a less invasive alternative for the treatment of LSS, which potentially lowers the risk of adjacent segment degeneration prior to fusion that provides equivalent stability once fusion is achieved.
ABSTRACT
BACKGROUND: Facet osteosynthesis can be performed to treat facet syndrome (FS) and reduce spinal instability following laminectomy in patients with lumbar spinal stenosis (LSS). The present study evaluated clinical and radiological outcomes following facet osteosynthesis with the FFX device. METHODS: Patients with FS or LSS were prospectively enrolled in a single-arm, multicenter study. The device was placed at affected levels with or without concomitant posterior lumbar interbody fusion (PLIF) procedures. The visual analog scale (VAS) for back and leg pain and Oswestry Disability Index (ODI) were evaluated preoperatively and postoperatively. Computed tomography scans to assess fusion and migration were performed 1 year following surgery. RESULTS: Fifty-three patients (26 men/27 women) with a mean age of 65.0 ± 9.6 years (range: 37-83 years) were enrolled. A total of 205 FFX devices were implanted with 15 patients undergoing concurrent PLIF procedures. There were no intraoperative or postoperative surgical complication reported, and no patient required revision surgery. Mean VAS leg and back pain scores significantly improved from 5.57 to 2.09 (P < .001) and 5.74 to 3.13 (P < .001), respectively, between the preoperative and 1 year follow-up assessments. Mean ODI scores also significantly improved from 44.7% to 24.0% (P < .001) during the same time period. Facet fusion occurred with 86.3% of device placements after 12 months. There was 1 (0.5%) asymptomatic device migration. Eight devices (3.9%) were considered misplaced. CONCLUSIONS: The use of the FFX device is associated with a significant reduction in both pain and disability following surgery with a high facet joint fusion rate. LEVEL OF EVIDENCE: 4. CLINICAL RELEVANCE: This is the first study reporting clinical experience using the FFX device to facilitate facet osteosynthesis. The ability of the device to relieve pain, reduce disability, and enhance lumbar facet fusion with a low rate of device misplacement and migration was demonstrated.
