Gamma irradiation: effects on biomechanical properties of human bone-patellar tendon-bone allografts

Development of cell-seeded patellar tendon allografts for anterior cruciate ligament reconstruction

Patellar tendon (PT) allografts for anterior cruciate ligament (ACL) reconstruction are potentially immunogenic and incorporate slowly compared with autografts. Our tissue-engineering approach to improve allograft efficacy is to (1) remove intrinsic cells from the graft to reduce antigenicity and then (2) seed the graft with extrinsic cells to improve ligamentization. To remove cells, tendons were soaked in 1% extraction solutions of tri(n-butyl)phosphate (TBP) or sodium dodecyl sulfate (SDS) for various time periods (24-72 h) and rinsed exhaustively. After treatment, we measured tendon cellularity, crimp structure, and mechanical properties. Treatment with either SDS or TBP removed approximately 70-90% of the intrinsic PT cells. Mechanical properties of treated PTs were similar to those of controls, despite changes in appearance. TBP- and SDS-treated PTs were then seeded with fibroblasts and cultured for up to 2 weeks in vitro. Fibroblast proliferation was retarded on SDS-treated PTs; in contrast, TBP-treated PTs supported cell proliferation similar to that of untreated controls. Extrinsic fibroblasts were successfully cultured on the TBP-treated PTs in vitro, creating viable tissue-engineered grafts potentially useful for ACL reconstruction. These modified allografts have the potential to be developed into mechanically functional delivery vehicles for cells, gene therapy vectors, or other biological agents.

Primary anterior cruciate ligament reconstruction using fresh-frozen, nonirradiated patellar tendon allograft: minimum 2-year follow-up

BACKGROUND

There are conflicting reports of allograft performance, immune response, tissue incorporation, and rerupture rates when used for anterior cruciate ligament reconstruction.

PURPOSE

To evaluate the clinical outcome of a fresh-frozen, nonirradiated, patellar tendon allograft for primary anterior cruciate ligament reconstruction surgery.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Patients who underwent endoscopic primary anterior cruciate ligament reconstruction with allograft tissue a minimum of 2 years ago were evaluated with physical examinations, the KT-1000 arthrometer, functional testing, radiographic evaluation, subjective assessment, and outcomes tools.

RESULTS

Fifty-nine patients (60 knees) were evaluated at an average of 51 months after surgery. Ninety-four percent of patients were mostly or completely satisfied. A negative pivot shift test result was noted in 90% of subjects. The KT-1000 arthrometer side-to-side differences were < or =3 mm in 95% of patients, and no patient exceeded 5 mm. The mean International Knee Documentation Committee score was 78 (SD = 19), and the mean Lysholm score was 82 (SD = 17). There were no clinical symptoms consistent with graft rejection or infection. Radiographic evaluation demonstrated infrequent significant tunnel widening.

CONCLUSIONS

Use of a fresh-frozen, nonirradiated allograft for primary reconstruction of the anterior cruciate ligament is a successful procedure both subjectively and functionally for restoring stability in patients selected for allograft reconstruction. In the patients selected for this surgical procedure, clinical, arthrometric stability testing, and subjective satisfaction were comparable to our previously published cohort studies using patellar tendon autograft at similar postoperative follow-up.

Viruses adsorbed on musculoskeletal allografts are inactivated by terminal ethylene oxide disinfection

In 1987 it was anticipated that unsterilized tissues would transmit virus diseases such as hepatitis and HIV-1 from infected donors so a freeze-drying process for musculoskeletal tissue was developed to include terminal ethylene oxide (EO) exposure for 14 h. We found no studies of EO efficacy when viruses were associated with human allografts so we studied the antiviral effect of terminal EO disinfection using all but the final freeze-drying phase of this clinical processing protocol (CPP). Specifically we looked at EO inactivation of HIV-1, a human hepatitis B surrogate and test viruses known to be highly resistant to disinfecting agents, including irradiation. Freeze-drying, ordinarily required after EO disinfection and part of the CPP, was not done. Suspensions of HIV-1, Bovine viral diarrhea, Reovirus type 3, Duck hepatitis B, Poliomyelitis and Canine parvovirus were adsorbed on glass, demineralized bone powder, and preprocessed strips of femoral cortex, iliac wedges, cancellous blocks and patellar bone-tendon-bone preparations and subjected to EO disinfection. Test viruses were inactivated at the end of 7 h of EO disinfection, providing a safety factor in the CPP of at least 100%. Because allografts can transmit viruses, terminal EO disinfection should provide safer musculoskeletal allografts than non-disinfected tissues or those irradiated with a standard irradiation dose. New spontaneously appearing viruses would probably be inactivated with this terminal EO disinfection but they and viral bioweapons will require individual validation to assure viral inactivation.

Clostridium infections associated with musculoskeletal-tissue allografts

BACKGROUND

Allografts are commonly used in orthopedic reconstructive surgery. In 2001, approximately 875,000 musculoskeletal allografts were distributed by U.S. tissue banks. After the death from Clostridium sordellii sepsis of a 23-year-old man who had received a contaminated allograft from a tissue bank (Tissue Bank A), the Centers for Disease Control and Prevention initiated an investigation, including enhanced case finding, of the methods used for the recovery, processing, and testing of tissue.

METHODS

A case of allograft-associated clostridium infection was defined as a culture-proven infection of a surgical site within one year after allograft implantation, from January 1998 to March 2002. We traced tissues to tissue banks that recovered and processed these tissues. We also estimated the rates of and risk ratios for clostridium infections for tissues processed by the implicated tissue bank and reviewed processing and testing methods used by various tissue banks.

RESULTS

Fourteen patients were identified, all of whom had received allografts processed by Tissue Bank A. The rates of clostridium infection were 0.12 percent among patients who received sports-medicine tissues (i.e., tendons, femoral condyles, menisci) from Tissue Bank A and 0.36 percent among those who received femoral condyles in particular. The risk-ratio estimates for clostridium infections from tissues processed by Tissue Bank A, as compared with those from other tissue banks, were infinite (P<0.001) for musculoskeletal allografts, sports-medicine tissues, or tendons. Because Tissue Bank A cultured tissues only after treating them with a nonsporicidal antimicrobial solution, some test results were probably false negatives. Tissues from implicated donors were released despite the isolation of clostridium or bowel flora from other anatomical sites or reports of infections in other recipients.

CONCLUSIONS

Clostridium infections were traced to allograft implantation. We provide interim recommendations to enhance tissue-transplantation safety. Tissue banks should validate processes and culture methods. Sterilization methods that do not adversely affect the functioning of transplanted tissue are needed to prevent allograft-related infections.

Bone and tissue allograft use by orthopaedic surgeons

The purpose of our study was to determine the involvement of orthopaedic surgeons in the process of acquiring allografts they transplant. A questionnaire regarding allograft acquisition and use was directed to 340 hospitals. In approximately 85% of the institutions, nonorthopaedic personnel selected and acquired the allografts. In most, those responsible for providing surgeons with allografts had little or no knowledge of the practices of tissue banking and allograft transplantation biology. In about 15% of the hospitals, the surgeon was involved in the selection of the source of allografts. It is imperative that orthopaedic surgeons who transplant bone and tissue allografts become actively involved in determining the source and processing of tissue transplants they place in their patients.

The biomechanical effects of low-dose irradiation on bone-patellar tendon-bone allografts

BACKGROUND

Despite evidence that low-dose irradiation of 2 Mrad (20 kGy) is not virucidal for patellar tendon allografts and reduces tissue strength, many tissue bank protocols include low-dose irradiation.

HYPOTHESIS

Maintaining tissue mechanical integrity may be particularly relevant toward accelerated rehabilitation of the injured knee, where the cyclic function of patellar tendon allografts is critical.

STUDY DESIGN

Controlled laboratory study.

METHODS

The cyclic and failure mechanical properties of paired bone-patellar tendon-bone allografts, with and without current low-dose irradiation of 20 kGy, were evaluated. Specimens were loaded from 50 N to 250 N for 1000 cycles at 0.5 Hz and subsequently loaded to failure at a strain rate of 100% per second.

RESULTS

After 1000 cycles, grafts elongated 27% more when irradiated than when not (4.4 +/- 1.5 mm vs 3.4 +/- 1.0 mm; P = .03). Failure load averaged 1965 +/- 512 N for irradiated grafts and 2457 +/- 647 N for nonirradiated grafts (P = .007).

CONCLUSIONS

The diminished strength of irradiated grafts may contribute to overt anterior cruciate ligament graft failure, and the increase in cyclic elongation may also be detrimental to graft function.

CLINICAL RELEVANCE

These results suggest that one should consider the use of nonirradiated allografts as an alternative to irradiated grafts in anterior cruciate ligament reconstruction.

Lyophilization does not inactivate infectious retrovirus in systemically infected bone and tendon allografts

BACKGROUND

A review of multiple transplantations of human immunodeficiency virus-infected musculoskeletal allografts found that recipients of lyophilized (freeze-dried) bone or tendon from an infected donor all tested negative for human immunodeficiency virus. The finding that 75% of the recipients of fresh-frozen bone from the same donor contracted human immunodeficiency virus has led to speculation that freeze-drying may render retroviral-infected musculoskeletal allografts noninfectious.

HYPOTHESIS

Lyophilization does not inactivate retrovirus in systemically infected bone and tendon.

STUDY DESIGN

Controlled laboratory study.

METHODS

Tendons and cortical bone segments from cats systemically infected with feline leukemia virus were used in this study. Feline embryonic fibroblast cells were cultured in the presence of fresh-frozen or freeze-dried cortical bone or tendon segments. At each passage, feline leukemia virus p27 antigen was measured in media by enzyme-linked immunosorbent assay, and feline leukemia virus (pro)viral nucleic acids were quantified by real-time quantitative polymerase chain reaction in the DNA extracted from cells.

RESULTS

Enzyme-linked immunosorbent assay results and quantitative polymerase chain reaction results demonstrated retroviral antigen and proviral DNA in all cultured cell replicates after exposure to fresh-frozen or freeze-dried bones or tendons.

CONCLUSION

Freeze-drying (lyophilization) of retroviral-infected cortical bone and tendon does not inactivate retrovirus.

CLINICAL RELEVANCE

These results conclusively demonstrate that freeze-drying should not be relied on to inactivate infectious retrovirus in systemically infected musculoskeletal allografts.

Cefuroxime, rifampicin and pulse lavage in decontamination of allograft bone

The risk of bacterial infection through allogenic bone transplantation is one of the major problems facing tissue banks. Different screening methods and decontamination procedures are being used to achieve a safe surgical result. The purpose of this study was to investigate the contamination rate in fresh frozen bone allografts after treating them with different decontamination methods. The allografts were contaminated by rubbing on the operating theatre floor for 60 min, after which they were rinsed either with sterile physiological saline, cefuroxime or rifampicin solution or they were washed with low-pressure pulse lavage of sterile physiological saline. Our findings show that low-pressure pulse lavage with sterile saline solution is very effective in removing bacteria from bone allograft, when compared with the antibiotic solutions tested.

The safe and effective use of allograft tissue--an update

The use of allograft tissue in orthopaedic surgery has increased tremendously over the last several years. Tissue availability, reduced surgical times, and lack of donor site morbidity are attractive characteristics to surgeons and patients alike. Although complications, such as disease transmission, are relatively uncommon when using allograft tissue, they do occur. This article will review the literature concerning the safe and effective use of allograft tissue, as well as present four case reports of Clostridium septicum infection caused by implantation of contaminated allograft tissue.

Anterior cruciate ligament reconstruction: allograft versus autograft

PURPOSE

This study was performed to compare the minimal 2-year outcome of anterior cruciate ligament (ACL) reconstruction using bone-patellar tendon-bone (BPTB) allografts versus autografts, both augmented with an iliotibial band tenodesis.

TYPE OF STUDY

Retrospective review.

METHODS

Forty-six of 52 BPTB ACL reconstructions using allografts and 33 of 37 BPTB ACL reconstructions using autografts were followed up at a mean of 2.75 and 3.36 years, respectively. All patients had an iliotibial band tenodesis. Evaluations included the Lysholm II scale, a questionnaire, physical examination findings, and KT-1000 arthrometry.

RESULTS

No statistically significant differences were seen between groups in Lysholm II scores or in any subjective category. Most patients (91% allograft; 97% autograft) had good to excellent Lysholm II scores. Sixty-five percent of allograft patients and 73% of autograft patients returned to their preinjury activity level. More allograft patients complained of retropatellar pain (16% v 9% for autograft patients). Fifty-three percent of allograft patients versus 23% of autograft patients had a flexion deficit of 5 degrees or more when compared with the normal contralateral side. When comparing KT-1000 side-to-side differences, we found no significant differences between groups. Ninety-one percent of both groups had maximum side-to-side differences less than 5 mm. Three allograft patients (6.5%) had traumatic ruptures at 12, 19, and 43 months postoperatively versus none in the autograft group. All three allograft patients who sustained postoperative traumatic ruptures had received fresh frozen, nonirradiated allografts.

CONCLUSIONS

Results of ACL reconstruction using allografts or autografts augmented with an iliotibial band tenodesis were comparable. The BPTB autograft should remain the gold standard, although the BPTB allograft in ACL reconstruction is a reasonable alternative.

Allograft transplantation in the knee: tissue regulation, procurement, processing, and sterilization

Use of musculoskeletal allografts has become increasingly popular, with widespread use among knee surgeons. The advantages and disadvantages of their use have been documented. In the knee, allografts are used for ligament reconstruction, meniscal transplantation, and articular surface reconstruction. The purpose of this review is to present issues surrounding the allograft industry, including regulation of tissues and tissue banks and procurement, processing, sterilization, and storage of allograft tissue. Tissue bank regulation is ultimately under the jurisdiction and authority of the Food and Drug Administration; some individual states regulate tissue banks. The American Association of Tissue Banks is a scientific organization that encourages education, research, and voluntary accreditation of tissue banks. It promotes safety and standards for retrieval, processing, storage, and distribution of transplantable human tissue. Allograft tissues are generally harvested and processed aseptically, which may not prevent contamination. Tissue sterilization is difficult and controversial. Tissue banks historically have used one of two methods of sterilization, ethylene oxide or gamma radiation. Both methods have risks and benefits. Newer methods of sterilization are being developed. Allograft tissue that is not transplanted fresh can be freeze-dried or deep frozen for storage. Ultimately, allograft transplantation in the knee facilitates knee form and function and enhances the patient's quality of life. Orthopaedic surgeons who use allograft tissue must understand the tissue banking process to provide safe and effective tissues to their patients.

Characterization of the mechanical properties of demineralized bone

Demineralized bone has had limited use as a medical implant, although, recently Jackson et al. (Am J Sports Med 1996;24(4):405-414) examined using demineralized bone as an anterior cruciate ligament (ACL) replacement and found that within 1 year the demineralized bone had remodeled from a haversian system (bone-like) into a ligament-like structure. Little research has been done to characterize the mechanical properties of demineralized bone and examine its potential as a ligament replacement. This research examined the mechanical properties of demineralized bone as a function of acid saturation time and methods of processing and sterilization using specimens from various anatomic locations. Bone specimens were manufactured from the tibia, metatarsus, femur, radius, and humerus of bovine bone. Tensile strength, strain, and modulus of elasticity were examined for various acid saturation times and sterilization treatments. Additionally, viscoelastic properties, creep and stress relaxation, and fatigue properties were examined. The findings indicate that completely demineralized bone has mechanical properties similar to the ACL and, therefore, has increased likelihood for success in ACL reconstruction surgery.

Donor cell survival and repopulation after intraarticular transplantation of tendon and ligament allografts

The specific cells within ligaments and tendons are important to maintain the unique structural and material properties of these tissues. The use of tendon and ligament allografts with living cells for ligament reconstruction would be desirable assuming that these cells would survive after transplantation and continue to function. We assessed the fate of donor cells in fresh allografts of the patellar and anterior cruciate ligaments after transplantation. The cells in these allografts used to reconstruct the anterior cruciate ligament did not survive. This was demonstrated using a DNA probe technique that clearly distinguished donor cells from host cells in the Spanish goat model. The donor cells were replaced by host cells in a rapid manner. The host cells that repopulated the allografts assumed the histologic similarity to the fibroblasts they replace. Simultaneous full-thickness skin transplants in the same animals were not rejected during the interval of rapid loss of donor DNA from the allografts. The absence of rejection of the skin grafts at the one-week interval suggests that no pre-existing antibody associated with an immune reaction was responsible for the rapid loss of DNA in the allografts. The clinical basis for utilizing intra-articular allografts with living donor cells needs further justification to account for their increased expense, more complicated surgical logistics, and higher potential risk of disease transmission.

The real contamination of femoral head allografts washed with pulse lavage

At the Tampere Bone Bank, all the discarded femoral heads from September 1997 to May 2000 were recultured. The grafts had been washed with pulse lavage at harvesting. 48 grafts had been discarded because of a positive culture and 85 with negative cultures because of positive or insufficient serological information. The femoral heads were split into halves, which were recultured as a whole in thioglycolate broth for 14 days. The contamination of previously culture positive and negative femoral heads did not differ. In only 2 cases did we find the same type of bacteria in the primary as in the new culture. Most of the primary contamination proved to be false positive. The real contamination seems to be very low, at least after pulse lavage washing of the femoral head.

Histologic analysis of the tibial bone tunnel after anterior cruciate ligament reconstruction using solvent-dried and gamma-irradiated fascia lata allograft

Anterior cruciate ligament (ACL) reconstruction using free tendon graft requires biologic fixation in the bone tunnel. This report describes the intratunnel histology retrieved from a 47-year-old woman who underwent high tibial osteotomy 17 months after ACL reconstruction using a hybrid graft (a solvent-dried and gamma-irradiated fascia lata allograft as a core wrapped with iliotibial autograft). The patient underwent revision because of pain resulting from osteoarthrotic change, and the graft appeared to be taut and healthy on second-look arthroscopy. The sample was taken from the site of the metaphyseal osteotomy site. Histologic examination of the samples was performed with a light microscope (H&E and Masson trichrome stain). Biologic fixation of the graft to the bone was evident from observation of collagen fiber continuities, resembling Sharpey fibers. Integration of the autograft and allograft seemed to have occurred; the junction between the allograft and the autograft could not be determined. However, there was a difference in ligamentization depending on location. In the peripheral region of the graft (the autograft region), the collagen fibers showed a distinct crimped pattern; the fibroblasts were arranged regularly along the major axis of the collagen fiber bundle. In the central part of the graft (the allograft region), remodeling seemed to be delayed. There were acellular, bubbly or myxoid degeneration areas in which the fiber bundles were less oriented and there was increased vascularity.

Gamma irradiation of HIV-1

The potential for transmission of human immunodeficiency virus (HIV) type 1 has created serious concern for the continued clinical use of bone and soft-tissue allografts. Tissue banks have employed 1.5-2.5 Mrad for sterilization of bone and tendon allografts, which, according to the current literature, approaches the level at which the tissue quality is adversely affected for implantation. Our working hypothesis was that gamma irradiation at increasing doses can proportionately inactivate HIV type 1. The objective of this study was to inactivate HIV type 1 by irradiation, as determined by its capacity to infect human T-lymphocytes and established cell lines in vitro. The replicative competence of HIV type 1 was also assessed by the presence of reverse transcriptase activity, enzyme-linked immunoadsorbent assay (ELISA), immunofluorescence assays for p24 viral core antigen, and the formation of syncytia induced by HIV type 1 in the cultures inoculated with irradiated virus. The results demonstrated the presence of active viral replication in previously noninfected cells in the supernatant samples that were exposed to as much as 5.0 Mrad. The data for the 10-Mrad sample were indeterminate due to cellular damage. These data suggest that gamma irradiation (1.5-2.5 Mrad) does not constitute a virucidal dose for HIV type 1. Current technologies for screening have greatly improved, and the surgeon should rely on tissue bank screening procedures and other methods of preparation rather than sterilization by gamma radiation techniques in choosing allograft material.

High-pressure saline washing of allografts reduces bacterial contamination

60 fresh-frozen bone allografts were contaminated on the operating room floor. No bacterial growth was detected in 5 of them after contamination. The remaining 55 grafts had positive bacterial cultures and were processed with three methods: soaking in saline, soaking in antibiotic solution or washing by high-pressure saline. After high-pressure lavage, the cultures were negative in three fourths of the contaminated allografts. The corresponding figures after soaking grafts in saline and antibiotic solution were one tenth and two tenths, respectively. High-pressure saline cleansing of allografts can be recommended because it improves safety by reducing the superficial bacterial bioburden.

Impaction allografting with cement for the management of femoral bone loss

Impaction allografting with cement is the only technique currently available which reverses the diminution of bone stock that occurs in a revision hip arthroplasty, and as such, has great potential. It is particularly appropriate in the younger patient, though older patients may also benefit from the technique. Although the short term results are encouraging, there is a need for further basic science research to determine the optimal graft material and prosthesis design. Refinements in surgical instrumentation and technique will continue to improve the predictability of the clinical result and expand the indications for this important addition to the available options in revision hip arthroplasty.

Collagen shortening. An experimental approach with heat

Decreasing joint laxity is a clinical goal of ligament reconstructions. This in vitro study examined the structural and histologic effects of heat shrinkage of human collagen. Two preliminary studies were performed to assess the effect of heat on fresh frozen human tendons obtained from a local tissue bank. As heat was applied to tissue in a saline solution, the percent shrinkage was plotted against temperature. A second study used a freebeam Nd:YAG laser to maximally shrink patellar tendons measuring percent shrinkage versus energy applied. Finally, the effects of 10% shrinkage of fresh frozen human patellar tendons were analyzed mechanically and histologically. Consistent tendon shrinkage curves were found with increasing temperatures in a saline solution. A sharp increase in shrinkage to approximately 70% of resting length was noted around 70 degrees C. Tendon shrinkage by laser induced heat was precise and dose related. Tensile testing of the tendons shortened 10% of their resting length showed a decrease in load to failure to approximately 1/3 compared with that of historical control specimens. Histologic sections showed a well demarcated site of diffuse denaturation and degeneration of collagenous elements. Normal collagen was present adjacent to these thermal changes. These experiments showed that collagen tissue can be shortened precisely by the application of heat. Future studies need to examine the in vivo biologic response of shortened collagen tissue with time, especially recollagenization, restoration of length, and the long term biomechanical effects.

Soft tissue for allograft reconstruction of the human knee: a survey of the American Association of Tissue Banks

With increasing use and availability of musculoskeletal soft tissue allografts, orthopaedic surgeons need current knowledge about allograft processing, costs, and availability. In conjunction with the American Association of Tissue Banks, a comprehensive survey consisting of specific questions on several topics in tissue banking was sent to 42 member banks or banks undergoing accreditation review that distribute musculoskeletal tissues. Donors came from organ procurement organizations, coroners' offices, hospital morgues, and donations; the average age of the donors was 35. Most of the 36 tissue banks responding to the questionnaire harvest patellar and Achilles tendons. Patellar tendon demand exceeded supply. Tissue processing was done by outside organizations approximately 50% of the time. Of the four types of tissue sterilization processes performed, gamma irradiation was the most common. Doses of sterilizing gamma irradiation varied from 1 to 3.5 mrad. The average approximate costs of fresh-frozen tissue were $800 for patellar tendon allograft, $615 for Achilles tendon, and $640 for menisci. There was no consensus of opinion of how to size or sterilize meniscal allografts. As demand increases for soft tissue allografts, it is essential that the orthopaedic surgeon is knowledgeable about the clinical impact of tissue banking.