– Before implantation

– After implantation

Contributing Mechanisms to Anterior Cruciate Ligament Injuries

History

As always, a thorough history should be obtained. This should include age, prior activity level, mechanism of injury, symptoms of preinjury or postinjury instability and pain, and history of previous or concomitant knee injuries. Patient expectations, including desired activity level, are critical in helping to guide selection of autograft or allograft reconstruction. A history of immunocompromise or previous graft failure is also important and may influence graft selection.

Physical Examination

Imaging

Indications and Contraindications

The approach to graft election for ACL reconstruction must be determined on an individual basis after a thorough review of the risks and benefits of autograft and allograft sources. Patients should make an informed decision about graft type used for ACL reconstruction. However, there are populations of patients in whom allograft may be preferable over autograft7,9:

Patients in whom allograft is less desirable include the following:

Allograft Selection

The surgeon has multiple options when it comes to choosing allograft tissue, including patellar tendon, hamstring, Achilles tendon, tibialis anterior tendon, and tensor fascia lata. These may be procured from one of the many tissue banks currently in practice. It has been reported that there are more than 80 tissue banks that are current members of the AATB, with at least 60 more banks that are not currently members.²² It is prudent for the surgeon to be knowledgeable about the soft tissue bank’s methods of procurement, sterilization, and preparation before using its allografts, because these factors can significantly affect a patient’s outcome.

Although the number of infections is likely underreported, allograft transplantation infection rates are very low; the reported incidence is less than 1% (0.0004% to 0.014%).33,34 Despite this low incidence, many surgeons continue to be concerned with the risk of allograft disease transmission.³³ This phenomenon has been well documented^35,36 with regard to transmission of human immunodeficiency virus (HIV), hepatitis B virus (HBV), and hepatitis C virus (HCV), group A streptococcus, Clostridium species, and prions. In addition, many surgeons have concerns about regulatory practices and the biomechanical properties of tissue after sterilization.

Currently, all human cells or tissues intended for transplantation into a human recipient are regulated as HCT/P, or “human cell, tissue, and cellular and tissue-based product.”34,37 Any institution that recovers, processes, stores, or handles allograft tissue consequently not only must register with the Center for Biologics Evaluation and Research³³ of the U.S. Food and Drug Administration (FDA), but also is strongly encouraged to seek certification from the AATB’s voluntary accreditation program, which ensures that tissue banks that seek its certification follow strict guidelines for tissue processing. Because of past disease transmission, the FDA now mandates that all donor tissue be screened for HIV types 1 and 2, HBV, HCV, Treponema pallidum, and human transmissible spongiform encephalopathies with use of advanced nucleic acid testing (NAT) techniques.³⁴ NAT sharply reduces the diagnostic window and excludes donors with high viremia.³⁸ In addition, the AATB requires members to conduct NAT testing and provide negative Clostridium and Streptococcus pyogenes tissue culture results.^34,37 Although accreditation by the AATB is not required, tissue banks are urged to seek certification. Lack of accreditation can be a warning to the surgeon about the quality of the allografts provided by the tissue bank.

After appropriate donor screening, including exhaustive reviews of medical and social histories for risk factors for infectious disease, allograft tissue must undergo processing to ensure that pathogens are not concomitantly transferred. It should be noted that the Current Good Tissue Practice does not necessarily mandate aseptic handling or sterilization before transplantation of donor tissue; however, tissue recovery is typically performed with use of aseptic technique, in a standard operating room setting.34,37 Tissue procured under these conditions is not necessarily sterile—contamination may still be introduced by health care workers or the donor’s endogenous flora.³⁴

After procurement, specimens are sterilized. There is currently no single preferred sterilization process; however, the two main processes for sterilization are irradiation and proprietary chemical processing. The FDA maintains that biologic medical devices are acceptable if a sterility assurance level (SAL) of 10⁻³ (1 in 1000 chance that a living microbe exists) is attained. Human tissues may be considered sterile only if these specimens have an SAL of 10⁻⁶. However, allografts that have not been treated with gamma or electron-beam irradiation or ethylene oxide are not likely to be sterile.³⁹ Irradiation of soft tissue allografts is a delicate balancing act. Gamma radiation sterilization is an effective technique^33,40 that works by inducing excitation of molecules and ions for radical-induced chemical reactions, which subsequently leads to demise of pathogens. Although irradiation of 25 to 40 kGy can inactivate HIV and eliminate spores, the free-radical formation resulting from these doses has been shown to significantly alter the biomechanics of soft tissue grafts. Generation of free radicals distorts the integrity of the allograft tissue, which has been demonstrated in a number of studies showing decreasing allograft biomechanical integrity and enzyme resistance in irradiated tendons^41,42 with increasing doses of irradiation (Table 73-1).^43–45 The underlying reasons for this poor biomechanical integrity are not yet well understood. Gamma irradiation above 20 to 25 kGy is now seldom used because of this concern.²²

Related posts:

Open Repair of Posterior Shoulder Instability Autologous Chondrocyte Implantation in the Knee Arthroscopic Rotator Cuff Repair: Double-Row Techniques Surgical Treatment of Posterolateral Instability of the Elbow Primary Repair of Osteochondritis Dissecans in the Knee Arthroscopic Meniscus Repair: All-Inside Technique

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