Alcohol-induced Adipogenesis in Bone and Marrow: a Possible Mechanism for Osteonecrosis

Clinical Orthopaedics and Related Research. May, 2003  |  Pubmed ID: 12771833

The effect of alcohol on rabbit bone marrow and on the differentiation of mouse bone marrow stromal cells was investigated. Alcohol was administered intragastrically at a dose of 10 mL/kg/day for 1 to 6 months. Alcohol induced a significant increase in serum lipid peroxides, triglyceride, and cholesterol, and a reduction in superoxide dismutase activity. Fatty infiltration in the liver and adipogenesis in bone marrow were found histologically after alcohol administration. Fat cell hypertrophy and proliferation and diminished hematopoiesis in the subchondral area of the femoral head were observed. Triglycerides were deposited in osteocytes, which became pyknotic, and the percentage of empty osteocyte lacunae increased. None of these abnormal changes were detectable in the control group. In the in vitro study, the marrow stromal cells were treated with increasing (0.03, 0.09, and 0.15 mol/L) concentrations of ethanol for 4 to 21 days. Alcohol induced the differentiation of the cells into adipocytes. The number of adipocytes increased with longer durations of exposure to ethanol and with higher concentrations. Cells treated with ethanol also showed diminished alkaline phosphatase activity and expression of osteocalcin. These novel findings indicate that alcohol can directly induce adipogenesis, decrease osteogenesis in bone marrow stroma, and produce intracellular lipid deposits resulting in the death of osteocytes, which may be associated with the development of osteonecrosis, especially in patients with long-term and excessive use of alcohol.

Lovastatin Inhibits Adipogenic and Stimulates Osteogenic Differentiation by Suppressing PPARgamma2 and Increasing Cbfa1/Runx2 Expression in Bone Marrow Mesenchymal Cell Cultures

Bone. Oct, 2003  |  Pubmed ID: 14555271

The mechanism whereby lovastatin can counteract steroid-induced osteonecrosis and osteoporosis is poorly understood. We assessed the effect of lovastatin on a multipotential cell line, D1, which is capable of differentiating into either the osteoblast or the adipocyte lineage. The expression of bone cell and fat cell transcription factors Cbfa1/Runx2 and PPARgamma2, respectively, were determined. 422aP2 gene expression was analyzed. Osteocalcin promoter activity was measured by cotransfecting the cells with the phOC-luc and pSV beta-Gal plasmids. Lovastatin enhanced osteoblast differentiation as assessed by a 1.8x increase in expression of Cbfa1/Runx2 and by a 5x increase in osteocalcin promoter activity. Expression of PPARgamma2 was decreased by 60%. By enhancing osteoblast gene expression and by inhibiting adipogenesis, lovastatin may shunt uncommitted osteoprogenitor cells in marrow from the adipocytic to the osteoblastic differentiation pathway. Future evaluation of lovastatin and other lipid-lowering drugs will help determine their potential as therapeutic agents for osteonecrosis and osteoporosis.

Steroid Effects on Osteogenesis Through Mesenchymal Cell Gene Expression

Osteoporosis International : a Journal Established As Result of Cooperation Between the European Foundation for Osteoporosis and the National Osteoporosis Foundation of the USA. Jan, 2005  |  Pubmed ID: 15205891

We have studied the mechanism of steroid-induced osteonecrosis by examining the effect of dexamethasone on a multipotential cell line, D1, which is derived from bone marrow and is capable of differentiating into either the osteoblast or the adipocyte lineage. The expression of bone cell and fat cell transcription factors Cbfa1/Runx2 and PPARgamma2, were determined. Osteocalcin promoter activity was measured by co-transfecting the cells with the phOC-luc and pSV beta-Gal plasmids. Dexamethasone increased PPARgamma2 gene expression 2-fold, while Cbfa1/Runx2 gene expression and osteocalcin promoter activity decreased by 50-60%, and VEGF protein, measured by ELISA, decreased by 55%. These changes indicate enhanced adipogenesis and decreased osteogenesis by mesenchymal cells in vitro, together with a decrease in VEGF, a potent angiogeneic factor, suggesting that dexamethasone may shunt uncommitted osteoprogenitor cells in marrow from osteoblastic differentiation into the adipocytic pathway, leading to diminished vascularization and eventual osteonecrosis.

Treatment of Posttraumatic Adhesive Capsulitis of the Ankle: a Case Series

Foot & Ankle International / American Orthopaedic Foot and Ankle Society [and] Swiss Foot and Ankle Society. Aug, 2005  |  Pubmed ID: 16115416

Adhesive capsulitis of the ankle is a challenging diagnostic and therapeutic problem. Limited information concerning diagnosis and treatment is available in the musculoskeletal literature.

Patellofemoral Instability After Total Knee Arthroplasty

Clinical Orthopaedics and Related Research. May, 2006  |  Pubmed ID: 16672884

Despite advances in surgical technique and implant design, complications involving the extensor mechanism and patellofemoral joint after total knee arthroplasty (TKA) continue to be the most common cause of pain and the most commonly cited reason for revision TKA surgery. A thorough understanding of the etiologies of patellofemoral instability, careful preoperative planning, and meticulous surgical techniques will optimize clinical outcome. Evaluation of patellofemoral stability should begin in the operating room. Postoperatively, thorough history, physical examination, and dedicated radiographic studies should be obtained. Computed tomography scan is the most accurate and reliable way to assess component positioning. Treatment of patellofemoral instability is directed by its etiology. Revision of one or both components is indicated if malpositioning is present. If the components are determined to be in satisfactory positions, soft tissue procedures can be pursued. Future advancements in prosthetic design and the routine use of computer-assisted navigation systems will minimize patellofemoral instability. Level of Evidence: Therapeutic study, Level V (expert opinion). See the Guidelines for Authors for a complete description of levels of evidence.

Outcomes of Total and Unicompartmental Knee Arthroplasty for Secondary and Spontaneous Osteonecrosis of the Knee

The Journal of Bone and Joint Surgery. American Volume. Nov, 2006  |  Pubmed ID: 17079371

The reported outcomes of patients who underwent total or unicompartmental knee arthroplasty for secondary and spontaneous osteonecrosis of the knee are often from studies that lack the number of subjects necessary to generate meaningful conclusions. We systematically reviewed the available literature in order to define the outcomes of patients after total knee arthroplasty for secondary osteonecrosis and after total or unicompartmental knee arthroplasty for spontaneous osteonecrosis of the knee.

Alcohol-induced Adipogenesis in a Cloned Bone-marrow Stem Cell

The Journal of Bone and Joint Surgery. American Volume. Nov, 2006  |  Pubmed ID: 17079381

Alcohol has been shown to be associated with osteoporosis and osteonecrosis in patients and in animal models. Recent studies have demonstrated that alcohol contributes to abnormal lipid metabolism in the stromal cells of bone marrow, but the mechanisms have not been defined. The purpose of this study was to evaluate the effects of alcohol on the differentiation of a stem cell that was cloned from bone marrow.

Use of Genetically Engineered Bone-marrow Stem Cells to Treat Femoral Defects: an Experimental Study

The Journal of Bone and Joint Surgery. American Volume. Nov, 2006  |  Pubmed ID: 17079384

Treatment of osteonecrosis continues to be a challenging problem. The replacement of necrotic bone with graft materials that promote osteogenesis and angiogenesis may provide better outcomes for early stage disease. In this study, genetically engineered bone-marrow stem cells were used to enhance repair of a defect in the distal aspect of the femur.

Antibiotic-impregnated Cement Spacers for the Treatment of Infection Associated with Total Hip or Knee Arthroplasty

The Journal of Bone and Joint Surgery. American Volume. Apr, 2007  |  Pubmed ID: 17403814

Advances in Hip Arthroplasty in the Treatment of Osteonecrosis

Instructional Course Lectures. 2007  |  Pubmed ID: 17472309

Osteonecrosis of the femoral head is a devastating disease for which many patients will eventually require total hip arthroplasty. Standard total hip arthroplasties have historically had poor results in patients with osteonecrosis. More recently, reports have shown excellent results with second- and third-generation designs that incorporate advances in bearing technology. However, there are still certain subpopulations of patients (those with sickle cell disease, those with systemic lupus erythematosus, and those who have undergone renal transplantation) that have less than optimal results. Other hip arthroplasty alternatives include bipolar hemiarthroplasty, limited femoral resurfacing, and metal-on-metal resurfacing. Bipolar hemiarthroplasty historically and currently has consistently poor results in most studies and should be avoided in patients with osteonecrosis. In multiple reports, limited femoral arthroplasty has demonstrated reasonable midterm and long-term outcomes as a temporizing procedure, with results being less predictable than for standard total hip arthroplasty. Recently, ceramic-on-ceramic and metal-on-metal resurfacing hip arthroplasty has emerged as a viable option that has been used to treat patients with osteonecrosis of the femoral head, and several studies have shown promising short-term outcomes. Overall, however, recent studies have shown more optimal outcomes with hip arthroplasty than resurfacing hip arthroplasty, which makes standard hip replacements, as well as other arthroplasty alternatives, more attractive for young patients with this disease.

Late Presentation of a Mycotic Popliteal Artery Pseudoaneurysm in the Setting of a Revised Total Knee Arthroplasty Complicated by Both Prior Infection and Periprosthetic Fracture: a Case Report

Annals of Vascular Surgery. Jul, 2007  |  Pubmed ID: 17532606

Reports of adverse arterial events associated with total knee arthroplasty (TKA), such as ischemia, thrombosis, arterial injury, or pseudoaneurysm, are relatively rare in the orthopedic and vascular literature and are most commonly associated with direct trauma to the vessel. Additionally, arterial complications typically present within a short postoperative time frame. A delayed presentation of a mycotic arterial pseudoaneurysm in the setting of a revision arthroplasty complicated by infection and fracture has not, to the best knowledge of the authors, been described in the literature. We report the delayed presentation of a mycotic pseudoaneurysm in the setting of a revision TKA previously complicated by both infection and periprosthetic fracture. One year after fracture repair, the patient presented with acute thigh swelling and was diagnosed with a mycotic pseudoaneurysm of the right proximal popliteal artery. He was treated with surgical excision, reverse saphenous vein interpositional grafting, and a long-term course of broad-spectrum antibiotics. In the setting of a revision TKA and previous complications, the risk of future complications is increased and may not always involve direct vascular trauma. In patients with previously infected joints and new-onset vascular events, mycotic pseudoaneurysm must be included in the differential diagnosis.

Adverse Effects of Increased Body Mass Index and Weight on Survivorship of Total Knee Arthroplasty and Subsequent Outcomes of Revision TKA

The Journal of Knee Surgery. Jul, 2007  |  Pubmed ID: 17665781

To investigate the effects of increased weight and body mass index (BMI) on total knee arthroplasty (TKA) survivorship and on functional outcomes and quality of life following revision TKA, a prospective cohort study of 291 consecutive revision TKA patients was performed. Average patient BMI was 32.3 +/- 7.7, and 57% of patients were obese (BMI > or = 30). The obese group was not significantly different from the nonobese group regarding reasons for prosthesis failure; however, they were more likely to experience certain comorbidities. Body mass index and weight were both significant predictors of survivorship of primary TKA (regression coefficient BMI = -1.852, P = .004; regression coefficient weight = -0.405, P = .000) in multivariate regression. At 6-month follow-up, improvement of Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) stiffness, WOMAC difficulty of function, and Knee Society Score (KSS) function scales at 6 months after revision TKA was significantly lower (at the 0.001 level, two tailed) in patients with higher BMI, weight, or both. In regression analysis, BMI was a significant predictor of Short Form-36, WOMAC difficulty of function, and KSS. Weight and BMI have deleterious effects on the longevity of primary TKA and functional and quality of life outcomes following revision TKA. These findings indicate a need for more effective management of these patients.

Treatment Options and Allograft Use in Revision Total Hip Arthroplasty the Acetabulum

The Journal of Arthroplasty. Oct, 2007  |  Pubmed ID: 17919594

One of the most challenging aspects of revision total hip arthroplasty is management of bone loss. The acetabulum is particularly difficult, with its complex morphology and proximity to major neurovascular structures. We present a reliable classification system of pelvic and acetabular bone loss based on preoperative radiographs, and this classification system directs treatment of bone loss. The type and application of allograft bone required for the reconstruction will be reviewed for each level of bone loss. Good ability to prognosticate each level of treatment is available from follow-up studies based on survival. We know of no other scientifically developed and validated classification of pelvic bone loss that predicts the likely success of the applied treatment.

Surgical and Molecular Advances in Osteonecrosis: Editorial Comment

Clinical Orthopaedics and Related Research. May, 2008  |  Pubmed ID: 18350344

Preventive Effects of Puerarin on Alcohol-induced Osteonecrosis

Clinical Orthopaedics and Related Research. May, 2008  |  Pubmed ID: 18350350

Alcohol can induce adipogenesis by bone marrow stromal cells and may cause osteonecrosis of the femoral head. Currently, there are no medications available to prevent alcohol-induced osteonecrosis. We hypothesized puerarin, a Chinese herbal medicine with antioxidative and antithrombotic effects, can prevent alcohol-induced adipogenesis and osteonecrosis. Both bone marrow stromal cells (in vitro) and mice (in vivo) were treated either with ethanol or with ethanol and puerarin, with an untreated group serving as a control. In the in vitro study, the number of adipocytes, contents of triglycerides, and levels of PPAR gamma mRNA expression were decreased and alkaline phosphatase activity, contents of osteocalcin, and levels of osteocalcin mRNA expression were increased in cells treated with both alcohol and puerarin, compared with cells treated with alcohol only. In the in vivo study, marrow necrosis, fat cell hypertrophy and proliferation, thinner and sparse trabeculae, diminished hematopoiesis, and increased empty osteocyte lacunae in the subchondral region of the femoral head were observed in mice treated with alcohol. However, no such changes were seen in femoral heads of mice treated with alcohol and puerarin. The data suggest puerarin can inhibit adipogenic differentiation by bone marrow stromal cells both in vitro and in vivo and prevents alcohol-induced osteonecrosis in this model.

Diagnosis and Treatment of the Infected Primary Total Knee Arthroplasty

Instructional Course Lectures. 2008  |  Pubmed ID: 18399596

A diagnosis of infection in the painful primary total knee replacement is not always a straightforward endeavor. No single, fail-proof diagnostic study for infection exists. Often multiple diagnostic studies that include imaging, blood work, and joint aspiration as well as history and physical examination need to be considered. Infection may not always be determined before surgery, in which case intraoperative frozen sections can help to confirm infection or refute a negative workup. Treatment options vary, depending on the timing in the infection process and the source of the infection and may consist of simpler treatment courses, such as irrigation, débridement, and polyethylene exchange, to more complex treatment courses, such as two-stage revision with an antibiotic spacer to fusion or amputation. The orthopaedic surgeon uses an essential armamentarium of diagnostic and treatment options to determine the presence of infection and tailor the individual treatment of each patient.

Mandated Venous Thromboembolism Prophylaxis: Possible Adverse Outcomes

The Journal of Arthroplasty. Sep, 2008  |  Pubmed ID: 18555656

The purpose of this study was to assess the prevalence and seriousness of adverse outcomes owing to mandatory venous thromboembolism (VTE) prophylaxis. A retrospective study of administrative claims data was conducted to look at the rate of VTEs and other complications in patients undergoing hip and knee arthroplasty. Additional analysis was done to determine whether patient characteristics could explain findings. Although rates of VTE remain unchanged from 2003 to 2007, the rate of immediate postprocedure hematoma, seroma, and hemorrhage went from 1.4% in 2003 to 9.6% in 2006. Return to a more conservative prophylaxis approach resulted in a marked decrease in rates of significant bleeding events. Although preventing VTEs is an important quality concern, mandating prophylaxis for all patients could have unintended adverse outcomes. These guidelines might need to be reevaluated for hip and knee arthroplasty patients.

Lipofibromatous Hamartoma of a Digital Nerve

American Journal of Orthopedics (Belle Mead, N.J.). Aug, 2008  |  Pubmed ID: 18836614

Acute Sciatic Neuritis Following Total Hip Arthroplasty: a Case Report

Archives of Orthopaedic and Trauma Surgery. Jan, 2008  |  Pubmed ID: 17160417

Nerve injuries after total hip arthroplasty are relatively uncommon, but a higher prevalence has been reported in revision arthroplasties, in women and in patients with dysplastic hips. We report a case of a patient who had a painful neuritis of the sciatic nerve after primary arthroplasty, without any objective evidence of motor or sensory deficit and had complete relief of pain after the limb lengths were matched to the contra-lateral side after revision arthroplasty.

Impingement-free Hip Motion: the 'normal' Angle Alpha After Osteochondroplasty

Clinical Orthopaedics and Related Research. Mar, 2009  |  Pubmed ID: 19018605

Femoroacetabular impingement is considered a cause of hip osteoarthrosis. In cam impingement, an aspherical head-neck junction is squeezed into the joint and causes acetabular cartilage damage. The anterior offset angle alpha, observed on a lateral crosstable radiograph, reflects the location where the femoral head becomes aspheric. Previous studies reported a mean angle alpha of 42 degrees in asymptomatic patients. Currently, it is believed an angle alpha of 50 degrees to 55 degrees is normal. The aim of this study was to identify that angle alpha which allows impingement-free motion. In 45 patients who underwent surgical treatment for femoroacetabular impingement, we measured the angle alpha preoperatively, immediately postoperatively, and 1 year postoperatively. All hips underwent femoral correction and, if necessary, acetabular correction. The correction was considered sufficient when, in 90 degrees hip flexion, an internal rotation of 20 degrees to 25 degrees was possible. The angle alpha was corrected from a preoperative mean of 66 degrees (range, 45 degrees - 79 degrees) to 43 degrees (range, 34 degrees - 60 degrees) postoperatively. Because the acetabulum is corrected to normal first, the femoral correction is tested against a normal acetabulum. We therefore concluded an angle alpha of 43 degrees achieved surgically and with impingement-free motion, represents the normal angle alpha, an angle lower than that currently considered sufficient.

VEGF and BMP-6 Enhance Bone Formation Mediated by Cloned Mouse Osteoprogenitor Cells

Growth Factors (Chur, Switzerland). Oct, 2010  |  Pubmed ID: 20497064

New strategies such as combined utilization of growth factors may provide a better treatment for difficult fractures. We have demonstrated enhanced angiogenesis and osteogenesis through the actions of vascular endothelial growth factor (VEGF) and bone morphogenetic protein-6 (BMP-6) on the osteogenic differentiation of a cloned mouse osteoprogenitor cell in vitro and ectopic bone formation in vivo. Human VEGF and BMP-6 genes expressed together produced a significant increase in alkaline phosphatase activity, expression of the RunX2 and osteocalcin genes and mineralization. Microcomputed tomographic analysis of subcutaneous implants consisting of cells transfected with VEGF and BMP-6 cDNA and delivered on a 3D poly (lactic-co-glycolic acid) scaffold confirmed the additive effects between VEGF and BMP-6. Ectopic bone formation in the VEGF plus BMP-6 group was greatest compared to that in either VEGF or BMP-6 alone. This is the first study that demonstrates osteogenesis in vitro and in vivo through the additive effects of VEGF and BMP-6.

The Enhancement of Bone Allograft Incorporation by the Local Delivery of the Sphingosine 1-phosphate Receptor Targeted Drug FTY720

Biomaterials. Sep, 2010  |  Pubmed ID: 20621764

Poor vascularization coupled with mechanical instability is the leading cause of post-operative complications and poor functional prognosis of massive bone allografts. To address this limitation, we designed a novel continuous polymer coating system to provide sustained localized delivery of pharmacological agent, FTY720, a selective agonist for sphingosine 1-phosphate receptors, within massive tibial defects. In vitro drug release studies validated 64% loading efficiency with complete release of compound following 14 days. Mechanical evaluation following six weeks of healing suggested significant enhancement of mechanical stability in FTY720 treatment groups compared with unloaded controls. Furthermore, superior osseous integration across the host-graft interface, significant enhancement in smooth muscle cell investment, and reduction in leukocyte recruitment was evident in FTY720 treated groups compared with untreated groups. Using this approach, we can capitalize on the existing mechanical and biomaterial properties of devitalized bone, add a controllable delivery system while maintaining overall porous structure, and deliver a small molecule compound to constitutively target vascular remodeling, osseous remodeling, and minimize fibrous encapsulation within the allograft-host bone interface. Such results support continued evaluation of drug-eluting allografts as a viable strategy to improve functional outcome and long-term success of massive cortical allograft implants.

Blood Supply to the Chicken Femoral Head

Comparative Medicine. Aug, 2010  |  Pubmed ID: 20819379

The purpose of this study was to conduct a comprehensive evaluation of the vascular supply to the femoral head, including the vessels that give rise to the terminal perfusing branches. Using a casting agent, we highlighted the anatomy of the external iliac and ischiatic arteries with their associated branches after anatomic dissection of 24 hips from 12 Leghorn chickens. We confirmed published findings regarding perfusion of the femoral head and identified 3 previously undescribed arterial branches to this structure. The first branch (the acetabular branch of the femoralis artery) was supplied by the femoralis artery and directly perfused the acetabulum and femoral head. The second branch (the lateral retinacular artery) was a tributary of the femoralis artery that directly supplied the femoral head. Finally, we found that the middle femoral nutrient artery supplies a previously undescribed ascending intraosseous branch (the ascending branch of the middle femoral nutrient artery) that perfuses the femoral head. Precise understanding of the major vascular branches to the femoral head would allow for complete or selective ligation of its blood supply and enable the creation of a reproducible bipedal model of femoral head osteonecrosis.

Distal Femoral Fractures: Current Concepts

The Journal of the American Academy of Orthopaedic Surgeons. Oct, 2010  |  Pubmed ID: 20889949

The diversity of surgical options for the management of distal femoral fractures reflects the challenges inherent in these injuries. These fractures are frequently comminuted and intra-articular, and they often involve osteoporotic bone, which makes it difficult to reduce and hold them while maintaining joint function and overall limb alignment. Surgery has become the standard of care for displaced fractures and for patients who must obtain rapid return of knee function. The goal of surgical management is to promote early knee motion while restoring the articular surface, maintaining limb length and alignment, and preserving the soft-tissue envelope with a durable fixation that allows functional recovery during bone healing. A variety of surgical exposures, techniques, and implants has been developed to meet these objectives, including intramedullary nailing, screw fixation, and periarticular locked plating, possibly augmented with bone fillers. Recognition of the indications and applications of the principles of modern implants and techniques is fundamental in achieving optimal outcomes.

Emerging Ideas: Treatment of Precollapse Osteonecrosis Using Stem Cells and Growth Factors

Clinical Orthopaedics and Related Research. Sep, 2011  |  Pubmed ID: 21161735

Osteonecrosis (ON) of the femoral head is a devastating disease affecting young patients at their most productive age, causing major socioeconomic burdens. ON is associated with various etiologic factors, and the pathogenesis of the disease is unknown. Most investigators believe the disease is the result of secondary microvascular compromise with subsequent bone and marrow cell death and defective bone repair. QUESTIONS/HYPOTHESES: We hypothesize that local delivery of vascular endothelial growth factor (VEGF) and bone morphogenetic protein-6 (BMP-6), which induces angiogenesis and osteogenesis respectively, will reverse the disease process and provide a treatment for precollapse ON.

Combined VEGF and LMP-1 Delivery Enhances Osteoprogenitor Cell Differentiation and Ectopic Bone Formation

Growth Factors (Chur, Switzerland). Feb, 2011  |  Pubmed ID: 21222516

A novel strategy to enhance bone repair is to combine angiogenic factors and osteogenic factors. We combined vascular endothelial growth factor (VEGF) and LIM mineralization protein-1 (LMP-1) by using an internal ribosome entry site to link the genes within a single plasmid. We then evaluated the effects on osteoblastic differentiation in vitro and ectopic bone formation in vivo with a subcutaneously placed PLAGA scaffold loaded with a cloned mouse osteoprogenitor cell line, D1, transfected with plasmids containing VEGF and LMP-1 genes. The cells expressing both genes elevated mRNA expression of RunX2 and β-catenin and alkaline phosphatase activity compared to cells from other groups. In vivo, X-ray and micro-CT analysis of the retrieved implants revealed more ectopic bone formation at 2 and 3 weeks but not at 4 weeks compared to other groups. The results indicate that the combination of the therapeutic growth factors potentiates cell differentiation and may promote osteogenesis.

Local Delivery of FTY720 Accelerates Cranial Allograft Incorporation and Bone Formation

Cell and Tissue Research. Aug, 2011  |  Pubmed ID: 21863314

Endogenous stem cell recruitment to the site of skeletal injury is key to enhanced osseous remodeling and neovascularization. To this end, this study utilized a novel bone allograft coating of poly(lactic-co-glycolic acid) (PLAGA) to sustain the release of FTY720, a selective agonist for sphingosine 1-phosphate (S1P) receptors, from calvarial allografts. Uncoated allografts, vehicle-coated, low dose FTY720 in PLAGA (1:200 w:w) and high dose FTY720 in PLAGA (1:40) were implanted into critical size calvarial bone defects. The ability of local FTY720 delivery to promote angiogenesis, maximize osteoinductivity and improve allograft incorporation by recruitment of bone progenitor cells from surrounding soft tissues and microcirculation was evaluated. FTY720 bioactivity after encapsulation and release was confirmed with sphingosine kinase 2 assays. HPLC-MS quantified about 50% loaded FTY720 release of the total encapsulated drug (4.5 μg) after 5 days. Following 2 weeks of defect healing, FTY720 delivery led to statistically significant increases in bone volumes compared to controls, with total bone volume increases for uncoated, coated, low FTY720 and high FTY720 of 5.98, 3.38, 7.2 and 8.9 mm(3), respectively. The rate and extent of enhanced bone growth persisted through week 4 but, by week 8, increases in bone formation in FTY720 groups were no longer statistically significant. However, micro-computed tomography (microCT) of contrast enhanced vascular ingrowth (MICROFIL®) and histological analysis showed enhanced integration as well as directed bone growth in both high and low dose FTY720 groups compared to controls.