Comparison of unilateral and bilateral polymethylmethacrylate-augmented cannulated pedicle screw fixation for the management of lumbar spondylolisthesis with osteoporosis

Reversed windshield-wiper effect leads to failure of cement-augmented pedicle screw: Biomechanical mechanism analysis by finite element experiment

The failure mode of cement-augmented pedicle screw (CAPS) was different from common pedicle screw. No biomechanical study of this failure mode named as "reversed windshield-wiper effect" was reported. To investigate the mechanisms underlying this failure mode, a series of finite element models of CAPS and PS were modified on L4 osseous model. Nine models were created according to the cement volume at 0.5 mL interval (range: 1-5 mL). Pullout load and cranio-caudal loads were applied on the screws. Stress and instantaneous rotation center (IRC) of the vertebra were observed. Under cranio-caudal load, the stress concentrated on the screw tip and pedicle region. The maximal stress (MS) at the screw tip region was +2.143 MPa higher than pedicle region. With cement volume increasing, the maximal stress (MS) at the screw tip region decreased dramatically, while MS at pedicle region was not obviously affected. As dose increased to 1.5 mL, the MS at pedicle region became higher than screw tip region and the maximal stress difference was observed at 3.5 mL. IRC of the vertebra located at the facet joint region in PS model. While IRC in CAPS models shifted anteriorly closer to the vertebral body with the increasing of cement volume. Under axial pull-out load, the maximal stress (MS) of cancellous bone in CAPS models was 29.53-50.04% lower than that 2.228 MPa in PS model. MS in the screw-bone interface did not change significantly with cement volume increasing. Therefore, the possible mechanism is that anterior shift of IRC and the negative difference value of MS between screw tip and pedicle region due to cement augmentation, leading to the screw rotate around the cement-screw complex as the fulcrum point.

Beneficial influence of single-stage posterior surgery for the treatment of lumbar brucella spondylitis combined with spondylolisthesis

We aimed to evaluate the clinical efficacy of the single-stage posterior surgical treatment for patients of lumbar brucella spondylitis combined with spondylolisthesis. In this study, we performed a retrospective analysis of 16 patients with lumbar brucellosis spondylitis combined with spondylolisthesis from January 2015 to January 2019. All patients underwent single-stage posterior lumbar debridement, reduction, interbody fusion, and instrumentation. Preoperative and postoperative of the visual analog scale (VAS), the Oswestry disability index (ODI), erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) were compared. In addition, the spondylolisthesis reduction rate, reduction loss rate, interbody fusion rate, and complication rate were recorded. VAS, ODI, ESR, and CRP were conducted with repeated analysis of variance data at different follow-ups. The postoperative follow-up was 12-36 months, with an average of (25.0 ± 8.1) months. VAS, ODI, ESR, and CRP were significantly better at 2-week and 1-year follow-up than preoperative results (P = 0.000, respectively). In addition, 1 year after the operation, VAS, ODI, ESR, and CRP showed a significant improvement (P = 0.000, respectively). The average spondylolisthesis reduction in 2 weeks after operation was (91.2 ± 6.7)%, and the median reduction loss rate in 1 year after operation was 8.0 (5.0, 9.8)%. At the last follow-up, all patients achieved interbody fusion, no loosening and fracture of instrumentation were found, and no recurrence happened. Single-stage posterior operation for lumbar debridement, reduction, interbody fusion, and instrumentation is beneficial for treating lumbar brucellosis spondylitis combined with spondylolisthesis. Furthermore, the reconstruction of spinal stability may relieve pain, heal lesions, and improve patients' living.

Comparison of the Unilateral and the Bilateral Pedicle Screw Fixation without Using an Interbody Cage: Randomized Clinical Trial

BACKGROUND: Lumbar spine instability is one of the main causes of low back pain and has become more prevalent in recent years. Bilateral pedicle screw fixation is used to perform posterior lumbar stabilization, which is complemented by the installation of an interbody cage. AIM: The aim of the study was evaluating of the results of unilateral and bilateral pedicle screw fixation without using of an interbody cage. METHODS: A prospective randomized study of 96 patients was carried out. Forty-seven patients were assigned to the group of the unilateral pedicle screw fixation versus 49 patients were moved to the group of the bilateral pedicle screw fixation of the lumbar spine. Of the 96 patients, 80 patients eventually were included in the study. However, seven patients in the first group and nine patients were lost to follow-up. Surgery timing, blood loss volume, clinical outcomes (scores on the Oswestry disability index [ODI], EQ-5D and visual analogue scale [VAS]) were evaluated in 6–12 months after surgical treatment. All the patients included in this study underwent functional and control computed tomography in 12 months after surgery. RESULTS: Both groups showed a significant improvement in VAS, EQ-5D, and ODI in 1 year after surgical treatment. The two groups significantly differed in the surgery timing (unilateral – 90.2 min; and bilateral – 129.4 min) and blood loss volume (unilateral – 152.7 ml; and bilateral – 230.1 ml), p < 0.05. CONCLUSIONS: Unilateral and bilateral pedicle screw fixation showed similar clinical results, while results in both types of fixation differed in slight manner. However, the duration of surgical treatment and intraoperative blood loss volume proved to be lower for the unilateral fixation group, which indicates that the use of the unilateral fixation can be the choice of performing posterior stabilization at a single-level instability of the spine without using an interbody cage.