Anterior cruciate ligament reconstruction using allografts: A review of the important issues

ANTERIOR CRUClATE LIGAMENT RECONSTRUCTION USING ALLOGRAFTS: A REVIEW OF THE IMPORTANT ISSUES MICHAEL J. GIBBONS, MD, and ARTHUR R. BARTOLOZZI, MD

The use of soft-tissue allografts for anterior cruciate ligament (ACL) reconstruction has increased over recent years. The potential advantages of using allografts instead of autografts include decreased surgical morbidity, decreased surgical time, increased graft selection, decreased postoperative pain, accelerated rehabilitation, and increased flexibility when autograft tissue is inadequate. Early clinical results using allografts for ACL reconstruction have been encouraging. However, before deciding to use an allograft, one must be aware of the potential disadvantages. There are concerns about the transmission of infectious diseases (including human immunodeficiency virus), the effectiveness and possible adverse effects of secondary sterilization, and the immunogenicity and healing potential of allografts. These important issues are discussed in this article. KEY WORDS: anterior cruclate ligament, allografts, disease transmission

The functional disability that results from traumatic disruption of the anterior cruciate ligament (ACL) in athletes is well documented, o's The problem is finding the treatment that will most effectively prevent this disability and allow the athlete full return to their pre-injury activity levels. Nonoperative treatment with rehabilitation and activity modification may be a reasonable treatment option for some patients. 67 Many active patients, especially athletes, will continue to have symptoms of instability and eventually develop premature osteoarthrosis. 67"6s Intraarticular reconstruction of the torn ACL is now the treatment of choice for patients with symptomatic instability and for athletes who wish to remain active. Recent advances, including arthroscopic-assisted techniques and the use of allografts, significantly reduce tissue morbidity and are gaining popularity. Before deciding to use an allograft to reconstruct a torn ACL, the orthopaedic surgeon should understand the advantages and potential complications associated with its use. The purpose of this article is to discuss the important issues related to the use of allografts for the reconstruction of the ACL.

HISTORY OF ALLOGRAFT USE Allografts were first used in clinical settings where the availability of autogenous tissue was limited, most commonly skin, dura, and blood vessels, s In the orthopaedic setting, bone allografts were initially used to fill large osseous defects secondary to t u m o r s . 69"71'97"98 During From the Rothman Institute, Philadelphia, PA. Address reprint requests to Arthur R. Bartolozzi, MD, Rothman Institute, 800 Spruce St, Philadelphia, PA 19107. Copyright 9 1992 by W. B. Saunders Company 1048-6666/92/0202-0007505.00/0

76

the past decade, the use of soft-tissue allografts has increased. Bright and Green 7 describe their favorable results in 47 patients who received freeze-dried fascia lata allografts for reconstruction of a variety of ligament and tendon disruptions. Subsequently, several authors have reported on the use of allografts to reconstruct the ACL in animals 5"22'46'47'85'95"]~176 and in humans. 45'64's3

ADVANTAGES OF ALLOGRAFTS There are many potential advantages associated with the use of allografts for ligament reconstruction. One of the greatest advantages of using an allograft instead of autograft is tissue preservation. When using an allograft there is decreased surgical morbidity because healthy tissue is not disrupted during graft procurement. A large patellar tendon graft can be used without the risks associated with patellar tendon harvesting, such as patellar fracture, ss'99 patellar tendon rupture, 6 disruptionof the extensor mechanism, and patellofemoral pain. 37"49"s1"8~ Other advantages include decreased surgical time and increased graft selection. One could potentially use grafts of any size, shape, and type depending on the needs at surgery. Ailografts may be useful in patients with multiple ligamentous injuries, systemic ligament laxity, small patellar tendon width, short patellar tendons, and for those with failed autogenous graft procedures.

ALLOGRAFT TISSUE BANKING The first reports of organized bone banks for orthopaedic surgery appeared in the 1940s. 12"43'44'54"1~ The widespread use of allogeneic tissue was made possible during the Korean Conflict w h e n the Navy formally developed the first large-scale facility for collecting and processing

Operative Techniques in Orthopaedics, Vol 2, No 2 (April), 1992: pp 76-85

human tissue. 7 Numerous tissue banks are now located throughout the United States. It is the responsibility of each tissue bank to provide clinically useful grafts that are safe for transplantation. The American Association of Tissue Banks (AATB) is an organization formed to provide guidelines for safe and efficacious tissue banking. The AATB has published a set of standards defining the appropriate methods of donor selection, tissue retrieval, processing, preservation, storage, labeling, and distribution. ~,2 The first step in allograft tissue processing is the acquisition of tissues. Before procuring any tissues, informed consent must be obtained directly from living donors or from either the next-of-kin or following the guidelines of the Uniformed Anatomical Gift Act for non-living donors. After consent is obtained, stringent donor selection criteria must be followed to eliminate high-risk donors (Tables 1 and 2). The AATB guidelines are designed to reduce the risk of transmission of infectious or neoplastic diseases. Only after careful donor screening may tissue procurement take place. Tissue may be procured using either sterile or clean, nonsterile techniques. Sterilely procured tissues are removed in the operating room using standard operating room practices. These tissues do not necessarily have to be secondarily sterilized. Tissues procured using clean techniques must be secondarily sterilized. The shelf life of allograft bone and tendon is prolonged by one of two preservation techniques: deep-freezing or freeze-drying (lyophilization). Deep-frozen tissues should be maintained at least -70~ Freeze-dried tissues may be stored at room temperature.

RISK OF TRANSMISSION OF INFECTIOUS DISEASE The potential risk of transmission of infectious diseases such as hepatitis and acquired immunodeficiency syndrome (AIDS) is concerning to both the surgeons and the patients. The exact risk of contracting AIDS from an allograft is not known. However, it has been estimated that the risk is somewhere around I per 1,000,000.1~ The TABLE 1. American Association of Tissue Banks Guidelines for Rejecting a Potential Tissue Donor Infection or sepsis by history, physical examination, and laboratory testing Positive blood culture History of intravenous drug abuse History of neoplasm other than basal cell carcinoma of the skin, carcinoma in situ of the uterus, or intracranial neoplasm. History of hepatitis, syphilis, slow virus infection, AIDS, AIDS-related complex (ARC), or high risk for AIDS or ARC History of autoimmune disease Positive serologic tests Toxic substances in potentially toxic amounts in the tissue to be collected Evidence of serious illness of unknown etiology History of neurologic degenerative disease History of receiving pituitary-derived human growth hormone (pit-hGH) NOTE. AATB 1987 and 1989. ACL RECONSTRUCTION USING ALLOGRAFTS

TABLE 2. US Public Health Service Current Criteria for Exclusion of High-Risk Donors Clinical or laboratory evidence of HIV infection Men who have had sex with another man one or more times since 1977 Past or present intravenous drug abusers Persons immigrating since 1977 from countries where heterosexual activity is thought to play a major role in the transmission of HIV, eg, Haiti, Central Africa Persons with hemophilia who have received clotting factor concentrates Sexual partners of any of the above Men and women who have engaged in prostitution since 1977 and persons who have been their heterosexual partners within the past 6 months NOTE. AATB, 1989.

estimated risk is reduced to 1 per 8,000,000 w h e n the grafts are frozen, u The AATB and the US Public Health Service have developed stringent donor selection criteria in an attempt to eliminate high-risk donors (Tables 1 and 2). In addition, donor serum should be sent to the laboratory and screened for VDRL, antibodies to h u m a n immunodefiency virus (HIV), and hepatitis A, B, and C. Unfortunately, not all tissue banks follow these screening procedures. Even if every tissue bank follows these guidelines and routinely tests donor serum, there is still a 6- to 8-week "window" period from HIV exposure to antibody formation. This means that a recently infected donor could test HIV-antibody negative and be considered a suitable donor. In fact, there is a recent report that several bone graft recipients have become HIV positive after receiving bone allografts from a single donor who initially tested negative for HIV. 42 There is also a reported case of HIV being transmitted from a bone allograft before routine screening for AIDS. 16 Research is currently being conducted to develop a sensitive and specific test for the HIV antigen.

SECONDARY STERILIZATION To reduce the risks of disease transmission, many tissue banks provide, and surgeons are requesting, allografts that have been secondarily sterilized. Many different techniques of secondary sterilization, including boiling, autoclaving, irradiation, antibiotic soaking, and chemical sterilization, have been advocated. 77 None of these has gained a universal acceptance because of concerns over ineffective sterilization, alterations in graft mechanical properties, toxicity, and loss of osteoinductive properties. Currently, the two most commonly used techniques include either ethylene oxide (ETO) or 3,-irradiation.

Sterilization With Ethylene Oxide The use of gaseous ETO to sterilize implantable devices and hospital instruments is widespread. There is little question that the agent has potent antibacterial and antiviral properties. 19 ' .~0. .60 . . .77 78 82.88 There is a question, however, regarding its safety. Both ETO and its major byproducts (ethylene chlorhydrin and ethylene glycol) have been shown to be toxic. 3 93 6 4.0. 4. 1. . . 55 59 72 76 There are 77

also questions regarding ETO's mutagenetic potential. 2s'26,s7 The safety issues have prompted the Food and Drug Administration (FDA) to set maximum allowable residual levels for ETO and its byproducts in medical devices. 93 Recently, Jackson 4s has reported on the use of freezedried ETO sterilized bone-patellar tendon-bone allografts in the reconstruction of the ACL. He found that 6.4% of these patients developed a characteristic persistent intraarticular reaction that seems to be related to the residual ethylene chlorhydrin. For these reasons, the use of ETO is currently not recommended as a method of secondary sterilization for allografts used for intra-articular reconstruction of the A C E

Sterilization With ~,-Irradiation Few tissue banks currently supply ETO-sterilized allografts because of the relatively high incidence of adverse reactions. 48 Instead, most of the tissue banks n o w supply grafts that are either sterilely procured and deepfrozen or secondarily sterilized with ~-irradiation. There are several characteristics that make gamma-rays from a cobalt 60 source suitable for use on bone and tendon allografts. (1) Gamma-rays have excellent tissue penetration24"56; (2) gamma-rays do not activate the tissue like other sources of irradiation such as electrons, neutrons, protons, and alpha particles7; and (3) ~/-irradiation is an effective sterilant. 7'17'9~ The time necessary to adequately sterilize tissue is usually 12 to 24 hours depending on the strength of the source and the distance of the specimen from the source. This prolonged exposure time can cause tissue heating, which is detrimental to the tissue. This heating problem is minimized by packing the tissues on dry ice during irradiation. The grafts should also be rotated 180 ~ front to back and top to bottom to ensure uniform irradiation. The dose of ~/-irradiation necessary for effective tissue sterilization is not well known. The International Atomic Energy Association adopted 2.5 Mrads as the standard irradiation dose for medical products. 94 Even doses of less than two Mrads have been shown to effectively sterilize medical p r o d u c t s ) 7 The current recommendation of the AATB for s e c o n d a r y sterilization of allografts by gamma irradiation is between 1.5 and 2.5 Mrads. 2 Data on the radiation sensitivity of micro-organisms demonstrates that the use of two Mrads of gamma irradiation will inactivate large classes of bacteria and viruses. 17'9~ There are s o m e rare v i r u s e s , such as Creutzfeld-Jakob, Kuru, and Scrapie, that are very resistant to "y-irradiation, 33 but these viruses are not likely to be clinically significant. The irradiation dose needed to kill the hepatitis viruses and HIV has not been adequately investigated. There is some evidence that small doses of irradiation, 0.2 Mrads, will make the virus noninfectious in tissue cultures. 89 More recently, Withrow et al 1~ showed that neither 2.9 Mrads of gamma irradiation nor ETO killed the feline leukemia virus (a retrovirus similar to HIV). In another study, Conway et al 2~ used a bone graft model to show that an irradiation dose of 0.4 Mrads delayed, but did not eliminate, the infectivity of HIV-I. Conway 2~ hypothesized, by estimating the bioburden of 78

virus, that a dose of 1.5 Mrads would not reliably inactivate HIV-I in bone allografts with an acceptable safety margin.

BIOMECHANICS OF SECONDARILY STERILIZED ALLOGRAFTS Even if ~/-irradiation proves to be an effective sterilant, there are concerns that high doses may adversely affect the mechanical properties of the allografts. Most of the studies to determine the effect of irradiation on material properties have been conducted using bone. These studies have shown that the compression, torsional, and bending strengths of frozen bone are not significantly reduced by ~/-irradiation if the dose level is kept below 3 Mrads (Table 3). 7,52,75,92. More recently, one of the authors (MJG) has shown that the maximum force and the strain energy to maxim u m force of a bone-patellar tendon-bone unit were significantly reduced after 3 Mrads of ~/-irradiation. 32 Analysis of the material properties of the mid substance of these allografts showed that the maximum stress, the maximum strain, and the strain energy density to maxim u m stress were significantly reduced following 3 Mrads of irradiation. 32 It should be noted that the subfailure properties of the tissue were less affected than the failure properties. This may indicate that allografts irradiated to 3 Mrads would tolerate subfailure in vivo stresses as well as the frozen grafts. None of the mechanical properties of the tendon unit or the material properties of the tissue mid substance were significantly altered, however, following 2 Mrads of "y-irradiation (Table 4). 32 Using a bone-patellar tendon-bone allograft, Haut 38 found no significant reduction in any material properties following 2 Mrads of ~/-irradiation. Butler et aP 5 showed that 3 Mrads of irradiation produced significant reductions in the maximum stress and strain energy density to maximum stress. Higher doses of irradiation caused even greater reductions in the material properties of the bone-patellar tendon-bone units) s Paulos 73 and Haut 3s reported a more significant deleterious effect when irradiation was performed on freeze-dried tissues. The effects of freezing alone without secondary sterilization do not change the material properties of tendon, ligament, or bone tissues. 52"66"74'75'96"103Thus, it appears that there is a dose-dependent effect of "y-irradiation on the material properties of the bone-patellar tendon-bone units. If the doses are kept at or below 2 Mrads of ",/-irradiation, the mechanical properties of frozen allografts are not significantly altered. The preceding studies represent only initial material properties of the allograft and say nothing of the effect of irradiation once the tissue is implanted.

HISTOLOGY OF ALLOGRAFT HEALING The healing of implanted allograft tendon closely parallels the healing of fresh autografts. 4's'21'83 These studies show that the sequence and completeness of healing is virtually identical for the allografts and the autografts. Healing occurs in specific phases: exudation, graft necroGIBBONS AND BARTOLOZZI

TABLE 3. Biomechanical Effects of Preservation/Sterilization on Bone Preservation/Sterilization Techniques

Authors Bright and Burstein

Komander

Triantafyllou et al

Pelker et al

Freeze-drying IRRAD (3.5 Mrads) IRRAD (3.5 Mrads) + freeze-drying IRRAD (1 Mrad) IRRAD (3 Mrads) IRRAD (6 Mrads) IRRAD (3 Mrads) + freeze-drying Freeze-drying IRRAD (3-4 Mrads) IRRAD (3-4 Mrads) + freeze-drying Freezing (-20~ Freezing ( - 70~ Liquid nitrogen Freeze-drying IRRAD (3 Mrads) IRRAD (3 Mrads) + freeze-drying Freeze-drying + IRRAD (3 Mrads)

Control Technique

Compression (%)

Torsion (%)

Bending (%)

Freezing Freezing Freezing

100 100 Significantly diminished 100 100 80 100

----

---

Freezing (-35~ Freezing (-35~ Freezing (-35~

----

----

55-90 50-75 10-30

Fresh Fresh Fresh Fresh Fresh Fresh

120 122 114 120 ---

100 100 100 32-39 100 40

-----

Freezing Freezing Freezing Freezing

(-78~ (-78~ (-78~ (-78~

Fresh

sis, revascularization, fibroblastic invasion, collagen synthesis, and finally, alignment of the mature fibers along the lines of stress. The only identifiable difference is that the allografts lag behind the autografts in their sequence of events by approximately 1 to 2 weeks. Studies using canine knees show the sequence of events involved in the healing of deep-frozen tendon allografts used specifically for ACL replacement, s'22'85"1~176 Three to 4 weeks postoperatively the allograft is partially covered by a richly vascularized synovial membrane. Except for the graft itself, which is avascular, all of the intra-articular tissues are hyperemic. The peripheral surface of the proximal and distal segments of the graft show some signs of invasion by spindle-shaped cells presumed to be fibroblasts. No evidence of an inflammatory Or rejection response can be observed. Six to 8 weeks postoperatively (Fig 1) the hyperemia of the intra-articular tissue is reduced and the synovial membrane almost completely surrounds the graft. The most prominent histological feature during this time pe-

-

90 90 65 70

100 90 70 80

14

-

--

-

riod is the coagulative necrosis in the central core of the graft. The peripheral surface of the graft shows signs of both capillary budding and continued fibroblastic invasion. Twelve to 15 weeks postoperatively there is maximum cellularity along the entire length of the disorganized necrotic graft. Capillaries originating from the infrapatellar fat pad and the synovium surrounding the graft invade from the proximal and distal ends of the graft and eventually become evident throughout the length of the graft. Some portions of the graft bone junction begin to show columniation of fibrocartilage. Six months postoperatively (Fig 2) the vascularity and cellularity of the graft is decreased and there is active fibroplasia. Disorganized necrotic tissue is limited to the central core of the middle portion of the graft. The collagen at the distal and proximal portions of the graft begin to align along the longitudinal lines of stress. A large portion of the graft bone junction n o w resembles the normal ligament bone junction.

TABLE 4. Biomechanical Effects of Preservation/Sterilization on Bone-Patellar Tenclon-Bone AIIografts % of Control Author Gibbons et al (1991) Butler et al (1987) Paulos et al (1987)

Haut et al (1989)

Preservation/Sterilization Technique IRRAD (2 Mrads) IRRAD (3 Mrads) IRRAD (1.95 Mrads) Ethylene oxide + freeze-drying Freeze-drying Freeze-drying + IRRAD (2.5-3.5 Mrads) Freeze-drying + ethylene oxide IRRAD (2 Mrads) IRRAD (2 Mrads) then freeze-drying Freeze-drying then IRRAD (2 Mrads)

ACL RECONSTRUCTION USING ALLOGRAFTS

Control Technique

Modulus

Stress

Strain

Freezing (-30~ Freezing (-30~ Freezing Freezing

101 95 85 34

93 85 99 34

92 81 ---

Freezing. Freezing

---

83 45

140 88

Freezing

--

90

104

Freezing ( - 70~ Freezing ( - 70~

56 47

73 65

124 114

Freezing (-70~

42

24

67

Strain Energy Density 98 81

79

icantly less than the ACL controls. Nikolau 63 used fleshfrozen ACL allografts in dogs and showed that the mechanical integrity of the allografts was similar to that of the autografts with both achieving nearly 90% of the ACL control strength at 36 weeks. However, the ACL control values in this study were considerably less than the ACL control values in similar studies.

IMMUNOGENETIC POTENTIAL OF ALLOGRAFTS

e

N,,lillllliJHl

,,,

;:2,',

Fig 1. Photomicrograph, longitudinal section of patellar tendon allograft used for ACL reconstruction in a canine 6weeks postoperative. Prominent features include central area of avascularity, relative acellularity, and fragmentation of collagen bundles. The surface of the graft, open arrow, shows hypercellularity (H&E; original magnification • (Reprinted with permission, as)

One year postoperatively (Fig 3) the graft resembles a mature ligament with its fibers aligned along the longitudinal lines of stress. These histological studies suggest that the allograft provides the structural flame work for intraligamentous creeping substitution. The nonviable allograf{-undergoes necrotic degeneration and acts as a "scaffold" for neovascularization, invasion of fibroblasts, and subsequent fibroplasia. The vascularity of the invading fibroblast comes from the infra-patellar fat pad, stumps from the d a m a g e d ACL, and other intra-articular soft tissue (Fig 4).

BIOMECHANICAL PROPERTIES OF HEALING ALLOGRAFTS The biomechanical properties of soft-tissue grafts used for ACL reconstruction have been reported. 6s Animal studies have shown that once implanted, the maximum force-to-failure of these grafts is significantly less than the ACL controls. Six months postoperatively autografts were only 15% to 28% of the contralateral ACL maximum force. 13'14"81 Even at 1 year postoperatively, these grafts were only 30% to 52% of ACL controls} 3As Similar studies using allograft substitutes for the ACL show that they are also significantly weaker than the ACL controls, but the~. are not different than the autografts (Table 5). Shino ~ used fresh-frozen patellar tendon allografts in dogs and showed that the mean maximum tensile strength at 30 weeks postoperative was only about 30% of the control ACL's. There were no significant differences between the mechanical properties of the allografts and the autografts. Vasseur 95 found that the ultimate loads of the femur-ACL allograft:tibia complex were only 15% of all controls at 9 months postoperative. Other investigators 47"1~176 have also shown that the ultimate loads of the allograft ACL replacements are signif80

The potential for bone-tendon allografts to invoke an immune response has been extensively studied. The potential sources of immunogenicity from bone allografts are many. The primary sources of immunogenetic potential appear to be the cellular population due to the presence of surface antigens associated with a major histocompatibility complex (MHC). 3~ The matrix components, especially proteoglycans, may also be capable of stimulating an immune response. 3~ However, the collagen is weakly immunogenetic due to the lack of the MHC surface antigens. 61"91 In tendon, as in bone, the cellular components are the main source of immunogenicity because of the MHC surface antigens. The collagen in tendon has little immunogenetic potential. 61 Several investigators have clearly shown that fresh allografts will invoke an immune response and may lead to graft rejection. 5"23"3~ The immunogenicity of allografts appears to be significantly altered by the currently used preservation techniques. The immunogenetic potential of allografts is greatly reduced w h e n they are deep-frozen and thawed 23"3~ and almost completely eliminated by freeze-drying.23'3~ Irradiation also appears to diminish the immunogenicity of allografts. 27"3~ The exact mechanism for this alteration in immunogenicity is not clear. The most likely explanation is an alteration in the MHC surface antigens. In animal studies, transplantation of flesh allograft tendons caused a marked inflammatory rejection response. 5 In contrast, histological studies of deep-frozen allografts used for ACL reconstructions showed no evidence of immunogenetic rejection of the grafts, s'63"ss In similar studies using freeze-dried allografts, there were no signs of immune reaction. 22"46'47A~176 Clinical trials in humans have shown that frozen and freeze-dried allografts can be successfully used in a variety of reconstructive procedures without signs of rejection. 7"28'35"62'64"83'84'86 There is a report of an immune response to freeze-dried bone-patellar tendon-bone ACL allografts in humans. 78 Rodrigo speculates that the immune response is from an auto-HLA antibody induced by the allograft and that this reaction will lead to a poor clinical result. In summary, fresh-bone and soft-tissue allografts are capable of stimulating an immune response. The main source of immunogenicity from these grafts appears to be the MHC surface antigens (HLA in humans) on the cellular components of the grafts. Processing the grafts by deep-freezing, freeze-drying, and ~/-irradiation appears to decrease the immunogenicity of the tissues. Even if an GIBBONS AND BARTOLOZZI

Fig 2. Photomicrographs, longitudinal sections of aliograft patellar tendon used for ACL reconstruction in a canine 30-weeks postoperative. (A) Central area now shows normal cellularity, longitudinally oriented collagen bundles, intrinsic vessels (H&E; original magnification x30). (B) The graft-bone junction shows columniation of fibrocartilage (H&E; original magnification x50). (Reprinted with permission. 8s)

immune response is elicited, there is no direct correlation between the presence of this immune response and the ultimate clinical results.

CLINICAL STUDIES USING ALLOGRAFTS FOR RECONSTRUCTION OF ANTERIOR CRUCIATE LIGAMENT Recently, several authors have reported their results using allografts for reconstruction of the ACL in humans. Indelicato et al 4s compared the clinical results of sterilely procured fresh-frozen and freeze-dried patellar tendon allografts. Significant improvement was demonstrated in both groups compared with the nonoperative leg at follow-up of 24 to 36 months. Subjectively, 79% of the patients with the freeze-dried grafts and 93% of the patients with the frozen allografts rated their knees as "normal" or "improved." Of the 21 parameters evaluated, only

b t

Fig 3. Photomicrograph, longitudinal section of allograft tendon 52 weeks after ACL reconstruction. The cells and collagen bundles are arranged in a regular and longitudinal pattern. Intrinsic vessels are visible. The allograft resembles the normal ACL (H&E; original magnification x12). (Reprinted With permission. 8s) ACL RECONSTRUCTION USING ALLOGRAFTS

Fig 4. Sagittal section of dog's knee 4 months after ACL replacement using a frozen patellar tendon allograft processed using the spalteholz vascular-injection technique. Note the presence of vessels migrating from the proximal and distal portions of the graft (Spalteholz; original magnification • 10). (Reprinted with permission, s) 81

TABLE 5. Biomechanical Properties of AIIografts Used for ACL Reconstruction % of ACL Control Author Shino et al (1984)

Nikolaou et al (1986)

Webster & Werner (1983) Curtis et al (1985)

Jackson et al (1987)

Animal Model

Time Post-op

Graft

Dog

30 wks

Autograft PT (4-4.5 mm)

30 wks 30 wks 52 wks 8 wks 8 wks 16 wks 16 wks 24 wks 24 wks 36 wks 36 wks 78 wks 32 wks

Frozen allograft PT (4-4.5 mm) Frozen allograft PT (8-9 mm) Frozen allograft PT (8-9 mm) Autograft ACL Frozen allograft ACL Autograft ACL Frozen allograft ACL Autograft ACL Frozen allograft ACL Autograft ACL Frozen allograft ACL Frozen allograft ACL FD allograft flexor tendon

3 wks 6 wks 12 wks 24 wks 52 wks

FD allograft FD allograft FD allograft FD allograft FD ACL

Dog

Dog Dog

Goat

Strain to Max Load

Energy to Failure

30

104

36

28 35 36 46 50 81 66 84 67 87 90 88 29

82 127 78 ----

41 57 47 45 38

144 16 15 52 25

93 44 30 39 81

Max Load

FL FL FL FL

------

63 49 80 61 68 80 88

Stiffness

84 97 93 97 91 89 101 99 98

m

m

m

m

35

Abbreviations: PT, patellar tendon; FD, freeze-dried; FL, fascia lata.

three were significantly different b e t w e e n the two groups: subjective episodes of giving way, the "instability" category of the Lysholm knee score, and the pivot shift test on examination. There were no signs of graft rejection. Shino et al s3 reported on the use of deep-frozen tendon allografts (Achilles, tibialis anterior, tibialis posterior, and peroneus). They reported their subjective and functional results as 57% excellent, 37% good, and 2% fair. Physical examination showed that 87% had a negative Lachman test and 87% had a negative pivot shift. Their average follow-up was 57 months (36 to 90 months). They had no signs of graft rejection. In a prospectivestudy, Noyes et a164 reported their results of deep-frozen .bone-patellar tendon-bone and freeze-dried fascia lata allografts in patients with isolated ACL injuries. Mean follow-up in their study was 40 months (25 to 67 months). Using the KT-1000 arthrometer, 69% of the patients had less than 3 m m of increased anterior-posterior displacement of the operated knee compared with the nonoperative knee. Twenty six percent had 3 to 5 m m and only 5% had more than 5 m m of displacement. The knees that had the bone-patellar tendon-bone grafts had significantly less anterior/posterior translation than the knees that received the fascia lata aUograft. Using their strict rating system, the results were rated as 38% excellent, 51% good, and 11% fair or poor. Again, no evidence of graft rejection or infection was noted. Silvaggio and Fu 87 have reported their results using flesh-frozen sterilely procured bone-patellar tendon-bone allografts in 33 patients with 2-year follow-up. KT-1000 testing showed less than 2 m m anterior-posterior translation in most cases. Thirty. of the patients had unrestricted activity without episodes of instability. The early clinical results of the senior author (ARB) of this article, using fresh-frozen and irradiated bone82

patellar tendon-bone allografts, are similar to those in the literature. In 52 patients followed for 6 to 40 months, 16% had anterior-posterior displacement of 3 to 5 m m greater than the nonoperated knee, and 4% had displacement between 5 and 8 m m greater than the nonoperated knee. Eighty percent had less than 3 mm. Overall subjective results of good and excellent have been achieved in 90% of patients. Distinct advantages with the use of allograft tissue have been noted, including less postoperative pain, faster and more comfortable rehabilitation, no donor site complications, decreased surgical time, and increased surgical flexibility due to the variety of graft selection.

ALLOGRAFT AVAILABILITY The limited number of donors is a well-known problem in organ transplantation. A similar problem also exists in allografts used in the orthopaedic setting. The demand for bone-patellar tendon-bone allografts may already exceed the supply. 29'64 This problem may get worse especially with clinical studies now reporting favorable outcomes using the allografts. To meet the increasing demand, there has been an increase in the n u m b e r of commercial tissue banks. There may be a temptation by some tissue banks to loosen rather than tighten the donor screening criteria so less potential donors are rejected. Even though the AATB has set a recommended standard, not all tissue banks comply with these standards. It is important that a surgeon who chooses to use an allograft be familiar with the AATB recommendations and that he is confident that the tissue banks are following these recommendations. As suggested by Noyes, 64 the surgeon may even wish to set his own set of criteria for donor selection. GIBBONS AND BARTOLOZZI

sUMMARY M a n y factors affect t h e s u c c e s s of A C L r e c o n s t r u c t i o n i n c l u d i n g graft s e l e c t i o n , 65"67"68 i s o m e t r i c p l a c e m e n t of the graft, 39 s e c u r e graft fixation, 53 a n d a p p r o p r i a t e r e h a bilitation. 67 C u r r e n t l y , t h e u s e of a u t o g e n o u s p a t e l l a r t e n d o n u s i n g a n a r t h r o s c o p i c - a s s i s t e d t e c h n i q u e is c o n s i d e r e d to b e the g o l d s t a n d a r d b y m o s t s u r g e o n s . H o w ever, t h e u s e of allografts h a s m a n y p o t e n t i a l a d v a n t a g e s as j u s t d e s c r i b e d . T h e s h o r t - t e r m clinical trials u s i n g allografts h a v e b e e n v e r y e n c o u r a g i n g . D e s p i t e t h e optimistic e x p e r i m e n t a l a n d e a r l y clinical r e s u l t s , o n e m u s t consider the potential d i s a d v a n t a g e s i n c l u d i n g u n c e r t a i n l o n g - t e r m r e s u l t s a n d t h e possibility, of t r a n s m i s s i o n of infectious d i s e a s e a s s o c i a t e d w i t h the u s e of allograft tissues.

19. 20.

21.

22.

23.

24.

25.

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