Rainer H. Meffert

The effect of low intensity pulsed ultrasound applied to rabbit tibiae during the consolidation phase of distraction osteogenesis

The purpose of this study was to determine if low intensity pulsed ultrasound (LIPU) accelerated the maturation of regenerate bone when applied after distraction in a rabbit model. A mid‐tibial osteotomy was performed in 26 New Zealand white rabbits and an external fixator applied anteromedially. After a seven day latency period, the tibiae were distracted 0.5 mm every 12 h for 10 days. Thirteen of the rabbits received LIPU for 20 min/day (treatment group) and 13 received sham LIPU (control group) from day 17 until sacrifice on day 37. Radiographs were taken weekly after distraction and the total and mineralized areas of the callus were measured. After sacrifice, dual‐energy X‐ray absorptiometry, torsional testing to failure, and histomorphometry were performed. Ultrasound‐treated tibiae were a mean of 68.8 ± 3.8% as stiff as and 68.2 ± 6.0% as strong as the contralateral tibiae. Control tibiae were 78.7 ± 7.0% as stiff as and 70.2 ± 7.9% as strong as the contralateral tibiae. The differences in stiffness and strength were not significant (p = 0.39 and 0.81, respectively) with the number of the animals tested in the study. The treatment group was 91.6% as dense as the contralateral side and the control group was 88.5% as dense as the contralateral side (p = 0.84). Radiographs revealed a significantly larger callus in the LIPU‐treated tibiae at 1, 2 and 3 weeks after distraction compared to control tibiae (p < 0.01, 0.008 and 0.05, respectively). Histomorphometry revealed significantly less fibrous tissue in the LIPU‐treated tibiae (p < 0.05) and a strong trend towards more bone in the LIPU‐treated tibiae compared to controls (p = 0.06). LIPU was found to increase the size of the distraction callus and it might alter the composition of regenerate bone but it did not have a positive effect on the mechanical properties or density of regenerate bone when applied during the consolidation phase of distraction osteogenesis. Published by Elsevier Science Ltd. on behalf of Orthopaedic Research Society.

Distraction osteogenesis after acute limb-shortening for segmental tibial defects. Comparison of a monofocal and a bifocal technique in rabbits.

Background: Segmental bone defects can be treated with immediate limb-shortening followed by monofocal or bifocal distraction osteogenesis. In the present study, the efficacy of monofocal distraction osteogenesis was compared with that of bifocal distraction osteogenesis in a rabbit model. Methods: Twenty-four skeletally mature New Zealand White rabbits were divided into two equal groups: one group had monofocal distraction osteosynthesis, and the other had bifocal distraction osteosynthesis. In both groups, a one-centimeter-long segment of bone was resected from the midpart of the tibial shaft. In the monofocal reconstruction group, the limb was immediately shortened to close the segmental defect and the defect was allowed to heal for ten days. Lengthening was then begun at this site, with use of a specially designed external fixator, at a rate of 0.5 millimeter per twelve hours. In the bifocal reconstruction group, the segmental defect was closed immediately and the fragments were fixed with microplates. A subperiosteal osteotomy was performed proximal to the tibiofibular junction, and lengthening was performed at the site of the osteotomy. The animals in both groups were killed twenty days after the lengthening was completed. New-bone formation then was evaluated with use of radiographs, densitometry, biomechanical testing, and histological and histomorphometric analysis. Results: Osseous consolidation occurred in all but one of the animals. Biomechanical testing demonstrated that the tibiae that had been treated with use of the simple monofocal reconstruction technique tended to have greater torsional stiffness (p = 0.14) and strength (p = 0.09). Follow-up radiographs revealed that both groups had a significant decrease in radiolucent area (p < 0.05), which occurred at essentially the same rate after lengthening. No significant differences were found between the groups with respect to new-bone mineral density, new-bone area, or the amount of callus. Thus, after resection of a diaphyseal bone segment comprising 10 percent of the original length of the tibia and acute shortening, limb reconstruction was completed successfully through distraction osteogenesis with use of either a monofocal or a bifocal technique in rabbits. Conclusions: In the present study, both monofocal and bifocal techniques of shortening and distraction osteogenesis were effective for the reconstruction of segmental bone defects. Under some conditions, the monofocal method may provide a simpler means of treating such defects. Clinical Relevance: Damage to the soft-tissue envelope as well as venous and lymphatic stasis impose limits on the amount of limb-shortening that can be achieved with use of the monofocal method and also influence the indications for this procedure in the clinical setting.

Resorbable ciprofloxacin/polyglycol acid carrier in the local therapy of chronic osteitis

SummaryPolyglycolic test cylinders (PGA) of different sizes and with a different amount of Ciprofloxacin were synthezised and tested in vitro. The monofil 3,2×5 mm sized cylinders containing 3 mg of Ciprofloxacin showed the best release of the antibiotic up to half a year (measured by HPLC). In vivo setting: in the right femur of 66 rabbits osteomyelitis was induced by injection of 3×106 cfu of staph, aureus after the bone marrow had been sclerosed with sodium morrhuate 5%. Two weeks later test cylinders were implanted into the femoral shaft of 30 animals. Thirty-six animals served as controls. Criteria evaluated: weight change, laboratory findings, microbiological, radiological and histopathological parameters. The concentration of Ciprofloxacin was measured in serum, urine and wound secretion by HPLC. All animals developed osteomyelitis. Swabs from the marrow of all treated animals were sterile. The histopathological findings in the control group showed the mild or strong chronic-persistent form of osteomyelitis. In the therapy group even after 2 weeks we mainly found the the chronic-fibrous form. The test-cylinders were well tolerated in the marrow. Levels of the drug were measured in serum, urine and wound secretion.RésuméDes cylindres test d’acide polyglicolique (PGA) de différentes tailles et avec un gradient variable de ciprofloxacine furent synthétisés et testés in vitro. Le cylindre monofil (taille 3,2×5 mm) contenant 3 mg de ciprofloxacine a montré le meilleur relargage d’antibiotiques jusqu’à 6 mois (mesuré par HPLC). Dans l’étude in vivo, une ostéomyélite fut induite dans le fémur droit de 66 lapins par injection de 3×106 cfu de staphylocoque aureus après destruction médullaire par du sodium morrhuate 5%. Deux semaines après les cylindres test furent implantés dans le fémur de 30 animaux. Les 36 autres animaux servant de groupe témoins. Les critères d’evaluation furent. : la courbe de poids, les analyses biologiques, microbiologiques, radiologiques et histopathologiques. La concentration de ciprofloxacine fut mesurée dans le sérum, les urines et la plaie par HPLC. Tous les animaux développèrent une ostéomyélite. Le prélèvement de la moëlle de tous les animaux traités fut stérile. Les études histopathologiques du groupe témoin montrèrent une ostéomyélite persistante plus ou moins importante. Dans le groupe traité après 2 semaines les auteurs trouvent une forme fibreuse chronique. Les cylindres tests furent bien tolérés dans la moëlle.

Resorbierbare Antibiotikumträger zur lokalen Behandlung der chronischen Osteitis — Polyglykolsaure/Poly-L-Laktid als Träger Experimentelle Untersuchungen in vitro

Resorbable polyglycolic acid (PGA)- and poly-L-lactic acid (PLLA) cylinders were investigated in vitro to explore their properties as an antibiotic deposit (Ciprobay, Bayer Leverkusen) with prolonged release. PGA cylinders sized 3.2 x 5 mm, 4.5 x 5 mm and 4.5 x 7 mm respectively were shaped in monofil and polyfil technique. The Ciprofloxacin concentration varied from 0.5 mg to 5.0 mg of each cylinder. The cylinders were eluated in phosphate buffer, pH-value of 7.4, at 37 degrees C. The daily antibiotic release was measured by high performance liquid chromatography. Best combinations we could find demonstrated an initial delivery of Ciprofloxacin in vitro of 67 mg/l. The average daily release was about 16 mg/l during the first 36 days. After complete hydrolysis of the PGA carriers the recovery of Ciprofloxacin reached up to 6.5% and 11.6% respectively. For 40 bioactive cylinders (size phi 3.5 mm x 5 mm, containing 4 mg Ciprofloxacin) were eluated with phosphate buffer (pH 7.4 at 37 degrees C) respectively fresh human blood plasma and tested under various conditions. A gentamicin-polymethylmetacrylate (PMMA) chain (Septopal, E. Merck, Darmstadt) was exposed to equal test conditions for comparison. The quantities of released Ciprofloxacin and Gentamicin were analysed by a microbiological method (bioassay). Initially released rates of Ciprofloxacin were measured very high (up to 180 mg/l) but decreased rapidly within the first 5 days (4.2-22.5 mg/l). The release of Gentamicin produces an initial sharp decrease in concentration during the first 3 days (from 227.5 mg/l to 77.5 mg/l); this is then followed by an almost constant release over a long period of time (about 20 mg/l).(ABSTRACT TRUNCATED AT 250 WORDS)SummaryResorbable polyglycolic acid (PGA)- and poly-L-lactic acid (PLLA) cylinders were investigated in vitro to explore their properties as an antibiotic deposit (Ciprobay®, Bayer Leverkusen) with prolonged release. PGA cylinders sized 3.2 × 5 mm, 4.5 × 5 mm and 4.5 × 7 mm respectively were shaped in monofil and polyfil technique. The Ciprofloxacin concentration varied from 0.5 mg to 5.0 mg of each cylinder. The cylinders were eluated in phosphate buffer, pH-value of 7.4, at 37°C. The daily antibiotic release was measured by high performance liquid chromatography. Best combinations we could find demonstrated an initial delivery of Ciprofloxacin in vitro of 67 mg/l. The average daily release was about 16 mg/l during the first 36 days. After complete hydrolysis of the PGA carriers the recovery of Ciprofloxacin reached up to 6.5% and 11.6% respectively. For 40 bioactive cylinders (size ϕ 3.5 mm x 5 mm, containing 4 mg Ciprofloxacin) were eluated with phosphate buffer (pH 7.4 at 37°C) respectively fresh human blood plasma and tested under various conditions. A gentamicin-polymethylmetacrylate (PMMA) chain (Septopal®, E. Merck, Darmstadt) was exposed to equal test conditions for comparison. The quantities of released Ciprofloxacin and Gentamicin were analysed by a microbiological method (bioassay). Initially released rates of Ciprofloxacin were measured very high (up to 180 mg/l) but decreased rapidly within the first 5 days (4.2–22.5 mg/l). The release of Gentamicin produces an initial sharp decrease in concentration during the first 3 days (from 227.5 mg/l to 77.5 mg/l); this is then followed by an almost constant release over a long period of time (about 20 mg/l). Within the observed period of 92 days we could not find an obvious degradation of the cylinders. The loss of mass in relation to initial weight came to 8.4% in average. The recovery of incorporated Ciprofloxacin was 6.5% in average.ZusammenfassungAls resorbierbare Antibiotikumträger mit prolongierter Freisetzung des Chemotherapeutikums Ciprofloxacin (Ciprobay®, Bayer-Leverkusen) wurden aus Polyglykolsäure (PGS) and Poly-L-Laktid (PLLA) hergestellte Zylinder mit unterschiedlichen Wirkstoffkonzentrationen (0,5–5 mg/Zylinder) in vitro getestet. Die Höhe der Freisetzung des Wirkstoffs wurde im Eluat (Phosphatpuffer oder Plasma) mittels HPLC oder Bioassay bestimmt and mit der aus Gentamicin-PMMA-Kugeln verglichen (gleiche Versuchsbedingungen). Die besten, his zum 155. Tag verfolgten Varianten ergaben Ciprofloxacinkonzentrationen deutlich über der MHK osteitisrelevanter Keime. Im Beobachtungszeitraum konnte ein Zerfall der PLLA-Träger nicht beobachtet werden (Massenabnahme durchschnittlich 8,4%). Aufgrund des frühzeitigeren Zerfalls und der besseren Freisetzungskinetik werden die PGS-Wirkstoffträger für in-vivo-Versuche ausgewählt.