Clinical experiences with a PEEK-based dynamic instrumentation device in lumbar spinal surgery: 2 years and no more

Enhancing PEEK surface bioactivity: Investigating the effects of combining sulfonation with sub-millimeter laser machining

Due to its superior mechanical properties and chemical stability, Polyetheretherketone (PEEK) has emerged as an alternative to conventional metal implants. However, the bio-inertness of PEEK's surface has limited its applications. Ambient sulfonation has been adopted to enhance bioactivity, but its nanoscale topographic changes are insufficient for implant-bone interlock. To further improve bone-implant interlock, this study employs CO2 laser machining to create sub-millimeter (0.5 mm) grooves on PEEK's surface, aiming to encourage bone ingrowth and strengthen the implant-bone interface. This research investigated the physical and chemical properties and bio-interaction of PEEK surface modified by sulfonation (SPEEK), laser machining (L-PEEK), and combination of both technique (L-SPEEK). X-ray photoelectron spectroscopy (XPS) spectra revealed that sulfonation compensates for the surface chemical shift instigated by laser ablation, aligning the surface chemistry of L-SPEEK with that of SPEEK. Furthermore, L-PEEK surfaces presented pores with sizes ranging from 1 to 600 μm, while SPEEK surfaces exhibited pores between 5 and 700 nm. All tested samples demonstrated non-cytotoxicity, with L-SPEEK exhibiting the highest mineralization and ALP activity as 2 and 2.1 times that of intrinsic PEEK, after 21 days of incubation. Microscopic imaging reveals a notably higher extracellular content on L-SPEEK compared to the other groups. This study underscores the potential of combining sub-millimeter laser machining with sulfonation in enhancing early osteogenic markers, providing a promising pathway for future PEEK-based orthopedic applications.

Complications in Spinal Fusion Surgery: A Systematic Review of Clinically Used Cages

Spinal fusion (SF) comprises surgical procedures for several pathologies that affect different spinal levels, and different cages are employed in SF surgery. Few clinical studies highlight the role of cages in complications beyond the outcomes. The aim of this systematic review is to collect the last 10 years' worth of clinical studies that include cages in SF surgery, focusing on complications. Three databases are employed, and 21 clinical studies are included. The most-performed SF procedure was anterior cervical discectomy and fusion (ACDF), followed by lumbar SF. The polyetheretherketone (PEEK) cage was the most-used, and it was usually associated with autograft or calcium phosphate ceramics (hydroxyapatite (HA) and tricalcium phosphate (βTCP)). For lumbar SF procedures, the highest percentages of subsidence and pseudoarthrosis were observed with PEEK filled with bone morphogenetic protein 2 (BMP2) and βTCP. For ACDF procedures, PEEK filled with autograft showed the highest percentages of subsidence and pseudoarthrosis. Most studies highlighted the role of surgical techniques in patient complications. There are many interacting events that contextually affect the rate of clinical success or failure. Therefore, in future clinical studies, attention should focus on cages to improve knowledge of chemical, biological and topographical characteristics to improve bone growth and to counteract complications such as cage loosening or breaking and infections.

Subgaleal Effusion and Brain Midline Shift After Cranioplasty: A Retrospective Study Between Polyetheretherketone Cranioplasty and Titanium Cranioplasty After Decompressive Craniectomy

Cranioplasty with polyetheretherketone (PEEK) has recently shown better cerebral protection performance, improved brain function, and aesthetic contour compared with titanium mesh. However, whether patients undergoing PEEK cranioplasty tend to develop subgaleal effusions remains elusive. This retrospective study included patients who underwent cranioplasty with PEEK implants or titanium mesh after decompressive craniectomy between July 2017 and July 2020. Patient information, including general information, location, size of the defect, subgaleal depth, and brain midline shift was collected and statistically analyzed. There were 130 cases of cranioplasty, including 35 with PEEK implants and 95 with a titanium mesh. Patients who underwent cranioplasty with a PEEK implant had a higher subgaleal effusion rate than those who underwent cranioplasty with titanium mesh (85.71% vs. 53.68%, P < 0.001), while a midline shift >5 mm was more frequently observed in the PEEK group than in the titanium group (20% vs. 6.3%, P = 0.021). The PEEK material was the only factor associated with subgaleal effusion after cranioplasty (OR 5.589, P = 0.002). Logistic regression analysis further showed that age was a protective factor against midline shift in the PEEK cranioplasty group (OR 0.837, P = 0.029). Patients who underwent cranioplasty with PEEK implants were more likely to develop severe subgaleal effusion and significant brain midline shifts than those with titanium mesh implants.

Biomechanical investigation of topping-off technique using an interspinous process device following lumbar interbody fusion under vibration loading

Topping-off technique has been proposed to prevent adjacent-segment degeneration/disease following spine fusion surgery. Nevertheless, few studies have investigated biomechanics of the fusion surgery with topping-off device under whole-body vibration (WBV). This biomechanical study aimed to investigate the vibration characteristics of human lumbar spine after topping-off surgery, and also to evaluate the effect of bony fusion on spine biomechanics. Based on a healthy finite-element model of lumbosacral spine (L1-sacrum), the models of topping-off surgery before and after bony fusion were developed. The simulated surgical procedures consisted of interbody fusion with rigid stabilizer at L4-L5 segment (rigid fusion) and dynamic stabilizer at degenerated L3-L4 segment. An interspinous implant, Device for Intervertebral Assisted Motion (DIAM, Medtronic Inc., Minnesota, USA), was used as the dynamic stabilizer. The stress responses of spine segments and implants under a vertical cyclic load were calculated and analyzed. The results showed that compared with rigid fusion alone, the topping-off technique significantly decreased disc stress at transition segment (L3-L4) as expected, and resulted in a slight increase in disc stress at its supra-adjacent segment (L2-L3). It indicated that the topping-off stabilization using DIAM might provide a good tradeoff between protection of transition segment and deterioration of its supra-adjacent segment during WBV. Also, it was found that bony fusion decreased stress in L4 inferior endplate and rigid stabilizer but had nearly no effect on stress in DIAM and L3-L4 disc, which was helpful to determine the biomechanical differences before and after bony fusion.

Upper and lower adjacent segment range of motion after fixation of different lumbar spine segments in the goat: an in vitro experiment

Objectives

The purpose of this study was to examine the biomechanical effects of fixation on range of motion (ROM) in the upper and lower adjacent segments of different lumbar spine segments in a goat spine model.

Methods

Fifteen goat spine specimens (vertebrae T12–S1) were randomly divided into three groups: A (single-segment fixation), B (double-segment fixation), and C (triple-segment fixation). Motion in different directions was tested using a spinal motion simulation test system with five external loading forces. Transverse, forward–backward, and vertical displacement of the upper and lower adjacent segments were measured.

Results

As the external load increased, the upper and lower adjacent segment ROM increased. A significantly greater ROM in group C compared with group A was found when the applied external force was greater than 75 N. The upper adjacent segment showed a significantly greater ROM than the lower adjacent segment ROM within each group.

Conclusions

Adjacent segment ROM increased with an increasing number of fixed lumbar segments. The upper adjacent segment ROM was greater than that of the lower adjacent segments. Adjacent segment stability after lumbar internal fixation worsened with an increasing number of fixed segments.

Hydroxyapatite-incorporation improves bone formation on endosseous PEEK implant in canine tibia

BACKGROUND

Poly Ether Ether Ketone (PEEK) has been considered as a potential alternative material for endosseous dental implants, for its low elastic modulus, biocompatibility, and low cost in customized device manufacture. Hydroxyapatite-incorporation is supposed to improve the poor osseointegration of PEEK.

METHODS

In the present study we analyzed the in vivo response of hydroxyapatite-incorporated PEEK (PEEK-HA) implants in canine tibia. PEEK-HA and PEEK implants were implanted and were examined 4 weeks and 12 weeks after implantation with radiology and histology. Commercial titanium dental implants served as controls.

RESULTS

The ratio of bone volume to tissue volume of PEEK-HA implants was higher than that of PEEK implants 4 weeks after implantation in the μ-CT analysis. The bone implant contact of PEEK and PEEK-HA implants showed no statistical difference in the histological examination, but newly-formed bone around PEEK-HA implants showed more signs of mineralization than that around PEEK implants.

CONCLUSION

The study suggested that bone formation was improved with hydroxyapatite-incorporation in PEEK. Hydroxyapatite-incorporated PEEK implants may represent a potential material for endosseous dental implant.

Biomechanical effects of posterior pedicle screw-based instrumentation using titanium versus carbon fiber reinforced PEEK in an osteoporotic spine human cadaver model

BACKGROUND

Aim of this biomechanical investigation was to compare the biomechanical effects of a carbon fiber reinforced PEEK and titanium pedicle screw/rod device in osteoporotic human cadaveric spine.

METHODS

Ten human fresh-frozen cadaveric lumbar spines (L1-L5) have been used and were randomized into two groups according to the bone mineral density. A monosegmental posterior instrumentation (L3-L4) using titanium pedicle screws and rods was carried out in group A and using carbon fiber reinforced PEEK in group B. A cyclic loading test was performed at a frequency of 3 Hz, starting with a peak of 500 N for the first 2000 cycles, up to 950 N for 100,000 cycles under a general preload with 100 N. All specimens were evaluated with regard to a potential collapse of the implanted pedicle screws. A CT supported digital measurement of cavities around the pedicle at 3 defined measuring points was performed. Finally, the maximum zero-time failure load of all specimens was determined using a universal testing machine (80% F_max).

FINDINGS

Regarding maximum axial force (group A: 2835 N, group B: 3006 N, p = 0.595) and maximum compression (group A: 11.67 mm, group B: 15.15 mm, p = 0.174) no statistical difference could be shown between the two groups. However, significant smaller cavity formation around the pedicle screws could be observed in group B (p = 0.007), especially around the screw tip (p < 0.001).

INTERPRETATION

Carbon fiber reinforced PEEK devices seem to be advantageous in terms of microscopic screw loosening compared to titanium devices.

Biomechanical characterization of vertebral body replacement in situ: Effects of different fixation strategies

BACKGROUND AND OBJECTIVE

Artificial vertebral implant with a lateral or posterior screw-rod fixation system are usually employed in lumbar reconstruction surgery to rebuild the lumbar spine after partial resection due to a tumor or trauma. However, few studies have investigated the effect of the various fixation systems on the biomechanics of the reconstructed lumbar system. This study aims to evaluate the influence of different surgical fixation strategies on the biomechanical performance of a reconstructed lumbar spine system in terms of the strength and long-term stability.

METHODS

Two typical lumbar spine reconstruction case models that correspond to lateral or posterior fixation systems were built based on the clinical data. Finite element analyses were performed, and comparisons were made between the two models based on the predicted stress distribution of the reconstructed lumbar spine model, bone-growth area of the endplate, and the range of motion under various normal daily activities.

RESULTS

The load from the upper vertebral body was found to be effectively transmitted onto the lower vertebral body by a vertebral implant with the lateral fixation system; this was favorable for bone growth after surgery. However, significantly high stresses were concentrated around the interaction region between the screws and bone, owing to the uneven lateral fixation structure; this may increase the risk of bone fractures and screw loosening in the long term. For the posterior fixation case, stably posterior fixation structure was favorable to maintain stability for the reconstructed lumbar spine. However, the load was mainly transmitted via the fixation rod rather than the vertebral implant, owing to the stress shielding effect. Therefore, the predicted strain on the endplate were insufficient for bone ingrowth under most of the spinal activates, which could cause bone loss and prosthesis loosening.

CONCLUSIONS

In this study, the comparisons of the reconstructed lumbar spine system with lateral and posterior fixation strategies were conducted. The Pros and Cons of these two fixation strategies was deeply discussed and the associated clinical issues were provided. The results of this study will have a clear impact in understanding the biomechanics of the lumbar spine with different fixation strategies and providing necessary instructions to the design and application of the lumbar spinal fixation system.

Assessment of Rod Material Types in Spine Surgery Outcomes: A Systematic Review

BACKGROUND

Lumbar spine fusion surgery is traditionally performed with rigid fixation. Because the rigidity is often supraphysiologic, semirigid rods were developed. To the best of our knowledge, a comprehensive evaluation of rod material type on surgical outcomes has yet to be conducted.

METHODS

A systematic review based on PRISMA guidelines was conducted across 3 electronic databases. After examination for inclusion and exclusion criteria, data were extracted from the studies.

RESULTS

Seventeen studies, including 1399 patients, were included in this review. The mean rigid rod fusion rate is 92.2% and 95.5% for semirigid rods (P = 0.129). The mean improvement in back pain was 60.6% in rigid rods and 71.6% in semirigid rods. The improvement in leg pain was 81.9% and 77.2%, respectively. There were no differences in visual analog scale back pain score (P = 0.098), visual analog scale leg pain score (P = 0.136), or in functional improvement between rigid and semirigid rods (P = 0.143). There was no difference (P = 0.209) in the reoperation rate between rigid rods (13.1%) and semirigid rods (6.5%). There was a comparable incidence of adjacent segment disease (3%), screw fracture (1.7%), and wound infection (1.9%) between rod material types.

CONCLUSIONS

There is a moderate level of evidence supporting that surgical intervention results in high fusion rates regardless of rod material type. Surgical intervention improves back pain, leg pain, and function, with neither material type showing clear superiority. There are comparable rates of reoperation, development of adjacent segment disease, development of mechanical complications, and incidence of infection in both rigid and semirigid rods. Further studies regarding rod material type are warranted.

Finite element modelling of hybrid stabilization systems for the human lumbar spine

Intersomatic fusion is a very popular treatment for spinal diseases associated with intervertebral disc degeneration. The effects of three different hybrid stabilization systems on both range of motion and intradiscal pressure were investigated, as there is no consensus in the literature about the efficiency of these systems. Finite element simulations were designed to predict the variations of range of motion and intradiscal pressure from intact to implanted situations. After hybrid stabilization system implantation, L4-L5 level did not lose its motion completely, while L5-S1 had no mobility as a consequence of disc removal and fusion process. BalanC hybrid stabilization system represented higher mobility at the index level, reduced intradiscal pressure of adjacent level, but caused to increment in range of motion by 20% under axial rotation. Higher tendency by 93% to the failure was also detected under axial rotation. Dynesys hybrid stabilization system represented more restricted motion than BalanC, and negligible effects to the adjacent level. B-DYN hybrid stabilization system was the most rigid one among all three systems. It reduced intradiscal pressure and range of motion at the adjacent level except from motion under axial rotation being increased by 13%. Fracture risk of B-DYN and Dynesys Transition Optima components was low when compared with BalanC. Mobility of the adjacent level around axial direction should be taken into account in case of implantation with BalanC and B-DYN systems, as well as on the development of new designs. Having these findings in mind, it is clear that hybrid systems need to be further tested, both clinically and numerically, before being considered for common use.

Mobility-Preserving Surgery for Lumbar Spinal Stenosis: WFNS Spine Committee Recommendations

Background

Although decompression is the basis of surgical treatment for lumbar spinal stenosis (LSS), under various circumstances instrumented fusion is performed as well. The rationale for mobility-preserving operations for LSS is preventing adjacent segment disease (ASD). We review the rationale for mobility preservation in ASD and discuss related topics such as indications for fusion and the evolving role of minimally invasive approaches to lumbar spine decompression. Our focus is on systematic review and consensus discussion of mobility-preserving surgical methods as related to surgery for LSS.

Methods

Groups of spinal surgeons (members of the World Federation of Neurosurgical Societies Spine Committee) performed systematic reviews of dynamic fixation systems, including hybrid constructs, and of interspinous process devices; consensus statements were generated based on the reviews at 2 voting sessions by the committee several months apart. Additional review of background data was performed, and the results summarized in this review.

Results

Decompression is the basis of surgical treatment of LSS. Fusion is an option, especially when spondylolisthesis or instability are present, but indications remain controversial. ASD incidence reports show high variability. ASD may represent the natural progression of degenerative disease in many cases. Older age, poor sagittal balance, and multilevel fusion may be associated with more ASD. Dynamic fixation constructs are treatment options that may help prevent ASD.

Comparison of Nitinol and Titanium Nails Effectiveness for Lumbosacral Spine Fixation in Surgical Treatment of Degenerative Spine Diseases

Relevance. Surgical decompression and decompression with stabilization are highly effective for treatment of spinal canal stenosis at the level of lumbar spine. However, complications developing after application of rigid fixation systems resulted in active introduction of dynamic implants into clinical practice.

Purpose of the study — to compare effectiveness of nitinol and titanium nails for lumbosacral fixation in surgical treatment of degenerative spine diseases.

Materials and methods. 220 patients who underwent surgeries in 4 hospitals were randomized into two groups, each consisting of 110 patients (1:1 ratio): a group of patients who underwent stabilization of the vertebral motor segments with rods of nitinol with the required volume of decompression at the operation level and a group of patients who underwent stabilization of the vertebral motor segments with standard rods of titanium with the required volume of decompression at the intervention level. Patients suffered clinically significant spinal canal stenosis in one or two adjacent segments: from L3 to S1. Outcomes were evaluated during three years postoperatively by VAS scale for spine and lower limbs, and by ODI and SF-36 scales.

Results. All scales demonstrated better values in both groups of patients, namely, significant decrease of pain syndrome and improvement in mental and physical health. X-ray examination of all patients during the study period demonstrated restoration of lumbar lordosis. Group of patients with dynamic nails featured less complications rate related to metal implants including adjacent segment disease.

Conclusion. Transpedicular fixation of lumbosacral spine by nitinol nails is an effective technique allowing to preserve motion along with stable fixation.

Biomechanical testing of a polycarbonate-urethane-based dynamic instrumentation system under physiological conditions

BACKGROUND

Posterior dynamic stabilization systems are developed to maintain the healthy biomechanics of the spine while providing stabilization. Numerous dynamic systems incorporate polycarbonate urethane with temperature- and moisture-dependent material properties. In the underlying study, a novel test rig is used to evaluate the biomechanical performance of a system containing polycarbonate urethane.

METHODS

The test rig is composed of two hydraulic actuators. An environmental chamber, filled with water vapor at body temperature, is included in the set up. The translational and rotational degrees of freedom of vertebrae and pedicle screws are measured using a magnetic tracking system. The Transition® device is tested in five lumbar spines (L2-L5) of human cadavers. Pure moment tests are performed for flexion-extension, lateral bending, and axial rotation. Three test conditions are compared: 1. native specimens, 2. dynamic instrumentation at L4-L5, 3. dynamic instrumentation with decompression at L4-L5.

FINDINGS

The ranges of motion, the centers of rotation, and the pedicle screw loosening are calculated and evaluated. During daily motions such as walking, the loads on the lumbar spine differ from the standardized test protocols. To allow a reproducible data evaluation for smaller deformations, all moment-rotation curves are parameterized using sigmoid functions.

INTERPRETATION

In flexion-extension, the Transition® device provides the highest stiffening of the segment and the largest shift of the center of rotation. No shift in the center of rotation, and the smallest supporting effect on the segment is observed for axial rotation. In lateral bending, a mediate reduction of the range of motion is observed.