Myths and Facts About Allograft Use in Anterior Cruciate Ligament Reconstruction: A Detailed Review of the Literature

Abstract

• »Patient-Specific Graft Selection: Graft selection for anterior cruciate ligament reconstruction (ACLR) requires a nuanced approach that considers various patient-specific factors, such as age, activity level, comorbidities, and surgical goals. Generally, allografts are preferred for older patients with less active lifestyles, whereas autografts are more suitable for younger, active patients because of autografts' lower retear rates.
• »Impact of Sterilization Techniques: Sterilization and processing techniques significantly affect the biomechanical properties and outcomes of allografts. While high-dose irradiation reduces allograft strength and compromises healing, low-dose irradiation or nonirradiated grafts offer superior biomechanical and clinical outcomes. However, standardized sterilization protocols are yet to be established.
• »Comparative Outcomes of Allografts and Autografts: Evaluating the literature on allografts vs. autografts in ACLR remains challenging because of the significant variability in patient characteristics, outcome measures, graft strength testing, and sterilization techniques across studies.

Anterior cruciate ligament (ACL) tears are among the most common orthopedic injuries, with an estimated incidence between 30 and 78 per 100,000 people and between 200,000 and 400,000 ACL reconstructions (ACLRs) performed annually^1,2. Notably, for older patients who are increasingly active and seek to maintain their activity levels, age is no longer a significant barrier for ACLR. This shift has led to a broader demographic of patients undergoing ACLR, necessitating a more nuanced approach to surgical technique. As the number of ACLRs continues to rise, individualized graft selection is influenced by patient age and expectations, activity level, surgeon preference, associated comorbidities, concerns for infection, and previous graft failure.

Autograft utilization for ACLR began in the early 20th century, evolving various techniques until the 1960s, when the bone block method with the patellar tendon initiated modern ACLR practices³. However, early outcomes varied, leading to investigation in the 1980s aimed at reducing autograft limitations³. Allografts and synthetic grafts emerged as alternatives, with allografts showing promise because of decreased donor site morbidity³. Early studies indicated that, in comparison with synthetic grafts, allografts had lower failure rates and complication rates, prompting a shift away from synthetic grafts. With modern sterilization mitigating disease transmission risks, allografts have become a popular option for ACLR in specific patient demographics.

Allograft utilization has gained popularity in recent years, particularly in older patients with lower physical activity demands^4-6. The current literature indicates that allografts are used in 32.2% to 42% of ACLR cases, with rates varying based on geographic location and demographic factors^7-9. Commonly cited advantages of allografts include the absence of donor site morbidity, decreased operative time, predictable graft size, use in complex cases such as in the revision setting or multiligament injury, and comparable strength¹⁰. However, increased risk of graft failure, disease transmission, and delayed healing and return to sport are commonly reported disadvantages of allograft utilization^5,11. Furthermore, the increased costs associated with allografts and their limited availability outside of the United States are contributing factors to their relatively limited use^10,12.

Overall, given the expanding usage of allografts in an ACLR, the purpose of this review is to provide an updated review of the literature regarding allograft options, sterilization and processing techniques, graft biomechanics, and outcomes. This review also aims to address common myths related to the utilization of ACL allografts.

Myth 1: All Sterilization and Processing Methods Are Equal

Commonly used sterilization and processing techniques include irradiation, chemical, and thermal methods. While all methods aim to sterilize the graft, each approach has unique advantages, disadvantages, and associated outcomes. Irradiation is the most commonly used intervention to mitigate infectious complications of ACL allograft reconstruction; however, excessive irradiation is an established risk factor for graft failure^13-17. Increasing doses of Mrad damage collagen fibers and alter collagen crosslinks¹⁴, thereby affecting the mechanical integrity of the graft contributing to delayed graft healing and decreased load to failure (LTF)^13,15-17. Given the deleterious effects on mechanical strength and biology of the graft, a consensus on safe radiation dosages for grafts remains in question. Sun et al. compared irradiated ACL allografts with nonirradiated allografts and autografts, revealing higher failure rates associated with irradiation levels exceeding 2.5 Mrad^18-20. In a systematic review that categorized radiation levels of 2.0 to 2.5 Mrad as high and 1.2 to 1.8 Mrad as low, high-dose radiation had a significantly higher rate of failure²¹.

Meanwhile, lower doses of irradiation have shown promising outcomes for allograft preservation. Yanke et al. showed that 1.0 to 1.2 Mrad irradiation levels decreased graft stiffness by 20%, without affecting LTF, stress, elongation, and strain²². Dashe et al. demonstrated that irradiation doses between 1.8 and 2.2 Mrad preserve the structural integrity of the graft²³, whereas Engelman et al. observed no difference in graft survival in nonirradiated and low-dose irradiation (<2 Mrad) allografts compared with autografts²⁴. Although these findings are promising, low-dose irradiation has not been adopted for quadriceps tendon allografts because of their thickness. The radiation levels required to sterilize the center of the graft would adversely affect its outer structure. Consequently, allograft tissue banks are not preparing or pursuing irradiated quadriceps allografts as alternative sterilization methods are necessary to overcome these limitations. Quadriceps tendon allografts have biomechanical strength comparable with other graft types²⁵; however, irradiation is not currently a viable option for their sterilization.

As high-dose irradiation has drawn scrutiny for failure rates, lower-dose irradiation and nonirradiated sterilization techniques have become increasingly popular. There are numerous proprietary treatments on the market including BioCleanse, AlloTrue, Allowash, Allowash XG, Tutoplast, Supercritical Carbon Dioxide, Community Tissue Services, Clearent, and Musculoskeletal Transplant Foundation (MTF) (Table I). Roberson et al. investigated the effect of these graft processing techniques on outcomes and found no difference in graft failure between BioCleanse, AlloTrue, and MTF²⁶. In addition, they found Tutoplast to be the only technique that resulted in unsatisfactory failure rates (45% at 6 years), whereas the descriptions of other processing techniques were insufficient for thorough comparative analysis²⁶. This high failure rate of the Tutoplast grafts may be attributed to the sterilization method, which involves a combination of irradiation and acetone solvent drying, potentially impairing the in vivo remodeling of the transplant¹⁷. Many proprietary-processed grafts still use low-dose irradiation, further complicating outcome analysis. A large systematic review demonstrated that nonirradiated allografts may result in superior outcomes compared with even low-dose (<2.5 Mrad) irradiated grafts²⁷. However, International Knee Documentation Committee (IKDC) scores were higher in the irradiated group²⁷. In addition, a prospective randomized controlled trial found failure rates of 6.1%, 34.4%, and 8.8% in the autograft, irradiated allograft, and nonirradiated allograft groups, respectively¹⁸. The authors found decreased anterior and rotational stability in irradiated allografts but no difference in functional outcomes between autografts and nonirradiated allografts¹⁸. These findings underscore the need for further research to establish standardized sterilization protocols that optimize graft stability and patient outcomes.

TABLE I.

Processing Technique Characteristics

Process	Features
BioCleanse	No irradiation, excessive heat, or ethylene oxide
Allowash	No irradiation, commonly used before 2005
Allowash XG	Low-dose irradiation <2.0 Mrad, commonly used since 2005
AlloTrue	Low-dose irradiation <1.3 Mrad will be applied unless a request is made to omit it
MTF	Variable preprocessed irradiation dose between 1.2 and 1.8 Mrad, no hydrogen peroxide used
Tutoplast	Terminal irradiation between 1.78 and 2.01 Mrad
CTS	Unknown irradiation dosage used
Clearent	5 Mrad irradiation used, dimethyl sulfoxide and antioxidant to counteract irradiation
SCCO2	Adjunct to other processing techniques

CTS = Community Tissue Services, MTF = Musculoskeletal Transplant Foundation, SCCO₂ = Supercritical Carbon Dioxide.

Data sourced, with permission, from Roberson TA, Abildgaard JT, Wyland DJ, Siffri PC, Geary SP, Hawkins RJ, Tokish JM. ‘Proprietary processed’ allografts: clinical outcomes and biomechanical properties in anterior cruciate ligament reconstruction. Am J Sports Med. 2017;45(13):3158-67²⁶.

Various sterilization methods have inherent benefits and trade-offs. Tejwani et al. evaluated the revision rates of ACLR with multiple sterilization techniques, including BioCleanse, AlloTrue, Allowash, and irradiation²⁸. After adjusting for age, sex, and body mass index, BioCleanse and irradiation greater than 1.8 Mrad were associated with the highest risk of aseptic revision compared with the other processing methods used in the study²⁸. However, it is prudent to acknowledge that no previous study has demonstrated any change in the mechanical properties of grafts after BioCleanse was used in isolation²⁸. Other chemical treatments include the use of ethylene oxide and peracetic acid-ethanol²⁹. Ethylene oxide gas is commonly used to sterilize medical equipment and was historically popular but has now fallen out of favor because of host reactions, resulting in persistent intra-articular reactions and effusion risk in patients³⁰. Peracetic acid-ethanol is an emerging technique that was initially not recommended because of its association with slowed remodeling and reduced mechanical properties compared with controls, as reported by Scheffler et al.³¹ However, the most recent studies, including those by Zhou et al. and Zhang et al., have shown that when combined with low-dose gamma irradiation, peracetic acid-ethanol preserves the histological structure and biomechanical properties of allografts^32,33. Overall, no universal standard exists, and each proprietary process has unique benefits and drawbacks²⁹.

Infectious transmission is a significant concern with allograft utilization; however, it is important to recognize that it is a rare occurrence. In 1995, there were 1 reported case of HIV and 2 cases of hepatitis C virus (HCV) transmission from allografts³⁴. In addition, between 2001 and 2002, 26 cases of bacterial infections associated with tissue allografts were reported, 13 of which (50%) were caused by Clostridium³⁴. Despite aseptic processing, none of the allografts underwent a final terminal sterilization procedure³⁵. However, these instances are now largely historical as advancements in modern sterilization techniques have effectively mitigated these risks, making such transmissions exceedingly uncommon. The risk of viral and bacterial transmission from contaminated tissue is uncommon and estimated to range between 0.14% and 1.7%^34,36. The estimated risk of HIV transmission with connective tissue allografts is 1 in 1.6 million³⁴. For comparison, according to the Centers for Disease Control and Prevention, the risk of contracting HCV or HIV after a needle stick event is 1.8% and 0.3%, respectively³⁷. In addition, with proper harvesting and sterilization techniques, there is no difference in surgical infection rates between autografts and allografts³⁸. For example, Barker et al. reported infection rates of 1.44% for hamstring autografts, 0.49% for bone-tendon-bone (BTB) autografts, and 0.44% for allografts, underscoring the low infection risk associated with allografts³⁹. Current literature suggests that modern sterilization and processing techniques have effectively addressed infection concerns.

In summary, current recommendations for allograft sterilization prioritize low-dose irradiation, with levels between 1.0 and 2.0 Mrad considered effective for preserving graft integrity while minimizing failure rates. Although irradiation is the most commonly used method, concerns about its negative impact on mechanical properties, especially at high doses, have led to the development of alternative techniques such as AlloTrue, which show promising outcomes with fewer adverse effects. Despite differences in processing methods, no universal standard exists, and ongoing research is needed to optimize sterilization protocols that balance graft preservation with patient outcomes.

Myth 2: Younger Age and Male Gender Allografts Have Superior Outcomes

It has been suggested that younger and male allografts have better outcomes in ACL allograft utilization. While this relationship may be intuitive, the literature is mixed. A systematic review demonstrated that sex does not appear to have significant effects on the biomechanical strength of the graft⁴⁰. Yet, Shumborski et al. observed higher graft rupture rates in female donors older than 50 years compared with male donors younger than 50 years⁴¹. However, their cohort of patients was younger than 25 years, which is a known risk factor for increased failure rate.

The effect of allograft donor age remains controversial. Historical studies have shown that donor age may negatively affect the biomechanical and clinical outcomes in ACLR⁴², whereas more recent research indicates that age does not significantly affect clinical and biomechanical outcomes^43-45. Specifically, force at failure, tensile strength, modulus of elasticity, and percent elongation were not affected by the donor's age in biomechanical studies, and many clinical studies have failed to show any difference using postoperative Lysholm or Tegner scores^43-46. In a study analyzing donor grafts older than 50 years and younger than 50 years, Carter et al. found that donor age did not significantly affect clinical outcomes with nonirradiated, fresh-frozen tibialis tendon allografts⁴⁷. Both cohorts had comparable IKDC scores, KT-1000 measurements, and Lysholm scores at the 2-year follow-up⁴⁷. While many surgeons may be apprehensive to use allografts from older donors, promising clinical evidence suggests no difference in patient-reported outcomes.

However, several studies present nuanced findings. For example, Lansdown et al. reported inferior biomechanical properties of the graft in patients older than 40 years and particularly in patients older than 65 years⁴⁰. Similarly, Zaffagnini et al. found improved Lysholm scores in patients who received grafts from donors younger than 45 years compared with those from donors older than 45 years⁴⁸. Future research must further explore the nuanced impact of donor sex and age on graft biomechanics, rupture rates, and long-term outcomes.

Overall, the relationship between ACL allograft donor age, sex, and clinical outcomes remains inconclusive, with some studies suggesting no significant biomechanical or clinical differences based on age or sex, whereas others report higher failure rates in grafts from older female donors (particularly older than 50 years) or inferior outcomes with older donors, especially in younger, active patients. While recent evidence challenges historical concerns about donor age, conflicting findings highlight the need for further research to clarify these variables' nuanced impacts on graft performance and patient outcomes.

Myth 3: Biomechanical Strength Testing of Allografts Follows a Standardized, Uniform Method

Allograft options can be divided into 2 categories: soft tissue allografts and bone blocks. Soft tissue allograft options include tibialis anterior (TA), tibialis posterior (TP), peroneus longus (PL), semitendinosus (ST), and gracilis tendons. The primary bone block allografts used in ACLR are the bone-patellar tendon-bone (BPTB) allograft, quadriceps tendon (QT), and Achilles allograft (AT). QT and AT allografts promote bone-to-bone healing on one side and tendon-to-bone healing on the other, whereas BPTB stands out as the sole option facilitating bone-to-bone healing on both the femoral and tibial sides. Bone blocks are preferable to many surgeons as it is well-established that a bone-to-bone interface facilitates healing⁴⁹.

The strength of various allografts is often compared next with each other; however, this practice has limited utility given the differences in graft types, preparation methods, and testing protocols reported in the literature. From cadaveric specimens, it is commonly recognized that the native ACL has an LTF of 2,160 N in situ⁵⁰. Strength comparisons among allografts are complicated by the variability in graft type, thickness, preparation, and testing methodologies across studies. In addition, numerous factors can contribute to LTF and stiffness rates. A systematic review by Lansdown et al. found that decreased freezing time of graft, increased diameter of graft, the use of central third patella, and lower rates of radiation all improved biomechanical properties of the allograft⁴⁰. Recognizing these limitations is critical in accurately interpreting allograft strength data and guiding clinical practice. Table II summarizes common graft types and their respective measured LTF and stiffness measurements.

TABLE II.

Biomechanical Properties of Graft Choices

Graft	Load to Failure (N)	Stiffness (N/mm)	Sources
Native ACL
Young (cadaver)	2,160	242	50
Young (graft only)	1,730	182	42,51
Old (graft only)	734	129	42
Bone grafts
BPTB, 14-mm central tendon	2,900	1,153.5	51
BPTB, 10-mm central tendon	1,580.6-1,784	210-278	52,53
Achilles	915	217	25
Quadriceps, 10 mm (not irradiated or sterilized)	2,185.90	466.2	52
Quadriceps, 10 mm (irradiated and sterilized)	1,055.00	161	25
Soft tissue
Double tibialis anterior	3,412	344	54
Double tibialis posterior	3,391	302	54
Double peroneus longus	2,483	244	54
Single semitendinosus	1,060-1,216	213-559.5	51,55
Double semitendinosus (2 strands)	2,330	469	56
Single gracilis	837-838	336-482.8	51,55
Double gracilis (2 strands)	1,550	336	55
Quadruple hamstring gracilis + semitendinosus braided and folded (doubled)	2,422	238	53
Quadruple hamstring 4 strands (2 gracilis, 2 semitendinosus)	4,090	776	55

ACL = anterior cruciate ligament, and BPTB = bone-patellar tendon-bone.

In bone block grafts, BPTB is the most popular, with graft strength varying based on the diameter and cross-sectional area of the graft⁵⁷. Although Noyes demonstrated that a 14-mm graft exhibits significantly greater strength compared with the standard 10-mm graft, 14 mm grafts are not harvested in modern ACLR^51-53. Alternatives to BPTB graft, such as TA and QT bone block grafts, are also commonly used, with the measured LTF of 915 N for TA, approximately 1,100 N for irradiated QT grafts, and approximately 2,200 N for nonirradiated QT grafts^25,52.

Strengths of soft tissue grafts vary widely, with doubled tendons generally showing higher strength than single tendons. For specific values, see Table II. Therefore, when reviewing comparative evidence of varying grafts, it is important to consider whether the specimen is doubled. When comparing the graft strengths of the TA, TP, and PL grafts, the TA graft has been reported to have superior strength characteristics and has resulted in good clinical outcomes^57,58.

While allograft strength has been investigated thoroughly, the differences in testing methodology prevent accurate comparison among allografts. The quadrupled hamstring tendon has historically been reported to be the strongest, with an LTF of 4,000 N; however, this test was conducted using 4 separate tendons arranged in parallel^53,55. A braided and doubled-over gracilis and ST graft (also considered a quadruple hamstring graft) produced a lower LTF of 2,422 N⁵³. The most common LTF test strategy involves preloading a graft and then subsequent loading at a standardized frequency and force. The graft then undergoes a tensile test until graft failure. As such, a lack of standardization in graft definition, preparation, and testing methods affects strength values in the literature. These findings suggest a significant need for standardization to compare different allografts.

Myth 4: Allografts and Autografts Have Comparable Healing; Therefore, They Require the Same Rehabilitation Approach

The comparative healing dynamics between allografts and autografts play a critical role in ACLR outcomes. Although allografts follow a similar healing pattern to autografts, their utilization often results in a delayed healing timeline⁵⁹. Murmatsu et al. demonstrated in a study comparing the healing of allogenic vs. autologous tendons for ACLR that allogenic tendons have a delayed rate and onset of revascularization on magnetic resonance imaging (MRI)⁶⁰. Animal studies have further shown that ACL allografts are associated with a prolonged inflammatory response, decreased biological incorporation, and worse biomechanical properties compared with ACL autografts⁶¹. Specifically, the autografts in the study showed an increased LTF, superior anterior-posterior stability, greater cross-sectional area, and a higher concentration of collagen fibers⁶¹.

Allografts are particularly vulnerable to failure during initial fixation and between 6 and 10 weeks postsurgery as the graft develops vascularity and incorporates into the tunnel^59,62. Technical or iatrogenic injury can compromise graft integrity and strength during various stages, including graft preparation, passage, or fixation. Postoperatively, the graft is also vulnerable to injury during the reconstitution process. Between weeks 6 and 12 postoperatively, the graft undergoes an initial phase of acellularity and necrosis, followed by the repopulation of host cells to align itself with the path of the ACL⁵⁹. While this process occurs in both allograft and autograft utilization, it has been shown to proceed at a slower rate in allografts⁵⁹. Because of the delayed incorporation of allografts, an extended period of graft protection from biomechanical stresses is recommended^63,64. Based on MRI findings, the reconstitution and revascularization process has been reported to take up to 2 years^65,66. A 5-year follow-up study by Poehling et al. demonstrated that ACLR patients with allografts reported lower pain levels at 1 and 6 weeks postoperatively and fewer activity limitations at 6 weeks postoperatively compared with those with autografts⁶⁷. Given this notion that allograft ACLR patients might have lower pain levels and subsequently faster early rehabilitation phase, this may lead them to premature return to activity before the graft has fully healed⁴. Consequently, Barber et al. found that the use of patient-specific rehabilitation protocols resulted in similar failure rates and clinical outcomes between allograft and autograft ACLRs in young patients⁶⁸. In this study, the allograft rehabilitation protocol was more conservative than the autograft protocol, with a delayed range of motion progression, later initiation of pivoting activities, and prolonged brace use because of slower graft incorporation. While autograft patients were allowed a full range of motion immediately and began jogging at 8 weeks, allograft patients had restricted motion for the first 6 weeks, started jogging at 12 weeks, and delayed noncontact pivoting until 5 months⁶⁸. In addition, autograft patients wore a brace for the first year, whereas allograft patients continued brace use during pivoting sports for up to 2 years⁶⁸.

Myth 5: Even in Appropriate Patients, Allografts Have Inferior Patient Outcomes Compared With Autografts

Graft Rupture

Graft rupture is often considered the most important measure of ACLR outcomes, but it is a nuanced complication influenced by factors such as surgical technique, graft choice, and individual patient characteristics. While the use of allografts in appropriate patients is crucial, factors such as activity level, age, rehabilitation compliance, and biomechanics also significantly contribute to the risk of graft rupture. An appropriate patient for allograft ACLR is the one who may be of older age, has lower functional demands, is undergoing revision surgery, or has contraindications to autograft harvest, while understanding the trade-offs of slower graft incorporation.

In young, active patients, it is well-established that allograft utilization has higher rerupture rates than autografts^4,24,69,70. For instance, a systematic review found a 9.6% graft rupture rate in autografts vs. 25.0% with allografts in active patients younger than 25 years⁷⁰. However, for patients younger than 25 years with an isolated ACL tear or an ACL tear with meniscal repair, Carter et al. found that nonirradiated Achilles or tibialis tendon allografts led to favorable outcomes with low failure rates, with an average follow-up of 65 months⁷¹. By contrast, a systematic review by Krych et al. demonstrated a five-fold increase in rerupture after BTB allograft compared with BTB autograft, but this group did not stratify their outcomes by age⁷². Barber et al. reported that both subjective and objective outcomes of BPTB allograft were similar for patients older than 40 years and those younger than 40 years, demonstrating consistent results across all age groups⁷³. However, the higher rupture rates reported in younger ages may be influenced by factors such as increased activity levels, graft size variability, and compliance with postoperative rehabilitation protocols, underscoring the need for a nuanced approach in younger populations.

Older patients with lower physical activity demands may be better candidates for an allograft⁵. Maletis et al. demonstrated that patients older than 40 years who received an allograft had similar outcomes and revision rates compared with those with an autograft⁶. In addition, the risk of graft rupture significantly inversely correlates with age. Kaeding et al. found a 43% reduction in the odds of graft rupture with every 10-year increase in patient age when graft type was held constant⁴. However, even when age was controlled for, the utilization of allografts still led to a four-fold increase in the odds of graft tears compared with autografts⁴. Allograft utilization does assume more risk of graft rupture in all age groups; however, in an older patient with less demanding physical needs, it can be a suitable option because of its unique advantages, particularly less donor site morbidity. In the appropriate patient, allografts can have comparable outcomes with autografts.

Functional Patient Outcomes

Interpreting patient outcomes necessitates a critical approach as allograft outcomes may be inferior to those of autografts in inappropriate patient populations. While graft failure appears to be higher in patients who undergo an allograft ACLR, patient outcomes with allograft utilization are not ubiquitous. Understanding the outcomes associated with allograft utilization for ACLR is critical for informed decision-making on graft selection and optimal patient care. Return to sport is an important metric after ACLR. Keizer et al. demonstrated an increased rate of RTS in patients who received autografts compared with allografts at both the 1-year and 2-year follow-ups⁷⁴. At the 2-year mark, the rate of RTS was 43.3% for the patellar tendon allograft compared with 75% for the patellar tendon autograft⁷⁴. In another meta-analysis of BPTB and quadrupled hamstrings, the authors compared laxity, clinical failure, and Lysholm scores and found no difference between allograft and autograft ACLR⁶⁹. However, of the studies included, there was heterogeneity of allograft sterilization as some used irradiation (between 1.5 and 2 Mrad) while others did not. Five of the 9 included studies reported that allografts were nonirradiated. The pooled results demonstrated no difference in outcomes; however, this study did not stratify or control the outcomes by age⁶⁹ (Table III). Another study demonstrated that BPTB allograft patients had worse functional testing results than BPTB autograft; however, when comparing nonirradiated allografts with autografts, no significant differences were observed in any outcome measure⁷² (Table IV).

TABLE III.

Clinical Outcome Comparisons Based on Graft Choice

	All Allografts vs. Autograft OR (95% CI); p Value	Nonirradiated Allografts vs. Autograft
Graft failure	5.03 (1.38-18.33); 0.01	No statistically significant difference
Rate of reoperation	1.2 (0.44-3.27); 0.72	No statistically significant difference
Lachman examination	2.75 (0.70-10.81); 0.15	No statistically significant difference
Pivot shift	1.23 (0.51-2.98); 0.65	No statistically significant difference
Hop test	5.66 (3.09-10.36); <0.01	No statistically significant difference
IKDC scores	1.49 (0.21-10.38); 0.69	No statistically significant difference
Return to preinjury level	1.2 (0.72-2.0); 0.48	No statistically significant difference

Significance for bold entries was p values < 0.05.

CI = confidence interval, IKDC = International Knee Documentation Committee, and OR = odds ratio.

Data sourced, with permission, from Krych AJ, Jackson JD, Hoskin TL, Dahm DL. A meta-analysis of patellar tendon autograft versus patellar tendon allograft in anterior cruciate ligament reconstruction. Arthroscopy. 2008;24(3):292-8⁷².

TABLE IV.

Autograft vs. Allograft Meta-Analysis Finding Summary

Reference	Study Type	Sterilization	Study Heterogeneity	PROs	Physical Examination	Instrumented Laxity	Complications
75	RC	Fresh-frozen allografts or cryopreservation	BPTBA vs. BPTBa	No difference	No difference	No difference	No difference in anterior knee pain, no infections
76	RC	Fresh-frozen allografts or cryopreservation	BPTBA vs. BPTBa	No difference	No difference	No difference
77	PC	Fresh-frozen allografts or cryopreservation	Hamstring auto vs. hamstring allo	No difference	No difference	No difference	No infections
17	PC	Osmotic treatment, oxidation, and solvent drying with acetone	Excluded	Excluded	Excluded	Excluded	Kneeling pain 50% auto, 0% allo
56	RC	Fresh-frozen allografts or cryopreservation	BPTBA vs. BPTBa	No difference	Extension deficit	No difference
78	PC	Fresh-frozen allografts or cryopreservation	BPTBA v.s BPTBa	No difference	No difference	No difference	No difference in anterior knee pain
79	PC	Fresh-frozen allografts or cryopreservation	BPTBA v.s BPTBa	No difference	Extension deficit	No difference	Greater incisional complaints in autograft, no infections
80	RC	Fresh-frozen allografts or cryopreservation	BPTBA vs. BPTBa	Not reported	No difference	No difference	No infections
81	PC	Fresh-frozen allografts or cryopreservation	BPTBA vs. BPTBa	No difference	No difference	No difference	No difference in anterior knee pain

BPTB = bone-patellar tendon-bone, PC = prospective cohort, PRO = patient-reported outcome, and RC = retrospective cohort.

In a prospective study comparing ACLR with BPTB allograft vs. autograft, Kleipool et al. found no significant difference in knee patient-reported outcome measures at an average of 4-year follow-up⁷⁸. Another study similarly found no difference in laxity and knee scores 3 to 5 years after surgery⁵⁶. A retrospective series comparing allograft with autograft has also shown promising outcomes in allograft utilization, demonstrating comparable Lysholm scores (91% vs. 97%), return to preinjury activities (65% vs. 73%), postoperative pain (16% vs. 9%), and ROM deficits (53% vs. 23%), with no difference in KT-1000 measurements between groups⁷⁶.

In a large meta-analysis comparing BPTB autograft and allograft, Kraeutler et al.⁸² assessed functional outcome measures including IKDC scores, Lysholm scores, single-leg hop, and KT-1000 scores. They found statistically significant differences in autograft and allograft groups, with autograft groups having better single-leg hop, IKDC, Lysholm, and Tegner scores. However, the allograft cohort had improved return to preinjury level, pivot shift, and anterior knee pain (Table V).

TABLE V.

Autograft vs. Allograft Functional Outcomes

Reference	Study Type	Return to Sport/Preinjury	Functional Outcomes	Knee Scores	ROM-Deficit	Reoperation/Rupture Rates	Excluded Radiated Allografts?
76	RC	73% vs. 65%	ND	ND	23% vs. 53%		Yes
56	RC		ND	ND			Yes
82 *	MA	57.1% vs. 68.3%	ND	Lysholm 90.5 vs. 84.7		4.3% vs. 12.7%	No
72	MA	ND	ND			ND	Yes

IKDC = International Knee Documentation Committee, MA = meta-analysis, ND = no difference, RC = retrospective cohort, ROM = range of motion.

^*Subjective IKDC, Lysholm, Tegner, single-legged hop, and KT-1000 arthrometer were improved in autografts.

Overall, utilization of allografts in ACLR may result in higher graft failure and lower return-to-sport rates compared with autografts although some studies show similar functional outcomes between the two. Autografts generally offer better functional scores, but allografts can still yield promising results, especially in certain patient populations.

Conclusion

The utilization of allografts in ACLR is continually evolving. Directly comparing autografts with allografts remains a challenge because of the diversity of grafts, the variations in sterilization and preparation techniques, and the multitude of outcome parameters involved. Preserving graft integrity with sterilization techniques remains a challenge as it has consistently been shown to affect ACLR outcomes in all populations. However, low-dose irradiation or using nonirradiated grafts can lead to similar outcomes as autografts in appropriately selected patients. Improvements in sterilization and preparation techniques may improve graft quality in the future. Graft selection should be an individualized decision based on numerous factors including age, activity level, surgeon preference, and patient preference. While both allograft and autograft options may be suitable, using allograft in middle-aged to older, less active patients can achieve satisfactory results (Fig. 1).

Fig. 1.

Autograft vs. allograft decision tree. ACLR = anterior cruciate ligament reconstruction.

Sources of Funding

No funding was provided in the investigation of this study.