Clinical Orthopaedics and Related Research ®

A Publication of The Association of Bone and Joint Surgeons ®

Symposium: New Approaches to Allograft Transplantation 22 articles

Articles

Results of Chondrocyte Implantation with a Fibrin-Hyaluronan Matrix: A Preliminary Study

S. Nehrer MD, PhD, C. Chiari MD, S. Domayer MD, H. Barkay MSc, A. Yayon PhD, MD Fibrin, a homologous polymer, is the natural scaffold of wound healing and therefore a candidate as a carrier for cell transplantation. We explored a novel matrix-based implant cartilage repair composed of both fibrin and hyaluronan in a defined ratio that takes advantage of the biological and mechanical properties of these two elements. The matrix was seeded with autologous chondrocytes expanded in the presence of a proprietary growth factor variant designed to preserve their chondrogenic potential. We prospectively followed eight patients with symptomatic-chronic cartilage defects treated with this carrier. Patients had arthroscopy to harvest autologous chondrocytes then grown in autologous serum. Chondrocytes were cultured in the presence of the FGF variant and then seeded on the fibrin-hyaluronan matrix. About 4 weeks following biopsy, the patients underwent implantation of the constructs by miniarthrotomy. Three of the eight patients had transient effusion. Clinical performance was measured by Lysholm and IKDC scores, MRI, and the need for secondary surgery. The clinical outcome of a 1-year followup demonstrated increase of clinical scores. The MRI followup showed good filling of the defect with tissue having the imaging appearance of cartilage in all patients. Apart from the transient effusion in three patients we observed no other adverse events during the followup.,[object Object]

Engineering of Functional Cartilage Tissue Using Stem Cells from Synovial Lining: A Preliminary Study

Ming Pei MD, PhD, Fan He BS, Vincent L. Kish ASEE, Gordana Vunjak-Novakovic PhD Stem cells derived from synovial lining—synovial lining-derived stem cells or SDSCs—are a promising cell source for cartilage tissue engineering. We hypothesized that negatively selected SDSCs would form cartilage constructs and conventionally passaged SDSCs would be contaminated with macrophages, inhibiting SDSC-based chondrogenesis. We mixed SDSCs with fibrin gel and seeded the cells into polyglycolic acid scaffolds. After 3 days of incubation with a proliferative growth factor cocktail (containing transforming growth factor β1 [TGF-β1], insulin-like growth factor I [IGF-I], and basic fibroblast growth factor [FGF-2]), the cell-fibrin-polyglycolic acid constructs were transferred into rotating bioreactor systems and cultured with a chondrogenic growth factor cocktail (TGF-β1/IGF-I) for up to 4 weeks. Tissue constructs based on negatively selected SDSCs had cartilaginous characteristics; were rich in glycosaminoglycans and collagen II; exhibited high expression of mRNA and protein for collagen II, aggrecan, and Sox 9; exhibited a negligible level of mRNA and protein for collagens I and X; and had an equilibrium modulus in the range of values measured for native human cartilage. Conventional passage yielded SDSCs with contaminating macrophages, which adversely affected the quality of tissue-engineered cartilage. We thus propose functional cartilage constructs could be engineered in vitro through the use of negatively isolated SDSCs.

A Perspective: Engineering Periosteum for Structural Bone Graft Healing

Xinping Zhang PhD, Hani A. Awad PhD, Regis J. O’Keefe MD, PhD, Robert E. Guldberg PhD, Edward M. Schwarz PhD Autograft is superior to both allograft and synthetic bone graft in repair of large structural bone defect largely due to the presence of multipotent mesenchymal stem cells in periosteum. Recent studies have provided further evidence that activation, expansion and differentiation of the donor periosteal progenitor cells are essential for the initiation of osteogenesis and angiogenesis of donor bone graft healing. The formation of donor cell-derived periosteal callus enables efficient host-dependent graft repair and remodeling at the later stage of healing. Removal of periosteum from bone autograft markedly impairs healing whereas engraftment of multipotent mesenchymal stem cells on bone allograft improves healing and graft incorporation. These studies provide rationale for fabrication of a biomimetic periosteum substitute that could fit bone of any size and shape for enhanced allograft healing and repair. The success of such an approach will depend on further understanding of the molecular signals that control inflammation, cellular recruitment as well as mesenchymal stem cell differentiation and expansion during the early phase of the repair process. It will also depend on multidisciplinary collaborations between biologists, material scientists and bioengineers to address issues of material selection and modification, biological and biomechanical parameters for functional evaluation of bone allograft healing.

Material Properties of Fresh Cold-stored Allografts for Osteochondral Defects at 1 Year

Anil S. Ranawat MD, Armando F. Vidal MD, Chris T. Chen PhD, Jonathan A. Zelken BA, A. Simon Turner BVSc, Riley J. Williams MD 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°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.

Mechanoactive Scaffold Induces Tendon Remodeling and Expression of Fibrocartilage Markers

Jeffrey P. Spalazzi MS, Moira C. Vyner, Matthew T. Jacobs MS, Kristen L. Moffat MS, Helen H. Lu PhD Biological fixation of soft tissue-based grafts for anterior cruciate ligament (ACL) reconstruction poses a major clinical challenge. The ACL integrates with subchondral bone through a fibrocartilage enthesis, which serves to minimize stress concentrations and enables load transfer between two distinct tissue types. Functional integration thus requires the reestablishment of this fibrocartilage interface on reconstructed ACL grafts. We designed and characterized a novel mechanoactive scaffold based on a composite of poly-α-hydroxyester nanofibers and sintered microspheres; we then used the scaffold to test the hypothesis that scaffold-induced compression of tendon grafts would result in matrix remodeling and the expression of fibrocartilage interface-related markers. Histology coupled with confocal microscopy and biochemical assays were used to evaluate the effects of scaffold-induced compression on tendon matrix collagen distribution, cellularity, proteoglycan content, and gene expression over a 2-week period. Scaffold contraction resulted in over 15% compression of the patellar tendon graft and upregulated the expression of fibrocartilage-related markers such as Type II collagen, aggrecan, and transforming growth factor-β3 (TGF-β3). Additionally, proteoglycan content was higher in the compressed tendon group after 1 day. The data suggest the potential of a mechanoactive scaffold to promote the formation of an anatomic fibrocartilage enthesis on tendon-based ACL reconstruction grafts.

Chondrocyte Apoptosis: Implications for Osteochondral Allograft Transplantation

Hubert T. Kim MD, PhD, Margie S. Teng BS, Alexis C. Dang MD Osteochondral allograft transplantation is a useful technique to manage larger articular cartilage injuries. One factor that may compromise the effectiveness of this procedure is chondrocyte cell death that occurs during the storage, preparation, and implantation of the osteochondral grafts. Loss of viable chondrocytes may negatively affect osteochondral edge integration and long-term function. A better understanding of the mechanisms responsible for chondrocyte loss could lead to interventions designed to decrease cell death and improve results. Recent studies indicate that apoptosis, or programmed cell death, is responsible for much of the chondrocyte death associated with osteochondral allograft transplantation. Theoretically, some of these cells can be rescued by blocking important apoptotic mediators. We review the role of apoptosis in cartilage degeneration, focusing on apoptosis associated with osteochondral transplantation. We also review the pathways thought to be responsible for regulating chondrocyte apoptosis, as well as experiments testing inhibitors of the apoptotic pathway. These data suggest that key contributors to the apoptotic process can be manipulated to enhance chondrocyte survival. This knowledge may lead to better surgical outcomes for osteochondral transplantation.

Allograft Reconstruction After Sarcoma Resection in Children Younger Than 10 Years Old

D. Luis Muscolo MD, Miguel A. Ayerza MD, Luis Aponte-Tinao MD, German Farfalli Preservation of limb function in pediatric oncology patients is challenging with the ongoing growth of limbs contralateral to reconstructed limbs. We analyzed 22 patients younger than 10 years old who received an allograft after resection of a bone sarcoma with a minimum followup of 2 years (mean, 4 years; range, 2–14 years). The mean age was 7 years (range, 2–10 years). There were 16 boys and six girls with 17 osteosarcomas and five Ewing’s sarcomas. Thirteen reconstructions were performed with an intercalary allograft and nine with an osteoarticular allograft. Physes were uninvolved in five patients and one physis in 17. We documented outcomes using the Musculoskeletal Tumor Society functional and the International Society of Limb Salvage radiographic scoring systems. At last followup, three of the 22 patients died of their tumor, one was alive but with an amputation, and 18 retained their limbs. These 18 patients had an average functional score of 27 points and a mean radiographic score of 94%. Eight complications required a second surgery; in four, the allograft was removed (one infection, one local recurrence, two fractures) and in four, the allograft was preserved (two local recurrences, one fracture, one nonunion). We consider biologic reconstruction with allografts after sarcoma resection an appropriate reconstructive procedure in young children.,[object Object]

Enhancing Osteochondral Allograft Viability: Effects of Storage Media Composition

Margie S. Teng BS, Audrey S. Yuen BS, Hubert T. Kim MD, PhD Osteochondral allograft transplantation is a well-accepted treatment for articular cartilage damage. However, chondrocyte viability declines during graft storage, which may compromise graft performance. We first tested the hypothesis that the composition of commonly used storage media affects the viability of articular chondrocytes over time; we then tested the hypothesis that the addition of insulin growth factor-1 or the apoptosis inhibitor ZVAD-fmk could enhance the storage properties of serum-free media. Bovine osteochondral grafts were stored at 4°C in lactated Ringer’s, Dulbecco’s modified eagle’s media (DMEM), DMEM supplemented with either insulin growth factor-1 or ZVAD-fmk, and a commercial storage media. Chondrocyte viability in lactated Ringer’s declined rapidly to 20.4% at 2 weeks. Viability in DMEM declined more slowly to 54.8% at 2 weeks and 31.2% at 3 weeks. Viability in commercial storage media was 83.6% at 3 weeks and 44.8% at 4 weeks. Viability was increased in DMEM + insulin growth factor-1 (56.4%) and DMEM + ZVAD (52.4%) at 3 weeks compared with DMEM alone. These results confirm the hypotheses that media composition greatly influences chondrocyte viability during cold storage and that insulin growth factor-1 and ZVAD improve the storage properties of DMEM.

Radioprotection of Tendon Tissue via Crosslinking and Free Radical Scavenging

Aaron Seto MS, Charles J. Gatt MD, Michael G. Dunn PhD Ionizing radiation could supplement tissue bank screening to further reduce the probability of diseases transmitted by allografts if denaturation effects can be minimized. It is important, however, such sterilization procedures be nondetrimental to tissues. We compared crosslinking and free radical scavenging potential methods to accomplish this task in tendon tissue. In addition, two forms of ionizing irradiation, gamma and electron beam (e-beam), were also compared. Crosslinkers included 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and glucose, which were used to add exogenous crosslinks to collagen. Free radical scavengers included mannitol, ascorbate, and riboflavin. Radioprotective effects were assessed through tensile testing and collagenase resistance testing after irradiation at 25 kGy and 50 kGy. Gamma and e-beam irradiation produced similar degenerative effects. Crosslinkers had the highest strength at 50 kGy, EDC treated tendons had 54% and 49% higher strength than untreated, for gamma and e-beam irradiation respectively. Free radical scavengers showed protective effects up to 25 kGy, especially for ascorbate and riboflavin. Crosslinked samples had higher resistance to collagenase and over a wider dose range than scavenger-treated. Of the options studied, the data suggest EDC precrosslinking or glucose treatment provides the best maintenance of native tendon properties after exposure to ionizing irradiation.

The Effects of GDF-5 and Uniaxial Strain on Mesenchymal Stem Cells in 3-D Culture

Eugene Farng MD, Alfonso R. Urdaneta BS, David Barba BS, Sean Esmende BS, David R. McAllister MD Recent endeavors in tissue engineering have attempted to identify the optimal parameters to create an artificial ligament. Both mechanical and biochemical stimulation have been used by others to independently modulate growth and differentiation, although few studies have explored their interactions. We applied previously described fabrication techniques to create a highly porous (90%–95% porosity, 212–300 μm), 3-D, bioabsorbable polymer scaffold (polycaprolactone). Scaffolds were coated with bovine collagen, and growth and differentiation factor 5 (GDF-5) was added to half of the scaffolds. Scaffolds were seeded with mesenchymal stem cells and cultured in a custom bioreactor under static or cyclic strain (10% strain, 0.33 Hz) conditions. After 48 hours, both mechanical stimulation and GDF-5 increased mRNA production of collagen I, II, and scleraxis compared to control; tenascin C production was not increased. Combining stimuli did not change gene expression; however, cellular metabolism was 1.7 times higher in scaffolds treated with both stimuli. We successfully grew a line of mesenchymal stem cells in 3-D culture, and our initial data indicate mechanical stimulation and GDF-5 influenced cellular activity and mRNA production; we did not, however, observe additive synergism with the mechanical and biological stimuli.

Gene Therapy to Enhance Allograft Incorporation After Host Tissue Irradiation

Brandon G. Santoni PhD, A. Simon Turner BVSc, MS, Diplomate ACVS, Donna L. Wheeler PhD, Richard W. Nicholas MD, Tom J. Anchordoquy PhD, Nicole Ehrhart VMD, MS, Diplomate ACVS Structural bone allografts are used to reconstruct large skeletal defects after tumor surgery. Although allograft-related complications are declining, the use of perioperative radiation therapy is associated with a poorer outcome. Recently, BMP-2 levels in the host bed were reportedly diminished after exposure to radiation doses consistent with those used perioperatively to treat musculoskeletal sarcoma. Reintroduction of this osteogenic protein may circumvent the deleterious effects of preoperative radiation on allograft incorporation. We introduced a novel polymeric BMP-2 gene delivery system into the host-allograft junctions at the time of transplantation in an ovine tibial defect model with or without preoperative exposure to 50 Gy radiation. After 4 months, we noted no radiographic or histologic improvements in allograft incorporation after preoperative radiation and BMP-2 reintroduction; however, 50 Gy radiation was associated with increased porosity in the interface regions and poorer radiographic healing. We identified no BMP2-expressing cells or protein in the interface at the study end point, suggesting the polymeric gene delivery system was unable to promote extended expression of the protein or induce a healing response. Although gene therapy may hold promise as a novel technique to improve allograft incorporation, our data do not support that contention with the current approach.

Imaging Analysis of the In vivo Bioreactor: A Preliminary Study

Ginger E. Holt MD, Jennifer L. Halpern MD, Conor C. Lynch PhD, Clinton J. Devin MD, Herbert S. Schwartz MD The in vivo bioreactor is a hermetically sealed, acellular hydroxyapatite scaffold coated with growth factors that has a pulsating vascular pedicle leash threaded through its center. Tissue-engineered bone is created in weeks while the bioreactor remains embedded under the skin of an animal. The bioreactor also provides a model to study osteogenesis and pathologic scenarios such as tumor progression and metastasis by creating a controlled microenvironment that makes skeletogenesis amenable to genetic and physical manipulation. Animal euthanasia is required to quantitate bioreactor osteogenesis through histomorphometry. Nondestructive measures of new bone growth within the bioreactor are critical to future applications and are the primary questions posed in this study. We compared microcomputed tomography and micro-MRI assessments of bioreactor osteogenesis with conventional histomorphometric measurements in 24 bioreactors and asked if new bone formation could be calculated while the animal was alive. Microcomputed tomography visually, but not numerically, differentiated engineered new bone on its coral scaffold. Dynamic contrast-enhanced micro-MRI demonstrated augmented vascular flow through the bioreactor. Three-dimensional imaging can nondestructively detect tissue-engineered osteogenesis within the implanted bioreactor in vivo, furthering the usefulness of this unique model system.

HLA Sensitization and Allograft Bone Graft Incorporation

William G. Ward MD, Michael D. Gautreaux PhD, Dylan C. Lippert MS, Carol Boles MD Achieving union between host bone and massive structural allografts can be difficult. Donor and recipient human leukocyte antigen (HLA) mismatches and recipient antibody response to donor HLA antigens might affect union. In a prospective multiinstitutional study, we enrolled a consecutive series of patients receiving cortex-replacing, massive structural bone allografts to determine the rate of donor-specific HLA antibody sensitization and to investigate the potential effect of such HLA alloantibody sensitization on allograft incorporation. HLA typing of patients and donors was determined by molecular typing methods. Donor-specific HLA sensitization occurred in 57% of the patients but had no demonstrable effect on graft incorporation or union. The type of host-allograft junction did have a major effect on graft incorporation. Cortical-to-cortical allograft-to-host junctions healed more slowly (mean, 542 days) than corticocancellous to corticocancellous allograft-to-host junctions (mean, 243 days). Although HLA sensitization does not appear to delay structural allograft bone incorporation, further followup is required to determine if there is an association between HLA sensitization and long-term graft survival. Based on these preliminary data, measures to further minimize or modulate HLA sensitization or response are not indicated at present for the purposes of improving structural bone allograft union.,[object Object]

Quantification of Massive Allograft Healing with Dynamic Contrast Enhanced-MRI and Cone Beam-CT: A Pilot Study

Nicole Ehrhart VMD, MS, Susan Kraft DVM, PhD, David Conover MS, Randy N. Rosier MD, PhD, Edward M. Schwarz PhD [object Object]

Shaped, Stratified, Scaffold-free Grafts for Articular Cartilage Defects

EunHee Han MS, Won C. Bae PhD, Nancy D. Hsieh-Bonassera MS, Van W. Wong BS, Barbara L. Schumacher BS, Simon Görtz MD, Koichi Masuda MD, William D. Bugbee MD, Robert L. Sah MD, ScD One goal of treatment for large articular cartilage defects is to restore the anatomic contour of the joint with tissue having a structure similar to native cartilage. Shaped and stratified cartilaginous tissue may be fabricated into a suitable graft to achieve such restoration. We asked if scaffold-free cartilaginous constructs, anatomically shaped and targeting spherically-shaped hips, can be created using a molding technique and if biomimetic stratification of the shaped constructs can be achieved with appropriate superficial and middle/deep zone chondrocyte subpopulations. The shaped, scaffold-free constructs were formed from the alginate-released bovine calf chondrocytes with shaping on one (saucer), two (cup), or neither (disk) surfaces. The saucer and cup constructs had shapes distinguishable quantitatively (radius of curvature of 5.5 ± 0.1 mm for saucer and 2.8 ± 0.1 mm for cup) and had no adverse effects on the glycosaminoglycan and collagen contents and their distribution in the constructs as assessed by biochemical assays and histology, respectively. Biomimetic stratification of chondrocyte subpopulations in saucer- and cup-shaped constructs was confirmed and quantified using fluorescence microscopy and image analysis. This shaping method, combined with biomimetic stratification, has the potential to create anatomically contoured large cartilaginous constructs.

Controlled Release of Growth Factors on Allograft Bone in vitro

Zhinong Huang PhD, MD, WonHyoung Ryu PhD, Peigen Ren PhD, Rainer Fasching PhD, Stuart B. Goodman MD, PhD Allografts are important alternatives to autografts for treating defects after major bone loss. Bone growth factors have both local autocrine and paracrine effects and regulate the growth, proliferation, and differentiation of osteoprogenitor cells. To study the effects of prolonged, continuous, local delivery of growth factors on bone growth, we developed a new microelectromechanical system (MEMS) drug delivery device. Bone marrow cells from mice were seeded on mouse allograft discs and cultured in osteogenic media with osteogenic protein 1 (OP-1) and/or basic fibroblast growth factor (FGF-2) delivered from MEMS devices for 6 weeks. We monitored bone formation by changes of bone volume using micro-CT scanning and release of osteocalcin using ELISA. The data suggest the MEMS devices delivered constant concentrations of OP-1 and FGF-2 to the media. Bone marrow cells grew on the allografts and increased bone volume. Addition of OP-1 increased bone formation whereas FGF-2 decreased bone formation. Local delivery of growth factors over a prolonged period modulated the differentiation of osteoprogenitor cells on allograft bone.

Remodeling of ACL Allografts is Inhibited by Peracetic Acid Sterilization

Sven U. Scheffler MD, Johannes Gonnermann CMD, Julia Kamp CMD, Dorothea Przybilla, Axel Pruss MD Sterilization of allografts for anterior cruciate ligament (ACL) reconstruction has become an important prerequisite to prevent disease transmission. However, current sterilization techniques impair the biological or mechanical properties of such treated grafts. Peracetic acid (PAA) has been successfully used to sterilize bone allografts without these disadvantages and does not impair the mechanical properties of soft tissue grafts in vitro. We asked whether PAA sterilization would influence recellularization, restoration of crimp length and pattern, and revascularization of ACL grafts during early healing. We used an in vivo sheep model for open ACL reconstruction. We also correlated the histologic findings with the restoration of anteroposterior stability and structural properties during load-to-failure testing. PAA slowed remodeling activity at 6 and 12 weeks compared to nonsterilized allografts and autografts. The mechanical properties of PAA grafts were also reduced compared to these control groups at both time points. We conclude PAA sterilization currently should not be used to sterilize soft tissue grafts typically used in ACL reconstruction.

Radioprotectant and Radiosensitizer Effects on Sterility of γ-irradiated Bone

Seema A. Kattaya MS, Ozan Akkus PhD, James Slama PhD Gamma radiation is widely used to sterilize bone allografts but may impair their strength. While radioprotectant use may reduce radiation damage they may compromise sterility by protecting pathogens. We assessed the radioprotective potential of various agents (L-cysteine, N-acetyl-L-cysteine, L-cysteine-ethyl-ester and L-cysteine-methyl-ester) to identify those which do not protect spores of Bacillus subtilis. We hypothesized charge of these agents will affect their ability to radioprotect spores. We also determined ability of these radioprotectants and a radiosensitizer (nitroimidazole-linked phenanthridinium) to selectively sensitize spores to radiation damage by intercalating into the nucleic acid of spores. Spores were treated either directly in solutions of these agents or treated after being embedded and sealed in bone to assess the ability of these agents to diffuse into bone. L-cysteine and L-cysteine-ethyl-ester did not provide radioprotection. Positively charged L-cysteine-methyl-ester protected the spores, whereas positively charged L-cysteine-ethyl-ester did not, indicating charge does not determine the extent of radioprotection. The spores were sensitized to radiation damage when irradiated in nitroimidazole-linked phenanthridinium solution and sensitization disappeared after rinsing, suggesting nitroimidazole-linked phenanthridinium was unable to intercalate into the nucleic acid of the spores. Some cysteine-derived radioprotectants do not shield bacterial spores against gamma radiation and may be suitable for curbing the radiation damage to bone grafts while achieving sterility.

Fresh Osteochondral Allografts for Posttraumatic Knee Defects: Long-term Followup

A. E. Gross MD, FRCSC, O.Ont, W. Kim MD, F. Las Heras MD, D. Backstein D, MD, MEd, FRCSC, O. Safir MD, FRCSC, K. P. H. Pritzker MD, FRCPC Fresh osteochondral allograft transplantation has been an effective treatment option with promising long-term clinical outcomes for focal posttraumatic defects in the knee for young, active individuals. We examined histologic features of 35 fresh osteochondral allograft specimens retrieved at the time of subsequent graft revision, osteotomy, or TKA. Graft survival time ranged from 1 to 25 years based on their time to reoperation. Histologic features of early graft failures were lack of chondrocyte viability and loss of matrix cationic staining. Histologic features of late graft failures were fracture through the graft, active and incomplete remodeling of the graft bone by the host bone, and resorption of the graft tissue by synovial inflammatory activity at graft edges. Histologic features associated with long-term allograft survival included viable chondrocytes, functional preservation of matrix, and complete replacement of the graft bone with the host bone. Given chondrocyte viability, long-term allograft survival depends on graft stability by rigid fixation of host bone to graft bone. With the stable osseous graft base, the hyaline cartilage portion of the allograft can survive and function for 25 years or more.

Bisphosphonate Delivery to Tubular Bone Allografts

Gene R. DiResta PhD, Mark W. Manoso MD, Anwar Naqvi MS, Pat Zanzonico PhD, Peter Smith-Jones PhD, Wakenda Tyler MD, Carol Morris MD, John H. Healey MD Large structural allografts used for reconstruction of bone defects after revision arthroplasty and tumor resection fracture up to 27% of the time from osteolytic resorption around the fixation screw holes and tendon or ligament attachment sites. Treating structural allografts before implantation with bisphosphonates may inhibit local osteoclastic processes and prevent bone resorption and the development of stress risers, thereby reducing the long-term fracture rate. Taking advantage of allografts’ open-pore structure, we asked whether passive soaking or positive-pressure pumping was a more efficient technique for delivering bisphosphonates. We treated matched pairs of ovine tibial allografts with fluids containing Tc-99m pamidronate and toluidine blue stain to facilitate indicator distribution analysis via microSPECT-microCT imaging and light microscopy, respectively. Surfactants octylphenoxy polyethoxy ethanol or beractant were added to the treatment fluids to reduce flow resistance of solutions pumped through the allografts. Indicator distribution after 1 hour of soaking produced a thin ring around periosteal and endosteal surfaces, while pumping for 10 minutes produced a more even distribution throughout the allograft. Flow resistance was reduced with octylphenoxy polyethoxy ethanol but unaffected with beractant. Pumped allografts displayed a more homogeneous indicator distribution in less time than soaking while surfactants enhanced fluid movement.