Posterior intraprosthetic dislocation of cervical arthroplasty: illustrative case

BACKGROUND Cervical disc herniation is a common condition usually treated with anterior cervical discectomy and fusion (ACDF) or, more recently, with cervical disc arthroplasty (CDA). Both treatments offer similar clinical results. However, CDA has been found to offer fewer medium- to long-term complications as well as potential reduction of long-term adjacent disc degeneration. OBSERVATIONS A 40-year-old man was treated with cervical discectomy and arthroplasty due to a C6–C7 disc herniation with left C7 radiculopathy. After the treatment, his postoperative follow-up appointments were uneventful for 9 months. However, after 9 months, he reported cervical pain and a right C7 radiculopathy after neck extension. Imaging confirmed a posterior intraprosthetic dislocation, the first case reported to date. The patient was received emergency surgery under neuromonitoring, and the prosthesis was replaced by an ACDF and anterior plate. The insert presented a rupture of the anterior horn. The patient presented no preoperative or postoperative neurological deficit, and his follow-up review revealed no issues. LESSONS Posterior intraprosthetic dislocation is an extremely rare complication. It may occur with Mobi-C cervical arthroplasty in the case of rupture and oxidation of the polyethylene insert. Spine surgeons should be aware of this potential major complication.

Biomechanical Evaluation of the Lumbar Spine by Using a New Interspinous Process Device: A Finite Element Analysis

Minimally invasive decompression is generally employed for treating lumbar spinal stenosis; however, it results in weakened spinal stability. To augment spinal stability, a new interspinous process device (NIPD) was developed in this study. The biomechanical features of the NIPD were evaluated in this study. Three finite-element (FE) models of the entire lumbar spine were implemented to perform biomechanical analysis: the intact, defect (DEF), and NIPD models. The DEF model was considered for lumbar spines with bilateral laminotomies and partial discectomy at L3–L4. Range of motion (ROM), disc stress, and facet joint contact force were evaluated in flexion, extension, torsion, and lateral bending in the three FE models. The results indicated that ROM in the extension increased by 23% in the DEF model but decreased by 23% in the NIPD model. In the NIPD model, the cephalic adjacent disc stress in flexion and extension was within 5%, and negligible changes were noted in the facet joint contact force for torsion and lateral bending. Thus, the NIPD offers superior spinal stability and causes only a minor change in cephalic adjacent disc stress in flexion and extension during the bilateral laminotomy and partial discectomy of the lumbar spine. However, the NIPD has a minor influence on the ROM and facet joint force for lateral bending and torsion.

Biomechanical analysis of reduction technique for lumbar spondylolisthesis: anterior lever versus posterior lever reduction method

Background Reduction of lumbar spondylolisthesis during spinal fusion surgery is important for improving the fusion rate and restoring the sagittal alignment. Despite the variety of reduction methods, the fundamental mechanics of lumbar spondylolisthesis reduction remain unclear. This study aimed to investigate the biomechanical behavior while performing spondylolisthesis reduction with the anterior and posterior lever reduction method. Methods We developed an L4–L5 spondylolisthesis model using sawbones. Two spine surgeons performed the simulated reduction with a customized Cobb elevator. The following data were collected: the torque and angular motion of Cobb, displacement of vertebral bodies, change of lordotic angle between L4 and L5, total axial force and torque applied on the model, and force received by adjacent disc. Results Less torque value (116 N-cm vs. 155 N-cm) and greater angular motion (53o vs. 38o) of Cobb elevator were observed in anterior lever reduction. Moreover, the total axial force received by the entire model was greater in the posterior lever method than that in the anterior lever method (40.8 N vs. 16.38 N). Besides, the displacement of both vertebral bodies was greater in the anterior lever method. Conclusions The anterior lever reduction is a more effort-saving method than the posterior lever reduction method. The existing evidence supports the biomechanical advantage of the anterior reduction method, which might be one of the contributing factors to successfully treating high-grade lumbar spondylolisthesis with short-segment instrumentation.

Impact of patient-specific factors and spinopelvic alignment on the development of adjacent segment degeneration after short-segment lumbar fusion

Objectives: The main purpose of the study was to analyse the different demographical, morphological, and surgery-related parameters influencing the development or progress of degeneration in adjacent segments after routine, short-segment lumbar fusions.Summary of Background data: Adjacent segment degeneration (ASD) considered as a major long-term complication after lumbar fusions. Possible risk factors are related to the patients’ demographics, spinopelvic anatomy or preoperative lumbar intervertebral disc conditions. The current literature lacks of well-designed prospective studies focusing on the multidimensional nature of the condition.Methods: A prospective cohort of 100 patients who underwent one- or two-level lumbar transforaminal interbody fusions due to lumbar degenerative pathology was conducted. Demographical, radiological findings (spinopelvic parameters, adjacent segmental radiological as well as magnetic resonance imaging (MRI) features) and long-term outcome data (5-year) were analysed to identify factors associated with ASD. Results: ASD patients showed higher level of pain (p=0.004) and disability (p=0.020) at follow-up. In univariate analysis, older age, upper-level lumbar fusion (p=0.007), lower L4-S1 lordosis (p=0.039), PI-LL mismatch (p=0.021), Pfirrmann grade III or higher disc degeneration (p=0.002) and the presence of disc bulge/herniation were (p=0.007) associated with ASD. Final result of multivariate analysis showed major degenerative sign (disc degeneration and/or disc bulge) as a risk factor (OR 3.85, CI 1.43-10.37, p=0.006).Conclusion: By examining the role of different patient- and procedure-specific factors, we found that preoperative major degenerative signs at the adjacent segment increase the risk of ASD causing significantly worse outcome after short-segment lumbar fusion. Adjacent disc conditions should be considered carefully during surgical planning.

The biomechanical effects of S-type dynamic cage using Ti and PEEK for ACDF surgery on cervical spine varying loads

Anterior cervical discectomy with fusion (ACDF) is the common method to treat the cervical disc degeneration. The most serious problems in the fusion cages are adjacent disc degeneration, loss of lordosis, pain, subsidence, and migration of the cage. The objective of our work is to develop the three-dimensional finite element (FE) model from C3-C6 and virtually implant a designed S-type dynamic cage at C4-C5 segment of the model. The dynamic cage design will provide mobility in the early stage after ACDF surgery. Titanium (Ti) and PEEK (polyether ether ketone) were used as the material property for the cages. We applied the physiological motions at different loads from 0.5, 1, 1.5, 2.0 Nm to evaluate the dynamic cage design and the biomechanical performances of the designed S-type dynamic cage. It was observed that in all the loading condition the range of motion in the adjacent level was maintained and the maximum stress at the adjacent disc was reduced. The clinical significance of the S-type dynamic cage is better stress profile at the fusion level and adjacent segments which translates into higher rate of fusion, lower risk of cage subsidence, lower risk of adjacent segment degeneration, and good mechanical stability.

Surgical outcomes for late neurological deficits after long segment instrumentation for degenerative adult spinal deformity

OBJECTIVE The most catastrophic symptom of proximal junctional failure (PJF) following long instrumented fusion surgery for adult spinal deformity (ASD) is neurological deficits. Although previous reports have shown that PJF usually developed during the early postoperative period, some patients showed late neurological deficits. The aim of this study was to report the incidence, characteristics, and surgical outcomes of PJF with late neurological deficits. METHODS Patients surgically treated for ASD at a single institution were retrospectively reviewed. Among them, the patients requiring revision surgery for newly developed neurological deficits at least 6 months after the initial surgery were included. Patient demographic, radiographic, surgical, and clinical data were investigated. Neurological status was assessed using the Frankel grading system. RESULTS PJF with late neurological deficits developed in 18 of 385 patients (4.7%). The mean age at the onset of neurological deficits was 72.0 ± 6.0 years, and the median time from the initial surgery was 4.5 years. The most common pathology of PJF was adjacent disc degeneration and subsequent canal stenosis (11 patients). Five patients showed disc degeneration with aseptic bone destruction. Fractures at the upper instrumented vertebra (UIV), UIV + 1, and UIV + 2 occurred in 2, 3, and 2 patients, respectively. Ossification of the yellow ligament, which had not been found at the first surgery, was identified in 6 patients. Eight patients showed improvement of their neurological deficits and 10 patients showed no improvement by the final follow-up. Perioperative major complications occurred in 8 of 18 patients. CONCLUSIONS The incidence of PJF with late neurological deficits following ASD surgery was 4.7% in this cohort. The patients showed several morphological features. After revision surgery, perioperative complications were common and the prognosis for improved neurological status was not favorable.

The comparison between anterior and posterior approaches for removal of infected lumbar interbody cages and a proposal regarding the use of endoscope-assisted technique

Background In cases of postoperative deep wound infection after interbody fusion with cages, it is often difficult to decide whether to preserve or remove the cages, and there is no consensus on the optimal approach for removing cages. The aim of this study was to investigate the surgical management of cage infection after lumbar interbody fusion. Methods A retrospective study was conducted between January 2012 and August 2018. Patients were included if they had postoperative deep wound infection and required cage removal. Clinical outcomes, including operative parameters, visual analog scale, neurologic status, and fusion status, were assessed and compared between anterior and posterior approaches for cage removal. Results Of 130 patients who developed postoperative infection and required surgical debridement, 25 (27 levels) were diagnosed with cage infection. Twelve underwent an anterior approach, while 13 underwent cage removal with a posterior approach. Significant differences were observed between the anterior and posterior approaches in elapsed time to the diagnosis of cage infection, operative time, and hospital stay. All patients had better or stationary American Spinal Injury Association impairment scale, but one case of recurrence in adjacent disc 3 months after the surgery. Conclusions Both anterior and posterior approaches for cage removal, followed by interbody debridement and fusion with bone grafts, were feasible methods and offered promising results. An anterior approach often requires an additional extension of posterior instrumentation due to the high incidence of concurrent pedicle screw loosening. The use of an endoscope-assisted technique is suggested to facilitate safe removal of cages.

Wedging of vertebral bodies at the thoracolumbar spine in healthy individuals on whole body MRI screening: correlation with disc degeneration and disc herniation

Background There have been no reports on the relationship between wedging of vertebral bodies at the thoracolumbar spine and disc herniation in healthy individuals on magnetic resonance imaging (MRI). Purpose To investigate the degree of wedging of vertebral bodies at the thoracolumbar spine in healthy individuals who underwent whole-body (WB) MRI. We also assessed the correlation between wedging and adjacent disc pathology. Material and Methods This retrospective study comprised 200 healthy patients who underwent WB MRI as part of a regular health check from January 2019 to February 2019. We measured anterior and posterior vertical heights of each vertebral body between T10 and L2. The ratio of anterior height to posterior height (APR) was calculated, and we evaluated disc degeneration or disc herniation using WB MRI. Results The APR of T10 was significantly higher than at the other levels ( P < 0.05), and the APR of L1 was significantly lower ( P < 0.05). Men had a significantly smaller APR than women at T12 to L2 ( P < 0.05). Regarding the relationship between APR and disc degeneration, the group without disc degeneration had a higher APR, with statistical significance at T12, L1, and L2. Regarding the relationship between APR and disc herniation, the group without disc herniation had a higher APR, with statistical significance at T11, T12, L1, and L2. Conclusion Wedging of vertebral bodies is most prominent at L1. Although the values were statistically significant only at some levels, the patients with disc degeneration or herniation had more prominent wedge deformity of thoracolumbar spine.