Alex McLaren

Open reduction internal fixation of supracondylar fractures above total knee arthroplasties using the intramedullary supracondylar rod.

Seven patients who had low supracondylar fractures above total knee arthroplasties were treated using the intramedullary supracondylar rod. Six of the seven patients were steroid-dependent, long-standing severe polyarticular rheumatoid arthritics with marked osteopenia. The intramedullary supracondylar rod provided stable fixation that allowed early range of motion of the knee. Union occurred in good position in all patients; return to prefracture function was achieved in three months. The surgical procedure was reliable and was associated with minimal morbidity.

A virtual reality simulator for orthopedic basic skills: A design and validation study

Orthopedic drilling as a skill demands high levels of dexterity and expertise from the surgeon. It is a basic skill that is required in many orthopedic procedures. Inefficient drilling can be a source of avoidable medical errors that may lead to adverse events. It is hence important to train and evaluate residents in safe environments for this skill. This paper presents a virtual orthopedic drilling simulator that was designed to provide visiohaptic interaction with virtual bones. The simulation provides a realistic basic training environment for orthopedic surgeons. It contains modules to track and analyze movements of surgeons, in order to determine their surgical proficiency. The simulator was tested with senior surgeons, residents and medical students for validation purposes. Through the multi-tiered testing strategy it was shown that the simulator was able to produce a learning effect that transfers to real-world drilling. Further, objective measures of surgical performance were found to be able to differentiate between experts and novices.

Xylitol and glycine fillers increase permeability of PMMA to enhance elution of daptomycin.

The elution of antibiotics from hand mixed antibiotic-laden polymethylmethacrylate (PMMA) must be increased to achieve clinical performance equivalent to commercially manufactured antibiotic beads (not available in the USA) in the management of musculoskeletal infections. Adding fillers such as glycine and dextran to polymethylmethacrylate increases the elution of antibiotics from antibiotic-laden PMMA. We propose xylitol, a naturally occurring sweetener with direct antibiofilm properties, as a filler material. To compare the efficacy of xylitol and glycine as fillers on the elution of antibiotics from PMMA, elution studies were performed on mixtures of Palacos® polymethylmethacrylate and daptomycin (1 gm) with xylitol or glycine as the filler (28 g). Xylitol and glycine enhanced the daptomycin activity eluted from the polymethylmethacrylate. Xylitol was more effective than glycine, having a greater increase in daptomycin release at all data points; on day one xylitol increased the elution of daptomycin 2.67 times whereas glycine increased it 1.78 times also on day one. The eluant concentration of daptomycin remained higher longer for xylitol; 3.90 μg/mL for xylitol versus 2.25 μg/mL for glycine on day 9. Xylitol is inexpensive and readily available. It can be hand mixed with PMMA, and is more effective than glycine as a filler to enhance daptomycin release. Considering possible antibiofilm activity, xylitol may be a more advantageous choice.

The effect of glycine filler on the elution rate of gentamicin from acrylic bone cement: a pilot study.

Elution of antibiotics from acrylic bone cement (polymethylmethacrylate [PMMA]) is dependent on the access of fluid to the depths of the cement that contains the antibiotic. Commercially prepared antibiotic beads that are porous have higher elution rates than hand-mixed, nonporous antibiotic PMMA mixtures. To increase the elution of gentamicin from hand-mixed PMMA, glycine was added as a filler to produce porosity. Elution of gentamicin from the antibiotic PMMA-glycine mixture increased with increasing amounts of glycine. With 3.6 g gentamicin powder and 14 g of crystalline glycine per batch of Palacos PMMA, the elution of gentamicin from the PMMA at 2 days was, similar to the previously documented elution of gentamicin from commercially prepared porous Septopal PMMA beads. With further investigation it may be possible to identify a specific filler and a volume of filler that can be hand mixed in antibiotic PMMA to produce the elution behavior that is needed for specific clinical requirements.

The effect of sampling method on the elution of tobramycin from calcium sulfate.

Release rate is a critical property of all drug delivery vehicles, including antibiotic-laden bioerodibles. In vitro elution studies, used to evaluate release rates, use different sampling methods, including changing the entire amount of buffer and partial exchanges each day. Two groups of 10% calcium sulfate-tobramycin pellets were eluted in 20 mL of buffer for 30 days. Group I had 5 mL of buffer withdrawn and replaced daily whereas Group II had the entire 20 mL of buffer changed daily. The results show that the complete exchange method caused a significantly faster release of antibiotic than the partial exchange method. In the complete exchange group, greater than 50% of the tobramycin was released by 24 hours, whereas in the partial exchange group, 50% of the antibiotic was not released until Day 6. The two methods of sampling used to evaluate this bioerodible material provide data that allow the user to anticipate how the material will function in relatively inert and volatile environments. The method used to sample the elution of antibiotics from bioerodible materials affects the amount of antibiotic eluted. It therefore is important to know the method of sampling when making a decision to use a bioerodible material to deliver antibiotics locally.

Particle size of fillers affects permeability of polymethylmethacrylate.

Particulate soluble filler added to polymethylmethacrylate increases its permeability, leading to increased elution. We asked whether particle size affects permeability and elution rate associated with a given volume fraction of filler. Permeability of filler-loaded PMMA was measured in 9 mm rods with a 32% volume fraction of four particle sizes (106 μm, 212 μm, 425 μm, 850 μm) and two filler materials (sucrose and xylitol) using a modified phenolphthalein-sodium hydroxide technique, which allowed quantitative serial observation on the same specimens. Fluid penetration was faster for larger particle sizes. The elution rate was greater for smaller particle sizes on qualitative visual assessment. Sucrose fillers were not different from xylitol fillers independent of particle size. For the volume fraction of 32%, larger particles lead to larger caliber porosity, less pore intercon nectivity, and faster fluid penetration. Smaller size particles lead to smaller caliber porosity, greater pore interconnectivity, smaller areas between the pores with no fluid penetration and greater increase in the effective surface area causing a greater elution rate.

Amphotericin B Delivery From Bone Cement Increases With Porosity but Strength Decreases

BackgroundAmphotericin B is a highly hydrophobic antifungal used for orthopaedic infections. There is disagreement about whether amphotericin B is released when it is loaded in polymethylmethacrylate (PMMA). It is unknown how much a poragen will increase amphotericin B release or decrease the compressive strength of the PMMA.Questions/purposesWe therefore measured amphotericin B release and the compressive strength of amphotericin B loaded bone cement with and without adding high-dose poragen.MethodsAntifungal-loaded bone cement was formulated with Simplex P cement and 200 mg amphotericin B with and without 10 g cefazolin (poragen) per batch. Twenty standardized test cylinders were eluted in deionized water for each formulation. Cumulative amphotericin B mass and compressive strength were measured. Data were analyzed using repeated-measures analysis of variance.ResultsAntifungal-loaded bone cement (ALBC) with 10 g poragen delivered more amphotericin B than ALBC containing amphotericin B alone by Day 15, 12.76 μg/cylinder (0.5%) versus 1.74 μg/cylinder (0.04%), respectively. With amphotericin B alone, compressive strength was unchanged and compressive strength did not decrease during elution. Adding 10 g poragen to ALBC with 200 mg amphotericin B decreased the compressive strength and compressive strength decreased further during elution, 80, 61, and 46 MPa at 0, 1, and 30 days, respectively.ConclusionsAmphotericin B is released in very small amounts from antifungal-loaded bone cement. Release can be increased by adding high-dose poragen, but compressive strength decreases sufficiently to limit its use for implant fixation.

Sucrose, xylitol, and erythritol increase PMMA permeability for depot antibiotics

Release of antibiotics from antibiotic-loaded PMMA is dependent on its permeability. Loading PMMA with soluble particulate filler has been proposed to increase permeability and antibiotic release for beads and spacers. We therefore assessed particulate sucrose, xylitol, and erythritol as fillers to increase the permeability and elution kinetics of filler-loaded PMMA. Based on lower solubility, we hypothesized that erythritol would not enhance permeability and elution as much as xylitol and sucrose. We made filler-loaded PMMA beads with each of the three fillers combined with phenolphthalein, and soaked in 0.1% NaOH solution. Permeability was assessed qualitatively by relative depth of phenolphthalein color change caused by penetration of NaOH solution into subsequently split beads. Elution was quantitatively assessed by spectrophotometric light absorption measurements of the eluent. Fluid penetration reached the center of 7-mm beads by day 15, similar for all three materials. Elution of phenolphthalein was greater for xylitol than for the other two materials. Particulate sucrose, xylitol, and erythritol fillers increase PMMA permeability and elution kinetics but relative solubility did not determine the relative degree of enhancement of permeability and elution by these materials.

Liposomal Formulation Increases Local Delivery of Amphotericin from Bone Cement: A Pilot Study

BackgroundAmphotericin is a highly toxic hydrophobic antifungal. Delivery of amphotericin from antifungal-loaded bone cement (ALBC) is much lower than would be expected for an equivalent load of water-soluble antibacterials. Lipid formulations have been developed to decrease amphotericin toxicity. It is unknown how lipid formulations affect amphotericin release and compressive strength of amphotericin ALBC.Questions/purposesWe asked if amphotericin release from liposomal amphotericin ALBC (1) changed with amphotericin load; (2) differed from release from amphotericin deoxycholate ALBC; (3) was an active drug; and (4) if liposomal amphotericin affected the bone cement strength.MethodsForty-five standardized test cylinders were fabricated from three formulations of ALBC: Simplex™ P bone cement with 200 mg liposomal amphotericin, 800 mg liposomal amphotericin, or 800 mg amphotericin deoxycholate per batch. For each ALBC formulation, cumulative released amphotericin was determined from five cylinders, and compressive strength was measured for 10 cylinders, five before elution and five after. Activity of released amphotericin was determined by growth inhibition assay.ResultsAmphotericin release was greater for increased load of liposomal amphotericin: 770 μg for 800 mg versus 118 μg for 200 mg. Amphotericin release was greater from liposomal ALBC than from deoxycholate ALBC: 770 μg versus 23 μg over 7 days for 800 mg amphotericin. Released amphotericin was active. Compressive strength of liposomal ALBC is decreased, 67 MPa and 34 MPa by Day 7 in elution for the 200-mg and 800-mg formulations, respectively.ConclusionsLiposomal amphotericin has greater amphotericin release from ALBC than amphotericin deoxycholate. Compressive strength of liposomal amphotericin ALBC decreases to less than recommended for implant fixation. Local toxicity data are needed before liposomal amphotericin ALBC can be used clinically.

Clavicular Length: The Assumption of Symmetry

Recent studies have shown subjectively worse outcomes associated with 15 to 20 mm of clavicle shortening. As a result, more than 15 mm of shortening has become a relative indication for operative management. Various methods to quantify shortening have been described in the literature. All measurement techniques described assume clavicular symmetry to assess clavicular shortening. The goal of this study was to assess the side-to-side variation in clavicle length in uninjured, skeletally mature adults.Clavicle length in 102 skeletally mature adults (age range, 22-91 years) was measured using computed tomography data. Clavicle length was defined as the distance between the lateral-most point of the clavicle in the acromioclavicular joint and the medial-most point of the clavicle in the sternoclavicular joint. The side-to-side difference in clavicular length was analyzed, and patients were organized into 2 groups: group 1 was symmetric (difference of less than 5 mm), and group 2 was asymmetric (difference of more than 5 mm). Mean difference in clavicle length for all patients was 4.25±3.8 mm (range, 0-23 mm). Clavicular symmetry was found in 73 (71.5%) of 102 patients. The remaining 29 patients had asymmetry greater than 5 mm. Asymmetry greater than 10 mm was found in 7 (7%) of 102 patients. Twenty-eight percent of clavicles were asymmetric, whereas 7% had clinically significant asymmetry that could affect treatment decisions.This finding calls into question previous methods developed to assess clavicular length in the setting of trauma because of the assumption of symmetry. Further studies are needed to evaluate the effect of hand dominance and pediatric trauma on this observation.