Cyst-Like Osteolytic Formations in Recombinant Human Bone Morphogenetic Protein-2 (rhBMP-2) Augmented Sheep Spinal Fusion.

Multiple case reports using recombinant human bone morphogenetic protein-2 (rhBMP-2) have reported complications. However, the local adverse effects of rhBMP-2 application are not well documented. In this report we show that, in addition to promoting lumbar spinal fusion through potent osteogenic effects, rhBMP-2 augmentation promotes local cyst-like osteolytic formations in sheep trabecular bones that have undergone anterior lumbar interbody fusion. Three months after operation, conventional computed tomography showed that the trabecular bones of the rhBMP-2 application groups could fuse, whereas no fusion was observed in the control group. Micro-computed tomography analysis revealed that the core implant area's bone volume fraction and bone mineral density increased proportionately with rhBMP-2 dose. Multiple cyst-like bone voids were observed in peri-implant areas when using rhBMP-2 applications, and these sites showed significant bone mineral density decreases in relation to the unaffected regions. Biomechanically, these areas decreased in strength by 32% in comparison with noncystic areas. Histologically, rhBMP-2-affected void sites had an increased amount of fatty marrow, thinner trabecular bones, and significantly more adiponectin- and cathepsin K-positive cells. Despite promoting successful fusion, rhBMP-2 use in clinical applications may result in local adverse structural alterations and compromised biomechanical changes to the bone.

An analysis of spine fusion outcomes in sheep pre-clinical models.

PURPOSE: The ovine model is often used to evaluate new spine fusion technologies prior to clinical testing. An important aspect of designing sheep surgery protocols is to select the appropriate postoperative time period for comparing fusion outcomes. Unfortunately, determining the ideal study endpoint is complicated by the fact that prior published studies have not used consistent timeframes. Thus, the primary aim of this study was to provide a reference for investigators as to the expected fusion outcomes of control groups at varying timepoints in sheep spine surgery models. METHODS: We identified published sheep fusion studies using autograft, interbody cages, and/or instrumentation. Fusion data were extracted, converted to a common scale, and analyzed across studied timepoints. RESULTS: Overall, 29 studies of 360 fusion levels were identified: 11 ALIF (158 levels), 3 PLIF/TLIF (28 levels), 8 PLF (90 levels), and 7 ACDF (84 levels). Studied timepoints ranged from 4 to 48 weeks postoperative. In general, fusion rates varied across techniques and instrumentation. The time to reach solid fusion differed by as many as 20 weeks between control groups. CONCLUSIONS: Recommended timeframes for future studies designed to show either superiority over controls or equivalent outcomes with controls were developed based on aggregate results. Designating ideal study endpoints for sheep fusion models has both ethical implications associated with responsible use of animals in research, and economic implications given the cost of animal research. The current results can guide the development of future research methods and help investigators choose appropriate study timelines for various control groups.

Effects of (60)Co gamma radiation dose on initial structural biomechanical properties of ovine bone--patellar tendon--bone allografts.

Gamma radiation is established as a procedure for inactivating bacteria, fungal spores and viruses. Sterilization of soft tissue allografts with high dose (60)Co gamma radiation has been shown to have adverse effects on allograft biomechanical properties. In the current study, bone-patellar tendon-bone (BPTB) allografts from 32 mature sheep were divided into two treatment groups: low-dose radiation at 15 kGy (n = 16) and high-dose radiation at 25 kGy (n = 16) with the contralateral limb serving as a 0 kGy (n = 32) non-irradiated control. Half of the tendons from all treatment groups were biomechanically tested to determine bulk BPTB mechanical properties, cancellous bone compressive properties, and interference screw pull-out strength. The remaining tissues were prepared, implanted, and mechanically tested in an acute in vitro anterior crucial ligament (ACL) reconstruction. Low-dose radiation did not adversely affect mechanical properties of the tendon allograft, bone, or ACL reconstruction compared to internal non-irradiated control. However, high-dose radiation compromised bulk tendon load at failure and ultimate strength by 26.9 and 28.9%, respectively (P < 0.05), but demonstrated no negative effect on the cancellous bone compressive properties or interference screw pull-out strength. Our findings suggest that low dose radiation (15 kGy) does not compromise the mechanical integrity of the allograft tissue, yet high dose radiation (25 kGy) significantly alters the biomechanical integrity of the soft tissue constituent.

Evaluation of ABM/P-15 versus autogenous bone in an ovine lumbar interbody fusion model.

A prospective, randomized study was performed in an ovine model to compare the efficacy of an anorganic bovine-derived hydroxyapatite matrix combined with a synthetic 15 amino acid residue (ABM/P-15) in facilitating lumbar interbody fusion when compared with autogenous bone harvested from the iliac crest. P-15 is a biomimetic to the cell-binding site of Type-I collagen for bone-forming cells. When combined with ABM, it creates the necessary scaffold to initiate cell invasion, binding, and subsequent osteogenesis. In this study, six adult ewes underwent anterior-lateral interbody fusion at L3/L4 and L4/L5 using PEEK interbody rings filled with autogenous bone at one level and ABM/P-15 at the other level and no additional instrumentation. Clinical CT scans were obtained at 3 and 6 months; micro-CT scans and histomorphometry analyses were performed after euthanization at 6 months. Clinical CT scan analysis showed that all autograft and ABM/P-15 treated levels had radiographically fused outside of the rings at the 3-month study time point. Although the clinical CT scans of the autograft treatment group showed significantly better fusion within the PEEK rings than ABM/P-15 at 3 months, micro-CT scans, clinical CT scans, and histomorphometric analyses showed there were no statistical differences between the two treatment groups at 6 months. Thus, ABM/P-15 was as successful as autogenous bone graft in producing lumbar spinal fusion in an ovine model, and it should be further evaluated in clinical studies.

Comparison of Achilles tendon repair techniques in a sheep model using a cross-linked acellular porcine dermal patch and platelet-rich plasma fibrin matrix for augmentation.

The primary goal of this study was to evaluate a cross-linked acellular porcine dermal patch (APD), as well as platelet-rich plasma fibrin matrix (PRPFM), for repair of acute Achilles tendon rupture in a sheep model. The 2 surgically transected tendon ends were reapproximated in groups 1 and 2, whereas a gap was left between the tendon ends in group 3. APD was used to reinforce the repair in group 2, and autologous PRPFM was used to fill the gap, which was also reinforced with APD, in group 3. All sheep were humanely euthanized at 24 weeks after the repair, and biomechanical and histological testing were performed. Tensile strength testing showed a statistically significant difference in elongation between the operated limb and the unoperated contralateral limb in groups 1 and 3, but not in group 2. All operated tendons appeared healed with no apparent fibrosis under light and polarized microscopy. In group 1, all surgical separation sites were identifiable, and healing occurred via increasing tendon thickness. In group 2, healing occurred with new tendon fibers across the separation, without increasing tendon thickness in 2 out of 6 animals. Group 3 showed complete bridging of the gap, with no change in tendon thickness in 2 out of 6 animals. In groups 2 and 3, peripheral integration of the APD to tendon fibers was observed. These findings support the use of APD, alone or with PRPFM, to augment Achilles tendon repair in a sheep model.

Effect of intravenous ketamine and lidocaine on isoflurane requirement in sheep undergoing orthopedic surgery.

Intravenous ketamine and lidocaine infusions may be useful adjuncts to inhalation anesthesia for sheep undergoing orthopedic surgery. In this study, 50 female sheep underwent experimental stifle surgery (29 received a meniscal implant and 21 received sham surgery). To induce anesthesia in the sheep, the authors intravenously injected ketamine and diazepam. They administered isoflurane in oxygen to maintain anesthesia and used mechanical ventilation to maintain normal arterial carbon dioxide pressure. Some sheep received intravenous infusions of ketamine and lidocaine during surgery, whereas others did not. Sheep that received a meniscal implant without ketamine-lidocaine required approximately 23% greater isoflurane concentrations than sheep that were given ketamine-lidocaine. These findings suggest that intravenous infusion of ketamine and lidocaine decreases the requirement for isoflurane during orthopedic surgery on anesthetized sheep.

Material properties of fresh cold-stored allografts for osteochondral defects at 1 year.

Little is known about the long-term properties of fresh cold-stored osteochondral allograft tissue. We hypothesized fresh cold-stored tissue would yield superior material properties in an in vivo ovine model compared to those using freeze-thawed acellular grafts. In addition, we speculated that a long storage time would yield less successful grafts. We created 10-mm defects in medial femoral condyles of 20 sheep. Defects were reconstructed with allograft plugs stored at 4 degrees C for 1, 14, and 42 days; control specimens were freeze-thawed or defect-only. At 52 weeks, animals were euthanized and retrieved grafts were analyzed for cell viability, gross morphology, histologic grade, and biomechanical and biochemical analysis. Explanted cold-stored tissue had superior histologic scores over freeze-thawed and defect-only grafts. Specimens stored for 1 and 42 days had higher equilibrium moduli and proteoglycan content than freeze-thawed specimens. We observed no difference among any of the cold-stored specimens for chondrocyte viability, histology, equilibrium aggregate modulus, proteoglycan content, or hypotonic swelling. Reconstructing cartilage defects with cold-stored allograft resulted in superior histologic and biomechanical properties compared with acellular freeze-thawed specimens; however, storage time did not appear to be a critical factor in the success of the transplanted allograft.

Histological evaluation of an impacted bone graft substitute composed of a combination of mineralized and demineralized allograft in a sheep vertebral bone defect.

Demineralized bone matrix (DBMs) preparations are a potential alternative or supplement to autogenous bone graft, but many DBMs have not been adequately tested in clinically relevant animal models. The aim of current study was to compare the efficacy of a new bone graft substitute composed of a combination of mineralized and demineralized allograft, along with hyaluronic acid (AFT Bone Void Filler) with several other bone graft materials in a sheep vertebral bone void model. A drilled defect in the sheep vertebral body was filled with either the new DBM preparation, calcium sulfate (OsteoSet), autologous bone graft, or left empty. The sheep were euthanized after 6 or 12 weeks, and the defects were examined by histology and quantitative histomorphometry. The morphometry data were analyzed by one-way analysis of variance with the post hoc Tukey-Kramer test or the Student's t-test. All of the bone defects in the AFT DBM preparation group showed good new bone formation with variable amounts of residual DBM and mineralized bone graft. The DBM preparation group at 12 weeks contained significantly more new bone than the defects treated with calcium sulfate or left empty (respectively, p < 0.05, p < 0.01). There was no significant difference between the DBM and autograft groups. No adverse inflammatory reactions were associated with any of the three graft materials. The AFT preparation of a mixture of mineralized and demineralized allograft appears to be an effective autograft substitute as tested in this sheep vertebral bone void model.

Histological and mechanical evaluation of self-setting calcium phosphate cements in a sheep vertebral bone void model.

We investigated the histological and compressive properties of three different calcium phosphate cements (CPCs) using a sheep vertebral bone void model. One of the CPCs contained barium sulfate to enhance its radiopacity. Bone voids were surgically created in the lumbar region of 23 ovine spines - L3, L4, and L5 (n = 69 total vertebral bodies) - and the voids were filled with one of the three CPCs. A fourth group consisted of whole intact vertebrae. Histologic evaluation was performed for 30 of the 69 vertebrae 2 or 4 months after surgery along with radiographic evaluation. Compressive testing was performed on 39 vertebrae 4 months after surgery along with micro-CT analysis. All three CPCs were biocompatible and extremely osteoconductive. Osteoclasts associated with adjacent bone formation suggest that each cement can undergo slow resorption and replacement by bone and bone marrow. Compressive testing did not reveal a significant difference in the ultimate strength, ultimate strain, and structural modulus, among the three CPCs and intact whole vertebrae. Micro-CT analysis revealed good osseointegration between all three CPCs and adjacent bone. The barium sulfate did not affect the CPCs biocompatibility or mechanical properties. These results suggest that CPC might be a good alternative to polymethylmethacrylate for selected indications.

Hydrogel meniscal replacement in the sheep knee: preliminary evaluation of chondroprotective effects.

BACKGROUND: Meniscal allograft transplantation has become a viable surgical alternative for a select group of patients with deficient or irreparable menisci. Subjective results are encouraging; long-term success, durability, and safety of allograft meniscal transplantation are uncertain. PURPOSES: To evaluate a novel hydrogel meniscal replacement implant in an ovine model and assess chondroprotective effects of this hydrogel meniscal replacement using several validated outcome measures. STUDY DESIGN: Controlled laboratory study. METHODS: Fourteen skeletally mature sheep underwent hydrogel meniscal replacement; 45 additional animals had previously undergone 1 of 3 operations: lateral meniscectomy (24), meniscal allograft transplant (17), and sham (4). Animals were sacrificed at 2, 4, or 12 months. Cartilage was assessed by magnetic resonance imaging, gross inspection, biomechanical testing, and semiquantitative histological analysis. RESULTS: There were no differences between the sham operation and nonoperated control limbs. Compared with meniscectomy, hydrogel meniscal replacement resulted in significantly decreased cartilage degeneration with all outcome parameters (P < .05). Compared with nonoperated control limbs, hydrogel meniscal replacements demonstrated no significant differences at 2 months in any category. By 4 months, hydrogel limbs demonstrated significantly greater cartilage degeneration than did nonoperated control limbs in all categories. Compared with meniscal allograft transplantation animals, hydrogel meniscal replacements demonstrated no differences at 2 months but had significantly increased cartilage degeneration in the peripheral zone of the tibial plateau at 4 months (P < .05). At 1 year, all hydrogel implants had developed complete radial splits in the posterior third of the implant. CONCLUSION: Although promising preliminary results for hydrogel meniscal replacement were seen at early time points, significant cartilage degeneration and implant failure were seen at 1 year, and overall performance was worse than was allograft transplantation. Improvements in hydrogel material properties and surface characteristics and more accurate size matching may improve outcomes. CLINICAL RELEVANCE: Improvements in the hydrogel material properties and surface characteristics and more accurate size matching may lead to the use of hydrogel implants in humans.

Efficacy of silicated calcium phosphate graft in posterolateral lumbar fusion in sheep.

BACKGROUND CONTEXT: Conditions requiring posterior lumbar spinal fusion remain a clinical challenge. Achieving arthrodesis using autogenous bone graft is inconsistent when rigid internal fixation such as transpedicular instrumentation is applied. Synthetic materials, particularly calcium phosphate-based ceramics, have shown promise for spine fusion applications, especially when combined with autograft. Silicate substitution has been shown to enhance the bioactivity of calcium phosphates and may obviate the need for autologous supplementation. PURPOSE: Determine efficacy of silicated calcium phosphate (Si-CaP) compared with autograft to generate solid lumbar fusion. STUDY DESIGN: Comparison of healing of instrumented posterolateral lumbar fusion in ewes at 2 and 6 months using Si-CaP or iliac crest autograft. METHODS: Eighteen skeletally mature ewes underwent implantation of either autograft or Si-CaP in the space spanning the L4-L5 transverse process. In vivo quantitative computed tomography (CT) scans were made at 2-month intervals and after euthanasia. Harvested spine segments were radiographed and biomechanically tested in bending at 6 months. Histological assessments were made at 2 and 6 months. RESULTS: Animals receiving Si-CaP graft were biomechanically and radiographically equivalent to those receiving autograft. Fusion mass density and volume were higher for the Si-CaP group throughout the healing period. Si-CaP regenerated normal bone tissue morphology, cellularity, and maturation with no inflammatory responses despite the fact that no autograft, bone marrow aspirate, or blood was mixed with the material. Histomorphometrically, fusion mass was higher for Si-CaP and bony bridging was equivalent when compared with autograft treatment. CONCLUSIONS: Si-CaP was biomechanically, radiographically, and histologically equivalent to autograft in generating a solid, bony, intertransverse process fusion in an ovine model. Both treatment groups achieved 100% bridging fusion after 6 months of healing.

Experiences with sheep as an animal model for shoulder surgery: strengths and shortcomings.

Sheep (and goats) are a convenient large-animal model for rotator cuff repair because of availability, ease of handling and housing, animal cost, and acceptance to society as a research animal. Tenotomy of the infraspinatus tendon and subsequent reattachment to the proximal humerus is useful to address the biomechanical, histologic, and biochemical processes of rotator cuff repair. Detaching this tendon and immediately reattaching it does not represent the clinical picture but serves as a relatively rapid way to screen different suture anchors, suture patterns, scaffolds, growth factors, and other biologics or a combination of these treatments to enhance the healing process. To minimize spontaneous reattachment and reproduce a chronic rotator cuff injury, the end of the tendon can be covered and then reattached 4 weeks later if bone-to-tendon healing is to be evaluated. This chronic model is useful to understand the biology (degree of muscle atrophy and fatty infiltration) of rotator cuff muscles as well as innovative methods of repair. Close-stall confinement is required during the convalescence in acute and chronic studies. Ultrasound in the awake animal can be used to monitor gap formation and tissue organization. Sheep have also been used to determine whether capsular healing after plication is equivalent to open capsular shift.

An in vivo comparison of the modified Mason-Allen suture technique versus an inclined horizontal mattress suture technique with regard to tendon-to-bone healing: a biomechanical and histologic study in sheep.

The purpose of this study is to examine long-term tendon-to-bone healing, by use of a sheep animal model, after rotator cuff repairs performed with 2 different suture techniques: an inclined horizontal mattress suture pattern placed with special arthroscopic instrumentation (HMS) and the modified Mason-Allen pattern (MMA). After a pre hoc power analysis, 18 skeletally mature sheep were randomly assigned to either the HMS or MMA repair technique, with contralateral limbs used for the control group. At 26 weeks, the animals were euthanized. Six sheep from each group underwent biomechanical testing. Load-to-failure and stiffness results indicated no statistically significant difference between the 2 groups. Avulsion of the tuberosity was the primary mode of failure for both groups. In the remaining 6 sheep, histologic evaluation demonstrated that, regardless of treatment, the tendon appeared completely healed in the bony trough. Because the long-term biomechanical and histologic properties of healed tendons repaired with an HMA technique are equal to those obtained with an MMA technique, the inclined horizontal mattress suture may be appropriate for arthroscopic rotator cuff repair. Short-term studies are necessary to determine whether these findings are true early after tendon repair, when failure may be most common.

Polyetheretherketone as a biomaterial for spinal applications.

Threaded lumbar interbody spinal fusion devices (TIBFD) made from titanium have been reported to be 90% effective for single-level lumbar interbody fusion, although radiographic determination of fusion has been intensely debated in the literature. Using blinded radiographic, biomechanic, histologic, and statistical measures, we evaluated a radiolucent polyetheretherketone (PEEK)-threaded interbody fusion device packed with autograft or rhBMP-2 on an absorbable collagen sponge in 13 sheep at 6 months. Radiographic fusion, increased spinal level biomechanical stiffness, and histologic fusion were demonstrated for the PEEK cages filled with autograft or rhBMP-2 on a collagen sponge. No device degradation or wear debris was observed. Only mild chronic inflammation consisting of a few macrophages was observed in peri-implant tissues. Based on these results, the polymeric biomaterial PEEK may be a useful biomaterial for interbody fusion cages due to the polymer's increased radiolucency and decreased stiffness.

Regeneration of bicortical defects in the iliac crest of estrogen-deficient sheep, using new biodegradable polyurethane bone graft substitutes.

Porous scaffolds for cancellous bone graft substitutes were prepared from new experimental biodegradable aliphatic polyurethane elastomers with varying hydrophilicity. The ratios of the hydrophilic-to-hydrophobic content in the polymers were 30-70, 50-50, and 70-30%, respectively. The hydrophilic component consisted of poly(ethylene oxide) diol and the hydrophobic component of poly(epsilon-caprolactone) diol. To promote the materials' biological performance, the calcium complexing moiety, the polysaccharide, and vitamin D(3) were incorporated into the polymer chain upon synthesis. The scaffolds had an interconnected porous structure with an average pore size in the range of 300-2,000 microm and pore-to-volume ratios of (85 +/- 5)%. The bone substitutes were implanted (press-fit) in biocortical 10 x 10 mm(2) defects created in the tuber coxae of 21 skeletally mature Warhill ewes, which were ovariectomized 12 months prior to implantation. At the time of euthanasia at 18 and 25 months, all the defects in the ilium implanted with polyurethane bone substitutes had healed with new bone. The extent of bone healing depended on the chemical composition of the polymer from which the implant was made, although for the same material there were animal-related differences in healing. The structure of the newly formed cancellous bone was radiographically and histologically similar to the native bone. The implants from polymers with the incorporated calcium-complexing additive were the most effective promoters of bone healing, followed by those with vitamin D(3) and polysaccharide-containing polymer. There was no bone healing in the control defects.

The effects of augmentation with Swine small intestine submucosa on tendon healing under tension: histologic and mechanical evaluations in sheep.

BACKGROUND: Rotator cuff failure after surgery may be attributed to inferior tissue healing properties that result from repetitive cyclic loading during early rehabilitation. Enhancing the biological healing process may reduce the incidence of failures after rotator cuff repairs. HYPOTHESIS: Augmentation of rotator cuff tissue using swine small intestine submucosa in a sheep model will improve the rate and quality of tissue repair. STUDY DESIGN: Controlled laboratory study. METHODS: We resected and reattached 26 sheep infraspinatus tendons under tension, with 13 animals receiving a small intestine submucosa patch (augmented group). Animals were sacrificed at 12 weeks, and biomechanical testing and histologic evaluation were performed. Biomechanical testing was completed in 10 tendons from each group. Specimens were loaded to failure at a constant displacement to obtain the load deformation curve used to calculate load to failure and stiffness of the healed bone-tendon interface. Histologic testing addressed tissue healing at the bone-tendon interface. RESULTS: The load-to-failure data did not indicate a significant difference between the augmented and nonaugmented groups (1252 +/- 402 N vs 985 +/- 459 N, respectively; P > .05). However, the augmented group had significantly better stiffness than the nonaugmented group (215 +/- 44 N/mm vs 154 +/- 63 N/mm, respectively; P = .03). Histologic data revealed that the infraspinatus tendon in all specimens inserted into the bone through a zone of fibrocartilage, although none of the patches were intact. CONCLUSION: Although there were no differences in the load-to-failure data between the 2 groups, the statistically significant improvement in stiffness for the augmented group is clinically relevant. Stiffness is the biomechanical parameter representing the tissue response to subdestructive loads seen with early rehabilitation. Augmenting the repair with a collagen matrix improved the early healing characteristics of the repair construct. CLINICAL RELEVANCE: Enhancing the biological process of tendon healing under tension by using a collagen matrix patch may improve the ultimate success of rotator cuff repair.

Meniscal allograft transplantation in the sheep knee: evaluation of chondroprotective effects.

BACKGROUND: Early protection of articular cartilage, before degenerative changes appear on radiographs, should result in better long-term results, but scientific evidence regarding the effectiveness of meniscal transplantation is lacking. PURPOSE: To assess the chondroprotective effects of a new meniscal allograft transplantation animal model and evaluate a magnetic resonance imaging parameter, T2 mapping, in articular cartilage after meniscectomy and meniscal transplantation. STUDY DESIGN: Controlled laboratory study. METHODS: Forty-five skeletally mature sheep were placed into 3 surgical groups: lateral meniscectomy (n = 24), meniscal allograft transplant (n = 17), and sham (n = 4). Animals were sacrificed at 2, 4, or 12 months. Cartilage was assessed by gross inspection, magnetic resonance imaging, T2 mapping, biomechanical testing, and semiquantitative histologic analysis. RESULTS: There were no differences between the sham operation and nonoperated control limbs. Compared with control limbs, meniscectomy resulted in significant increases in cartilage degeneration by all objective criteria (P < .01). Compared with meniscectomy, meniscal allograft transplantation resulted in significant decreases in cartilage degeneration (P < .02). There were significant correlations between T2-mapping data and all other traditional outcomes measures (P < .05, r(2) = 0.37-0.67). Compared with the nonoperated control limbs, allograft transplants demonstrated no significant differences at 2 months in any category, except magnetic resonance imaging data. By 4 months, nonoperated control limbs demonstrated significantly less wear compared to allograft limbs in all categories except modified Mankin scores. CONCLUSION: This model demonstrated significant chondroprotection compared with meniscectomy but demonstrated more cartilage wear at 4 months compared to control limbs. A high degree of allograft cell viability and vascular ingrowth was seen in allograft explants. T2 mapping may provide an accurate noninvasive measure of early cartilage degeneration after meniscectomy, as well as cartilage protection after meniscal allograft transplantation. CLINICAL RELEVANCE: This study establishes a reliable animal model for meniscal allograft transplantation and provides evidence for the utility of T2 mapping at clinically relevant magnetic resonance imaging field strengths for evaluation of early cartilage degeneration.

In vivo BMP-7 (OP-1) enhancement of osteoporotic vertebral bodies in an ovine model.

BACKGROUND CONTEXT: Prevention of osteoporotic vertebral fractures could help at-risk individuals avoid the pain and morbidity associated with these fractures. Currently, patients with osteoporosis are treated with systemic medications to reduce fracture risk. Although effective, these therapies do not eliminate fractures and also tend to have a gradual time-dependent effect on fracture risk. The mechanism of action of the bone morphogenetic protein (BMP) family theoretically makes these molecules candidates for rapidly enhancing local bone structure. STUDY DESIGN: An in vivo study analyzing the effects of BMP-7 (osteogenic protein 1 [OP-1]) treatment on osteopenic ovine vertebral architecture and biomechanics. PURPOSE: We tested the hypothesis that local injection of OP-1 into osteopenic ovine vertebrae will improve bone mass and trabecular distribution, thereby reducing bone fragility and fracture risk. We specifically evaluated compressive biomechanics and morphology of osteopenic ovine vertebral bodies 6 months after local OP-1 treatment. STUDY DESIGN: In vivo animal study. METHODS: Skeletally mature sheep (n=24) underwent ovariectomy and were placed on low cation relative to anion diet. These interventions reduce bone density and induce skeletal fragility. After 6 months, sheep were randomly assigned to six treatment groups based on OP-1 dose (370 mg or 0 mg) and carrier with 4 animals/treatment group. Carriers A and B were poly-L-glycolic acid (PLGA) biospheres with different release kinetics (B allowing sustained BMP release); Carrier C was carboxymethylcellulose. After creating an 8-mm-diameter defect in the midvertebral body, sheep underwent intravertebral body implantation at two nonadjacent levels. Animals were euthanized 6 months after implantation and bone mineral density (BMD), biomechanics, and histomorphometry were assessed. Two-way analysis of variance was used to determine effects of OP-1 (alpha=0.05). RESULTS: An 81.9%, 333.2%, and 39.9% increase in stiffness was seen for OP-1 treated vertebra with Carriers A, B, and C respectively. Although these effects did not reach statistical significance, trends toward improvement were evident. Histology showed varied degrees of bony healing in the injection sites. Histomorphometrically, OP-1 treated vertebrae showed improvements in percent bone of up to 38% and star volume of up to 55% (with Carrier B). Improvements in whole vertebral body BMD were not detected for any treatment. CONCLUSION: In this study, local OP-1 treatment showed a positive trend in improving mechanical strength and histomorphometric parameters of osteopenic vertebra, despite the absence of consistent change in BMD. Controlled slow release of OP-1 using PLGA microspheres appeared to be the most effective method of protein delivery. In conclusion, we feel that the pilot data suggest that the use of OP-1 in the treatment of vertebral osteoporosis in an attempt to enhance bone strength merits further study.

Evaluation of the effects of dietary n-3 fatty acid supplementation on the pharmacokinetics of doxorubicin in dogs with lymphoma.

OBJECTIVE: To determine the effect of dietary n-3 fatty acids on the pharmacokinetics of doxorubicin in dogs with lymphoma. ANIMALS: 23 dogs with lymphoma in stages IIIa, IVa, and Va. PROCEDURE: Dogs receiving doxorubicin chemotherapy were randomly allocated to receive food with a high (test group) or low (control group) content of n-3 fatty acids. Serum doxorubicin and doxorubicinol concentrations were measured via high-performance liquid chromatography before and 6 to 9 weeks after initiation of the diets. Lymph node concentrations of doxorubicin were assessed 6 hours after the initial treatment. Dogs' body composition was assessed by means of dual-energy x-ray absorptiometry scans. RESULTS: No significant differences in doxorubicin pharmacokinetics were detected between treatment groups. Significant differences existed between the first and second sampling times among all dogs for area under the curve, maximum serum concentration, and clearance. Differences in body composition did not affect measured pharmacokinetic variables. The terminal elimination half-life was longer in dogs in which a long-term remission was achieved than in dogs that did not have remission. CONCLUSIONS AND CLINICAL RELEVANCE: Dietary supplementation of n-3 fatty acids is common in veterinary patients with neoplasia, but supplementation did not affect doxorubicin pharmacokinetics in this population of dogs. Explanations for the beneficial effects of n-3 fatty acids other than alterations in the pharmacokinetics of chemotherapy drugs should be investigated. Dogs may metabolize drugs differently prior to remission of lymphoma than when in remission. The pharmacokinetics of doxorubicin at the time of the first administration may predict response to treatment.