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Allografts

Allograft Tissues

  • The aggregate risk of disease transmission with allogeneic tissue is a reflection of the rigor of the screening and testing of potential donors and the kind of allogeneic tissue that is transplanted.
  • Pathogens of principal concern: HIV, hepatitis B and C.
  • Detection of viral disease in potential donors is limited by an initial period of viremia were the donor may have infection but viral levels, or antibody levels not yet high enough to be detected by blood tests.
  • By AATB standards serologic testing is done for hepatitis B surface antigen, hepatitis B core antibody, hepatitis C antibody, syphilis, human T-lymphotrophic virus-1 antibody, HIV I and II antibodies, and HIV P24 antigen.
  • MTF allograft screening: All tissue and blood samples are tested for infectious diseases, including testing for AIDS with Nucleic Acid Testing (NAT by TMA), HCV, HIV-1, HIV-2, HTLV-I, HTLV-II, HB Core, RPR, HCV-Ab, HBs Ag, HIV-1 NAT, HCV-NAT.
  • The only documented incidents of disease transmission involved frozen, unprocessed grafts such as patellar tendons or femoral heads (which are particularly
    at risk because of the presence of marrow contents)
  • Risk of viral transmission for tissue obtained under AATB guidelines: processed freeze-dried bone chips = @0: frozen, unprocessed femoral head =1 in 1 million.
  • Allografts and autografts undergo a similar remodeling process, but allograft tissues remodel at a slower rate and be compromised by an immunoligic host responce.

Allograft Bone or Tendon Risks

  • Viral infection: 1/1,000,000
  • Bacterial infection:
  • Immunologic reaction: Generally limited to graft resorption / failure.
  • search AATB for Safety info for patients.

Allograft Preparation

  • Cryopreservation: cellular water is removed with dimethyl sulfoxide or glyceral followed by controlled rate freezing to prevent ice cyrstal formation.
  • Freeze-drying: tissue water is replaced with alcohol to a moisture level of 5%, then alcohol is removed under vacuum.
  • Fresh-Frozen: tissue is frozen twice and packaged without solution to -80° C.
  • Fresh: not frozen, maintains maximum cellular viability.

ACL Allografts

  • Allograft quadriceps, patellar, Achilles, hamstring, and anterior and posterior tibialis tendons.
  • Sterilization: ethylene oxide or gamma irradiation can reduce risk of infection, but may weaken grafts. Low-dose (1.0 Mrad-1.2 Mrad) gamma irradiation of bone-patellar-tendon-allograft has been shown to produce a 20% decrease in graft stiffness.  Gamma irradiation doses >3.0 Mrad are necessary to kill viruses.
  • Preservation: Structural properties of deep-frozen (-80°C) or freeze-dried grafts are not significantly different from those of fresh grafts.
  • Immunologic response: Remains debatable. Donor-specific antibodies have been found in synovial fluid and serum of patiens with fresh-frozen BTB allografts, but have not been associated with any clinical abnormalities or obvious alterations in graft incorporation.
  • Most common sterilization technique: aseptic harvest and cleaning process consisting of antibiotic soaks, multiple cultures, and low-dose radiation (<3.0 Mrad).  Deep freezing or cleansing with 4% chlorhexidine gluconate does not adversely affect allograft biomechanical properties.  

Allograft Review References

  • Stevenson S, in Ortho Basic Science pg 567
  • Shelton WR, JAAOS 1998;6:165
  • Shelton WR, JAAOS 1998;6:169
  • American Association of Tissue Banks
  • FDA guidelines
  • Sobel AD, Hohman D, Jones J, Bisson LJ. Chlorhexidine gluconate cleansing has no effect on the structural properties of human patellar tendon allografts. Arthroscopy. 2012 Dec;28(12):1862-6