Keywords
anterior cruciate ligament - grafting - knee
Introduction
Anterior cruciate ligament (ACL) rupture is a common injury in the general population, with an incidence of up to 75 per 100,000 people per year,[1] particularly in active individuals involved in contact sports. Although a reconstructed ACL does not completely restore the original structure or biomechanical properties of the native ACL,[2] the graft used for reconstruction must not only have structural and mechanical properties that resemble those of the native ligament, it must also exhibit minimal antigenicity and sufficient innate biological potential to incorporate into the host's bone. When selecting graft types, there are several considerations: autograft versus allograft and soft tissue-only grafts versus grafts with bone fragments. Examples of allografts are shown in [Fig. 1].
Fig. 1 Photo of allografts ready to be prepared. Grafts with a bone part (Patellar) and without bone parts (Tibial Posterior) are observed.
The commonly used autografts are: patellar with bone fragment, knee flexors, quadriceps (with or without patellar bone fragment); Among allografts, additional options include anterior and posterior tibial, peroneal, and calcaneal.[3]
[4]
[5]
[6]
[7] In [Fig. 2] different types of grafts are demonstrated.
Fig. 2 Different types of grafts: (A) patellar tendon graft, (B) quadriceps tendon graft with bone plug, (C) sextuple flexor graft.
Optimal graft selection depends not only on the properties of the graft, but mainly on the patient's characteristics and expectations.
Autograft versus Allograft
Autograft versus Allograft
All allografts demonstrated slower rates of incorporation compared to autografts, as well as a higher failure rate of approximately 25% in the active population (43 versus 75%).[8] Current evidence suggests the use of allografts in specific circumstances such as multiligament knee reconstructions, inadequate autograft tissue, or in older, less active populations.[9] The theoretical advantages of allografts are: elimination of donor site morbidity, less pain, shorter surgical and rehabilitation times and better cosmetic results.[10] Krych et al.[11] reported a fivefold higher risk of rerupture in cases that used an allograft. When excluding irradiated and chemically processed grafts, there was no difference in rerupture rate; however, their systematic review included only 6 studies. Kraeutler et al.[12] demonstrated similar results with a risk of rerupture approximately 3 times higher in the allograft group (12.7% vs. 4.3%). They also demonstrated increased knee laxity, and worse results in the single-leg hop test and subjective satisfaction.[12]
The prospective cohort study carried out by Kaeding et al.[13] evaluated the number of variables to determine predictors of graft rupture in the 2 years after reconstruction. Allograft use and young age significantly increased the risk of graft rupture.[13] Other recent studies have found increased rates of graft rupture in patients who received allografts and had a high level of postoperative activity.[14]
[15]
[16]
In laboratory and clinical studies, autografts show better results than irradiated and processed allografts.[17] Allografts may be considered for less active patients who are willing to accept the increased risk of graft failure.[17]
In an outpatient surgery setting, the autograft group had a significantly lower bill than the allograft group.[18] The decrease in surgical time did not compensate for the cost of the allograft (around $1,000).[18]
Regarding graft processing, it is believed that sterilization techniques alter biomechanical properties and the more a graft is processed, the worse its performance.[17] Park et al.[19] performed a systematic review of irradiated versus non-irradiated allografts with at least two years of follow-up, demonstrating worse functional scores in the irradiated group, decreased stability for Lachman, pivot-shift and KT-1000 testing, and increased risk of revision. The study by Tian et al.[20] demonstrated similar results. Allograft sterilization techniques alter the mechanical properties of allografts and are categorized into radiation or ethylene oxide. The extent of change in mechanical properties is dependent on the irradiation exposure dose.[7]
Farago et al.[21] reviewed 29 years of articles that evaluated the impact of sterilization techniques on tendons. Review results support that the technique with the greatest biomechanical preservation was freezing followed by radiation at 14.8-28.5 kGy.[21] However, allograft failure is not solely attributed to sterilization techniques, whereas allograft failure rates still remain high when comparing fresh allografts to autografts.[21]
Synthetic Grafts
Synthetic grafts were initially used in the 1980s as an option, offering advantages such as the absence of donor site morbidity, shorter surgical time, and reduced risk of disease transmission.[22]
[23]
[24] And potentially the possibility of an earlier return to sports.[22]
[23]
[24] However, early studies reported satisfactory short-term results, but in the medium and long term, there were complications such as an immune response, foreign body synovitis, tunnel osteolysis, fractures of the femur and tibia near the tunnels, and late graft failure.[22]
[23]
[24]
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[26] This resulted in a decline in the use of synthetic grafts, but there is currently renewed interest in a new generation of artificial grafts that have shown favorable results when used in special circumstances, such as in the older population.[24]
[25] It has gained some popularity among athletes recently due to the potential for immediate graft stability, faster rehabilitation, and a quicker return to sports.[27] A systematic review conducted by Machotka et al.[28] on the Ligament Advanced Reinforcement System (LARS) recommended caution when considering the use of synthetic grafts, as more studies are needed. In the study by Bianchi et al.[29] comparing LARS and knee flexor grafts, the LARS group demonstrated greater stability, and no patient required revision surgery. LARS can be considered in patients who require a rapid recovery, while being aware of the risk of graft failure and iatrogenic osteoarthritis.[30]
[31]
Hybrid Graft
It consists of a combination of auto and allografts and was initially described in 2015.[32] These grafts, typically formed from a combination of autologous flexor graft and soft tissue allograft, have gained interest from orthopedists for use in ACL reconstructions.[33] They are generally used in cases of small size of flexor grafts.[32] When planning to use hybrid grafts, only the semitendinosus graft can be removed instead of the semitendinosus and gracilis. Therefore, the use of hybrid grafts can reduce postoperative morbidity at the donor site.[33] A non-irradiated posterior tibial or peroneus longus allograft is generally used. In addition to the benefit of lower donor site morbidity, hybrid grafts also allow the graft to have a larger diameter than the semitendinosus/gracilis autograft, which may reduce the risk of postoperative failure. Therefore, hybrid grafts may be an option for older patients.[33]
Peroneus Longus Tendon Autologous Graft
Peroneus Longus Tendon Autologous Graft
As an autologous graft, the peroneus longus muscle tendon is an old option, however it has received greater attention in recent years due to its biomechanical properties similar to the native ACL ligament and the hamstring graft..[34]
[35]
[36]
[Fig. 3] shows the graft and its removal.
Fig. 3 Peroneus brevis graft: (A) small access route for graft removal with minimal morbidity and (B) peroneus brevis tendon graft ready to be prepared on the table with good length and good thickness.
More recent studies have evaluated its use in ACL reconstruction as well as postoperative function and donor site morbidity. These studies consistently demonstrate positive results, supporting the viability of autologous peroneus longus tendon graft as a good graft option in reconstructions.[37]
[38]
[39]
[40]
In terms of functional results, patients undergoing ACL reconstruction using the peroneus longus tendon autograft achieved excellent scores on several assessment tools, the main ones being the IKDC, Modified Cincinnati, Tegner-Lysholm, AOFAS and FADI scores.[35]
[41]
[42]
These scores indicate good knee function, ankle stability, and overall patient satisfaction. Functional results comparable to traditional graft options such as autologous hamstring tendon graft were also achieved.[35]
[43]
[44] Furthermore, autologous peroneus longus tendon graft has demonstrated advantages over other graft options. It featured a larger graft diameter, which may contribute to improved mechanical properties and stability.[35]
[36]
[39]
[45] It was associated with less thigh hypotrophy, indicating a reduction in muscle loss at the donor site. Donor ankle activity was not compromised as evidenced by positive scores on ankle function assessment tools and jumping tests.[35]
[36]
[40]
Another factor that makes the peroneus longus muscle tendon an ideal candidate for ACL reconstruction is that it is technically safe and easy to remove.[46] The tendon is superficially located and its position is not difficult to access by adjacent structures, such as the tendons of the hamstring muscle.[46]
[47]
Morbidity at the donor site was minimal, with no significant differences observed in ankle eversion and plantarflexion strength of the first ray between the donor site and the contralateral healthy site.[35]
[36] These findings suggest that autologous peroneus longus tendon graft does not cause significant morbidity at the donor site.[48]
In conclusion, ACL reconstruction using autologous peroneus longus tendon graft is a scientifically supported procedure with favorable results. It offers functional results comparable to traditional graft options such as hamstring tendon and can be used as an alternative to the autologous grafts most commonly used for ACL reconstruction: the patellar tendon and the tendon of the hamstring muscle.
Autologous Quadricipital Tendon Graft
Autologous Quadricipital Tendon Graft
The autologous quadriceps tendon (QT) graft for ACL reconstruction, despite currently being one of the least used grafts, has seen an increase in popularity in recent years, both for primary reconstructions and revisions.[49]
[50] QT graft can be used with or without a bone fragment removed from the patella. The advantages of removing the QT graft with a bone fragment are a longer graft and a possible better integration of the bone part of the graft into the tunnel created for the graft. The disadvantages are possible residual pain at the site of removal of the patellar bone block and the risk of fracture of the patella. Despite these differences, a recent systematic review compared the use of the QT graft with or without a bone fragment and showed that both grafts are safe and viable, with comparable clinical results, complications and revision rates.[51] Furthermore, QT graft can be used with partial or full thickness, with no difference between them in a recent systematic review.[52]
When compared to other graft options, the QT graft has benefits such as lower morbidity at the donor site (defined as anterior knee pain, difficulty or inability to kneel or both) when compared to the patellar tendon autograft.[53] In a cohort study, ACL reconstruction using a QT graft showed a lower rate of re-rupture when compared to autologous flexor graft.[54] In a recent study with 6,652 ACL reconstructions, cases using QT graft had a lower rate of septic arthritis when compared to cases using flexor grafts, patellar tendon grafts or allografts.[55] Regarding biomechanics, QT graft has an elastic modulus similar to that of the native ACL, which, at least from a theoretical point of view, is positive as it would allow biomechanics closer to the biomechanics of the knee before the injury.[56]
[57] Meanwhile, both the patellar tendon graft and the flexor graft have a significantly higher modulus of elasticity than that of the native ACL.[57]
[58] As for the load to failure, QT graft presents a load similar to the load of the flexor graft and a load significantly greater than the loads of the patellar tendon graft and the native ACL.[56]
[57]
[58]
[59]
[60] Finally, regarding the clinical results of graft rupture rate and patient-reported outcomes, the current literature does not present significant differences when QT graft is compared to patellar tendon and flexor grafts.[61]
Discussion
The study by Arnold et al.[61] demonstrated the result of research conducted over the last 14 meetings of the ACL group regarding the preferred graft type in ACL reconstructions. Over time, the choice of graft type can be divided into 4 phases: dominance of the autologous patellar graft with a bone fragment; dominance of the autologous patellar graft with a bone fragment with an increase in the use of autologous flexor grafts; dominance of autologous flexor grafts with a decrease in the use of autologous patellar grafts with a bone fragment and an increase in allograft use; and finally, dominance of autologous flexor grafts with the maintenance of the levels of flexor graft selection and an increase in autologous quadriceps grafts. Currently, more than 50% of the respondents state that their first choice is autologous flexor grafts, while fewer than 40% use autologous patellar grafts with a bone fragment. Allografts increased in popularity from 2006 to 2012, reaching 12% of choices in 2012. Currently, only 1% of the respondents use allografts as their first choice, and none use allografts with a bone fragment. Autologous quadriceps grafts have increased in frequency of selection since 2014, with a peak of over 10% in 2018.[61]
When selecting a graft for a primary ACL reconstruction, we must take into account a series of factors, including age, activity level, previous injuries, among others. Each graft option has its advantages and disadvantages. Patellar and knee flexor autografts are still the most used, but there are other options as shown in the initial part of this article. Allografts, quadriceps autograft and peroneus longus autograft are options and their main advantages and disadvantages are shown in [Table 1].
Table 1
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Types of graft
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Advantages
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Disadvantages
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Allograft
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- Absence of donor site morbidity
- Choice of graft size
- Shorter surgical time
- Better cosmetic result
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- High cost
- Low availability
- Risk of disease transmission
- Higher re-rupture rate (mainly in young people with high demand)
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Peroneus longus
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- Easy withdrawal technique
- Less hypotrophy of the thigh
- Larger graft diameter
- Good functional results
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- Donor site morbidity
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Quadriceptal
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- Possibility of use with or without bone plug
- Modulus of elasticity similar to native LCA
- Good functional results
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- Donor site morbidity (residual pain and risk of patella fracture in cases of bone plug)
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Final Considerations
Patellar autograft with bone fragment remains the first choice for high-performance athletes who wish to return to their pre-injury sporting level, and flexor autograft is the first choice for patients with lower sporting demands. Allografts may be an alternative in patients with a lower level of physical activity, especially in those over 40 years of age. Quadriceptal and peroneus longus autografts have shown favorable functional results and are options of choice.
