A meta-analysis of stability of autografts compared to allografts after anterior cruciate ligament reconstruction

Allografts have recently become increasingly popular for anterior cruciate ligament reconstruction (ACLR) in the United States even though many studies have shown high allograft failure rates (Gorschewsky et al. in Am J Sports Med 33:1202, 2005; Pritchard et al. in Am J Sports Med 23:593, 2005; Roberts et al. in Am J Sports Med 19:35, 2006) and no meta-analysis or systematic review of allograft clinical stability rates in comparison to autog rafts has previously been performed. We hypothesized that allografts would demonstrate overall lower objective stability rates compared to autografts. To test this hypothesis we performed a meta-analysis of autograft and allograft stability data. A pubmed literature search of all allograft series in humans published in English was performed. Articles were then bibliographically cross-referenced to identify additional studies. Series inclusion criteria were arthrometric follow-up data using at least 30 lb or maximum manual force, stratified presentation of stability data and minimum two-year follow-up. Twenty allograft series were thus selected and compared to a previously published data set of all BPTB and Hamstring (HS) autograft ACLR series using the same study inclusion criteria and analytic and statistical methodology. IKDC standards of 0–2 mm (normal) and >5 mm (abnormal) side-to-side differences were adopted to compare studies. Normal stability for all autografts was 72 versus 59% for all allografts (P < 0.01). Abnormal stability was 5% for all autografts versus 14% for all allografts (P < 0.01). Bone-patellar-tendon-bone (BPTB) autograft normal stability was 66% versus 57% for BPTB allografts (P < 0.01). Abnormal BPTB autograft stability was 6 versus 16% for BPTB allograft. Hamstring autograft normal or abnormal stability rates were 77% and 4% and were compared to soft tissue allografts as a group which were 64% and 12% (P < 0.01). This is the first meta-analysis comparing autograft to allograft stability in ACLR. Allografts had significantly lower normal stability rates than autografts. The allograft abnormal stability rate, which usually represents graft failure, was significantly higher than that of autografts: nearly three times greater. It would therefore appear that autografts are the graft of choice for routine ACLR with allografts better reserved for multiple ligament-injured knees where extra tissue may be required.     

Comparison of fresh osteochondral autografts and allografts: a canine model

BACKGROUND: Osteochondral autografts and allografts have been widely used in the treatment of isolated grade IV articular cartilage lesions of the knee. However, the authors are not aware of any study that has prospectively compared fresh osteochondral autografts to fresh allografts with regard to imaging, biomechanical testing, and histology. HYPOTHESIS: The imaging, biomechanical properties, and histologic appearance of fresh osteochondral autograft and fresh allograft are similar with respect to bony incorporation into host bone, articular cartilage composition, and biomechanical properties. STUDY DESIGN: Controlled laboratory study. METHODS: Eighteen adult dogs underwent bilateral knee osteochondral graft implantation after creation of an Outerbridge grade IV cartilage defect. One knee received an autograft, and the contralateral knee received a fresh allograft. Nine dogs were sacrificed at 3 months, and 9 dogs were sacrificed at 6 months. Graft analysis included gross examination, radiographs, magnetic resonance imaging, biomechanical testing, and histology. RESULTS: Magnetic resonance imaging demonstrated excellent bony incorporation of both autografts and allografts. Biomechanical testing demonstrated no significant difference between autografts versus allografts versus control at 3 or 6 months (P = .36-.91). A post hoc calculation showed 80% power to detect a 30% difference between allograft and control. Histologic examination showed normal cartilage structure for both autografts and allografts. CONCLUSION: Fresh osteochondral autograft and fresh allograft tissues are not statistically different with respect to bony incorporation, articular cartilage composition, or biomechanical properties up to 6 months after implantation. CLINICAL RELEVANCE: The use of fresh allograft tissue to treat osteochondral defects eliminates morbidity associated with harvesting autograft tissue without compromising the results of the surgical procedure.     

Healing of the patellar tendon autograft after posterior cruciate ligament reconstruction--a process of ligamentization? An experimental study in a sheep model.

Forty-eight skeletally mature sheep underwent posterior cruciate ligament reconstruction with free patellar tendon autografts in one knee; the contralateral knee served as a control. Immediate rehabilitation without immobilization followed. Autograft healing was evaluated by histologic, roentgenographic, and biomechanical techniques up to 2 years postoperatively. After implantation, the autograft tissue underwent necrosis and degeneration, followed by a gradual healing process comprising revascularization, cellular migration, and formation of an extracellular matrix. The autograft bone pegs were osseously incorporated by 6 weeks. After an initial loss of strength, the material properties of the operated knee recovered to only about one-third that of the control. Better alignment of the collagen fiber bundles resulted in increased material properties, up to approximately 50% of the control at 52 weeks. After 2 years, the autograft tissue was found to differ structurally and mechanically from a ligament, suggesting that the autograft may never approach normal ligament characteristics. Degenerative alterations, the wide-spread presence of type III collagen, and abnormal accumulations of glycosaminoglycans in the autograft correlated with a maximum stress of 60% and an elastic modulus of 70% of the control. Although ligamentization was not seen, the staging of autograft healing into different phases based on distinct morphologic manifestations (necrosis, revitalization, collagen formation, and remodeling) and correlating with changing mechanical properties may provide a rationale for rehabilitation protocols with a realistic evaluation of the loading capacity of the replacement tissue.     

Comparison of tibial tunnel enlargement after anterior cruciate ligament reconstruction using patellar tendon autograft or allograft

This retrospective study was designed to compare tibial tunnel enlargement in patients with autograft or allograft anterior cruciate ligament reconstructions. The changes were related to position of the tibial tunnel and clinical outcome. Twenty-six patients with autograft reconstructions and 41 with allograft reconstructions were studied at a mean follow-up of 59 months (range, 41 to 84) after surgery. The average tunnel enlargement on the anteroposterior view was 2.2 mm (SD, 2.5) for autografts and 2.8 mm (SD, 2.1) for allografts. On the lateral view, the tunnel enlargement was 2.6 mm (SD, 2.4) and 3.4 mm (SD, 2.6) for autografts and allografts, respectively. No significant differences were found between the autograft and allograft groups. A trend was found in the correlation between the position of the tibial tunnel and the tunnel enlargement: more anteriorly placed tunnels had more enlargement. The changes in tunnel diameter did not relate to knee functional score or laxity. There was a significant correlation between malposition of the tibial tunnel and poor clinical scores. A significant negative correlation was found between postoperative follow-up time and tunnel enlargement in both groups. We conclude that placement of the tibial tunnel is a determining factor in tibial tunnel enlargement and clinical knee scores after anterior cruciate ligament replacement with an autograft or allograft. Tunnel enlargement tends to be less at a longer postoperative follow-up.     

Anterior cruciate ligament allograft transplantation. Long-term function, histology, revascularization, and operative technique

In recent years much effort has been devoted to finding a satisfactory replacement for the injured ACL. None of the reconstruction techniques used in the past can be considered ideal because of their inability to duplicate the complex geometry, structure, and function of the ligament. Current advances in allograft transplantation and cryopreservation have led us to design and implement an experimental model for testing the feasibility of cryopreserved ACL allotransplantation. Groups of dogs were used to evaluate the effect of cryopreservation on ligament strength and to compare the relative performance of both autograft and allograft ACL transplants up to 18 months after implantation. The ligaments were examined mechanically, histologically, and microangiographically. The cryopreservation process and duration of storage had no effect on the biomechanical or structural properties of the ligament. The mechanical integrity of the allografts was similar to that of the autografts, with both achieving nearly 90% of control ligament strength by 36 weeks. Revascularization approached normal by 24 weeks in both autograft and allograft. No evidence of structural degradation or immunological reaction was seen. Based on these results, we believe that a cryopreserved ACL allograft can provide the ideal material for ACL reconstruction. We have outlined a surgical technique for harvesting and implanting this graft clinically.     

Meniscal transplantation using fresh and cryopreserved allografts. An experimental study in goats.

A comparative study of three subgroups of meniscal transplants was undertaken in the goat model: Group 1 (autograft) involved removal and immediate reimplantation of the meniscus; Group 2, fresh meniscal allografts; and Group 3, cryopreserved (30 days) meniscal allografts. Six months after surgery, tissues were evaluated for gross degenerative changes, proteoglycan concentration (as assessed by uronic acid), water content, vascularity, histology, and cell viability. The contralateral knee served as control for all comparisons. There was no statistical difference in the amount of arthritis present and all transplants demonstrated an essentially normal peripheral vascularity compared to controls. Sections revealed reduced numbers of cells in the central portions of the transplanted menisci and these viable cells demonstrated different behavior in multiplication in tissue culture compared to contralateral controls. Grossly and microscopically, the implanted menisci differed little from the controls. The measurement of proteoglycan concentration and water content of the transplanted meniscal cartilage suggest alterations that may affect the long-term mechanical properties. The autograft specimens showed the water content was very slightly increased (3% to 6%), while the proteoglycan concentration was increased (42% in terms of uronic acid). In contrast, the water content of the fresh allograft group and the cryopreserved group was increased 12% to 24%. Proteoglycan concentration in these groups was decreased up to 56% in portions of some menisci compared to controls. Fresh and cryopreserved meniscal allografts showed peripheral healing, revascularization, cellularity, and incorporation, and grossly appeared good at 6 months in the goat model. The biochemical changes in the extracellular matrix at 6 months raises questions on the long-term function of these transplanted menisci.     

Freeze-dried allografts for anterior cruciate ligament reconstruction

Freeze-dried allografts represent a viable and functional alternative to fresh-frozen allograft and autograft constructs. Compared with fresh-frozen allograft constructs, freeze-dried soft tissue allograft constructs have many advantages including limited immunogenicity, ease of graft storage, comparable mechanical properties of soft tissue constructs, and the potential for improved biologic incorporation. This article reviews the fundamental processing of freeze-dried allografts and summarizes the clinical and basic science studies supporting the safe and effective use of freeze-dried allograft constructs for anterior cruciate ligament reconstruction. It also discusses potential directions of future research on tissue-engineered anterior cruciate ligament constructs using freeze-dried tendon constructs.     

Fresh-frozen allograft anterior cruciate ligament reconstruction

Reconstruction of the anterior cruciate ligament provides consistently good to excellent results allowing return to work and sport. Allograft tissue is an alternative to autografts when appropriate donor tissue is not available or its use is not advisable for other reasons. The technique and results for allograft use are similar to those for autograft, making its use appropriate in a variety of clinical scenarios. This article reviews the indications for allograft ACL reconstruction, graft options, and technique for allograft use.     

Meniscal substitutes – human experience

A number of clinical series have described the effect of meniscus allograft replacement in humans. The general indication has been disabling pain following loss of a meniscus in a skeletally mature individual. Overall, healing of the graft to the capsule occurs in up to 80% of all transplants. Revascularization and cell repopulation is found in all grafts but is highly variable. The risk for graft failure seems to be greater with irradiated grafts and in patients with grade III or IV osteoarthritic changes. In most series, patients experienced a decrease in pain and an increase in activity level postoperatively. In many series, concominant surgery (cruciate ligament reconstruction or osteotomy) had been performed. Meniscus replacement with frozen or cryopreserved allografts seems to give the most promising short-term results in patients with post-meniscectomy pain. Controlled, randomized prospective studies are needed to confirm a long-term benefit and better define transplantation indications. Viable meniscus allografts seem to survive transplantation, as donor cells were found in the graft after 2 years. Clinically, pain was reduced and activity increased following transplantation, but after 4 years some of these gains were lost. There was no correlation between postoperative findings on MRI and clinical outcome. Meniscal replacement with a quadriceps tendon autograft in humans resulted in pain reduction, but at second-look arthroscopy, only 2 of 9 tendon autografts looked like a meniscus. Six were in position but still looked like tendons. Total medial meniscus replacement by quadriceps tendon autrograft is still an experimental procedure. There is no proof at present that meniscal substitutes (meniscus allografts or tendon autografts) in humans can protect the hyaline cartilage of the knee from the degeneration, following loss of a meniscus. There is some evidence in animal experiments that under circumstances not yet exactly known, a meniscus substitute can have a protective effect on articular cartilage. Three factors have been identified that prevent proper meniscal function: poor fixation of the meniscal horns, no contact of the graft with the articulating surfaces under load and incorrect positioning of the horns. Meniscal allograft transplantation sensitizes humoral and cell mediated immune systems. Bone plugs attached to meniscal allograft tissue may increase cell surface antigenicity. Deep freezing and especially freeze drying of meniscal tissue decreases host immunogenicity. Cryopreservation maintains the content of donor HLA encoded antigens and is likely more sensitizing to the host. The clinical importance of immune responses to meniscal allografts is not known, but it has not been shown to result in graft failure or rejection. Prospective studies are needed.     

Effect of hemorrhage on medial collateral ligament healing in a mouse model

BACKGROUND: Medial collateral ligament injuries heal by a scar response. HYPOTHESIS: Increased hemorrhage at the site of medial collateral ligament injury improves healing. STUDY DESIGN: Controlled laboratory study. METHODS: Ninety-six mice were divided into two groups. Group 1 mice underwent knee medial collateral ligament transection with the opposite knee as a sham-operated control and group 2 animals additionally had 0.25 ml of tail cut blood pipetted to the medial collateral ligament transection site and sham-operated opposite knee. Ligament specimens were harvested at 3, 7, 21, and 28 days. RESULTS: Immunohistochemical analysis demonstrated peak macrophage counts at day 7 in all transected specimens. Macrophage counts were higher in group 2 than in group 1 at all time points, with a statistically significant increase of macrophages noted at day 7. In situ hybridization demonstrated increased collagen gene expression, with peaks at 7 and 28 days after transection. Group 2 animals showed increased gene expression at all time points as compared with group 1, with a statistically significant increase noted at 7 and 28 days. Biomechanical testing demonstrated progressive healing at each time point. At 28 days, the load to failure was 67% that of the sham-operated knee. CONCLUSIONS: This study suggests there is an increased healing response with bleeding at the ligament injury site. Clinical Relevance: Identification of the factors involved with increased healing may allow manipulation of the healing response in the clinical setting.     

Graft selection in surgicalreconstruction of the multiple-ligament-injured knee

Knowledge of the various graft options available for reconstruction of the knee with multiple ligamentous injuriesis necessary for the surgeon and patient to make an informed decision. Allograft is frequently used for such reconstructions, because multiple grafts are often necessary. Allograft avoids the morbidity associated with autograft harvest, allows smaller incisions, and saves operative time. A concern with the use of allograft, however, is the small but serious risk of disease transmission, including viral and bacterial infections. Allograft is also expensive and its availability may be limited. Some patients may prefer reconstruction with autograft tissue. Bone-patellar tendon-bone autograft is strong, stiff, and allows bony fixation at both ends. Harvest complications, primarily anterior knee pain, are drawbacks to using this source. Hamstring tendon autograft harvest results in less donor-site morbidity and comparable strength to bone-patellar tendon-bone autograft when bundled. Quadriceps tendon autograft also has been used in knee reconstruction, offering a strong graft with less morbidity than bone-patellar tendon-bone autograft harvest. Quadriceps tendon harvest is technically challenging, however. Achilles tendon and anterior tibialis allografts, as well as both autograft/allograft patellar tendon, quadriceps tendon, and hamstring tendon can all be used to reconstruct the anterior cruciate ligament, posterior cruciate ligament, or collateral ligament complexes. Ultimately, the choice of graft is dependent on surgeon and patient preference, availability of graft sources, and the number of ligaments requiring reconstruction or augmentation.     

A biomechanical and histological evaluation of the structure and function of the healing medial collateral ligament in a goat model

This study evaluated the healing process of an isolated medial collateral ligament (MCL) rupture at 12 weeks in a goat model. Using a robotic/UFS testing system, knee kinematics in multiple degrees of freedom and in situ forces in the healing MCL in response to (1) a 67-N anterior tibial load and (2) a 5-Nm valgus moment were evaluated as a function of angles of knee flexion. Then a uniaxial tensile test of femur-MCL-tibia complexes (FMTCs) was preformed to obtain the structural properties of the FMTC and mechanical properties of the healing MCL substance. The histological appearance of the healing MCL was also examined for collagen and cell organization. The anterior tibial translation in response to a 67-N anterior tibial load was found to range from 1.9 to 2.4 mm, which was not significantly different from the sham-operated, contralateral control knee. In response to a 5-Nm valgus moment, however, MCL injury caused a 40% or more increase in valgus rotations over sham-operated controls for all angles of knee flexion tested. The magnitudes of the in situ forces in the healing MCLs for neither external loading conditions differed from sham-operated controls. For the structural properties of the healing FMTC, the stiffness returned to sham-operated control levels, but ultimate load at failure remained 60% of sham-operated control values. In terms of mechanical properties of the healing MCL, its tangent modulus and stress at failure were only 40% of sham-operated control values. Histologically, the collagen and cell organization at the femoral and tibial insertions as well as the midsubstance remained disorganized. Comparing these data to those previously reported at 6 weeks, there was a marked improvement in the in situ forces in the healing MCL and of the stiffness of the FMTC. Also, the data obtained for the goat model revealed a faster healing process than those for the rabbit model. These findings suggest that greater post-injury activity levels may render the goat to be a better animal model for studying the healing process of the MCL.     

A literature review of autograft and allograft anterior cruciate ligament reconstruction

Knee anterior cruciate ligament reconstructive surgery has significantly evolved and now includes the option of using an allograft. This has resulted in numerous studies evaluating the advantages and disadvantages of allografts. The purpose of this literature review is to evaluate this research and present important findings to allow the selection of the most appropriate graft source when considering allograft versus autograft reconstruction.     

Allograft anterior cruciate ligament reconstruction in a sheep model. The effect of synthetic augmentation.

The purpose of this study was to assess the effect of synthetic augmentation of a bone-patellar tendon-bone allograft on the basis of biomechanical, morphologic, and histologic evaluation. The anterior cruciate ligament was reconstructed in the left knee of 66 adult sheep. Half the knees received bone-patellar tendon-bone grafts alone, while the other half were augmented. All of the knees, including the contralateral controls, had gross and histologic examination, hydroxyproline assay for collagen content, and biomechanical testing in groups at 0, 4, 16, and 52 weeks postoperatively. Biomechanical testing included anteroposterior translation, ultimate tensile strength, energy to failure, stiffness, and mode of failure. Eight fresh bone-patellar tendon-bone allografts were compared to eight cryopreserved bone-patellar tendon-bone allografts for baseline data on the effects of the cryopreservation. Cryopreservation did not have any effect on graft characteristics. Gross and histologic examination did not reveal any significant difference between the augmented and nonaugmented groups at any of the time periods. In addition, hydroxyproline content of the allograft was not altered by augmentation throughout the study period. Biomechanical laboratory evaluation demonstrated the augmented group had significantly reduced anteroposterior translation (P less than 0.05) at 52 weeks compared to the nonaugmented group. The ultimate tensile strength was significantly higher (P less than 0.05) in the augmented group at 4 weeks, but at 52 weeks both groups had attained only 50% of the normal anterior cruciate ligament strength. Stiffness and energy to failure were similar in both groups at all time periods. From the results of this study, synthetic augmentation appears to improve initial strength and prevent late allograft laxity while allowing normal remodeling processes to occur in the bone-patellar tendon-bone allograft anterior cruciate ligament reconstruction.     

Natural history of a hamstring tendon autograft used for anterior cruciate ligament reconstruction in a sheep model

The purpose of this study was to describe the histologic structure of the intraarticular segment of a semitendinosus tendon autograft used for anterior cruciate ligament reconstruction over the first year after surgery. We performed an anterior cruciate ligament reconstruction in a single hindlimb of 11 sheep using a doubled semitendinosus tendon autograft secured to the femur with an endoscopic button and polyester tape and to the tibia with sutures tied around a screw. The histologic structure of the intraarticular segment of the graft at 4, 8, 12, 24, and 52 weeks after surgery was compared with that of the normal semitendinosus tendon and anterior cruciate ligament. The random collagen fiber orientation progressed to a longitudinal orientation from the peripheral to the central areas of the graft over the initial 12 weeks after surgery. A uniform sinusoidal crimp pattern similar to that seen in the normal anterior cruciate ligament was identified under polarized light in nearly one-half of each graft by 24 weeks. Further maturation was noted at 52 weeks. Graft necrosis was not evident at any time period. This study showed that semitendinosus tendon autografts transform into a histologic structure similar to that of the normal anterior cruciate ligament over the initial year after surgery, as has been described for patellar tendon grafts.     

Cruciate reconstruction using freeze dried anterior cruciate ligament allograft and a ligament augmentation device (LAD). An experimental study in a goat model

One ACL in each of 11 mature goats was replaced with a freeze dried bone-ACL-bone allograft and a ligament augmentation device (LAD). The LAD was released from its tibial fixation at 3 months postoperation. Biomechanical, microvascular, and histological changes were evaluated 1 year following implantation. The reconstructed knees had a significantly greater total AP translation (3.1 +/- 0.5 mm) (mean and SEM) than the contralateral controls (1.0 +/- 0.1 mm). Differences in primary AP translation were responsible for 59% of the difference in total translation, with only a 0.6 mm difference in secondary translation. Neutral stiffness in the reconstructive knee was 22% of control, while stiffness at 30 N of anterior force was approximately 35% of controls. Ligament stiffness in the linear region for the ACL allograft/LAD was 53% of the control value of 691 N/mm. The maximum load of the allograft/LADs was 1,052 +/- 145 N, or 43% of the contralateral ACL control strength (2,448 +/- 144 N). Five of the six allografts failed at the femoral insertion. Energy (39%) to maximum load was less for allograft/LADs than controls but elongation to maximum load was the same as control. Histologic evaluation of the allograft/LADs revealed soft tissue cellular ingrowth into the LAD in the extraarticular portions. No bony growth into the LAD was observed. The collagen fibers of the graft appear to be arranged in a longitudinal orientation although some areas show chaotic collagen fibers. Microangiography revealed a periligamentous and endoligamentous vascular pattern reminiscent of a normal ACL and complete revascularization of the bone plugs.     

富血小板血浆凝胶在同种异体肌腱重建前交叉韧带后腱-骨愈合中的作用

目的 观察富血小板血浆(platelet-rich plasma,PRP)凝胶对同种异体跟腱重建兔前交叉韧带(ACL)后腱一骨愈合的影响.方法 24只兔行双侧ACL重建;一侧膝关节移植物予自体PRP凝胶预处理(实验组),另一侧膝关节移植物不予处理(对照组).于术后2,6和12周行组织学、免疫组化和生物力学评价.结果 2周和6周时Burak评分实验组高于对照组.12周时对照组腱-骨界面为成熟瘢痕组织,而实验组显示该界面为成熟纤维软骨带.免疫组化显示实验组血管内皮生长因子(VEGF)的阳性表达在早期较对照组高,TGF-β1的表达持续高于对照组.生物力学分析显示2周及6周时实验组极限负荷[(15.3±2.9)N、(33.2±6.9)N]明显高于对照组((7.9±1.4)N、(23.7±4.9)N](P＜0.05).结论 PRP凝胶可促进同种异体移植肌腱早期腱-骨愈合.     

Allografts in the treatment of anterior cruciate ligament injuries

Symptomatic knee instability is a common complaint among athletic individuals after a torn anterior cruciate ligament (ACL) of the knee. Allograft ACL reconstruction has gained popularity for primary and revision reconstructions. This graft choice has become popular with good intermediate term results combined with decreased operative times, hospital costs, and improved immediate postoperative pain and function. Intermediate follow-up has demonstrated similar results with autograft reconstructions, without the addition of donor site morbidity. Multiple allograft options exist for ACL reconstruction. The most commonly selected grafts include patellar tendon, Achilles tendon, and tibialis allografts. The use of a tibialis allograft provides a stout graft for reconstruction, while minimizing bone tunnel size. Bone-patella-bone allografts provide bone to bone fixation options with flexibility in tunnel selection sizing.