Xinqian Chen

Osteogenic protein-1 induced bone formation in an infected segmental defect in the rat femur.

The goal of this study was to use a segmental defect model in the rat femur to determine if osteogenic protein‐1 (OP‐1) is capable of inducing bone formation in the presence of bacterial contamination. A 6 mm segmental defect was surgically created and stabilized with a polyacetyl plate and Kirschner wires in one femur in each of 126 Sprague–Dawley rats. The animals were divided into eight groups in which the defect was either left untreated, or subjected to various combinations of OP‐1 (11 or 50 μg), lyophilized bovine type I collagen (carrier for the OP‐1), and 105 colony‐forming units of Staphylococcus aureus. The animals were euthanized at either 2, 4, or 9 weeks. Quantitative radiographic and histologic analyses were performed on the harvested tissue. The initial contamination progressed to infection in all animals receiving bacteria, as determined by qualitative bacteriology. There was very little, if any, bone formation in the untreated defects, and in the contaminated defects with or without collagen carrier. Bone formation was significantly greater in contaminated defects with either dose of OP‐1, compared with contaminated defects without OP‐1. The 50 μg dose of OP‐1 induced significantly more bone formation than the 11 μg dose, both with and without bacteria. This investigation has demonstrated that OP‐1 maintains its osteoinductive capability in a contaminated segmental defect. OP‐1 may potentially be used in the clinical management of contaminated fractures.

Recombinant Human Osteogenic Protein-1 Induces Bone Formation in a Chronically Infected, Internally Stabilized Segmental Defect in the Rat Femur

BACKGROUND Recombinant human osteogenic protein-1 (rhOP-1), combined with a collagen carrier, has been shown to induce new-bone formation in a variety of animal models. The purpose of the present investigation was to test the hypotheses that rhOP-1 would accelerate bone formation in an internally stabilized, chronically infected, critical-size defect in the rat femur and that this effect would be enhanced by the administration of systemic antibiotic. METHODS A 6-mm segmental defect was created surgically, stabilized with a polyacetyl plate and six Kirschner wires, and contaminated with 10(4) colony-forming units of Staphylococcus aureus in one femur in each of 168 Sprague-Dawley rats. After two weeks, these infected defects were débrided surgically and were assigned to one of six treatment groups. The defects in the thirty animals in the first group received lyophilized collagen carrier mixed with 200 microg of rhOP-1 dissolved in buffer, the defects in the thirty animals in the second group received carrier with 20 microg of rhOP-1 in buffer, and the defects in the twenty-four control animals in the third group received carrier mixed with buffer without rhOP-1. The last three groups were treated identically to the first three groups, except that the animals also received the antibiotic ceftriaxone for twenty-eight days after débridement. The animals were killed at two, four, eight, or twelve weeks after débridement. Newly mineralized callus within the defect, and adjacent to and bridging the outside of the defect, was assessed with use of quantitative high-resolution radiography, microcomputed tomography, torsional failure testing, and histological analysis of undecalcified sections. RESULTS Bacterial cultures confirmed the presence of a chronic infection during the study period in all animals. At the later time-points, significantly more newly mineralized callus was present within and adjacent to the débrided defects that had been treated with 200 microg of rhOP-1, whereas minimal amounts of callus were present within and adjacent to the defects that had been treated without rhOP-1 and with 20 microg of rhOP-1. At eight and twelve weeks after débridement, there was significantly more newly mineralized callus in the group that had been treated with 200 microg of rhOP-1 with antibiotic than in the group that had been treated with 200 microg of rhOP-1 without antibiotic (p < 0.05). At twelve weeks, the values for torque, energy to failure, and linear stiffness for femora that had been treated with 200 microg of rhOP-1 with antibiotic were not significantly different from the values for intact, contralateral control femora, whereas the values for femora that had been treated with 200 microg of rhOP-1 without antibiotic remained significantly lower than those for the intact, contralateral controls (p < 0.05). CONCLUSIONS Recombinant human osteogenic protein-1 maintained its osteoinductive capability in the presence of chronic infection, and this property was enhanced by antibiotic therapy. No substantial callus formed in the infected defects without a sufficiently high dose of rhOP-1. CLINICAL RELEVANCE The treatment of an infection at the site of a fracture often necessitates removal of internal fixation. However, internal fixation is needed for fracture stability. This study presents an intervention that may accelerate fracture-healing in the presence of infection and colonized hardware, thereby permitting earlier removal of the hardware and more timely and effective treatment of the infection.

Union of a chronically infected internally stabilized segmental defect in the rat femur after debridement and application of rhBMP-2 and systemic antibiotic.

Objectives: The goal of this study was to determine whether recombinant human bone morphogenetic protein-2 (rhBMP-2) would induce new bone formation in an internally stabilized segmental defect with a chronic bacterial infection in the rat femur and whether treatment with systemic antibiotic would enhance this effect. Methods: A 6-mm unilateral femoral segmental defect was surgically created in 120 Sprague-Dawley rats, internally stabilized with a polyacetyl plate and 6 Kirschner wires, and contaminated with 104 colony-forming units of Staphylococcus aureus. After 2 weeks, all defects were surgically debrided and implanted with 0, 20, or 200 μg of rhBMP-2 in a type 1 bovine collagen sponge. Half of the animals in each treatment group received 4 weeks of systemic antibiotic, and half did not. Animals were euthanized at 4 or 12 weeks after debridement. Bone formation within and adjacent to the defect was assessed using microcomputed tomography, torsional failure testing and undecalcified histology. Results: No substantial callus formed in the infected defects without rhBMP-2. Significantly more mineralized callus was induced with the higher dose of rhBMP-2 than with the lower dose (P = 0.001), with systemic antibiotic therapy than without (P < 0.001), and at 12 weeks after debridement compared with 4 weeks (P < 0.001). Conclusions: Recombinant human bone morphogenetic protein-2 maintained its osteoinductive capability in the presence of a chronic infection, and this property was enhanced by systemic antibiotic. This study presents an intervention that may potentially accelerate fracture healing in the presence of infection and colonized hardware, thereby permitting earlier removal of the hardware, and more timely and effective treatment of infection.

Ceramic bone graft substitute with equine bone protein extract is comparable to allograft in terms of implant fixation: A study in dogs

Background and purpose We studied whether osseointegration and fixation of plasma-sprayed titanium implants grafted with β-TCP granules (Ossaplast) can be improved by adding an osteogenic signal (Colloss E). The results were compared to implants grafted with fresh frozen morselized allograft with and without the Colloss E device. Methods 4 porous-coated Ti implants were placed in the proximal humeri in each of 10 dogs. All implants were surrounded by a 2.5-mm defect, which was grafted with: (A) β-TCP, (B) β-TCP+20 mg Colloss E, (C) allograft, or (D) allograft+20 mg Colloss E. The observation time was 4 weeks. Results Mechanical testing showed that the β-TCP group with Colloss E was twice as well fixed as the control group grafted with β-TCP granules alone, and comparable to both allograft groups. We found that every control implant in the β-TCP grafted group was covered by a dense fibrous membrane. No fibrous tissue was seen in the β-TCP group augmented with Colloss. These implants were well osseointegrated, with new bone covering 10–25% of the implant surface. Both treated groups had increased graft resorption compared to their respective control groups. Colloss E had no effect on new bone formation or fibrous tissue reduction around the allografted implants. Interpretation The Colloss E device improved early osseointegration of implants grafted with β-TCP granules and increased their mechanical implant fixation to the level of allografted implants. The experiment indicates that ceramic bone substitutes may be a viable alternative to allograft when combined with an osteogenic signal such as Colloss E.

Effect of Nicotine and Tobacco Administration Method on the Mechanical Properties of Healing Bone following Closed Fracture

We previously showed different effects of tobacco and nicotine on fracture healing, but due to pump reservoir limits, maximum exposure period was 4 weeks. To allow flexibility in pre‐ and post‐fracture exposure periods, the objective of this study was to compare a new oral administration route for nicotine to the established pump method. Four groups were studied: (1) pump saline, (2) pump saline + oral tobacco, (3) pump saline/nicotine + oral tobacco, and (4) pump saline + oral nicotine/tobacco. Sprague–Dawley rats (n = 84) received a transverse femoral fracture stabilized with an intramedullary pin 1 week after initiating dosing. After 3 weeks, no difference was found in torsional strength or stiffness between oral nicotine/tobacco or pump nicotine + tobacco, while energy absorption with oral nicotine/tobacco was greater than pump nicotine + tobacco (p < 0.05). Compared to saline control, strength for oral nicotine/tobacco was higher than control (p < 0.05), and stiffnesses for pump nicotine + tobacco and oral nicotine/tobacco were higher than control (p < 0.05). No differences in energy were found for either nicotine–tobacco group compared to saline control. Mean serum cotinine (stable nicotine metabolite) was different between pump and oral nicotine at 1 and 4 weeks, but all groups were in the range of 1–2 pack/day smokers. In summary, relevant serum cotinine levels can be reached in rats with oral nicotine, and, in the presence of tobacco, nicotine can influence mechanical aspects of fracture healing, dependent on administration method. Caution should be exercised when comparing results of fracture healing studies using different methods of nicotine administration.

Osteogenic protein-1 induces bone formation in the presence of bacterial infection in a rat intramuscular osteoinduction model

Objective: Evaluate the ability of osteogenic protein-1 to induce formation of de novo bone in the presence of bacterial infection and metal in an intramuscular osteoinduction model in the rat. Design: Prospective experimental design with assessment time points of up to 4 weeks. Setting: Intramuscular pocket surgically created along each side of the spine. Animals: One-hundred-twenty adult male Sprague-Dawley rats. Interventions: Each intramuscular pocket received 0, 10, or 25 μg of osteogenic protein-1 combined with a lyophilized collagen carrier, and 0 or 5 × 105 colony-forming units of Staphylococcus aureus. Pockets in 48 animals received a metal implant. Animals were killed at 1, 2, 3, or 4 weeks. Main Outcome Measurements: High-resolution radiographs of resulting nodules of bone/soft tissue were digitized, and areas of newly formed bone were quantified using an image analysis workstation. The nodules were decalcified for histology, and calcium content of the decalcifying solution was quantified by flame atomic absorption spectrophotometry. Results: There were minimal levels of calcium and area of new bone formation in nodules from pockets containing collagen carrier without osteogenic protein-1, for both infection and noninfection conditions. Calcium content and area of newly formed bone were significantly greater: 1) in infected pockets with osteogenic protein-1, compared to infected pockets without osteogenic protein-1; and 2) in noninfected pockets with osteogenic protein-1, compared to infected pockets with osteogenic protein-1. The presence of metal did not have a significant effect. Conclusion: Osteogenic protein-1 maintained its osteoinductive capability in a contaminated intramuscular pocket in the rat, albeit at a lower level than without infection. This finding supports further study using a more clinically realistic model.

Alendronate treatment in the revision setting, with and without controlled implant motion

Introduction Bisphosphonates have been proposed to delay or prevent loosening of joint replacement implants by reducing bone resorption. It is known, however, that implant motion prevents the bone anchorage necessary to maintain secure implant fixation. Methods We used our experimental implant model with controlled motion to evaluate the relative effects of implant motion and bisphosphonate. We implemented our established 8-week experimental revision protocol to obtain a bony and soft tissue setting of revision joint replacement in 16 dogs. At 8 weeks, we had stabilized half of the implants. The other half of the implants continued pistoning. Half of the dogs were exposed to alendronate (oral). Results Stabilization of the revision implant was more effective at improving fixation (higher shear strength) than administering alendronate. As expected, the fibrous membrane remained under unstable conditions, even with alendronate. With alendronate and stabilized implants, increased bone was observed near the sclerotic shell of the revision cavity, but it was reduced with alendronate when the implant was unstable. Interpretation Our findings suggest that it may be difficult for alendronate administration alone to rescue implants that are already loose. In implants that have not progressed to loosening, alendronate may increase bone density at the border with the sclerotic shell, but the effect of this bone in delaying eventual loosening is not known.

Fixation of Hydroxyapatite-Coated Revision Implants Is Improved by the Surgical Technique of Cracking the Sclerotic Bone Rim

Revision joint replacement has poorer outcomes that have been associated with poorer mechanical fixation. We investigate a new bone‐sparing surgical technique that locally cracks the sclerotic bone rim formed during aseptic loosening. We inserted 16 hydroxyapatite‐coated implants bilaterally in the distal femur of eight dogs, using a controlled weight‐bearing experimental model that replicates important features of a typical revision setting. At 8 weeks, a control revision procedure and a crack revision procedure were performed on contralateral implants. The crack procedure used a splined tool to perform a systematic local perforation of the sclerotic bone rim of the revision cavity. After 4 weeks, the hydroxyapatite‐coated implants were evaluated for mechanical fixation by a push‐out test and for tissue distribution by histomorphometry. The cracking revision procedure resulted in significantly improved mechanical fixation, significantly more bone ongrowth and bone volume in the gap, and reduced fibrous tissue compared to the control revision procedure. The study demonstrates that the sclerotic bone rim prevents bone ingrowth and promotes fixation by fibrous tissue. The effect of the cracking technique may be due to improved access to the vascular compartment of the bone. The cracking technique is a simple surgical method that potentially can improve the fixation of revision implants in sclerotic regions important for obtaining the fixation critical for overall implant stability.