Effect of Ultrasound Frequency and Treatment Duration on Antibiotic Elution from Polymethylmethacrylate Bone Cement

Introduction. The objective of this study was to evaluate the effect ofultrasound frequency and treatment duration on antibiotic-impregnatedpolymethylmethacrylate (PMMA) antibiotic elution rates andmechanical strength.Methods.xTwo batches of PMMA were prepared: one with five gramsof vancomycin powder and one without. Each batch was dividedinto two frequency groups: kHz and MHz. Each frequency groupwas divided into two duration groups: two minutes and ten minutes.Elution samples were measured daily using flow injection analysis.After one week of elution, ultrasound treatments were done daily untileach group’s average concentration fell below those of non-ultrasoundcontrol groups. After elution testing, compression testing determinedmechanical properties. Paired t-tests were used to compare dailyelution amounts to baseline values. Univariate ANOVAs were used totest for effects of both frequency and treatment duration on antibioticelution amounts and on mechanical properties.Results. All ultrasound treatments resulted in significant increasesin antibiotic elution. Frequency and duration had significant effects ofincreasing antibiotic elution (p < 0.001). The kHz group produced significantlygreater antibiotic elution than the MHz group (p < 0.001).The 10-minute duration produced significantly greater antibioticelution than the two-minute duration (both p < 0.001). Frequencyand duration did not have significant effects on yield stress (p = 0.841and p = 0.179, respectively). Frequency had a significant effect (p =0.024) on modulus, but duration did not (p = 0.136).Conclusions. Ultrasound frequency and treatment duration significantlyaffect antibiotic elution from PMMA which may be helpful fortreatment of periprosthetic joint infections during revision arthroplasty.Kans J Med 2019;12(2):45-49

EFFECTIVENESS OF SURGICAL RECONSTRUCTION TO RESTORE RADIOCARPAL JOINT MECHANICS AFTER SCAPHOLUNATE LIGAMENT INJURY. AN IN VIVO MODELING STUDY

Disruption of the scapholunate ligament can cause a loss of normal scapholunate mechanics and eventually lead to osteoarthritis. Surgical reconstruction attempts to restore scapholunate relationship and shows improvement in functional outcomes, but postoperative effectiveness in restoring normal radiocarpal mechanics still remains a question. The objective of this study was to investigate the benefits of surgical repair by observing changes in contact mechanics on the cartilage surface before and after surgical treatment. Six patients with unilateral scapholunate dissociation were enrolled in the study, and displacement driven magnetic resonance image based-surface contact modeling was used to investigate normal, injured and postoperative radiocarpal mechanics. Model geometry was acquired from images of wrists taken in a relaxed position. Kinematics were acquired from image registration between the relaxed images, and images taken during functional loading. Results showed a trend for increase in radiocarpal contact parameters with injury. Peak and mean contact pressures significantly decreased after surgery in the radiolunate articulation and there were no significant differences between normal and postoperative wrists. Results indicated surgical repair improves contact mechanics after injury and that contact mechanics can be surgically restored to be similar to normal. This study provides novel contact mechanics data on the effects of surgical repair after scapholunate ligament injury. With further work, it may be possible to more effectively differentiate between treatments and degenerative changes based on in vivo contact mechanics data

Evaluation of magnetic resonance imaging relaxation time in wrist cartilage with scapholunate ligament injury

Objective: The overall goal of this research is to identify completely non-invasive in vivo markers of cartilage degeneration following wrist injury in order to facilitate assessment and treatment of wrist injuries and prevention of osteoarthritis as a result of injury. In this study, the transverse relaxation time, T2, from magnetic resonance imaging (MRI) of the wrist cartilage of subjects exhibiting unilateral scapholunate dissociation was analyzed to evaluate changes in the biochemical status of the cartilage in the wrist following injury. Methods: Data collection consisted of MRI scans of the wrist using 2 separate 3T scanners. Fourteen subjects were analyzed, each subject completed scans to evaluate T2 relaxation times on both their injured and contralateral (normal) wrist. Scans were conducted with a maximum of 0.390625 mm/pixel in-plane pixel size and 1 mm slice thickness. A series of four time echo scans ranging from 15-80 ms were collected. T2 relaxation time for each subject was calculated by registering these echo time scans and fitting the corresponding intensity values to an exponential decay curve. Results: The T2 results from all subjects indicated no statistically significant changes with presence of injury. The use of two separate MRI scanners of the same strength of magnet coil did not cause a significant change in measurement values. Conclusions: Our data suggests that either T2 relaxation time does not change with the presence of scapholunate injury in the wrist or that the change was insufficient to be detected in this study. The results from this study may function as a baseline for future studies examining the potential positive effect surgical repair has on T2 relaxation times

Antibiotic Elution and Mechanical Strength of PMMA Bone Cement Loaded With Borate Bioactive Glass

A grant from the One-University Open Access Fund at the University of Kansas was used to defray the author's publication fees in this Open Access journal. The Open Access Fund, administered by librarians from the KU, KU Law, and KUMC libraries, is made possible by contributions from the offices of KU Provost, KU Vice Chancellor for Research & Graduate Studies, and KUMC Vice Chancellor for Research. For more information about the Open Access Fund, please see http://library.kumc.edu/authors-fund.xml.Introduction: Local delivery of antibiotics using bone cement as the delivery vehicle is an established method of managing implant-associated orthopedic infections. Various fillers have been added to cement to increase antibiotic elution, but they often do so at the expense of strength. This study evaluated the effect of adding a borate bioactive glass, previously shown to promote bone formation, on vancomycin elution from PMMA bone cement. Methods: Five cement composites were made: three loaded with borate bioactive glass along with 0, 1, and 5 grams of vancomycin and two without any glass but with 1 and 5 grams vancomycin to serve as controls. The specimens were soaked in PBS. Eluate of vancomycin was collected every 24 hours and analyzed by HPLC. Orthopedic-relevant mechanical properties of each composite were tested over time. Results: The addition of borate bioactive glass provided an increase in vancomycin release at Day 1 and an increase in sustained vancomycin release throughout the treatment period. An 87.6% and 21.1% increase in cumulative vancomycin release was seen for both 1g and 5g loading groups, respectively. Compressive strength of all composites remained above the weight-bearing threshold of 70 MPa throughout the duration of the study with the glass-containing composites showing comparable strength to their respective controls. Conclusion: The incorporation of borate bioactive glass into commercial PMMA bone cement can significantly increase the elution of vancomycin. The mechanical strength of the cement-glass composites remained above 70 MPa even after soaking for 8 weeks, suggesting their suitability for orthopedic weight-bearing applications.Marc A. and Elinor J. Asher Orthopedic Research Endowmen

Initial Response of Mature, Experienced Runners to Barefoot Running: Transition to Forefoot Strike

Introduction Forefoot strike has been advocated for many runnersbecause of the relatively lower impact and push-off forces comparedto a heel strike. The purpose of this study was to explore the abilityof mature (> 30 years old), experienced runners to transition from aheel foot strike to a forefoot strike when first introduced to barefootrunning on a treadmill. We hypothesized: 1) mature runners who heelstrike while wearing traditional training shoes would persist in heelstriking immediately following a switch to barefoot, 2) mean shoeheel-to-toe drop would be significantly greater in runners who persistin heel striking when running barefoot compared to those who transitionto a forefoot strike pattern, and 3) there would be a significantdecrease in heel striking in the barefoot condition as running speedsincreased. Methods This was a controlled crossover laboratory study. Thirty-three experienced runners (average 23.4 miles per week) withan average age of 45.6 years were recruited for this study. The participantsfirst ran in their standard running shoes and subsequentlybarefoot. A motion capture system was utilized to detect and analyzeany transition from heel strike to forefoot strike made by study participants. Results Of the 26 participants who were classified as heel strikerunners in their running shoes, 50% (13/26, p = 0.001) transitionedto forefoot strike when changing from running in shoes to runningbarefoot. Conclusions The injuries associated with transition from standardrunning shoes to barefoot running or minimalist shoes may be influencedby the persistence of heel striking in mature runners. Olderexperienced runners may have limited ability to transition from heelto forefoot striking when first introduced to barefoot running. Maturerunners should be cautious when beginning a minimalist shoe orbarefoot running regimen

The effect of starting point placement technique on thoracic transverse process strength: an ex vivo biomechanical study

<p>Abstract</p> <p>Background</p> <p>The use of thoracic pedicle screws in spinal deformity, trauma, and tumor reconstruction is becoming more common. Unsuccessful screw placement may require salvage techniques utilizing transverse process hooks. The effect of different starting point placement techniques on the strength of the transverse process has not previously been reported. The purpose of this paper is to determine the biomechanical properties of the thoracic transverse process following various pedicle screw starting point placement techniques.</p> <p>Methods</p> <p>Forty-seven fresh-frozen human cadaveric thoracic vertebrae from T2 to T9 were disarticulated and matched by bone mineral density (BMD) and transverse process (TP) cross-sectional area. Specimens were randomized to one of four groups: A, control, and three others based on thoracic pedicle screw placement technique; B, straightforward; C, funnel; and D, in-out-in. Initial cortical bone removal for pedicle screw placement was made using a burr at the location on the transverse process or transverse process-laminar junction as published in the original description of each technique. The transverse process was tested measuring load-to-failure simulating a hook in compression mode. Analysis of covariance and Pearson correlation coefficients were used to examine the data.</p> <p>Results</p> <p>Technique was a significant predictor of load-to-failure (<it>P </it>= 0.0007). The least squares mean (LS mean) load-to-failure of group A (control) was 377 N, group B (straightforward) 355 N, group C (funnel) 229 N, and group D (in-out-in) 301 N. Significant differences were noted between groups A and C, A and D, B and C, and C and D. BMD (0.925 g/cm²[range, 0.624-1.301 g/cm²]) was also a significant predictor of load-to-failure, for all specimens grouped together (<it>P </it>< 0.0001) and for each technique (<it>P <</it>0.05). Level and side tested were not found to significantly correlate with load-to-failure.</p> <p>Conclusions</p> <p>The residual coronal plane compressive strength of the thoracic transverse process is dependent upon the screw starting point placement technique. The funnel technique significantly weakens transverse processes as compared to the straightforward technique, which does not significantly weaken the transverse process. It is also dependent upon bone mineral density, and low failure loads even in some control specimens suggest limited usefulness of the transverse process for axial compression loading in the osteoporotic thoracic spine.</p

Characterization of the Conversion of Bone Cement and Borate Bioactive Glass Composites

Borate bioactive glass 13-93B3 converts into an osteoconductive hydroxyapatite-like material in a liquid medium. In this study, 13-93B3 was incorporated into a commercial PMMA (poly(methyl methacrylate)) bone cement, and the conversion of the glass into a precipitate in solution was investigated with scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared (spectroscopy)-attenuated total reflection, and micro-Raman spectroscopy. Glass particles of 5, 33, and 100 µm diameter were each mixed with the PMMA cement to create 20, 30, and 40% glass-loaded composites. Precipitate formation was found to be a calcium-deficient apatite partially substituted with magnesium ions that resembles native bone material and would ideally encourage bone growth better than stoichiometric hydroxyapatite. Composites of bone cement and 13-93B3 show promise as a means of encouraging bone attachment to the surface of the bone cement