Hybrid surgery with PEEK rods for lumbar degenerative diseases: a 2-year follow-up study

Background Finite element analyses and biomechanical tests have shown that PEEK rods promote fusion and prevent adjacent segment degeneration. The purpose of this study was to evaluate the effects and complications of hybrid surgery with PEEK rods in lumbar degenerative diseases. Methods From January 2015-December 2017, 28 patients who underwent lumbar posterior hybrid surgery with PEEK rods were included in the study. The patients were diagnosed with lumbar disc herniation, lumbar spinal stenosis, or degenerative grade I spondylolisthesis. Before the operation and at the last follow-up, the patients completed lumbar anteroposterior and lateral X-ray, dynamic X-ray, MRI examinations. In addition, at the last follow-up the patients also completed lumbar CT examinations. The radiographic parameters, clinical visual analog scale (VAS) score and Oswestry disability index (ODI) score were compared. Results The average age of the patients was 44.8 ± 12.6 years, and the average follow-up duration was 26.4 ± 3.6 months. The VAS score improved from 6.3 ± 1.6 to 1.0 ± 0.9, and the ODI score decreased from 38.4 ± 10.8 to 6.8 ± 4.6. The fusion rate of the fused segment was 100%. There were no significant changes in the modified Pfirrmann classifications or disc height index for the nonfused segments and the upper adjacent segments from pre- to postoperatively. No cases of screw loosening, broken screws, broken rods or other mechanical complications were found. Conclusion Hybrid surgery with PEEK rods for lumbar degenerative diseases can yield good clinical results and effectively reduce the incidence of complications such as adjacent segment diseases.

Biomechanical Effects of Polyetheretherketone and Titanium Rods in Transforaminal Lumbar Interbody Fusion: A Finite Element Analysis

Background: Currently, the comprehensive biomechanical evaluation of polyetheretherketone (PEEK) rods in transforaminal lumbar interbody fusion (TLIF) is limited. The purpose of this study was to compare the biomechanical differences between titanium alloy (Ti) rods and PEEK rods in TLIF. Methods: L3-5 lumbar models were developed using the finite element method. Four surgical models of TLIF were constructed by simulating different fusion methods and rods: cage fusion with Ti rods, cage fusion with PEEK rods, bone graft alone with Ti rods, and bone graft alone with PEEK rods. The range of motion (ROM) and stress distribution of the surgical and adjacent segments were then compared. Results: Compared to the Ti rods, the PEEK rods increased the ROM by 0.7–20% at the L4/5 segment and decreased the ROM by 0.8–15.1% at the L3/4 segment. The disc stresses at the L3/4 level were similar among the surgical models (0.79–1.80 MPa). The peak stresses of the screws, rods, and bone-screw interfaces in the PEEK rod models were 0–1.2 times, 1.6–4.4 times, and 0–1.4 times lower than those of the Ti rod models, respectively. PEEK rods increased the average strain of the bone graft by 0.5–61.6% and the stresses of the cage by 0.9–44.1% and endplates by 2.1–52.9%. Conclusion: In TLIF, PEEK rods played a positive role in restoring the ROM. They also increased the strain of the bone graft, stresses of the endplates and cages, and the risk of rod fracture and reduced the stress of the screw-rod system. Bone grafts alone combined with PEEK rods had acceptable biomechanical behavior in TLIF.

Evaluating Screw Stability After Pedicle Screw Fixation With PEEK Rods

Study Design: Animal experiment. Objective: To evaluate whether the use of polyetheretherketone (PEEK) rods for posterior spinal fixation can improve screw stability. Methods: Sheep models of anterior-posterior cervical fusion were used in this study. Six sheep were randomly assigned to the PEEK rod group and titanium alloy group. A total of 8 screws and 2 fixing rods were implanted in each sheep. At 24 weeks postoperatively, a computed tomography (CT) evaluation, pull-out test, micro-CT evaluation and histological evaluation were conducted to evaluate screw stability in the harvested surgical segments. Result: According to the CT evaluation, there were no signs of screw loosening in either group. The pull-out force and energy of the PEEK rod group were significantly higher than those of the titanium alloy rod group. Denser and thicker trabecular bone around the screw was observed in the PEEK rod group according to the micro-CT reconstructed images, and quantitative analysis of the micro-CT data confirmed this finding. In the histological evaluation, more abundant and denser bone trabeculae were also observed in the PEEK rod group. However, there was no significant difference in the bone-screw interface between the 2 groups. Conclusion: Posterior spinal fixation with PEEK rods can increase screw stability by promoting bone growth around the screw but cannot promote bone integration at the bone-screw interface in an animal model study. This finding presents a new idea for clinical practices to reduce screw loosening rate.

A new concept of motion preservation surgery of the cervical spine: PEEK rods for the posterior cervical region

BACKGROUND: Laminectomy may cause kyphotic postoperative deformity in the cervical region leading to segmental instability over time. Laminoplasty may be an alternative procedure to laminectomy, as it protects the spine against post-laminectomy kyphosis; however, similar to laminectomy, laminoplasty may cause sagittal plane deformities by destructing or weakening the dorsal tension band. OBJECTIVE: Using finite element analysis (FE), we attempted to determine whether a posterior motion preservation system (PEEK posterior rod system concept) could overcome the postoperative complications of laminectomy and laminoplasty and eliminate the side effects of rigid posterior stabilization in the cervical region. METHODS: We compared PEEK rods in four different diameters with a titanium rod for posterior cervical fixation. The present study may lead to motion preservation systems of the cervical vertebra. RESULTS: When PEEK rod is compared with titanium rod, considerable increase in range of motion is observed. CONCLUSIONS: PEEK rod-lateral mass screw instrumentation systems may be useful in motion preservation surgery of the posterior cervical region.

Semi-rigid lumbar spine fixation with PEEK rods as a treatment option for mono-segmental degenerative disk disease

Long lasting back pain due to degenerative disc disease is one of the major reasons for reduced quality of life and work incapacity. In some of these patients conservative treatment will not improve back pain significantly. Therefore fusion surgery as a surgical option is offered to these patients. The main aim of this kind of treatment is the reduction of segmental motion leading to an improvement in pain. Rigid fixation leads to high fusion rates but may also contribute to stress shielding and adjacent segment degeneration. Therefore a semi-rigid stabilization with PEEK rods may be an option because it is associated with less implant related rigidity and is a less invasive procedure. The aim of this retrospective study was to evaluate the improvement in back pain after minimally invasive semi-rigid lumbar stabilization with screws and PEEK rods in 45 patients and to identify potential implant failures during a follow up of two years. Six weeks after surgery the patients showed a significant improvement in their back pain, which persisted during the whole observation time of two years (p<0.01). All patients who were still in working life returned to their jobs without extended work incapacity. No implant related complication associated with the surgical procedure was detected. During the follow up time of two years no implant failure was observed.

Decompression and Dynamic Transpedicular Stabilization Using Polyetheretherketone Rods and Pedicle Screws vs. Decompression Alone for Single-Level Spinal Canal Stenosis with Listhesis: A Retrospective Case-Control Study

Background Spinal stenosis is frequently caused by spondylolisthesis, and surgical treatment may be indicated. However, whether decompression alone or decompression with dynamic stabilization offers better surgical outcomes remains unclear. We compared the clinical and radiologic results of patients with single-level lumbar spinal stenosis and grade 1 spondylolisthesis undergoing microsurgical decompression alone or decompression with transpedicular dorsal dynamic stabilization. Methods We retrospectively analyzed 20 patients undergoing microsurgical decompression and dorsal dynamic transpedicular stabilization using polyetheretherketone (PEEK) rods in one center from 2011 to 2017. Twenty patients with the same diagnosis undergoing microsurgical decompression alone were used as controls. Reoperation of the index and neighboring segments, back/leg pain, neurologic deficits, and the use of pain medication were assessed. For stabilization patients, radiographic progression of degeneration in the neighboring segments, listhesis degree in the index segment, and implant failure were assessed. Results All patients had good clinical outcomes at 3 and 12 months postoperatively. In stabilization patients, the visual analog scale (VAS) score for leg pain decreased from 5 points (median) to 1.6 at 3 months and 0.6 at 1 year postoperatively. In controls, the VAS score improved from 4.8 points to 1.1 at 3 months and 0.3 at 1 year postoperatively. The VAS score for back pain in stabilization patients decreased from 7.6 points (median) to 1.7 at 3 months and 0.1 at 1 year postoperatively. In controls, it decreased from 7.7 points to 1.1 at 3 months and 0.2 at 1 year postoperatively. In patients with additional dynamic stabilization, a longer hospital stay (stabilization group: 8.7 ± 4.1; control: 6.2 ± 1.6 days), longer operative time (stabilization group: 132.7 ± 41.3; control: 83.2 ± 31.7 minutes), and higher complication rates (revision surgery performed in two stabilization patients) were found. Conclusion No indications in our study showed that additional dynamic stabilization with PEEK rods offers any advantage over decompression alone.

Biomechanical Study of a Novel, Expandable, Non-Metallic and Radiolucent CF/PEEK Vertebral Body Replacement (VBR)

Vertebral body replacement is well-established to stabilize vertebral injuries due to trauma or cancer. Spinal implants are mainly manufactured by metallic alloys; which leads to artifacts in radiological diagnostics; as well as in radiotherapy. The purpose of this study was to evaluate the biomechanical data of a novel carbon fiber reinforced polyetheretherketone (CF/PEEK) vertebral body replacement (VBR). Six thoracolumbar specimens were tested in a six degrees of freedom spine tester. In all tested specimens CF/PEEK pedicle screws were used. Two different rods (CF/PEEK versus titanium) with/without cross connectors and two different VBRs (CF/PEEK prototype versus titanium) were tested. In lateral bending and flexion/extension; range of motion (ROM) was significantly reduced in all instrumented states. In axial rotation; the CF/PEEK combination (rods and VBR) resulted in the highest ROM; whereas titanium rods with titanium VBR resulted in the lowest ROM. Two cross connectors reduced ROM in axial rotation for all instrumentations independently of VBR or rod material. All instrumented states in all planes of motion showed a significantly reduced ROM. No significant differences were detected between the VBR materials in all planes of motion. Less rigid CF/PEEK rods in combination with the CF/PEEK VBR without cross connectors showed the smallest reduction in ROM. Independently of VBR and rod material; two cross connectors significantly reduced ROM in axial rotation. Compared to titanium rods; the use of CF/PEEK rods results in higher ROM. The stiffness of rod material has more influence on the ROM than the stiffness of VBR material.