Maximum load to failure of high dose versus low dose gamma irradiation of anterior cruciate ligament allografts: A meta-analysis

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

» 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.

Patient Age and Activity Level, Posterior Tibial Slope, and Use of Allograft Are Significant Risk Factors for Anterior Cruciate Ligament Reconstruction Failure: A Systematic Review

Purpose

To assess the consistency of risk factor reporting for anterior cruciate ligament reconstruction (ACLR) failure after primary reconstruction, identify risk factors more frequently associated with ACLR failure, and help clinicians prevent reinjury in patients with risk factors for ACLR failure.

Methods

Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were used to conduct a systematic review. Initial title and abstract screening yielded 561 studies, from which 76 studies were assessed for eligibility. Thirty-two full-text studies met the following inclusion criteria: (1) clinical studies of anterior cruciate ligament injuries; (2) patients undergoing ACLR; (3) clinical outcome data, including failure rate; (4) studies assessing preoperative risk factors for failure; and (5) manuscripts published within the past 6 years. These studies were subdivided into those that defined ACLR failure as revision surgery or graft failure.

Results

Ten risk factors were included in the review for 22 studies defining ACLR failure as revision surgery. Eight risk factors were included in the review for 10 studies defining ACLR failure as graft failure. Posterior tibial slope (PTS) (80%, 4/5 studies), age (79%, 11/14 studies), and graft characteristics (71%, 5/7 studies) such as allograft versus bone-patellar tendon-bone autograft, high-dose radiation, and BioCleanse preparation technique were the most significant risk factors for revision ACLR. PTS (100%, 2/2 studies) and activity level (67%, 2/3 studies) were the most significant risk factors for graft failure.

Conclusions

Age, PTS, use of allograft, and activity level are significant preoperative risk factors that should be considered when attempting to prevent reinjury in ACLR candidates. Studies investigating risk factors for ACLR failure often fail to control for confounding variables that can influence outcomes.

Level of Evidence

Level IV, systematic review of Level II to IV studies.

Similarities in the kinematics of autografts and hybrid grafts for anterior cruciate ligament reconstruction: Minimum 2 years of follow-up

OBJECTIVE

To compare the clinical results of anterior cruciate ligament reconstruction (ACLR) with autografts and that with hybrid grafts of the same diameter.

METHODS

This study retrospectively included 102 patients who underwent ACLR from August 2017 to July 2019. According to graft type, the patients were divided into an autograft group (58 patients) and a hybrid graft group (44 patients). All grafts were 8.0 mm in diameter. The failure rate, knee kinematics with 6 degrees of freedom (DOFs), signal/noise quotient (SNQ), the Lachman test, pivot-shift test, Lysholm score, Tegner activity score, and International Knee Documentation Committee (IKDC) score were compared in each group after a minimum 2-year follow-up.

RESULTS

There was no significant difference in the failure rate between the autograft group (1.72%) and the hybrid graft group (2.27%) (P > 0.999). The SNQ values of the autograft group (16.42 ± 5.29 and 18.52 ± 5.30) at the middle and proximal sites were lower than those of the hybrid graft group (12.13 ± 5.62 and 16.35 ± 4.64; P = 0.020 and P < 0.001, respectively). In the autograft group, the results of range of motion at 6 DOFs and tibiofemoral kinematics at 5 DOFs (except internal-external rotation) were similar to those of the hybrid graft group (P > 0.05). The Lysholm score, Tegner activity score, IKDC score, Lachman test, and pivot-shift test showed no differences between the two groups (P > 0.05).

CONCLUSIONS

Autograft in ACLR has better graft maturity than hybrid grafts, but their kinematic characteristics are similar.

CLINICAL TRIAL REGISTRATION

ChiCTR2000037869.

A local, non-commercial tissue bank connected to an organ donor program can produce musculoskeletal allografts of uniform quality at very low costs - ten years' experience

It is common practice that allograft tissues for knee multiligament reconstruction, meniscus transplantation, cartilage replacement and other advanced procedures are made available through commercial banks. The aim was to present the 10-year experience with a local, non-commercial tissue bank, established in 2014. The allograft bank was connected to an existing organ donor program. Following organ procurement, the musculoskeletal tissue is removed and stored immediately, fresh frozen to - 80 degrees Celsius (except hyaline cartilage, which is stored at 5 degrees Celsius). The donor is tested for contagious disease and the grafts for bacteria. When all results are negative, the grafts are released. When thawed before use a swap is cultured. Consecutive, prospectively collected data were analyzed. There were 31 donations, resulting in 1160 grafts. Only 40 grafts (3.4%) had a positive bacteria culture and were discarded. 552 recipients have been treated by use of these allografts. All grafts had negative bacterial cultures in swaps obtained before thawing, and there were no recorded transplantation related complications. The expenses for local grafts were 10-15% of the costs for grafts obtained from foreign banks. Through the local donation program, it was possible to establish a tissue bank with controlled quality grafts at minimal costs, minimizing the need for transportation of frozen grafts retrieved in other countries. Centers for specialized orthopedic surgery using allograft tissue can be self-providing and reduce costs by retrieving and handling allograft tissues locally.

Outcomes of ACL Reconstruction Utilizing Supercritical CO2-Sterilized Allografts

Background

Allograft tendons are perceived to have a high ACL graft failure rate in primary anterior cruciate ligament (ACL) reconstruction (ACLR). Historical series may be biased by graft processing methods that degrade the biomechanical properties of donor tendons such as irradiation. Supercritical carbon dioxide (SCCO2) is a validated method of terminally sterilizing biomaterials at physiological temperatures without irradiation, but in vivo use of SCCO2-processed tendon allografts for primary ACLR has not been reported to date.

Hypothesis

ACLR with SCCO2 allografts would result in acceptable failure rates, subjective knee scores, and clinical evaluation at 2 years postoperatively.

Study Design

Case series; Level of evidence, 4.

Methods

Patients underwent primary ACLR with terminally sterilized SCCO2-processed human gracilis, peroneus longus, semitendinosus, tibialis anterior, and tibialis posterior tendon allografts. Patient demographics were collected, along with tendon donor age and sex. At 1 year postoperatively, subjective International Knee Documentation Committee (IKDC) and ACL-Return to Sport After Injury (ACL-RSI) scores were collected, as well as clinical evaluation. At 2 years postoperatively, the IKDC and ACL-RSI scores were repeated, and return to sports and further knee injuries were recorded.

Results

A total of 144 patients with a medianage of 26 (IQR 14) years formed the study group. Patients were predominately male (58%). The loss to follow-up rate was 8% (n = 12). The mean age of allograft tendon donors was 37 (range 17-58) years, and the majority were male (83%). The mean allograft diameter was 8.9 ± 1.0 mm. At 2 years, ACL graft failureoccurred in 5% (n = 7). All graft failureswere in patients aged ≤25 years (P = .007). Neither donor age (≤40 or >40 years) nor donor sex was associated with graft failure (P > .05). The median IKDC subjective score was 95 and ACL-RSI score was 75. There were no revisions for sepsis within the first 2 years postoperatively.

Conclusion

SCCO2 processing of allograft tendons demonstrated satisfactory clinical and patient-reported outcomes at 24 months postoperatively in a consecutive series of patients with primary ACLR, with similar ACL graft failure rates and subjective knee scores compared with those reported in published series of hamstring tendon autograft and fresh frozen nonirradiated allograft.

Estimation Failure Risk by 0.5-mm Differences in Autologous Hamstring Graft Diameter in Anterior Cruciate Ligament Reconstruction: A Meta-analysis

BACKGROUND

Because grafts are made in 0.5-mm increments clinically for anterior cruciate ligament (ACL) reconstruction, it is important to clarify how the failure rate decreases as the diameter increases. Moreover, it is important to know whether even a slight increase in the graft diameter decreases the risk of failure.

HYPOTHESIS

The risk of failure decreases significantly with each 0.5-mm increase in hamstring graft diameter.

STUDY DESIGN

Meta-analysis; Level of evidence, 4.

METHODS

The systematic review and meta-analysis have estimated the diameter-specific failure risk for each 0.5-mm increase in ACL reconstruction using autologous hamstring grafts. We searched for studies describing the relationship between graft diameter and failure rate published before December 1, 2021, in leading databases, such as PubMed, EMBASE, Cochrane Library, and Web of Science, according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. We included studies using single-bundle autologous hamstring grafts to investigate the relationship between failure rate and graft diameter of 0.5-mm intervals with >1-year follow-up. Then, we calculated the failure risk caused by 0.5-mm differences in autologous hamstring graft diameter. Assuming Poisson distribution for the statistical model, we employed an extended linear mixed-effects model in the meta-analyses.

RESULTS

Five studies containing 19,333 cases were eligible. The meta-analysis revealed that the estimated value of the coefficient of diameter in the Poisson model was -0.2357 with a 95% CI of -0.2743 to -0.1971 (P < .0001). With every 1.0-mm increase in diameter, the failure rate decreased by 0.79 (0.76-0.82) times. In contrast, the failure rate increased by 1.27 (1.22-1.32) times for each 1.0-mm decrease in diameter. The failure rate significantly decreased with each 0.5-mm increase in graft diameter in the range of <7.0 to >9.0 mm from 3.63% to 1.79%.

CONCLUSION

The risk of failure decreased correspondingly with each 0.5-mm increase in graft diameter in the range of <7.0 to >9.0 mm. Failure is multifactorial; however, increasing the graft diameter as much as possible to match each patient's anatomic space without overstuffing is an effective precaution that surgeons can take to reduce failures.

Impact of irradiation on load-to-failure in bone-patellar tendon-bone allografts: A systematic review and meta-analysis

Introduction

To evaluate the impact various levels of irradiation have on bone-patellar tendon-bone (BTB) allograft load-to-failure.

Materials and methods

Pubmed, Google Scholar and Embase were searched for studies reporting load-to-failure measurements of BTB allografts following gamma or eBeam irradiation. All systematic reviews, editorials, as well as studies that utilized animal models and/or other graft sources (achilles, hamstring, quadriceps) were excluded. Meta-analysis was performed to compare the impact of low dose (19 ≤ kGy), intermediate (20-49 kGy) and high dose (>50 kGy) gamma and eBeam radiation on load-to-failure.

Results

Twelve studies, containing a total of 429 BTB allografts (159 controls, 270 irradiated), were identified. Load-to-failure of BTB allograft was significantly decreased at intermediate (20-49 kGy) doses of radiation, while low (≤19 kGy) and high (>50 kGy) doses did not significantly change load-to-failure.

Conclusions

Intermediate doses of radiation may negatively impact the biomechanical integrity of BTB allograft in vitro. Future studies are required to examine clinical outcomes at varying irradiation levels.

Categorize the existing clamps used for tensile test of human graft- a systematic review

BACKGROUND

The use of tendon allografts for orthopedic repair has gained wide acceptance in recent years, most notably in anterior cruciate tendon reconstruction. Multiple studies support the use of tendon allografts and the benefits of its use are well accepted and understood. One of the important criteria of the use of tendon allografts is statistically similar histological and biomechanical properties to autographs. The aim of this systematic literature review is to investigate and categorize existing clamps used in the determination of the biomechanical properties of tendons such as maximum load, maximum strength, modulus of elasticity, ultimate strain, and stiffness. A variety of clamps for use during the endurance test of tendons were categorized according to the temperature used during the measurement. The clamps are divided into three groups: room temperature, cooled and heated clamps. The second goal of our review is to overview of clamps on the following aspects: name of clamp, author and date, type of clamps, type of endurance test (static or dynamic), type preloading (dynamic or static), type of tendon and measured and calculated parameters, and summarize in Table 3, as a comprehensive catalogue.

METHODS

This systematic review was carried out in keeping with the PRISMA 2020 E&E and the PRISMA-S guidelines and checklists. A search was conducted for publications dating between 1991 and February 28th 2022 through three electronic databases (Web of Science, Scopus, and PubMed). We used Critical Appraisal Skills Program checklist to check the quality of included articles.

RESULTS

The database search and additional sources resulted in 1725 records. 1635 records eliminated during the screening for various reasons (case report, other languages, book chapter, unavailable text/conference abstract, unrelated topic). The number of articles used in the final synthesis was 90. A variety of clamps for use during the endurance test of tendons were identified and categorized according to the temperature used during the measurement. Based on this, the clamps are divided into three groups: room temperature, cooled or heated clamps.

CONCLUSIONS

On the basis of the systematic literature review, mechanical parameters determined by usage with cooled clamps proved to be more reliable than with those at room temperature and with heated clamps. The collected information from the articles included name of clamp, author and date, type of clamps, type of endurance test (static or dynamic), type preloading (dynamic or static), type of tendon and measured and calculated parameters given in Table 3. summarized. The main advantage of the cooled clamps is that there is no limit to the type and length of the tendon. This study provides an overview of clamps and does not represent the modernity of any method.

Current trends in the anterior cruciate ligament part II: evaluation, surgical technique, prevention, and rehabilitation

Clinical evaluation and management of anterior cruciate ligament (ACL) injury is one of the most widely researched topics in orthopedic sports medicine, giving providers ample data on which to base their practices. The ACL is also the most commonly treated knee ligament. This study reports on current topics and research in clinical management of ACL injury, starting with evaluation, operative versus nonoperative management, and considerations in unique populations. Discussion of graft selection and associated procedures follows. Areas of uncertainty, rehabilitation, and prevention are the final topics before a reflection on the current state of ACL research and clinical management of ACL injury. Level of evidence V.

Aseptically Processed Allograft Implantation: A Safe Strategy for Knee Ligament Reconstructions

Postoperative infections after allograft implantation is a major concern in knee ligament reconstructions considering the theoretical risk of disease transmission and its potential severity. Here, we aimed to evaluate the postoperative infection rate after knee ligament reconstructions using aseptically processed allografts, and provide an overview of the allografts use in an academic tertiary hospital. A retrospective study was performed evaluating patients who underwent knee ligament reconstructions using aseptically processed allografts, including primary and revision surgeries, from 2005 to 2018. Demographic data, including the type of knee injury and trauma energy, and postoperative data were collected focusing on postoperative infections. Regarding these infected cases, further analyses were performed considering the presenting signs and symptoms, the isolated microorganism identified in culture, the time between graft implantation and diagnosis of infection (defined as acute, subacute, and late), and the need for graft removal. A total of 180 cases of ligament reconstructions were included. The mean follow-up was 8.2 (range: 2.1-15.6) years and the mean age at surgery was 34.1 (± 11.1) years. A total of 262 allografts were implanted in those 180 cases, 93 (35.5%) as bone plug allografts and 169 (64.5%) as soft tissue allografts. Common surgical indications included multiligament reconstruction (57.2%) and primary anterior cruciate ligament (ACL) reconstruction (15%). Seven cases (3.9%) presented postoperative infections. Knee pain (100%) and swelling (100%) were the most prevalent symptoms. Two cases (28.6%) presented sinus tract. Allografts were removed in two cases, the same cases that presented draining sinus (p = 0.04). High-energy trauma was the only statistically associated factor for infection (p = 0.04). No significant association between infection and the type of allograft (p > 0.99) or sex (p = 0.35) were observed. Four cases (57.1%) had monomicrobial staphylococcal infections. Based on that, the allograft-related infection rate was 1.7% (the remaining three infected cases). Nonirradiated, aseptically processed allografts have a low postoperative infection rate in knee ligament reconstructions, being a safe alternative for surgeries that require additional source, increased variety, and quantity of grafts.

The Graft Insertion Length in the Femoral Tunnel During Anterior Cruciate Ligament Reconstruction With Suspensory Fixation and Tibialis Anterior Allograft Does Not Affect Surgical Outcomes but Is Negatively Correlated With Tunnel Widening

PURPOSE

To investigate the surgical outcomes of anterior cruciate ligament (ACL) reconstruction using a low-dose irradiated tibialis anterior allograft with a fixed-loop cortical suspension device for the femur based on the graft insertion length (GIL) in the femoral tunnel.

METHODS

Between January 2010 and January 2018, the medical records of consecutive patients who underwent arthroscopic ACL reconstruction with a tibialis anterior allograft fixed with the EndoButton CL for the femur and who had at least 2 years of follow-up were retrospectively evaluated. Patients were classified into 3 groups based on the GIL in the femoral tunnel (group 1, GIL < 15 mm; group 2, GIL of 15-20 mm; and group 3, GIL > 20 mm), and their functional scores, knee laxity, and radiographic parameters were evaluated.

RESULTS

A total of 91 patients were analyzed. There were no statistically significant differences in the functional scores and knee laxity between the 3 groups at 2 years postoperatively. However, significant differences were observed in tunnel widening at 1 year postoperatively in the femur (P = .045 for absolute value and P = .004 for relative value) and the tibia (P = .014 for absolute value and P = .012 for relative value), revealing that both the femoral and tibial tunnels widened as the GIL decreased. Additional linear regression analyses were performed to identify whether the GIL independently affects tunnel widening. Consequently, the femoral tunnel depth, tunnel diameter, and GIL were found to independently influence femoral tunnel widening (P = .008, P = .019, and P < .001, respectively), whereas the tunnel diameter and GIL affected tibial tunnel widening (P < .001 and P = .004, respectively).

CONCLUSIONS

The GIL in the femoral tunnel during ACL reconstruction using a tibialis anterior allograft with a fixed-loop cortical suspension device for the femur has no significant association with the postoperative functional outcomes and knee laxity, but it has a negative correlation with tunnel widening in the femur and the tibia.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.

Functional results of allograft vs. autograft tendons in anterior cruciate ligament (ACL) reconstruction at 10-year follow-up

PURPOSE

The anterior cruciate ligament (ACL) tear is one of the most common sports injuries of the knee, and the arthroscopic reconstruction is the gold standard. Nevertheless, controversies about the surgical techniques and the type of graft still exist. Allografts have been considered by many surgeons as valid alternative to autografts. The aim of this study was to assess the effectiveness of allografts compared to autografts at approximately 10 years of follow-up, investigating the level of physical activity currently performed by patients of each group.

METHODS

Ninety-four patients, divided into two groups (allografts and autografts), have been retrospectively studied. The two groups did not significantly differ in preoperative sport activity level, age (mean 40.70 years for autografts and 41.23 for allografts) and characteristics. Allograft group received a fresh-frozen graft from the musculoskeletal tissues bank. Evaluations were made using the International Knee Documentation Committee (IKDC) and Lysholm score; every patient was interviewed for complications.

RESULTS

The mean follow-up time was approximately 10 years for both groups, with a minimum of 8 years. There were no statistically significant differences between the two groups. Average IKDC scores were 75.21 (SD 15.36) and 80.69 (SD 13.65) for the allograft and autograft groups, respectively. The mean Lysholm score was 87.57 (SD 9.43) for the allografts and 89.10 (SD 8.33) for the autografts. No major complications linked to the allograft tissue arose.

CONCLUSION

Both groups achieved almost the same functional outcomes at an average 10 years of follow-up, indicating fresh-frozen allografts as a reasonable alternative for ACL reconstruction.

LEVEL OF EVIDENCE

IV, Retrospective case-control study.

Comparing Hamstring Autograft With Hybrid Graft for Anterior Cruciate Ligament Reconstruction: A Systematic Review

PURPOSE

To systematically review the literature in an effort to compare the demographics and clinical outcomes of patients undergoing anterior cruciate ligament reconstruction (ACLR) with a hamstring tendon autograft (HT) versus an irradiated or nonirradiated hybrid autograft-allograft.

METHODS

A systematic review of the PubMed, Cochrane Library, and Embase databases was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. All English-language literature that reported general demographics and compared the clinical outcomes of patients undergoing primary ACLR with autograft versus hybrid graft (HG) with a minimum 2-year follow-up was reviewed by 2 independent reviewers. Search terms used were "anterior cruciate ligament" and "hybrid graft." Patients were assessed based on graft failure, anteroposterior laxity, and patient-reported outcomes (Knee Injury and Osteoarthritis Outcome Score, visual analog scale, Subjective International Knee Documentation Committee score, Lysholm, and Tegner scores). Study quality was evaluated with the Modified Coleman Methodology Score and ROBINS-I risk of bias tool.

RESULTS

Twelve studies (1 level II, 11 level III) met inclusion criteria (follow-up, 2.0-8.9 years), including 471 patients undergoing ACLR with an irradiated hybrid graft (IH), 89 patients with a nonirradiated hybrid graft, and 829 patients with HT. Graft diameter ranged from 7.5 to 10.0 mm and from 6.5 to 10.0 mm in HG and HT patients, respectively. Overall, graft failure ranged from 0% to 30.0% and from 0% to 28.3% in HG and HT patients, respectively (I² = 35.9%; 95% confidence interval 0%-74.8%). Among HG patients, graft failure ranged from 0%-30.0% and from 2.4%-4.2% in IH and nonirradiated hybrid graft groups, respectively (I² = 33.6%; 95% confidence interval, 0%-71.8%). Results for postoperative anteroposterior laxity and patient-reported outcomes were also inconsistent.

CONCLUSIONS

Patients undergoing ACLR with HT demonstrate inconsistent differences in clinical outcomes at midterm follow-up compared with IH patients.

LEVEL OF EVIDENCE

III, systematic review of level II and III studies.

Effects of SCCO2, Gamma Irradiation, and Sodium Dodecyl Sulfate Treatments on the Initial Properties of Tendon Allografts

Sterile and decellularized allograft tendons are viable biomaterials used in reconstructive surgeries for dense connective tissue injuries. Established allograft processing techniques including gamma irradiation and sodium dodecyl sulfate (SDS) can affect tissue integrity. Supercritical carbon dioxide (SCCO₂) represents a novel alternative that has the potential to decellularize and sterilize tendons with minimized exposure to denaturants, shortened treatment time, lack of toxic residues, and superior tissue penetration, and thus efficacy. This study attempted to develop a single-step hybrid decellularization and sterilization protocol for tendons that involved SCCO₂ treatment with various chemical additives. The processed tendons were evaluated with mechanical testing, histology, scanning electron microscopy (SEM), and Fourier-transform infrared (FTIR) spectroscopy. Uniaxial mechanical testing showed that tendons treated with SCCO₂ and additive NovaKill^TM Gen2 and 0.1% SDS had significantly higher (p < 0.05) ultimate tensile stress (UTS) and Young's modulus compared to gamma-irradiated and standard-SDS-treated tendons. This was corroborated by the ultrastructural intactness of SCCO₂-treated tendons as examined by SEM and FTIR spectroscopy, which was not preserved in gamma-irradiated and standard SDS-treated tendons. However, complete decellularization was not achieved by the experimented SCCO₂-SDS protocols used in this study. The present study therefore serves as a concrete starting point for development of an SCCO₂-based combined sterilization and decellularization protocol for allograft tendons, where additive choice is to be optimized.

Small hamstring autograft is defined by a cut-off diameter of 7 mm and not recommended with allograft augmentation in single-bundle ACL reconstruction

PURPOSE

The present study was to analyze graft failure rates of hamstring tendon (HT) autografts with a cut-off graft diameter of 8 mm or 7 mm, and compare clinical outcomes between augmented small HT with an allograft and non-augmented relatively large HT in single-bundle anterior cruciate ligament reconstruction (ACLR).

METHODS

A literature search of PubMed, EMBASE, and the Cochrane Library was performed based on the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analysis) guidelines. Studies to assess graft failure of autologous HT ACLR were reviewed, and graft failure rates with a cut-off graft diameter of 8 mm or 7 mm were further extracted. Clinical comparative studies of ACLR between augmented small HT with an allograft and non-augmented relatively large HT autografts were also included. Results are presented as risk ratio (RR) for binary data and weighted mean difference for continuous data with 95% confidence intervals (CI).

RESULTS

Nine studies with 2243 knees were included. Four studies examined the effect of HT autograft diameter on graft failure and five studies assessed clinical outcomes of allograft augmentation to small HT autografts. No significant difference was noted in graft failure with a cut-off diameter of 8 mm. No significant difference was found between diameters > 7 and ≤ 7 mm, but a significant difference was observed between diameters ≥ 7 and < 7 mm (RR = 0.49; 95% CI 0.26-0.92, I² = 0%, P = 0.03). A trend towards increased risk of graft failure was noted for allograft-augmented HT compared with non-augmented HT autografts (RR = 0.43; 95% CI 0.18-1.02, I² = 0%), but no significant differences were noted in IKDC, Lysholm, and Tegner scores between these groups.

CONCLUSION

The present study did support the use of 7 mm as a reference for cut-off diameter for small HT autografts, but not allograft augmentation to small HT autografts. These findings would guide clinical application of small HT autografts in single-bundle ACLR.

LEVEL OF EVIDENCE

IV.

Editorial Commentary: The Trend to Blend: Should We Be Using Hybrid Grafts in Adult Anterior Cruciate Ligament Reconstructions?

Hybrid anterior cruciate ligament grafts augmenting a small-diameter hamstring tendon autograft with nonirradiated allografts can be used with good results in adults. In teens, however, outcomes of hybrid grafts have not been well defined, and other solutions to small hamstring grafts including graft folding, contralateral autograft augmentation, or selection of a different autograft source could be considered.

Biomechanical considerations are crucial for the success of tendon and meniscus allograft integration-a systematic review

PURPOSE

This systematic review intends to give an overview of the current knowledge on how allografts used for the reconstruction of cruciate ligaments and menisci are integrated and specifically perform regarding their biomechanical function.

METHODS

Two reviewers reviewed the PubMed and Central Cochrane library with focus on the biomechanical integration of tendon ligament and meniscus allografts. The literature search was conducted in accordance with the PRISMA statement for reporting systematic reviews and meta-analyses.

RESULTS

The analysed literature on tendon allografts shows that they are more vulnerable to overstretching in the phase of degradation compared to autografts as the revascularization process starts later and takes longer. Therefore, to avoid excessive graft loads, allografts for cruciate ligament replacement should be selected that exhibit much higher failure loads than the native ligaments to counteract the detrimental effect of degradation. Further, placement techniques should be considered that result in a minimum of strain differences during knee joint motion, which is best achieved by near-isometric placement. The most important biomechanical parameters for meniscus allograft transplantation are secure fixation and proper graft sizing. Allograft attachment by bone plugs or by a bone block is superior to circumferential suturing and enables the allograft to restore the chondroprotective biomechanical function. Graft sizing is also of major relevance, because too small grafts are not able to compensate the knee joint incongruity and too large grafts may fail due to extrusion. Only adequate sizing and fixation together can lead to a biomechanically functioning allograft. The objective assessment of the biomechanical quality of allografts in a clinical setting is challenging, but would be highly desirable for monitoring the remodelling and incorporation process.

CONCLUSIONS

Currently, indicators like ap-stability after ACL reconstruction or meniscal extrusion represent only indirect measures for biomechanical graft integration. These parameters are at best clinical indicators of allograft function, but the overall integration properties comprising e.g. fixation and graft stiffness remain unknown. Therefore, future research should e.g. focus on advanced imaging techniques or other non-invasive methods allowing for in vivo assessment of biomechanical allograft properties.

The use of allograft tendons in primary ACL reconstruction

PURPOSE

Graft choice in primary anterior cruciate ligament (ACL) reconstruction remains controversial. The use of allograft has risen exponentially in recent years with the attraction of absent donor site morbidity, reduced surgical time and reliable graft size. However, the published evidence examining their clinical effectiveness over autograft tendons has been unclear. The aim of this paper is to provide a current review of the clinical evidence available to help guide surgeons through the decision-making process for the use of allografts in primary ACL reconstruction.

METHODS

The literature in relation to allograft healing, storage, sterilisation, differences in surgical technique and rehabilitation have been reviewed in addition to recent comparative studies and all clinical systematic reviews and meta-analyses.

RESULTS

Early reviews have indicated a higher risk of failure with allografts due to association with irradiation for sterilisation and where rehabilitation programs and post-operative loading may ignore the slower incorporation of allografts. More recent analysis indicates a similar low failure rate for allograft and autograft methods of reconstruction when using non-irradiated allografts that have not undergone chemically processing and where rehabilitation has been slower. However, inferior outcomes with allografts have been reported in young (< 25 years) highly active patients, and also when irradiated or chemically processed grafts are used.

CONCLUSION

When considering use of allografts in primary ACL reconstruction, use of irradiation, chemical processing and rehabilitation programs suited to autograft are important negative factors. Allografts, when used for primary ACL reconstruction, should be fresh frozen and non-irradiated. Quantification of the risk of use of allograft in the young requires further evaluation.

LEVELS OF EVIDENCE

III.

Hybrid graft vs autograft in anterior cruciate ligament reconstruction: a meta-analysis

Purpose

We conducted this meta-analysis to evaluate the efficacy of hybrid grafts in anterior cruciate ligament reconstruction (ACLR).

Methods

We performed an electronic search of the Cochrane Library, PubMed, Embase, and ScienceDirect from the inception of these databases to February 2018, based on the terms “anterior cruciate ligament or ACL reconstruction”, “autograft”, “hybrid”, and “augment”. Relevant journals and conference proceedings were searched manually. Quality assessment, data extraction, and calculation of data from the included studies were conducted independently by two reviewers using RevMan 5.1.

Results

One randomized controlled trial and eight nonrandomized controlled trials met inclusion criteria. Larger graft diameters were found in the hybrid-graft group (mean difference −1.47, P=0.0001). There was no significant difference in failure rate (OR 2.13, P=0.21), retearing (OR 2.23, P=0.12), revision of ACLR (OR 1.05, P=0.87) or reoperation (OR 1.27, P=0.35). Subgroup analysis showed that hybrid-graft patients with meniscus injury suffered more revision (OR 4.10, P=0.02) and reoperation (OR 5.74, P=0.001). Both autografts and hybrid grafts performed similarly in most knee-score systems. However, autograft patients had better KT-1000 (mean difference 0.24, P=0.05) and quality-of-life results on the Knee Injury and Osteoarthritis Outcome Score measure (mean difference 7.23, P=0.05).

Conclusion

This meta-analysis of the current literature indicates similar performance of hybrid or autologous grafts in ACLR, though hybrid grafts had larger diameters than autografts. Other potential factors to influence failure, revision, or postoperative knee function, such as irradiation, age at reconstruction, meniscus injury/treatment, and hybrid-graft remodeling, should be investigated further.

Autograft or Allograft? Irradiated or Not? A Contrast Between Autograft and Allograft in Anterior Cruciate Ligament Reconstruction: A Meta-analysis

PURPOSE

To compare the clinical outcomes and adverse events associated with irradiated and nonirradiated allografts in anterior cruciate ligament (ACL) reconstruction.

METHODS

PubMed, Web of Science, and EMBASE were searched for randomized controlled trials from January 1990 to March 2018 to compare autograft with allograft in ACL reconstruction. Both objective and subjective outcomes of the function and adverse events were meta-analyzed. Two comparisons were summarized: (1) autograft and nonirradiated allograft and (2) autograft and irradiated allograft. The bias risk was based on the Cochrane Handbook for Systematic Reviews of Interventions. The overall risk ratio or weighted mean difference was calculated using a fixed- or random-effects model. Heterogeneity between studies was evaluated by the Q and the I² statistics.

RESULTS

Eleven trials were included in this review for meta-analysis. A total of 1,172 patients were involved (465 autograft and 461 nonirradiated allograft; 141 autograft and 138 irradiated allograft patients). The average follow-up varied from 2 to >10 years. The mean patient age varied from 22 to 32.8 years. The total failure rate was 2.5%. Our analyses demonstrated better clinical outcomes in autograft than irradiated allograft, which could be observed clearly through the International Knee Documentation Committee score (3.84; 95% confidence interval [CI], 1.93-5.76; P < .0001; I² = 0%), Lysholm score (2.94; 95% CI, 0.66-5.22; P = .01; I² = 0%), and Tegner score (0.14; 95% CI, -0.08 to 0.36; P = .22; I² = 0%) with fewer adverse events 0.20 (95% CI, 0.11-0.39; P < .00001; I² = 0%). There were no significant differences in autograft and nonirradiated allograft groups (P = .47, P = .27, P = .24, and P = .24, respectively).

CONCLUSIONS

Autograft offered greater advantages in functional outcomes and adverse events than irradiated allograft in ACL reconstruction; however, there were no significant differences between autograft and nonirradiated allograft in ACL reconstruction.

LEVEL OF EVIDENCE

Level II, meta-analysis of Level I and Level II studies.

Editorial Commentary: Reduce the Failure Risk: A Challenge to Reduce the Risk of Using Hybrid Graft in Anterior Cruciate Ligament Reconstruction

Hybrid grafting (augmentation of small hamstring autografts with allograft tissue) is preferred by many surgeons for anterior cruciate ligament (ACL) reconstruction. Although a recent, well-conducted, systematic review reported no significant differences in failure risk between hybrid graft and autograft ACL reconstruction, a trend toward a greater failure risk using the hybrid graft existed in many of the included studies. Three potential causes of hybrid graft ACL reconstruction failure that are absent in autograft ACL reconstruction are different levels of graft revascularization and ligamentization, differences in the tendon-bone healing capacity between the allograft and autograft portions in the bone tunnel, and processing of the graft. Research advances in these areas will further reduce the failure risk of hybrid graft ACL reconstruction.

Effects of graft preconditioning on γ-irradiated deep frozen tendon allografts used in anterior cruciate ligament reconstruction

Preconditioning of the grafts prior to implantation into the knee is considered to reduce the loss of tension caused by graft viscoelasticity after anterior cruciate ligament reconstruction. The present study analyzed the impacts of different preconditioning forces on the biomechanical properties of the γ-irradiated deep frozen tendon allografts. A total of 36 tendon grafts were randomly divided into three groups and were preconditioned at 80 N (group 1), 160 N (group 2) and 320 N (group 3) for 10 min. Subsequently, the grafts were gradually completely relaxed for 1 min and subsequently received 25 cyclic loads of 0–80 N. Afterwards, the grafts were loaded to 80 N, which was maintained for 30 min. Finally, load was gradually increased until ultimate failure at maximum load (UFML) was obtained. There were significant differences in the stiffness and UFML values between the 3 groups (all P<0.05). The graft stiffness in group 3 significantly increased compared with the other 2 groups, and the stiffness of group 2 grafts increased compared with group 1. The UFML in group 3 was significantly lower compared with groups 1 and 2, while there was no significant difference between groups 1 and 2. In the present study, the results suggested that increasing the initial tension could effectively reduce the loss of stiffness due to viscoelasticity for the γ-irradiated deep frozen allogeneic tendon grafts. However, overloaded initial tension decreased the tensile strength.

Allograft Use Results in Higher Re-revision Rate for Revision Anterior Cruciate Ligament Reconstruction

Background:

The literature on revision anterior cruciate ligament (ACL) reconstruction (ACLR) outcomes is generally sparse, but previous studies have demonstrated that autograft use results in improved sports function and patient-reported outcome measures compared with allograft. However, knowledge is still lacking regarding the impact of graft type on rates of re-revision.

Purpose:

To investigate the clinical outcomes and failure rates of revision ACLRs performed with either allograft or autograft.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

A search of the Danish Knee Ligament Reconstruction Registry identified 1619 revision ACLRs: 1315 were autograft procedures and 221 were allograft procedures (type of graft was not identified for 83 procedures). Clinical outcomes after 1 year were reported via the Knee injury and Osteoarthritis Outcome Score (KOOS), the Tegner activity score, and an objective knee stability measurement that determined side-to-side differences in instrumented sagittal knee laxity. Failure was determined as re-revision. Outcomes for revision were provided for the full life of the registry, up to 10 years.

Results:

The re-revision rate was significantly higher for allograft compared with autograft (12.7% vs 5.4%; P < .001), leading to a hazard ratio for re-revision of 2.2 (95% CI, 1.4-3.4) for allografts compared with autografts when corrected for age. At 1-year follow-up, objective knee stability was significantly different (2.1 ± 2.1 mm for allograft vs 1.7 ± 1.8 mm for autograft; P = .01), and the KOOS subscale scores for symptoms, pain, activities of daily living, sports, and quality of life were 67, 76, 84, 49, and 46 for allograft and 67, 78, 84, 51, and 48 for autograft, respectively, with no difference between groups.

Conclusion:

In this observational population-based study, the ALCR re-revision rate was 2.2 times greater for allograft compared with autograft procedures. Allograft was associated with greater knee laxity at 1-year follow-up. However, subjective clinical outcomes and knee function were not inferior for allograft patients. These results indicate that autograft is a better graft choice for revision ALCR.

Editorial Commentary: When Is Too Small, Too Small? Allograft Augmentation of Autologous Hamstring Grafts During Anterior Cruciate Ligament Reconstruction

Soft tissue allograft augmentation of small hamstring autografts, so-called hybrid grafts, has been proposed as an option during anterior cruciate ligament reconstruction (ACL-R). However, notable concerns exist with both small autograft use and allograft use during ACL-R, particularly in young, active patients. We currently choose to augment hamstring autografts with diameters <8.0 mm, adding only enough allograft to create a hybrid graft with an overall diameter no larger than 8.5 mm. Based on the available evidence, surgeons continue to seek the tipping point where the benefit of additional allograft tissue exceeds the consequence of its use.

Comparison of Clinical Outcomes After Anterior Cruciate Ligament Reconstruction Using a Hybrid Graft Versus a Hamstring Autograft

PURPOSE

This study aimed to compare the clinical outcomes of patients who underwent anterior cruciate ligament (ACL) reconstruction with a hybrid graft versus an autograft after 3 years of follow-up.

METHODS

Among 57 patients with an ACL injury who underwent ACL reconstruction, 28 patients received a hybrid graft (gracilis and semitendinosus tendon autograft plus a soft tissue allograft) and 29 patients received an autograft (gracilis and semitendinosus tendon autograft). The 2 groups were compared after a minimum 3-year follow-up regarding International Knee Documentation Committee (IKDC) assessment of knee function and stability, pivot-shift test, Lachman test, and KT-1000 side-to-side differences. The patient-reported Tegner activity score, Lysholm score, and subjective IKDC score were also compared. Graft failures were identified by patient-reported outcomes, physical examinations, or magnetic resonance imaging, and were confirmed on second-look arthroscopy; failure rate was compared between groups.

RESULTS

At final follow-up, the 2 groups significantly differed in pivot-shift test result (P = .013) and Lachman test result (P = .027). The failure rate tended to be greater in the hybrid graft group (14.3%) than in the autograft group (3.4%) (P = .148). All 5 patients with failed graft reconstruction were revised after second-look arthroscopy. The KT-1000 side-to-side differences at final follow-up were significantly inferior in the hybrid graft group (3.5 ± 2.0) compared with the autograft group (2.5 ± 1.0, P = .024). The hybrid graft group also had a lower mean Lysholm score (P = .000) and subjective IKDC score (P = .006) than the autograft group. The mean Tegner activity score was 6.8 ± 0.8 in the hybrid graft group and 6.9 ± 0.6 in the autograft group (P = .436).

CONCLUSIONS

The knee stability and patient-reported scores in the autograft-irradiated allograft hybrid graft ACL reconstruction group were significantly inferior compared with those in the autograft ACL reconstruction group.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Cyclic Testing of 3 Medial Patellofemoral Ligament Reconstruction Techniques

Background:

Several techniques are available to secure the graft to the patella during medial patellofemoral ligament (MPFL) reconstruction. The biomechanical properties of these techniques remain unknown.

Purpose:

To compare the biomechanical properties of 3 MPFL patellar fixation techniques: bone tunnels (BT), PushLock anchors (PL), and tenodesis screws (TS).

Study Design:

Controlled laboratory study.

Methods:

Forty-five MPFL reconstructions were performed using 3 different reconstruction techniques (BT, PL, and TS). The specimens were randomly assigned, with 15 specimens in each of the 3 groups. Cyclic loading (500 cycles) and load-to-failure testing were performed. Gap formation after 100 and 500 cycles, ultimate load to failure, and stiffness were measured.

Results:

Six constructs failed during cyclic loading, 5 in the PL group (33%) and 1 in the TS group (6.7%). After 100 cycles, differences in gap formation were found between the PL and BT groups (4.48 vs 3.62 mm, P < .03) and between the PL and TS groups (4.48 vs 2.28 mm, P < .0001). After 500 cycles, differences in gap formation were found between the BT and TS groups (6.63 vs 4.16 mm, P < .002) and between the PL and TS groups (7.89 vs 4.16 mm, P < .005). The PL group was found to have a lower ultimate load to failure when compared with the BT group (161.4 vs 258.3 N, P = .019) and the TS group (161.4 vs 237.1 N, P = .009). Group differences in stiffness did not reach statistical significance among the 3 groups (PL, 33.72 N/mm; BT, 37.50 N/mm; TS, 43.00 N/mm).

Conclusion:

The TS and BT groups have more ideal biomechanical properties than the PL group, as demonstrated by less displacement during cyclic loading and a higher load to failure.

Clinical Relevance:

Fixation of the patellar limbs during MPFL reconstruction may be optimized with the use of TS or BT over a PL technique.