PEEK rods construct has been proposed to allow better load sharing among spinal components when compared to the more traditional Titanium rods constructs. However, such proposal has largely derived from single-load in-vitro testing and the biomechanical differences between the two constructs when subjected to fatigue loading remain unknown. Current study comparatively analyzed the in-vitro biomechanical performance of PEEK and Titanium rod constructs as spinal implants through a 5 hour fatigue loading test. The disc height and intradiscal pressure of the instrumented and adjacent levels pre- and post-loading were recorded for analysis. The stress levels on the rods and bone stress near the screw-bone interface were also collected to investigate the likely failure rates of the two constructs. The results showed that the Titanium rods construct demonstrated a minimum amount of loss of disc height and intradiscal pressure at the instrumented level, however, a significant loss of the disc height and intradiscal pressure at adjacent levels compared to the intact spine were identified. In contrast, the disc height and intradiscal pressure of the PEEK rods were found to be comparable to those of the intact spine for all levels. The PEEK rods group also showed significantly less bone stress near the screw-bone interface compared to the Titanium rods group. Current study has demonstrated the potential benefits of the PEEK rods construct in reducing the risks of adjacent segment disease and implant failure rates when compared to the more traditional Titanium rods construct

Despite the myriad new spinal instrumentation systems, scoliosis can rarely be fully corrected, especially when the curves are stiff. A novel superelastic nickel-titanium (nitinol) rod that maximises the ability to slowly correct spinal deformities by utilising the viscoelastic properties of the spine has been developed. This parallel, double-blinded, randomised controlled trial compared the safety and efficacy of these new rods to conventional titanium rods in 23 patients with adolescent idiopathic scoliosis. The superelastic nitinol rods were found to be safe, could gradually correct scoliosis curves, and ultimately resulted in better coronal and sagittal alignments compared to traditional rods. Despite the myriad new spinal instrumentation systems, scoliosis can rarely be fully corrected, especially when the curves are stiff. A novel superelastic nickel-titanium (nitinol) rod that maximises the ability to slowly correct spinal deformities by utilising the viscoelastic properties of the spine has been developed. This parallel, double-blinded, randomised controlled trial compared the safety and efficacy of these new rods to conventional titanium rods in 23 patients with adolescent idiopathic scoliosis. The superelastic nitinol rods were found to be safe, could gradually correct scoliosis curves, and ultimately resulted in better coronal and sagittal alignments compared to traditional rods

The purpose of this study is to evaluate risk factors for distal construct failure (DCF) in posterior spinal instrumented fusion (PSIF) in adolescent idiopathic scoliosis (AIS). We observed an increased rate of DCF when the pedicle screw in the lowest instrumented vertebra (LIV) was not parallel to the superior endplate of the LIV, however this has not been well studied in the literature. We hypothesise a more inferiorly angled LIV screw predisposes to failure and aim to find the critical angle that predisposes to failure. A retrospective cohort study was performed on all patients who underwent PSIF for AIS at the Starship Hospital spine unit from 2010 to 2020. On a lateral radiograph, the angle between the superior endplate of the LIV was measured against its pedicle screw trajectory. Data on demographics, Cobb angle, Lenke classification, instrumentation density, rod protrusion from the most inferior screw, implants and reasons for revision were collected. Of 256 patients, 10.9% (28) required at least one revision. The rate of DCF was 4.6% of all cases (12 of 260) and 25.7% of revisions were due to DCF. The mean trajectory angle of DCF patients compared to all others was 13.3° (95%CI 9.2° to 17.4°) vs 7.6° (7° to 8.2°), p=0.0002. The critical angle established is 11°, p=0.0076. Lenke 5 and C curves, lower preoperative Cobb angle, titanium only rod constructs and one surgeon had higher failure rates than their counterparts. 9.6% of rods protruding less than 3mm from its distal screw disengaged. We conclude excessive inferior trajectory of the LIV screw increases the rate of DCF and a screw trajectory greater than 11° predisposes to failure. This is one factor that can be controlled by the surgeon intraoperatively and by avoiding malposition of the LIV screw, a quarter of revisions can potentially be eliminated

Introduction. During revision surgery, the active electrode of an electrocautery device may get close to the implant, potentially provoking a flashover. Incidents have been reported, where in situ retained hip stems failed after isolated cup revision. Different sizes of discoloured areas, probably induced by electrocautery contact, were found at the starting point of the fracture. The effect of the flashover on the implant material is yet not fully understood. The aim of this study was to investigate the fatigue strength reduction of Ti-6Al-4V titanium alloy after electrocautery contact. Material and Methods. 16 titanium rods (Ti-6Al-4V, extra low interstitial elements, according to DIN 17851, ⊘ 5 mm, 120 mm length) were stress-relief annealed (normal atmosphere, holding temperature 622 °C, holding time 2 h) and cooled in air. An implant specific surface roughness was achieved by chemical and electrolytic polishing (Ra = 0.307, Rz = 1.910). Dry (n = 6) and wet (n = 6, 5 µl phosphate buffered saline) flashovers were applied with a hand-held electrode of a high-frequency generator (Aesculap AG, GN 640, monopolar cut mode, output power 300 W, modelled patient resistance 500 Ω). The size of the generated discoloured area on the rod's surface - representative for the heat affected zone (HAZ) - was determined using laser microscopy (VK-150x, Keyence, Japan). Rods without flashover (n = 4) served as control. The fatigue strength of the rods was determined under dynamic (10 Hz, load ratio R = 0.1), force-controlled four-point bending (FGB Steinbach GmbH, Germany) with swelling load (numerical bending stress 852 MPa with a bending moment of 17.8 Nm) until failure of the rods. The applied bending stress was estimated using a finite-element-model of a hip stem during stumbling. Metallurgical cuts were made to analyse the microstructure. Results. The control rods failed at the pushers of the setup (median: 94,550, range: 194,000 cycles). The rods with flashover failed directly at the HAZ significantly earlier than the control rods (p = 0.018). The analysis of the microstructure showed a transformation of the equiaxed α+β microstructure to a bimodal state. The size of the HAZs were equal for the dry (median: 1.51 mm. 2. , range: 5.68 mm. 2. ) and wet flashovers (median: 0.92 mm. 2. , range: 2.50 mm. 2. , p = 0.792). The cycles to failure were smaller for the dry flashover (median: 22,650 cycles, range: 5,700) than the wet flashover but not reaching statistical significance (median: 32,200, range: 57,900; p = 0.052). No correlation between the dimension of the HAZs and the cycles to failure was found (dry: r. 2. = 0.019, p = 0.8; wet: r. 2. = 0.015, p = 0.721). Discussion. Flashovers induced by an electrocautery device reduce the fatigue strength of Ti-6Al-4V. Since no correlation between the size of the HAZs and the cycles to failure was found, every contact between electrocautery devices and metal implants should be avoided. For any figures or tables, please contact authors directly

Background. One of the serious postoperative complications associated with joint replacement is bacterial infection. In our recent investigations, iodine supported titanium implants demonstrated antibacterial activity in both in vitro studies and clinical trials. But it is not clear whether iodine treated titanium implants produce strong bonding to bone. This study evaluated the bone bonding ability of titanium implants with and without iodine surface treatments. Methods. Titanium rods were implanted in intramedullary rabbit femur models, in regard to the cementless hip stem. The implant rods were 5mm in diameter and 25mm in length. Half of the implants were treated with iodine (ID implants) and the other half were untreated (CL implants). The rods were inserted into the distal femur; ID implants into the right femur and CL implants into the left. We assessed the bonding strength by a measuring pull-out test at 4, 8, and 12 weeks after implantation. The bone-implant interfaces were evaluated at 4 weeks after implantation. Results. Pull-out test results of the ID implants were 202, 355, and 344 N, at 4, 8, and 12 weeks, respectively, significantly higher than those of the CL implants (102, 216, and 227 N). Histological examination revealed that new bone formed on the surface of both types of implants, but significantly more bone made direct contact with the surfaces of the ID implants. Conclusion. This research showed that new type of coating, iodine coated titanium has low toxicity and good osteoconductivity

Introduction. Radiation cross-linking of ultrahigh molecular weight polyethylene (UHMWPE) has reduced the in vivo wear and osteolysis associated with bearing surface wear (1), significantly reducing revisions associated with this complication (2). Currently, one of the major and most morbid complications of joint arthroplasty is peri-prosthetic infection (3). In this presentation, we will present the guiding principles in using the UHMWPE bearing surface as a delivery device for therapeutic agents and specifically antibiotics. We will also demonstrate efficacy in a clinically relevant intra-articular model. Materials and Methods. Medical grade UHMWPE was molded together with vancomycin at 2, 4, 6, 8, 10 and 14 wt%. Tensile mechanical testing and impact testing were performed to determine the effect of drug content on mechanical properties. Elution of the drug was performed in phosphate buffered saline (PBS) for up to 8 weeks and the detection of the drug in PBS was done by UV-Vis spectroscopy. A combination of vancomycin and rifampin in UHMWPE was developed to address chronic infection and layered construct containing 1 mm-thick drug-containing UHMWPE in the non-load bearing regions was developed for delivery. In a lapine (rabbit) intra-articular model (n=6 each), two plug of the layered UHMWPE construct were placed in the trochlear grove of the rabbit femoral surface and a porous titanium rod with a pre-grown biofilm of bioluminescent S. Aureus was implanted in the tibia. Bioluminescent imaging was employed to visualize and quantify the presence of the bacteria up to 3 weeks. Results and Discussion. Increasing drug content decreased both the ultimate tensile strength (UTS) and the impact toughness of vancomycin-containing UHMWPE (Figure 1). Elution data and structural analysis suggested that a percolation threshold was reached at above 6 wt% drug in UHMWPE, which resulted in sustained drug delivery above the minimum inhibitory concentration (MIC; 1 mg/ml) for up to 8 weeks (Figure 2). The layered constructs implanted in rabbits were able to eradicate all detectable bacteria from the biofilm on the titanium surfaces implanted on the counterface (Figure 3), suggesting clinically relevant efficacy. Significance. To our knowledge, this is the first study showing the design and efficacy of an antibiotic-eluting UHMWPE bearing surface. Such a device has the potential of reducing all two-stage revisions to single-stage treatment with load-bearing components, enhancing the mobility and quality of life for the patients and reducing the cost of infection treatment in arthroplasty. For figures/tables, please contact authors directly.

Currently, no clinical options are available to prevent infections on uncemented orthopedic implants. Therefore we investigated the efficacy of DAC-hydrogel (disposable antibacterial coating(1), Novagenit, Italy) as carrier for various agents to prevent infections in an in vivo implant-model. Titanium rods were implanted in the left tibiae in New Zealand White rabbits. Prior to implantation, the implant bed was contaminated with 10∧5 colony forming units S. aureus. In the experimental groups, the hydrogel was loaded prior to be coated on the rods with: 2%(w/v) vancomycin (Van2 group, N=6), 5%(w/v) vancomycin (Van5 group, N=6), 10%(w/v) bioactive glass (BonAlive, Finland) (BAG group, N=6), which is antibacterial(2) and osteoconductive(3), or 0.5%(w/v) N-acetyl cysteine (NAC group, N=6), which inhibits bacterial growth and decreases biofilm formation(4). In the control group, empty hydrogel was applied (Gel group, N=12). Blood values were measured weekly. Following explantation on day 28, the anterior tibia was processed for bacterial culture. The posterior tibia and rod were used for measuring bone-implant contact using micro-CT and for histopathology. Results of the experimental groups were compared to the Gel group results. The blood values in the Van2 and Van5 groups were lower on day 7. Moreover, culture results demonstrated less animals with an infection in both groups at day 28. In accordance, these groups showed lower grades for infection. Further, the Van2 group demonstrated more bone-implant contact. These results suggest that infection was reduced in the Van2 and Van5 groups. In contrast, blood values, histological grades, and bone-implant contact of the BAG and NAC groups were comparable with the Gel group. These results suggest that infection was not prevented in the BAG and NAC groups. Local application of vancomycin-loaded DAC-hydrogel successfully reduced implant-related infections. Loading of the hydrogel with BAG or NAC did not prevent infection. It is possible that BAG in powder form, as used in the present study, dissolved before the antibacterial effect could take place. Instead, BAG granules may be a viable alternative. Next, it is possible that the NAC concentration was too low to prevent infections in an in vivo environment, although this concentration was proven effective in vitro for its antibacterial properties

Introduction. About 2% of primary total joint replacement arthroplasty (TJA) procedures become infected. Periprosthetic joint infection (PJI) is currently one of the main reasons requiring costly TJA revisions, posing a burden on patients, physicians and insurance companies. 1. Currently used drug-eluting polymers such as bone cements offer limited drug release profiles, sometimes unable to completely clear out bacterial microorganisms within the joint space. For this study we determined the safety and efficacy of an antibiotic-eluting UHMWPE articular surface that delivered local antibiotics at optimal concentrations to treat PJI in a rabbit model. Materials and Methods. Skeletally mature adult male New Zealand White rabbits received either two non-antibiotic eluting UHMWPE (CONTROL, n=5) or vancomycin-eluting UHMWPE (TEST, n=5) (3 mm in diameter and 6 mm length) in the patellofemoral groove (Fig. 1). All rabbits received a beaded titanium rod in the tibial canal (4 mm diameter and 12 mm length). Both groups received two doses of 5 × 10. 7. cfu of bioluminescent S. aureus (Xen 29, PerkinElmer 119240) in 50 µL 0.9 % saline in the following sites: (1) distal tibial canal prior to insertion of the rod; (2) articular space after closure of the joint capsule (Fig. 1). None of the animals received any intravenous antibiotics for this study. Bioluminescence signal (photons/second) was measured when the rabbits expired, or at the study endpoint (day 21). The metal rods were stained with BacLight. ®. Bacterial Live-Dead Stain and imaged using two-photon microscopy to detect live bacteria. Hardware, polyethylene implants and joint tissues were sonicated to further quantify live bacteria via plate seeding. Results. All control rabbits expired within 7 days (Fig. 2a). One rabbit in the test group expired at day 7 and another at day 15. All control rabbits had positive bioluminescence (live bacteria), while none of the test rabbits did (Fig 2b). Kidney (creatinine and BUN) and liver functions (ALT and ALP) remained normal for all rabbits. All control rabbits showed positive bacterial culture after sonication, while all test rabbits were negative. Two-photon imaging showed 75±10 % viability for bacteria adhered to the metal rods in the control and no viability in the test group. Discussion. This rabbit model showed that vancomycin eluted from UHMWPE is sufficient to eradicate S. aureus in joint space and in between the bone-implant interface of tibial canal. One limitation of this study is the lack of intravenous antibiotic treatment, which is standard clinical practice. In addition, joint infections are often associated with already formed biofilms, which were not tested in this study. However, safety data (normal kidney and liver functions) and complete eradication of S. aureus is an encouraging finding. Conclusion. Vancomycin-eluting UHMWPE effectively eliminated bacteria in a rabbit model of acute peri-prosthetic joint infection. This material is promising as a replacement liner to treat joint infections in revision surgery. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Hardware in or about the knee joint presents a number of challenges to the surgeon in performance of Total Knee Arthroplasty (TKA). Conventional instrumentation usually requires a modification of technique or removal of the metallic implants. Computer-Assisted TKA (CAOS) is another option, but adds complexity and time to the procedure. MRI-based Patient-Specific Instrumentation (PSI) cannot be used as metal causes unwanted artifact and renders the images for planning, useless. However, CT scans are not affected by metal and thus CT-based PSI can be used in TKA patients with pre-existing hardware. The present IRB approved study evaluates 12 consecutive knees (10 patients) with pre-existing hardware using CT-based PSI (MyKnee®, Medacta International, SA, Castel San Pietro, Switzerland). In this technique, CT scan of the lower extremity is obtained, and from these images, the knee is reconstructed 3-dimensionally. Surgical and implant-size planning are performed according to surgeon preference, with the goal to create a neutral mechanical axis. Once planned and approved, the blocks are made [Fig 1]. During surgery, the PSI cutting block is registered on the femur first and secured with smooth pins. The distal femoral resection is performed directly through the block. An appropriate sized 4-in-1 block is placed and the remaining femoral resections are performed. The tibial resection block is registered and resection performed. Final bone preparation, patella resurfacing, and trialing is performed as is standard to all surgical techniques. Of the 12 TKAs, there were 5 left and 7 right knees performed in 6 females and 6 males. The average BMI was 33.19 and average age was 53 (range 44–63). All diagnoses were either osteoarthritis or post-traumatic osteoarthritis. Follow-up averaged 59 weeks (range 18.6–113.7). Nine patients had pre-operative varus deformities with HKA deformities average of 171.9° (range 154°–178.5°). One patient had pre-operative valgus deformity of 184.5°. Two patients were neutral (180°). Post-operative alignment for all patients (n = 11) was 179° (range 177°–180°). All patients were within 3° neutral, post operatively. Four patients measured 180°, 4 measured at 179°, 2 measured at 178°, and only one at 177°. Hardware consisted of 5 patients with femur or tibia staples, 3 with plate(s) and screws [Fig. 2], 3 patients with ACL interference screws, and one titanium rod. No hardware was removed unless necessary for implantation. Only 3 patients required some hardware removal. The pre-operative Range of Motion (ROM) averaged 2.9° to 98.3° (Extension range 0–15° and flexion range 30–115°). Post-operative ROM was 2.9° to 101.3°. (Extension range 0–5° and flexion range 65–125°). Knee Society Score (KSS) improved from 42.3 to 82.3, and KSS Function Score improved from 52.1 to 77.5. No intraoperative complications were recorded. Average tourniquet time was 42.1 minutes (range 28–102). Regardless of the deformity, the patient's post-operative mechanical axes HKA averaged 179° (range 177–180). Clinical scores were typical for TKA patients with improvement in both KSS and ROM. In conclusion, early results using PSI in patients with pre-existing hardware in or about the joint, is safe, efficient, and accurate in performance of TKA

Hardware in or about the knee joint presents a number of challenges to the surgeon in performance of Total Knee Arthroplasty (TKA). Conventional instrumentation usually requires a modification of technique or removal of the metallic implants. Computer-Assisted TKA (CAOS) is another option, but adds complexity and time to the procedure. MRI-based Patient-Specific Instrumentation (PSI) cannot be used as metal causes unwanted artifact and renders the images for planning, useless. However, CT scans are not affected by metal and thus CT-based PSI can be used in TKA patients with pre-existing hardware. The present IRB approved study evaluates 12 consecutive knees (10 patients) with pre-existing hardware using CT-based PSI (MyKnee®, Medacta International, SA, Castel San Pietro, Switzerland). In this technique, CT scan of the lower extremity is obtained, and from these images, the knee is reconstructed 3-dimensionally. Surgical and implant-size planning are performed according to surgeon preference, with the goal to create a neutral mechanical axis. Once planned and approved, the blocks are made. During surgery, the PSI cutting block is registered on the femur first and secured with smooth pins. The distal femoral resection is performed directly through the block. An appropriate sized 4-in-1 block is placed and the remaining femoral resections are performed. The tibial resection block is registered and resection performed. Final bone preparation, patella resurfacing, and trialing is performed as is standard to all surgical techniques. Of the 12 TKAs, there were 5 left and 7 right knees performed in 6 females and 6 males. The average BMI was 33.19 and average age was 53 (range 44–63). All diagnoses were either osteoarthritis or post-traumatic osteoarthritis. Follow-up averaged 59 weeks (range 18.6–113.7). Nine patients had pre-operative varus deformities with HKA deformities average of 171.9° (range 154°–178.5°). One patient had pre-operative valgus deformity of 184.5°. Two patients were neutral (180°). Post-operative alignment for all patients (n=11) was 179° (range 177°–180°). All patients were within 3° neutral, post operatively. Four patients measured 180°, 4 measured at 179°, 2 measured at 178°, and only one at 177°. Hardware consisted of 5 patients with femur or tibia staples, 3 with plate(s) and screws, 3 patients with ACL interference screws, and one titanium rod. No hardware was removed unless necessary for implantation. Only 3 patients required some hardware removal. The pre-operative Range of Motion (ROM) averaged 2.9° to 98.3° (Extension range 0–15° and flexion range 30–115°). Post-operative ROM was 2.9° to 101.3°. (Extension range 0–5° and flexion range 65–125°). Knee Society Score (KSS) improved from 42.3 to 82.3, and KSS Function Score improved from 52.1 to 77.5. No intraoperative complications were recorded. Average tourniquet time was 42.1 minutes (range 28–102). Regardless of the deformity, the patient's post-operative mechanical axes HKA averaged 179° (range 177–180). Clinical scores were typical for TKA patients with improvement in both KSS and ROM. In conclusion, early results using PSI in patients with pre-existing hardware in or about the joint, is safe, efficient, and accurate in performance of TKA

The relationship between radiologic union and clinical outcome in thoracoscopic scoliosis surgery is not clear, as apparent non-union does not always correspond to a poor clinical result. Our aim was to evaluate CT fusion rates 2yrs after thoracoscopic surgery, and explore the relationship between fusion scores and; (i) rod diameter, (ii) graft type, (iii) fusion level, (iv) implant failure, and (v) lateral position in disc space. Between 2000 and 2006 a cohort of 44 patients had thoracoscopic scoliosis correction. Discectomies were performed and defect was packed with either autograft (n=14) or allograft (n=30). Instrumentation consisted of either 4.5mm (n=24) or 5.5mm (n=20) single titanium anterior rod and vertebral body screws. Fusion quality and implant integrity were evaluated 2yr following surgery using low-dose CT. At each disc space, left, right and mid-sagittal CT reconstructions were generated and graded using the Sucato 4-point scale (Sucato, 2004) which is based on calculated percentage of fusion across disc space. Fusion scores were measured for 259 disc spaces in 44 patients. Rod diameter had a strong effect on fusion score, with a mean score of 2.12±0.74 for 4.5mm Ti rod, decreasing to 1.41+0.55 for 5.5mm Ti rod, and to 1.09+0.36 for 5.5mm Ti-alloy rod. Mean fusion scores for autograft and allograft subgroups were 2.13±0.72 and 2.14±0.74 respectively. Fusion scores were highest in the middle of implant construct, dropping off by 20–30% toward the ends. Fusion scores adjacent to the rod (2.19±0.72) were significantly higher than on the contralateral side of the disc (1.24±0.85). Levels where rod fracture occurred (n=11) had lower fusion scores than those without fracture (1.09±0.67 vs 1.76±0.80). Levels where top screw pullout occurred (n=6) had lower CT fusion scores than those without (1.25±0.60 vs 1.83±0.76). Rod diameter (larger), intervertebral level (proximal or distal), lateral position in disc (further from rod) and rod fracture or screw pullout all reduce fusion scores, while graft type does not affect scores. The assumed link between higher fusion score and better clinical outcome must be treated with caution, because rod fractures did not necessarily occur in patients with lower fusion scores. It is possible that with a stiffer rod, less bony fusion mass is required for a stable construct. We propose that moderate fusion scores secure successful clinical outcomes in thoracoscopic scoliosis surgery