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- Discussion of Allografts:
    - see autograft menu and bone healing
    - allografts are most indicated when bone grafting is required along with need for mechanical structural support;
    - morselized bone graft:
    - structural bone grafts: 

    - fresh allografts
           - generally cause an unacceptable host immune reaction;
           - allografts may have major or minor histocompatibility mismatch;
                 - major mismatches will have more extreme immune reactions and associated graft resorption;
                 - major mismatches are associated w/ host antibody formation;
    - freezing allografts to below 60 deg Celsius;
           - will decrease immune response and will decrease the graft dedgradation by the host (changes are most evident w/ a major mismatch);
           - freezing markedly retards graft incorporation for both autogenous and allogenic grafts;
                 - w/ minor mismatches, freezing retards graft incorporation;
                 - w/ major mismatches, however, freezing actually increases graft incorporation (most likely, the reduced immune response caused
                          by freezing is more important than the negative effects of freezing on graft incorporation;)
           - biomechanical properties are only slightly affected by freezing;
    - freeze-drying
           - significantly reduces the immunogenic response;
           - significantly reduces biomechanical strength of the graft;
    - gamma sterilization:
           - 25,000 gray will sterilize HIV in liquid cultures;
           - 30,000 to 40,000 is necessary for sterilization of HIV in bone;
           - there is some concern about the effects of gamma sterilization on the biomechanical properities of the allograft;
                   - in order to avoid free radical formation, some authors advocate sterization in an argon environment;
           - in the report by Hammer AJ, et al. (1999), the authors found that bone irradiated at -78 celcius was less brittle and had less
                   collagen damage than bone irradiated at room temperature. 
           - elimination of HIV with gamma irradiation requires doses greater than 3.5 megarads, but levels of 4 megarads alter the mechanical
                   properties of human infrapatellar tendons;
           - references:
                   - Massive allografts sterilised by irradiation. Clinical results.
                   - Sterilisation of canine anterior cruciate allografts by gamma irradiation in argon. Mechanical and neurohistological properties retained one year after transplantation. 
                   - Changes in allograft bone irradiated at different temperatures.   
                   - Radiosensitivity of HIV-1--potential application to sterilization of bone allografts.  
                   - The effects of 4 Mrad of gamma irradiation on the initial mechanical properties of bone-patellar tendon-bone grafts
                   - Effective use of optimized, high-dose (50 kGy) gamma irradiation for pathogen inactivation of human bone allografts.
                   - Gamma irradiation of HIV-1.
                   - Sterilization of allograft bone: is 25 kGy the gold standard for gamma irradiation?

    - ethylene sterilization:
           - associated w/ unacceptable host reaction;
    - methods to enhance incorporation:
           - in the report by Delloye C, et al, the authors evaluated the effect of cortical perforation on graft incorporation using a sheep model;
                    - periosteal callus was similar in both groups, whereas endosteal callus was significantly more wide and extended in the perforated allografts;
    - references:
           - Tissue-typing in human massive allografts of frozen bone.
           - Histological characteristics of acute rejection in vascularized allografts of bone.
           - Perforations of Cortical Bone Allografts Improve Their Incorporation.

- Complications of Use:
    - generally 1/3 of patients who will require an allograft will have a complication;
    - infection:
          - risks of post operative infection is approximately 10-15%; 
          - always check an intraoperative allograft culture prior to graft usage;
          - references:
                 - Infection in bone allografts. Incidence, nature, and treatment.
                 - Frozen musculoskeletal allografts. A study of the clinical incidence and causes of infection associated with their use.
                 - Infection of massive bone allografts
                       - Invasive group-A streptococcal infection in an allograft recipient. A case report.
                 - Frozen cancellous bone allografts: positive cultures of implanted grafts in posterior fusions of the spine.
                 - Positive culture in allograft ACL-reconstruction: what to do? 
                 - Transmission of Elizabethkingia meningoseptica (formerly Chryseobacterium meningosepticum) to tissue-allograft recipients: a report of two cases.
                 - Are Dropped Osteoarticular Bone Fragments Safely Reimplantable in Vivo
                 - A Comparison of Five Treatment Protocols for Contaminated Bone Grafts in Reference to Sterility and Cell Viability

    - viral transmission:
          - processing of bone tissue removes most of the medullary contents (blood and marrow) which significantly decreases potential viral repository;
                 - this processing involves an ethanol wash, mechanical scrub and lavage, along with freeze drying of bone which will destroy
                           the majority of any remaining viruses;
                 - unfortunately, large osteochondral grafts (w/ associated soft tissue attachments) cannot be washed free of their medullary contents,
                           and therefore the potential risk of viral transmission is higher than with other types of allograft material (such as cancellous chips);
          - HIV transmission: (risks of transmitting HIV should be close to zero);
                   - bone will not be reliably sterilized by simple freezing (even to -80 deg);
                   - processing of bone tissue removes most of the medullary contents (which significantly decreases potential viral repository);
                          - this processing involves an ethanol wash along with freeze drying of bone which will destroy the majority of any remaining viruses;
                   - often the allograft sample will be radiated w/ 2.5 megarad prior to deep freezing;
                   - references:
                          - Bone transplantation and human immunodeficiency virus. An estimate of risk of acquired immunodeficiency syndrome (AIDS).
                          - Detection of HIV in bone allografts prepared from AIDS autopsy tissue
    - non-union: 10%
          - ref: The effect of internal fixation on the healing of large allografts.
    - fractures:
          - occur in 10-15%
          - references:
                 - Fractures of allografts. Frequency, treatment, and end-results.
                 - Fractures in Large-Segment Allografts.

- Specific Uses:
    - Bone Grafting for Tibial Fracture 
    - Bone Grafting for TKR 
    - role of allograft in cartilage defects:
         - osteochondral defects in the knee 
         - allografts for knee OCD injury
         - references:
               - Rib perichondrial grafts for the repair of full-thickness articular-cartilage defects. A morphological and biochemical study in rabbits.
               - The viability of articular cartilage in fresh osteochondral allografts after clinical transplantation.
               - The fate of articular cartilage after transplantation of fresh and cryopreserved tissue-antigen-matched and mismatched osteochondral allografts in dogs.
               - Resurfacing of the knee with fresh osteochondral allograft.
               - The immune response to osteochondral allografts in dogs.
               - Chondrocyte Viability in Refrigerated Osteochondral Allografts Used for Transplantation Within the Knee.
               - Chondrocyte Survival and Material Properties of Hypothermically Stored Cartilage: An Evaluation of Tissue Used for Osteochondral Allograft Transplantation.

- Use in Joint Arthroplasty:
    - acetabular bone grafting in THR 
    - reconstruction of femoral bone defects 
    - references:
           - Reconstruction for defects of the proximal part of the femur using allograft arthroplasty.
           - The incorporation of tibial allografts in total knee arthroplasty.

Allogeneic bone in the treatment of tumors, trauma, and congenital anomalies of the hand.

Autogenous cortical bone grafts in the reconstruction of segmental skeletal defects.

The use of large allografts for tumor reconstruction and salvage of the failed total hip arthroplasty.

Histological characteristics of acute rejection in vascularized allografts of bone