Voriconazole Is Cytotoxic at Locally Delivered Concentrations: A Pilot Study

Background

Fungal infections are rare but major problems when they involve orthopaedic implants. Preferred treatment in North America is two-staged: resection and then delayed reconstruction, with local delivery of an antifungal between stages. The effect of voriconazole, a hydrophobic antifungal, on local tissues and wound healing is unclear.

Questions/purposes

We asked: (1) Is voriconazole cytotoxic to fibroblasts or osteoblasts at target concentrations for local delivery? And (2) if cytotoxic, can fibroblasts or osteoblasts resume proliferation after voriconazole is removed?

Methods

We exposed 5000 fibroblasts or osteoblasts/well to voriconazole concentrations of 0, 1, 5, 10, 25, 100, 500, 1000, 5000, 10,000, and 20,000 μg/mL (n = 4 wells/concentration) in 24-well plates. At 3 and 7 days, cell growth was assessed with alamarBlue^® and light microscopy. After Day 7, exposure to voriconazole was stopped and incubation continued for 4 days in medium with no voriconazole. On Day 11, cell growth (recovery) was assessed with alamarBlue^® and light microscopy.

Results

Increasing voriconazole concentration to more than 100 μg/mL decreased osteoblast and fibroblast growth. Cell growth recovered after 7 days’ exposure to 1000 μg/mL or less.

Conclusions

Voriconazole is cytotoxic to osteoblasts and fibroblasts, but cell growth recovers over 4 days after exposure to 1000 μg/mL or less.

Clinical Relevance

Cytotoxicity seen from voriconazole to mouse osteoblasts and fibroblasts occurs at concentrations achievable clinically from local delivery. It may be prudent to limit the dose of voriconazole in antibiotic-loaded bone cement.     

Voriconazole Is Delivered From Antifungal-Loaded Bone Cement

Background

Local delivery of antifungals is an important modality in managing orthopaedic fungal infection. Voriconazole is a powder antifungal suitable for addition to bone cement that is released from bone cement but the mechanical properties of antimicrobial-loaded bone cement (ALBC) made with voriconazole are unknown.

Questions/Purposes

(1) Is voriconazole release dose-dependent? (2) Is released voriconazole active? (3) Is the loss of ALBC’s compressive strength caused by voriconazole dose- and elution-dependent?

Methods

Sixty standard test cylinders were fabricated with ALBC: 300 or 600 mg voriconazole per batch eluted for 30 days in deionized water. Voriconizole concentration in the eluate was measured using high-performance liquid chromatography. Cumulative-released voriconizole was calculated. Biologic activity was tested. Compressive strength was measured before and after elution. The effect of dose and time on release and compressive strength were analyzed using repeated-measure analysis of variance.

Results

Fifty-seven percent and 63% of the loaded voriconazole were released by Day 30 for the 300-mg and 600-mg formulations, respectively. The released voriconazole was active on bioassay. Compressive strength was reduced from 79 MPa to 53 MPa and 69 MPa to 31 MPa by 30 days for the 300-mg and 600-mg formulations, respectively.

Conclusions

Voriconazole release from ALBC increases with dose and is bioactive. Loss in compressive strength is greater after elution and with higher dose.

Clinical Relevance

Three hundred milligrams of voriconazole in ALBC would be expected to deliver meaningful amounts of active drug in vivo. The compressive strength of ALBC with 600 mg voriconazole is less than expected compared to commonly used antibacterials.     

Strength of Antimicrobial Bone Cement Decreases with Increased Poragen Fraction

Background

Adding soluble particulate poragens to antimicrobial-loaded bone cement increases the permeability of the bone cement and increases the antimicrobial release, but the mechanical effect of adding poragens is not well known.

Questions/purposes

We therefore asked the following questions: (1) Does the poragen fraction in antimicrobial-loaded bone cement affect its antimicrobial release? (2) Does poragen fraction in antimicrobial-loaded bone cement affect its compressive strength; and (3) Does the effect on compressive strength change over time in elution?

Methods

Antimicrobial-loaded bone cement made in the proportions of 40 g polymer powder, 20 mL monomer liquid, 1 g tobramycin powder and one of six different doses of poragen powder (0, 1, 2, 4, 8, or 16 g of particulate xylitol per batch) was formed into standardized test cylinders and eluted for 30 days. We determined the cumulative recovered tobramycin and the change in compressive strength over 30 days of elution.

Results

Antimicrobial release progressively increased with increasing poragen fraction. Compressive strength progressively decreased with increasing poragen fraction and with increasing time in elution. Poragen fractions greater than 2 g per batch caused the compressive strength to decrease below 70 MPa over 30 days of elution.

Clinical Relevance

The use of poragens can increase elution of antimicrobials from antimicrobial-loaded bone cement. However, for implant fixation, to avoid deleterious reduction of compressive strength, the amount of poragen that can be added in addition to 1 g of antimicrobial powder may be limited to 2 g per batch.     

Changes in the cross-sectional area of deep posterior extensor muscles of the cervical spine after anterior decompression and fusion: 10-year follow-up study using MRI

Purpose

To evaluate changes in the transverse area of deep posterior muscles of the cervical spine 10 years after anterior cervical decompression and fusion (ACDF), in comparison with healthy volunteers.

Methods

Thirty-one patients (22 males, 9 females, mean age at follow-up 59.3 years, mean follow-up 12.1 years) who had undergone preoperative MRI and non-instrumented ACDF within levels C3-4 to C5-6 were enrolled. 32 asymptomatic volunteers (17 males, 15 females; mean age, 54.7 years; mean follow-up, 11.7 years) who underwent MRI between 1993 and 1996 served as controls. Follow-up MRI was performed on both patients and control subjects, and the cross-sectional areas of deep posterior muscles were measured digitally at levels C3-4, 4-5, and 5-6.

Results

The mean total cross-sectional area in the ACDF and control groups was 4,693.6 ± 1,140.9 and 4,825.8 ± 1,048.2 mm² in the first MR study (P = 0.63), and 4,616.7 ± 1,086.0 and 5,036.7 ± 1,105.6 mm² at follow-up (P = 0.13). The total cross-sectional area in the ACDF group slightly decreased, while that in the control group increased (−77.1 ± 889.7 vs. 210.9 ± 622.0 mm², P = 0.14). The mean change in the cross-sectional area had no significant correlation with clinical symptoms, including neck pain or JOA score.

Conclusions

ACDF patients did not show a marked decrease in the cross-sectional area of the deep posterior cervical muscles, but as compared with control subjects there was a slight decrease. A decrease in the cross-sectional area of these muscles after ACDF may not result in the axial symptoms as seen in patients treated by posterior surgery.     

A needle micro-osmometer for determination of glycosaminoglycan concentration in excised nucleus pulposus tissue

Purpose

Aggrecan is one of the major macromolecular components of the intervertebral disc (IVD) and its loss is an early sign of degeneration. Restoration of aggrecan, and hence of biomechanical properties, is a major objective of biological therapies. At present, assessment of aggrecan concentration via its glycosaminoglycan (GAG) content is accomplished using biochemical and histological methods which require sacrifice of tissue. A minimally invasive method for assessing GAG, and hence aggrecan, which can avoid destruction of tissue, would be of benefit.

Methods

We have developed a needle micro-osmometer that is capable of measuring flux of saline into excised human nucleus pulposus (NP) tissue. Using the isotropic osmotic stress technique to assess the swelling pressure of the excised NP tissue and assuming negligible collagen tensile stress, we were able to relate the flux to the tissue fixed charge density (FCD). GAG concentration is evaluated from its FCD via the radioactive tracer technique. Samples representing different ages (28–59 years) and degeneration grades (1–4) were analyzed.

Results

The flux is controlled by both the osmotic pressure difference across the probe’s semi-permeable membrane and by the tissue permeability. A linear correlation was found between flux and the tissue FCD. The equation describing the linear fit is FCD/(total tissue hydration) = 1.97 × 10⁻⁴ + 8283 × flux (R = 0.836, p < 10⁻⁴). Thus, by measuring saline flux, the concentration of GAG can be determined.

Conclusions

Micro-osmometry provides a reliable and minimally invasive tool for assessing GAG content in excised NP tissue. This method may be usefully applied in tissue engineering applications. It may also be useful for in vivo measurements if the question of the degenerative effect of needle puncture can be overcome.     

Effectiveness of local cooling for enhancing tissue ischemia tolerance in people with spinal cord injury

Objective

To investigate the effects of localized cooling and cooling rate on pressure-induced ischemia for people with and without neurological deficits.

Design

A 2 × 3 mixed factorial design with two groups: (1) people with spinal cord injury (SCI) and (2) people without neurological deficits (control), and three test conditions: (1) pressure only, (2) pressure with fast cooling (−4°C/min), and (3) pressure with slow cooling (−0.33°C/min).

Setting

University laboratory.

Participants

Fourteen controls and 14 individuals with SCI.

Interventions

Pressure on the sacrum was 0.4 kPa for 5 minutes, then 8 kPa for 20 minutes, and finally 0.4 kPa for 15 minutes. Fast and slow cooling to 25°C applied during 8 kPa of pressure.

Outcome measures

Reactive hyperemia and its spectral densities in the metabolic, neurogenic, and myogenic frequency ranges.

Results

In controls, reactive hyperemia was greater in pressure only as compared with both cooling conditions. No change was noted in all spectral densities in both cooling conditions, and only neurogenic spectral density increased without cooling. In subjects with SCI, no difference was noted in reactive hyperemia among conditions. However, metabolic and myogenic spectral densities increased without cooling and all spectral densities increased with slow cooling. No change was noted in all spectral densities with fast cooling.

Conclusion

Local cooling reduced the severity of ischemia in controls. This protective effect may be masked in subjects with SCI due to chronic microvascular changes; however, spectral analysis suggested local cooling may reduce metabolic vasodilation. These findings provide evidence towards the development of support surfaces with temperature control for weight-bearing soft tissues.     

Liposomal Formulation Decreases Toxicity of Amphotericin B In Vitro and In Vivo

Background

Liposomal amphotericin B is locally delivered to treat fungal orthopaedic infections but little is known about local tissue toxicity, if any, that might be associated with local delivery.

Questions/purposes

(1) Is liposomal amphotericin B cytotoxic in vitro? (2) Is locally delivered liposomal amphotericin B toxic to tissue in vivo?

Methods

Mouse fibroblasts (BA LB/3T3 A31) and osteoblasts (MC3T3) were exposed to two formulations of amphotericin B (liposomal and deoxycholate) at concentrations of 0, 1, 5, 10, 100, 500, and 1000 μg/mL. Cell viability was determined by MTT assay after 1, 3, and 5 hours of exposure and a proliferation assay after 1, 4, and 7 days of exposure and then after 3 recovery days without drug. Tissue exposure occurred by local delivery of liposomal amphotericin B, 200 or 800 mg/batch antifungal-loaded bone cement (ALBC), or amphotericin B deoxycholate, 800 mg/batch ALBC in rat paraspinal muscles. White blood cell count (WBC) and serum amphotericin B levels were obtained on Days 1 and 3. Rats were euthanized at 2 and 4 weeks and semiqualitative histopathology was performed.

Results

Liposomal amphotericin B is cytotoxic in vitro but not toxic to tissues in vivo. All cells survived concentrations up to 1000 μg/mL for 5 hours, 100% ± 0%, but none survived ≥ 100 μg/mL for 7 days, 0% ± 0%. Fibrosis was seen adjacent to ALBC without inflammation or necrosis, indistinguishable from controls for both liposomal amphotericin B doses. Amphotericin B serum levels were all less than 1 µg/mL and WBC counts were all normal.

Conclusions

In vitro cytotoxicity to liposomal amphotericin B occurred but no adverse tissue reaction was seen in vivo.

Clinical Relevance

Local delivery of liposomal amphotericin B in ALBC was well tolerated by mouse tissue; however, clinical studies are needed to confirm this finding in humans.     

Loss of Cement-bone Interlock in Retrieved Tibial Components from Total Knee Arthroplasties

Background

Aseptic loosening continues to be a short- and long-term complication for patients with cemented TKAs. Most studies to this point have evaluated tibial component fixation via radiographic changes at the implant-bone interface and quantification of component migration; direct assessment of morphologic features of the interface from functioning TKAs may provide new information regarding how TKAs function and are fixed to bone.

Questions/purposes

In a postmortem retrieval study, we asked: (1) What are the morphologic features at the cement-trabecular bone interface in retrieved tibial components? (2) Do constructs with greater time in service have less cement-trabecular bone interlock? (3) Do constructs with more estimated initial interlock sustain more interlock with in vivo service?

Methods

Fourteen postmortem retrieved tibial components with time in service from 0 to 20 years were sectioned and imaged at high resolution, and the current contact fraction, estimated initial interdigitation depth, current interdigitation depth, and loss of interdigitation depth were quantified at the cement-bone interface. Estimated initial interdigitation depth was calculated from the initial mold shape of the cement mantle that forms around the individual trabeculae at the time of surgery. Loss of interdigitation depth was the difference between the initial and current interdigitation depth.

Results

There was resorption of trabeculae that initially interlocked with the cement in the postmortem retrievals as evidenced by the differences between current interdigitation and the estimated original interdigitation. The current contact fraction (r² = 0.54; p = 0.0027) and current interdigitation depth (r² = 0.33; p = 0.033) were less for constructs with longer time in service. The current contact fraction for implants with 10 or more years in service (6.2%; 95% CI, 4.7%–7.7%) was much less than implants with less than 10 years in service (22.9%; 95% CI, 8.9%–37%). Similarly, the current interdigitation depth for implants with 10 or more years in service (0.4 mm; 95% CI, 0.27–0.53 mm) was much less than implants with less than 10 years in service (1.13 mm; 95% CI, 0.48–1.78 mm). The loss of interdigitation depth had a strong positive relationship with time in service (r² = 0.74; p < 0.001). Using a two-parameter regression model, constructs with more initial interdigitation depth had greater current interdigitation depth (p = 0.011), but constructs with more time in service also had less current interdigitation depth (p = 0.008).

Conclusions

The cement-trabecular bone interlock obtained initially appears to diminish with time with in vivo service by resorption of the trabeculae in the cement interlock region.

Clinical Relevance

Our study supports the surgical concept of obtaining sufficient initial cement interlock (approximately 3 mm), with the acknowledgment that there will be loss of interlock with time with in vivo service.     

Fractures in Geriatric Mice Show Decreased Callus Expansion and Bone Volume

Background

Poor fracture healing in geriatric populations is a significant source of morbidity, mortality, and cost to individuals and society; however, a fundamental biologic understanding of age-dependent healing remains elusive. The development of an aged-based fracture model system would allow for a mechanistic understanding that could guide future biologic treatments.

Questions/purposes

Using a small animal model of long-bone fracture healing based on chronologic age, we asked how aging affected (1) the amount, density, and proportion of bone formed during healing; (2) the amount of cartilage produced and the progression to bone during healing; (3) the callus structure and timing of the fracture healing; and (4) the behavior of progenitor cells relative to the observed deficiencies of geriatric fracture healing.

Methods

Transverse, traumatic tibial diaphyseal fractures were created in 5-month-old (n = 104; young adult) and 25-month-old (n = 107; which we defined as geriatric, and are approximately equivalent to 70–85 year-old humans) C57BL/6 mice. Fracture calluses were harvested at seven times from 0 to 40 days postfracture for micro-CT analysis (total volume, bone volume, bone volume fraction, connectivity density, structure model index, trabecular number, trabecular thickness, trabecular spacing, total mineral content, bone mineral content, tissue mineral density, bone mineral density, degree of anisotropy, and polar moment of inertia), histomorphometry (total callus area, cartilage area, percent of cartilage, hypertrophic cartilage area, percent of hypertrophic cartilage area, bone and osteoid area, percent of bone and osteoid area), and gene expression quantification (fold change).

Results

The geriatric mice produced a less robust healing response characterized by a pronounced decrease in callus amount (mean total volume at 20 days postfracture, 30.08 ± 11.53 mm³ versus 43.19 ± 18.39 mm³; p = 0.009), density (mean bone mineral density at 20 days postfracture, 171.14 ± 64.20 mg hydroxyapatite [HA]/cm³ versus 210.79 ± 37.60 mg HA/cm³; p = 0.016), and less total cartilage (mean cartilage area at 10 days postfracture, 101,279 ± 46,755 square pixels versus 302,167 ± 137,806 square pixels; p = 0.013) and bone content (mean bone volume at 20 days postfracture, 11.68 ± 3.18 mm³ versus 22.34 ± 10.59 mm³; p < 0.001) compared with the young adult mice. However, the amount of cartilage and bone relative to the total callus size was similar between the adult and geriatric mice (mean bone volume fraction at 25 days postfracture, 0.48 ± 0.10 versus 0.50 ± 0.13; p = 0.793), and the relative expression of chondrogenic (mean fold change in SOX9 at 10 days postfracture, 135 + 25 versus 90 ± 52; p = 0.221) and osteogenic genes (mean fold change in osterix at 20 days postfracture, 22.2 ± 5.3 versus 18.7 ± 5.2; p = 0.324) was similar. Analysis of mesenchymal cell proliferation in the geriatric mice relative to adult mice showed a decrease in proliferation (mean percent of undifferentiated mesenchymal cells staining proliferating cell nuclear antigen [PCNA] positive at 10 days postfracture, 25% ± 6.8% versus 42% ± 14.5%; p = 0.047).

Conclusions

Our findings suggest that the molecular program of fracture healing is intact in geriatric mice, as it is in geriatric humans, but callus expansion is reduced in magnitude.

Clinical Relevance

Our study showed altered healing capacity in a relevant animal model of geriatric fracture healing. The understanding that callus expansion and bone volume are decreased with aging can help guide the development of targeted therapeutics for these difficult to heal fractures.

Electronic supplementary material

The online version of this article (doi:10.1007/s11999-014-3829-x) contains supplementary material, which is available to authorized users.     

Muscle spasticity associated with reduced whole-leg perfusion in persons with spinal cord injury

Objective

To determine the association between peripheral blood flow and spasticity in individuals with spinal cord injury (SCI).

Design

A cross-sectional study with measurements of muscle spasticity and whole-limb blood flow in individuals with SCI.

Setting

University of Texas at Austin and Brain & Spine Recovery Center, Austin, TX, USA.

Participants

Eighteen individuals (14 males and 4 females) with SCI were classified into high (N = 7), low (N = 6), and no (N = 5) spasticity groups according to the spasticity levels determined by the modified Ashworth scale scores.

Interventions

Whole-limb blood flow was measured in the femoral and brachial arteries using Doppler ultrasound and was normalized to lean limb mass obtained with dual-energy X-ray absorptiometry.

Outcome measures

Limb blood flow and muscle spasticity.

Results

Age, time post-SCI, and the American Spinal Injury Association impairment scale motor and sensory scores were not different among groups with different muscle spasticity. Femoral artery blood flow normalized to lean leg mass was different (P = 0.001) across the three spasticity groups (high 78.9 ± 16.7, low 98.3 ± 39.8, no 142.5 ± 24.3 ml/minute/kg). Total leg muscle spasticity scores were significantly and negatively correlated with femoral artery blood flow (r = −0.59, P < 0.01). There was no significant difference in brachial artery blood flow among the groups.

Conclusions

Whole-leg blood flow was lower in individuals with greater spasticity scores. These results suggest that a reduction in lower-limb perfusion may play a role, at least in part, in the pathogenesis leading to muscle spasticity after SCI.     

Wear in total knee arthroplasty—just a question of polyethylene?: Metal ion release in total knee arthroplasty

Purpose

Biological reactions against wear particles are a common cause for revision in total knee arthroplasty. To date, wear has mainly been attributed to polyethylene. However, the implants have large metallic surfaces that also could potentially lead to metal wear products (metal ions and debris). The aim of this study was to determine the local release of cobalt, chromium, molybdenum and titanium in total knee arthroplasty during a standard knee wear test.

Methods

Four moderately conforming fixed-bearing implants were subjected to physiological loadings and motions for 5×10⁶ walking cycles in a knee wear simulator. Polyethylene wear was determined gravimetrically and the release of metallic wear products was measured using high resolution-inductively coupled plasma-mass spectrometry.

Results

A polyethylene wear rate of 7.28 ± 0.27 mg/10⁶ cycles was determined and the cumulative mass of released metals measured 1.63 ± 0.28 mg for cobalt, 0.47 ± 0.06 mg for chromium, 0.42 ± 0.06 mg for molybdenum and 1.28 ± 0.14 mg for titanium.

Conclusion

For other metallic implants such as metal-on-metal total hip arthroplasty, the metal wear products can interact with the immune system, potentially leading to immunotoxic effects. In this study about 12 % by weight of the wear products were metallic, and these particles and ions may become clinically relevant for patients sensitive to these materials in particular. Non-metallic materials (e.g. ceramics or suitable coatings) may be considered for an alternative treatment for those patients.     

Toward the interpretation of the combined effect of size and body weight on the tribological performance of total knee prostheses

Purpose

The research questions of the present study were: (1) Is total knee prosthesis wear behaviour influenced by implant size, body weight and their combined effect? (2) Are these findings significant and helpful from a clinical point of view?

Methods

Two very different sizes of the same total knee prosthesis (TKP), previously tested with ISO 14243 parameters, were tested on a knee simulator for a further two million cycles using a modified ISO 14243 load waveform. Roughness examination was performed on the metallic components. Gravimetric and micro-Raman spectroscopic analyses were carried out on the polyethylene inserts.

Results

The average volumetric mass loss was 69 ± 3 mm³ and 88 ± 4 mm³ for smaller and bigger size, respectively. Bigger TKPs are little influenced by an increased load, while the wear trend of the smaller TKP showed a redoubled slope, and more significant morphology changes were observed. However, the two sizes seem to behave similarly when subjected to a load increase of 15 %; the slope of the volumetric mass loss trend was comparable for the two sets of inserts, which did not appear significantly different also at the molecular level. Roughness average parameters of the lateral femoral condyle support this evidence.

Conclusions

It can be asserted that the body weight and implant size are relevant to the understanding of TKP wear behaviour. A post-implantation body weight increase in a patient with smaller knee dimensions could results in more critical effects on prosthesis long-term performance.     

VEGF Improves Skeletal Muscle Regeneration After Acute Trauma and Reconstruction of the Limb in a Rabbit Model

Background

Complicated tibial fractures with severe soft tissue trauma are challenging to treat. Frequently associated acute compartment syndrome can result in scarring of muscles with impaired function. Several studies have shown a relationship between angiogenesis and more effective muscle regeneration. Vascular endothelial growth factor (VEGF) is associated with angiogenesis but it is not clear whether it would restore muscle force, reduce scarring, and aid in muscle regeneration after acute musculoskeletal trauma.

Questions/purposes

Therefore, we asked whether local application of VEGF (1) restores muscle force, (2) reduces scar tissue formation, and (3) regenerates muscle tissue.

Methods

We generated acute soft tissue trauma with increased compartment pressure in 22 rabbits and shortened the limbs to simulate fracture débridement. In the test group (n = 11), a VEGF-coated collagen matrix was applied locally around the osteotomy site. After 10 days of limb shortening, gradual distraction of 0.5 mm per 12 hours was performed to restore the original length. Muscle force was measured before trauma and on every fifth day after trauma. Forty days after shortening we euthanized the animals and histologically determined the percentage of connective and muscle tissue.

Results

Recovery of preinjury muscle strength was greater in the VEGF group (2.4 N; 73%) when compared with the control (1.8 N; 53%) with less connective and more muscle tissue in the VEGF group. The recovery of force was related to the percentage of connective tissue versus muscle fibers.

Conclusions

Local application of VEGF may improve restoration of muscle force by reducing connective tissue and increasing the relative amount of muscle fibers.

Clinical Relevance

VEGF may be useful to improve skeletal muscle repair by modulating muscle tissue regeneration and fibrosis reduction after acute trauma.     

Chitosan Sponges to Locally Deliver Amikacin and Vancomycin: A Pilot In Vitro Evaluation

Background

Open orthopaedic wounds are ideal sites for infection. Preventing infection in these wounds is critical for reducing patient morbidity and mortality, controlling antimicrobial resistance and lowering the cost of treatment. Localized drug delivery has the potential to overcome the challenges associated with traditional systemic dosing. A degradable, biocompatible polymer sponge (chitosan) that can be loaded with clinician-selected antibiotics at the point of care would provide the patient and clinician with a desirable, adjunctive preventive modality.

Questions/purposes

We asked (1) if an adaptable, porous chitosan matrix could absorb and elute antibiotics for 72 hours for potential use as an adjunctive therapy to débridement and lavage; and (2) if the sponges could elute levels of antibiotic that would inhibit growth of Staphylococcus aureus and Pseudomonas aeruginosa?

Methods

We fabricated a degradable chitosan sponge that can be loaded with antibiotics during a 60-second hydration in drug-containing solution. In vitro evaluation determined amikacin and vancomycin release from chitosan sponges at six time points. Activity tests were used to assess the release of inhibitory levels of amikacin and vancomycin.

Results

Amikacin concentration was 881.5 μg/mL after 1 hour with a gradual decline to 13.9 μg/mL after 72 hours. Vancomycin concentration was 1007.4 μg/mL after 1 hour with a decrease to 48.1 μg/mL after 72 hours. Zone of inhibition tests were used to verify inhibitory levels of drug release from chitosan sponges. A turbidity assay testing activity of released amikacin and vancomycin indicated inhibitory levels of elution from the chitosan sponge.

Clinical Relevance

Chitosan sponges may provide a potential local drug delivery device for preventing musculoskeletal infections.     

Antimicrobial Release From Prefabricated Spacers Is Variable and the Dose Is Low

Background

High-dose antimicrobial-loaded bone cement (ALBC) is recommended to treat orthopaedic infections. Elution characteristics from prefabricated ALBC spacers and how they compare with hand-mixed ALBC are not well described.

Questions/purposes

(1) How does antimicrobial release from prefabricated spacers compare with release from hand-mixed ALBC over time? (2) Is antimicrobial release uniform across the surface of prefabricated ALBC spacers? (3) Do variations exist between different prefabricated spacer components? (4) Do textured surfaces release more antimicrobial than smooth surfaces?

Methods

Six prefabricated ALBC spacer components, two hip and four knee, and three hand-mixed ALBC formulations were studied in this comparative laboratory study. Gentamicin was eluted from 41 discrete sites over the surfaces of six spacer components and compared with elution from 15 ALBC specimens, five from each of three hand-mixed formulations. Elution was compared between spacer sites, components, and surface texture. Statistical analysis was performed by analysis of variance and Tukey’s multiple-comparison test or t-test.

Results

Gentamicin release was highest in the first 24 hours for both prefabricated ALBC spacers and hand-mixed ALBC. Elution decreased over 7 days similarly for both. At Day 7, prefabricated ALBC spacers eluted more than hand-mixed 1 g ALBC (1 g ALBC: 1.49 ± 0.34, prefabricated: 3.59 ± 1.48, mean difference = 2.1 [0.2–4.0], p = 0.04) but eluted less than 5 g ALBC (9.21 ± 1.31, mean difference = −5.6 [−3.5 to −7.7], p < 0.001) and less than 10 g ALBC (35.8 ± 1.69, mean difference = −32.2 [−29.8 to −34.6], p < 0.001). Release varied from 2.7 to 9.9 µg/mm² over the surface of the spacers and from 3.5 to 5.5 µg/mm² between components with no component different than the others (Tukey). Release from textured surfaces was inconsistent.

Conclusions

Antimicrobial release from prefabricated ALBC spacers is consistent with low-dose ALBC. Variation across the surface and between components is small compared with changes in antimicrobial load.

Clinical Relevance

Antimicrobial release from prefabricated ALBC spacers is consistent with local antimicrobial delivered from other low-dose ALBC formulations.     

In vitro study of elution kinetics and bio-activity of meropenem-loaded acrylic bone cement

Background

Use of antibiotic-loaded acrylic bone cement to treat orthopaedic infections continues to remain popular, but resistance to routinely used antibiotics has led to the search for alternative, more effective antibiotics. We studied, in vitro, the elution kinetics and bio-activity of different concentrations of meropenem-loaded acrylic bone cement.

Methods

Meropenem-loaded bone cement cylinders of different concentrations were serially immersed in normal saline. Elution kinetics was studied by measuring the drug concentration in the eluate, collected at pre-determined intervals, by high-performance liquid chromatography. Bio-activity of the eluate of two different antibiotic concentrations was tested for a period of 3 weeks against each of the following organisms: Staphylococcus aureus ATCC 2593 (MSSA), Enterococcus faecalis ATCC 29212, Pseudomonas aeruginosa ATCC 27853, Escherichia coli ATCC 25922, S. aureus ATCC 43300 (MRSA) and Klebsiella pneumoniae ATCC 700603 (ESBL).

Results

Meropenem elutes from acrylic bone cement for a period of 3–27 days depending on the concentration of antibiotic. Higher doses of antibiotic concentration resulted in greater elution of the antibiotic. The eluate was found to be biologically active against S. aureus ATCC 2593 (MSSA), P. aeruginosa ATCC 27853, E. coli ATCC 25922 and K. pneumoniae ATCC 700603 (ESBL) for a period of 3 weeks.

Conclusions

The elution of meropenem is in keeping with typical antibiotic-loaded acrylic bone cement elution characteristics. The use of high-dose meropenem-loaded acrylic bone cement seems to be an attractive option for treatment of resistant Gram-negative orthopaedic infections but needs to be tested in vivo.     

Association of rs11190870 near LBX1 with adolescent idiopathic scoliosis susceptibility in a Han Chinese population

Purpose

To investigate whether rs11190870 near LBX1 correlates with the susceptibility or curve progression of adolescent idiopathic scoliosis (AIS) in a Han Chinese population.

Methods

A total of 949 AIS patients and 976 age-matched healthy controls were recruited. All the subjects were genotyped using the PCR-based invader assay. Case–control study and case-only study were performed to define the contribution of rs11190870 to predisposition and curve severity of AIS. Additionally, we further conducted a meta-analysis of the study findings together with those of previously reported studies.

Results

A significant association of rs11190870 with AIS was observed in the Han Chinese population (P = 1.8 × 10⁻⁹; odd ratio = 1.51; 95 % confidence interval = 1.33–1.71), and AIS patients with TT genotype had a larger Cobb angle than those with TC or CC genotype (P = 0.005). The meta-analysis confirmed that the positive association of this SNP with AIS in the East Asian population.

Conclusions

The SNP rs11190870 near LBX1 is associated with both susceptibility and curve progression of AIS.