Stand-alone Group Research Articles

Finite element analysis of biomechanical investigation on diverse internal fixation techniques in oblique lumbar interbody fusion

BackgroundTo establish a three-dimensional finite element model of the lumbar spine and investigate the impact of different fixation techniques on the biomechanical characteristics of oblique lumbar interbody fusion (OLIF).MethodsThe study aimed to establish and validate a comprehensive three-dimensional model of the lower lumbar spine (L3-S1) using the finite element method. L4-L5 was selected as the surgical segment, and four distinct OLIF surgical models were constructed: Stand-alone (SA), unilateral cortical bone trajectory screw (UCBT), bilateral cortical bone trajectory screw (BCBT), and bilateral pedicle screw (BPS). The models were underwent a pure moment of 10N·m to simulate lumbar extension, flexion, left bending, right bending, left and right rotation movements. Subsequently, the range of motion (ROM), cage stress, and fixation stress were calculated.ResultsIn the L3-L5 segment, the BCBT group showed the most limited range of motion (ROM) under exercise load, indicating superior stability within this group. The ROM and cage stress values were found to be highest in the SA group. In contrast, the cage and internal fixation stress in the BPS group were observed to be lowest (9.91 ~ 53.83MPa, 44.93 ~ 84.85 MPa). With the exception of right bending and right rotation, the UCBT group demonstrated higher levels of internal fixation stress (102.20 ~ 164.62 MPa).ConclusionsThe study found that OLIF-assisted internal fixation improved segmental stability and reduced cage stress. The BPS group had advantages over the CBT group in preventing endplate damage and reducing the risk of cage subsidence. However, BCBT group has distinct merits in maintaining surgical segment stability, distributing stress load on the spinal motor unit, and reducing the likelihood of adjacent segment degeneration (ASD).

Anterior cervical discectomy and fusion with zero-profile versus stand-alone cages for two-level cervical spondylosis: A retrospective cohort study.

To assess the mid-long-term clinical and radiological outcomes of zero-profile (ZP) compared with stand-alone (ST) cages for two-level anterior cervical discectomy and fusion (ACDF). We included 77 patients (39 women and 38 men) who underwent two-level ACDF between May 5, 2016, and May 5, 2020, and who were followed up for at least 1 year. The subjects were divided into the ST (n = 38) and ZP (n = 39) group. For the evaluation of functional status, Japanese Orthopedic Association (JOA), Neck Disability Index (NDI), and Visual Analogue Scale (VAS) scores were used. Additionally, radiological outcomes and procedure complications were observed at final follow-up. Both groups had excellent clinical outcomes at the final follow-up. There were no significant intergroup (ZP vs. ST) differences in the fusion rate (91.02% vs. 90.79%, P > 0.05) and postoperative dysphagia (15.4% vs. 2.6%, P = 0.108). However, the disc height at the final follow-up in the ZP group was higher than that in the ST group (6.86 ± 0.84 vs. 6.17 ± 1.03, P = 0.002). The ZP group accomplished a lower loss of cervical lordosis (18.46 ± 4.78 vs. 16.55 ± 4.36, P = 0.071), but without reaching statistical significance. ACDF with either ZP or ST cages turns out to be a dependable strategy for two-level ACDF in terms of clinical results. However, compared with the ST, the ZP cage may achieve a significantly lower loss of disc height.

Oblique lateral interbody fusion combined with different internal fixations for the treatment of degenerative lumbar spine disease: a finite element analysis

BackgroundLittle is known about the biomechanical performance of different internal fixations in oblique lumbar interbody fusion (OLIF). Here, finite element (FE) analysis was used to describe the biomechanics of various internal fixations and compare and explore the stability of each fixation.MethodsCT scans of a patient with lumbar degenerative disease were performed, and the l3-S1 model was constructed using relevant software. The other five FE models were constructed by simulating the model operation and adding different related implants, including (1) an intact model, (2) a stand-alone (SA) model with no instrument, (3) a unilateral pedicle screw model (UPS), (4) a unilateral pedicle screw contralateral translaminar facet screw model (UPS-CTFS), (5) a bilateral pedicle screw (BPS) model, and (6) a cortical bone trajectory screw model (CBT). Various motion loads were set by FE software to simulate lumbar vertebral activity. The software was also used to extract the range of motion (ROM) of the surgical segment, CAGE and fixation stress in the different models.ResultsThe SA group had the greatest ROM and CAGE stress. The ROM of the BPS and UPS-CTFS was not significantly different among motion loadings. Compared with the other three models, the BPS model had lower internal fixation stress among loading conditions, and the CBT screw internal fixation had the highest stress among loads.ConclusionsThe BPS model provided the best biomechanical stability for OLIF. The SA model was relatively less stable. The UPS-CTFS group had reduced ROM in the fusion segments, but the stresses on the internal fixation and CAGE were relatively higher in the than in the BPS group; the CBT group had a lower flexion and extension ROM and higher rotation and lateral flexion ROM than the BPS group. The stability of the CBT group was poorer than that of the BPS and LPS-CTFS groups. The CAGE and internal fixation stress was greater in the CBT group.

Clinical Outcomes between Stand-Alone Zero-Profile Spacers and Cervical Plate with Cage Fixation for Anterior Cervical Discectomy and Fusion: A Retrospective Analysis of 166 Patients.

Stand-alone (SA) zero-profile implants are an alternative to cervical plating (CP) in anterior cervical discectomy and fusion (ACDF). In this study, we investigate differences in surgical outcomes between SA and CP in ACDF. We conducted a retrospective analysis of 166 patients with myelopathy and/or radiculopathy who had ACDF with SA or CP from Jan 2013–Dec 2016. We measured surgical outcomes including Bazaz dysphagia score at 3 months, Nurick grade at last follow-up, and length of hospital stay. 166 patients (92F/74M) were reviewed. 92 presented with radiculopathy (55%), 37 with myelopathy (22%), and 37 with myeloradiculopathy (22%). The average operative time with CP was longer than SA (194 ± 69 vs. 126 ± 46 min) (p < 0.001), as was the average length of hospital stay (2.1 ± 2 vs. 1.5 ± 1 days) (p = 0.006). At 3 months, 82 patients (49.4%) had a follow-up for dysphagia, with 3 patients reporting mild dysphagia and none reporting moderate or severe dysphagia. Nurick grade at last follow-up for the myelopathy and myeloradiculopathy cohorts improved in 63 patients (85%). Prolonged length of stay was associated with reduced odds of having an optimal outcome by 0.50 (CI = 0.35–0.85, p = 0.003). Overall, we demonstrate that there is no significant difference in neurological outcome or rates of dysphagia between SA and CP, and that both lead to overall improvement of symptoms based on Nurick grading. However, we also show that the SA group has shorter length of hospital stay and operative time compared to CP.

Cage Subsidence and Fusion Rate in Extreme Lateral Interbody Fusion with and without Fixation

To examine the subsidence rate in patients undergoing extreme lateral interbody fusion (XLIF) using data from a 2-year retrospective study to assess the effect of supplemental fixation on the stand-alone procedure. Demographic and perioperative data for all patients who underwent XLIF for degenerative lumbar disorders between June 2012 and January 2016 were collected and divided into 4 groups: the stand-alone (SA), lateral fixation, unilateral pedicle screw, and bilateral pedicle screw (BPS) groups. The disk height (DH), lumbar lordotic (LL) angle, and segmental lordotic (SL) angle were measured preoperatively and 3 days, 3 months, 1 year, and 2 years postoperatively. Clinical outcomes were evaluated using Japanese Orthopaedic Association (JOA) and visual analog scale (VAS) scores. Fusion was defined according to computed tomography scan. There were 126 vertebrae in 107 patients treated. SL angle, LL angle, and DH significantly increased postoperatively in all groups. Although the preoperative and 2-year postoperative DHs in the SA group were similar, the other measures showed significant differences from baseline at each follow-up visit. No significant effects on SL angle or DH were found in any of the groups. Asignificant difference in the LL angle was found in the BPS group compared with the other groups. At the last follow-up, high-grade subsidence was found in 26.89% of all cases, the fusion rate was 85.71%, and the VAS and JOA scores were significantly improved in all groups. Supplemental fixation did not significantly influence cage subsidence or SL angle. Only BPS fixation significantly improved the LL angle. The 2-year fusion rate was satisfactory.

A radiographic follow-up study of stand-alone-cage and graft-plate constructs for single-level anterior cervical discectomy and fusion.

Anterior cervical discectomy and fusion (ACDF) may be performed using an interbody cage or graft with an anterior plate or with a stand-alone (SA) interbody device without the anterior plate. The pros and cons of each vary. This study examined the radiographic outcome of the two techniques with a focus on implant subsidence. A retrospective review of cases of singe level ACDF by a single surgeon was undertaken. Medical and radiographic records were reviewed to determine subsidence, pre- and post-operative segmental and total lordosis in cohorts of both stand-alone and graft-and-plate constructs. The post-operative radiographs of 35 patients with a SA cage were compared with 41 patients with an allograft block and anterior plate (graft and plate; GP). There was no significant difference in overall subsidence between the two groups although there was a trend toward less clinically significant subsidence (2 mm) in the SA group. For single level ACDF, a SA device appears to be comparable in terms of undesired subsidence. Further studies with different implants and materials may offer further insight.

Trabecular metal spacers as standalone or with pedicle screw augmentation, in posterior lumbar interbody fusion: a prospective, randomized controlled trial.

This prospective randomized comparative trial compared radiological and clinical outcome of Trabecular Metal™ (TM) spacers in PLIF, used as standalone (SA) devices, to TM spacers in PLIF with pedicle screw fixation (PF), in patients with single-level degenerative disc disease (DDD). Patients (n = 80) with chronic low back pain and single-level degenerative disc were randomly assigned to the SA PLIF (n = 40) or PLIF with PF (n = 40). The primary radiological outcome was the evaluation of a long-term (±6 years; range 6.0-7.7 years) stable construct measured by dynamic X-rays. CT scan does not allow judging the bony bridging between vertebrae, because of Tantalum artefacts. The clinical evaluation (6 weeks, 6, 12 and 24 months) consisted of the Oswestry Disability Index (ODI) score, intensity of low back pain (Visual Analogue Scale) and quality of life (Short Form-36). At 6-year follow-up, X-rays showed a stable construct in 94 % of patients treated by SA TM-500 spacers and in 97 % of those with additional PF. Neither subsidence nor migration was observed in either the SA or the PF group. The average improvement in ODI scores at 24-month clinical follow-up was 14.4 and 13.8 for the SA and PF group, respectively. The VAS score showed an average improvement of 6.4 (SA) and 6.7 (PF), 2 years after implantation. No significant difference between groups was observed at all the evaluation points. In this study, TM spacers were found to provide a solid construct at more than 6-year follow-up after PLIF for DDD both with and without additional pedicle fixation. The clinical, but also radiological results were not significantly different between both cohorts. Future studies focusing on the differences of SA and PF at L4/5 level should be powered to study differences in post-surgery stability at the long term.