Implantation of allogenic synovial stem cells promotes meniscal regeneration in a rabbit meniscal defect model.

BACKGROUND: Indications for surgical meniscal repair are limited, and failure rates remain high. Thus, new ways to augment repair and stimulate meniscal regeneration are needed. Mesenchymal stem cells are multipotent cells present in mature individuals and accessible from peripheral connective tissue sites, including synovium. The purpose of this study was to quantitatively evaluate the effect of implantation of synovial tissue-derived mesenchymal stem cells on meniscal regeneration in a rabbit model of partial meniscectomy. METHODS: Synovial mesenchymal stem cells were harvested from the knee of one New Zealand White rabbit, expanded in culture, and labeled with a fluorescent marker. A reproducible 1.5-mm cylindrical defect was created in the avascular portion of the anterior horn of the medial meniscus bilaterally in fifteen additional rabbits. Allogenic synovial mesenchymal stem cells suspended in phosphate-buffered saline solution were implanted into the right knees, and phosphate-buffered saline solution alone was placed in the left knees. Meniscal regeneration was evaluated histologically at four, twelve, and twenty-four weeks for (1) quantity and (2) quality (with use of an established three-component scoring system). A similar procedure was performed in four additional rabbits with use of green fluorescent protein-positive synovial mesenchymal stem cells for the purpose of tracking progeny following implantation. RESULTS: The quantity of regenerated tissue in the group that had implantation of synovial mesenchymal stem cells was greater at all end points, reaching significance at four and twelve weeks (p < 0.05). Tissue quality scores were also superior in knees treated with mesenchymal stem cells compared with controls at all end points, achieving significance at twelve and twenty-four weeks (3.8 versus 2.8 at four weeks [p = 0.29], 5.7 versus 1.7 at twelve weeks [p = 0.008], and 6.0 versus 3.9 at twenty-four weeks [p = 0.021]). Implanted cells adhered to meniscal defects and were observed in the regenerated tissue, where they differentiated into type-I and II collagen-expressing cells, at up to twenty-four weeks. CONCLUSIONS: Synovial mesenchymal stem cells adhere to sites of meniscal injury, differentiate into cells resembling meniscal fibrochondrocytes, and enhance both quality and quantity of meniscal regeneration.

Comparison of bulb syringe and pulsed lavage irrigation with use of a bioluminescent musculoskeletal wound model.

BACKGROUND: Despite the fact that wound irrigation is a common surgical procedure, there are many variables, including delivery device, irrigant type, and fluid volume, that have yet to be optimized. The purpose of this study was to compare, with use of transgenic bioluminescent bacteria and standard quantitative microbiological methods, the efficacy of pulsed lavage and bulb syringe irrigation in reducing wound bacterial counts. METHODS: A caprine model of a complex, contaminated musculoskeletal wound was developed with use of a bioluminescent strain of Pseudomonas aeruginosa that can be quantified. Luminescent activity was recorded as relative luminescent units with use of a photon-counting camera six hours after the wound was created and inoculated. Twelve goats were randomly assigned to either the pulsed lavage group or the bulb syringe irrigation group. Each wound was irrigated with normal saline solution in 3-L increments for a total of 9 L and was imaged after each 3-L increment. In addition, quantitative culture samples were obtained from different tissues within the wound before and after irrigation. RESULTS: Pulsed lavage decreased the amount of relative luminescent units by 52%, 64%, and 70% at 3, 6, and 9 L, respectively. The bulb syringe irrigation reduced the amount of relative luminescent units by 33%, 44%, and 51% at these same time-points. Significant differences in luminescence were noted between the two groups after both 6 and 9 L of irrigation (p < or = 0.04). The correlation coefficients between relative luminescent units and quantitative cultures for the condition before irrigation and after irrigation were r = 0.96 and 0.83, respectively. CONCLUSIONS: Pulsed lavage was more effective than bulb syringe irrigation in reducing bacterial luminescence after both 6 and 9 L of irrigation. Both device and volume effects can be demonstrated with use of this model. Bioluminescent bacteria provide a method to visualize bacterial distribution and to quantify the bacteria in a wound. CLINICAL RELEVANCE: Pulsed lavage is a more effective and efficient method of irrigation to remove bacteria in a complex musculoskeletal wound. In the model we used, pulsed lavage irrigation with 3 L of saline solution resulted in a reduction of approximately the same amount of bacteria as did irrigation with 9 L with use of a bulb syringe.

Tobramycin-impregnated calcium sulfate prevents infection in contaminated wounds.

Open fractures often are associated with increased rates of infection and nonunion, multiple surgical procedures, and delayed return to preinjury activity. Antimicrobial bone graft substitutes used as an alternative to antibiotic cement beads and/or delayed autologous bone grafting may provide a useful adjunct in patients with open fractures. A stable, unicortical defect was created and contaminated with 30 microL of 5 x 10 colony-forming units/mL of Staphylococcus aureus in the proximal tibial metaphysis of Spanish goats. The negative control group received no treatment, the carrier group received synthetic bone graft alone, the positive control group received tobramycin antibiotic cement, and the treatment group received tobramycin antimicrobial synthetic bone graft (calcium sulfate). After a 3-week evaluation period, intraosseous microbiologic specimens were obtained. The Staphylococcus aureus contaminant was recovered in 11 of 12 animals (mean = 6.9 x 10 colony-forming units/g marrow) in the negative control group and in all animals (mean = 2.2 x 10 colony-forming units/g marrow) in the carrier group. Bacteria were not found in the antibiotic-treated groups. The tobramycin-impregnated calcium sulfate was effective in preventing infection in a contaminated defect. It could be beneficial in reducing the number of surgeries and recovery time because it is bioabsorbable and osteoconductive.

Effectiveness of local antibiotic delivery with an osteoinductive and osteoconductive bone-graft substitute.

BACKGROUND: The morbidity associated with open fractures and open fracture treatment is well established. An osteoinductive and osteoconductive bone-graft substitute that prevents infection would decrease the number of procedures required to treat contaminated fractures by eliminating the need for surgical removal of cement beads and perhaps autograft harvest. We hypothesized that the combination of tobramycin-impregnated calcium sulfate pellets and demineralized bone matrix would prevent the establishment of infection in a contaminated fracture model. METHODS: A unicortical 12-mm-diameter defect was created in the proximal tibial metaphysis of twenty-nine Spanish goats. After contaminating the wounds with an infective dose of Staphylococcus aureus, we divided the animals into four groups. The negative control group received no treatment, the positive control group received tobramycin-impregnated polymethylmethacrylate beads, the demineralized bone matrix group received 2.5 mL of demineralized bone matrix, and the experimental group received tobramycin-impregnated calcium sulfate pellets with 2.5 mL of demineralized bone matrix. Radiographs were made and intraosseous tissue cultures were performed on postoperative day 21. RESULTS: The cultures showed no evidence of intramedullary infection in the experimental or the positive control group, but they were positive for Staphylococcus aureus in six of the seven goats in the negative control group and seven of the eight goats in the demineralized bone matrix group. CONCLUSIONS: The combination of tobramycin-impregnated calcium sulfate pellets and demineralized bone matrix was effective in preventing intramedullary Staphylococcus aureus infection in a contaminated goat fracture model.