Practice Essentials
Multiple techniques are available for reconstruction of the anterior cruciate ligament (ACL). Controversy certainly exists as to which autograft is best and which methods of placement and fixation should be used. An obvious issue is, What is the better choice when both autografts and allografts are available to the surgeon and patient? [1, 2] (See Treatment for a discussion of the advantages and disadvantages of autografts and allografts.)
The supremacy of free bone-patellar tendon-bone autograft was briefly challenged in the 1970s and 1980 by proponents of artificial ligaments in the form of Gore-Tex and Proplast. Poor experiences with these nontissue substitutes led surgeons to choose other graft materials, including allografts. This trend was accelerated after Jackson and others developed the technique of arthroscopically assisted ACL reconstructions during the mid-1980s. [3]
Instances exist in which autograft is not available because of multiple reconstructions or combined ligament injuries. In addition, after discussing the advantages and drawbacks of the various graft materials available, patients may choose not to use autograft material. In these situations, other graft sources must be considered.
The 2014 guideline on the management of ACL injuries formulated by the American Association of Orthopaedic Surgeons (AAOS) recommended that practitioners use either autograft or appropriately processed allograft tissue in patients undergoing ACL reconstructions, on the grounds that the measured outcomes are similar, though with the caveat that these results may not be generalizable to all allografts or all patients (eg, young or highly active patients). [4]
This article deals with the grafts available and is aimed at providing the reader with an increased confidence in choosing from various materials. It does not cover surgical indications or techniques, which are addressed in other articles in Medscape Drugs & Diseases.
Anatomy
The anatomy of the knee is reflective of its function in ambulation. Knee stability and pain-free range of motion (ROM) are important in maintaining daily function. Most commonly, overuse, age, and traumatic injuries cause structural damage to the knee that may limit its function. Therefore, a thorough understanding of the anatomy of the knee is essential to properly diagnosing and treating knee pathology.
The ligaments of the knee joint can be divided into the extracapsular ligaments and the intra-articular ligaments. The extracapsular (external) ligaments are as follows:
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Patellar ligament
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Medial collateral ligament (MCL)
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Lateral collateral ligament (LCL)
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Oblique popliteal ligament
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Arcuate popliteal ligament
The intra-articular ligaments are as follows:
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ACL
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Posterior cruciate ligament (PCL)
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Posterior meniscofemoral ligament
The ACL attaches posterior to the attachment of the medical meniscus on the anterior intercondylar area of the tibia and passes superior, posterior, and lateral, where it attaches to the posterior part of the medial side of the lateral condyle of the femur.
The PCL arises from the posterior intercondylar area and passes on the medial side of the ACL to attach to the anterior part of the lateral surface of the medial condyle of the femur.
The menisci are wedge-shaped and attach at their ends to the intercondylar area of the tibia. The medial meniscus is C-shaped and firmly adheres to the deep surface of the MCL medially, the ACL anteriorly, and the PCL posteriorly. Because of these attachments, the medial meniscus is less mobile than the lateral meniscus.
For more information about the relevant anatomy, see Knee Joint Anatomy.
Pathophysiology
An image depicting ACL injury can be seen below.
Anterior cruciate ligament reconstruction aims to reduce instability episodes in an attempt to preserve the meniscus. When meniscal injury has occurred, the knee becomes degenerate with time.
Prognosis
Long-term published clinical studies comparing allografts with autografts have not been numerous. Indelicato et al [5] and Shelton et al [6] showed generally good results in comparison of the tissues. One study showed improved long-term outcomes with autograft over allograft as well as with not smoking and with normal body mass index. [7] In another study, an overall trend of fewer patellofemoral symptoms and better ROM with allografts was noted. Shelton described a trend of increased pivot glide with allograft, which was not statistically significant.
Although happy with their allograft results, all of these authors remained cautious with their outlook, echoing the sentiments of Beynnon that it may take years to see a pattern for overall failure for any graft type. [8]
Beynnon theorized that the initial and 2- to 3-year outcome studies may not accurately assess longer-term results. [9] He showed that reestablishing anteroposterior (AP) stability does not predict future graft behavior. Using strain gauges in autograft reconstructions, he showed that strain characteristics established at the time of surgery were a more powerful predictor of long-term results. Grafts that varied most from normal strain patterns in the early postoperative period showed long-term failure. This is disturbing when bench studies have shown that tensioning allografts in the human cadaver knee to fully achieve AP joint stability increased forces in the graft at all angles of flexion.
Authors have long proclaimed dangerous strain and shearing in terminal extension. Of particular note, the good results that Indelicato [5] and Shelton [6] achieved all predated the era of accelerated rehabilitation protocols popularized by Shelbourne. [10] In fact, the allograft protocols included limited arcs and crutch weightbearing for up to 12 weeks.
With all of this in mind and with the knowledge that allografts take longer to remodel and mature, the following question remains: Should there be concern with allografts in general, and specifically in relation to ongoing trends in accelerated rehabilitation? Although Shelbourne did not suggest this, should his autograft axiom be applied? It allows activity based on the status of rehabilitation and not on graft biology.
Alternatively, should these patients be restricted as is commonly done in grafts without bone plugs due to fixation concern? This question is especially important with the potential earlier aggressive rehabilitation and return to activity that allografts allow by virtue of their decreased morbidity as compared with autografts. [11, 12, 13]
The type of allograft, sterilization process, and patient characteristics also may have some effect on outcomes. Irradiated grafts in some studies show higher failure rates. [14, 15] Allograft use in younger and more athletic populations have also shown higher failure rates in studies. [16]
In a study comparing autografts with allografts in 99 young patients with a symptomatic ACL-deficient knee (100 knees) who were followed up for a minimum of 10 years, more than 80% of all of the grafts were intact and had maintained stability at follow-up; however, the failure rate was three times higher in the allograft group than in the autograft group. [17]
In a meta-analysis and systematic review of prospective studies evaluating irradiated allograft against autograft for ACL reconstruction, Wang et al found that the former was inferior to the latter with respect to knee stability and subjective evaluation but that the two types of graft did not differ significantly with respect to function and complications. [18] However, only a limited number of randomized controlled trials were included in the analysis, and more such studies, with longer follow-up periods, would be required to define failure rates more accurately.
Biz et al evaluated the medium-term clinical outcomes of 43 patients undergoing ACL reconstruction using either a bone–patellar tendon–bone allograft (n = 22) or a hamstring autograft (n = 21). [19] At follow-up evaluation, the two patient groups showed similar results with respect to subjective assessment, objective clinical evaluation, and proprioceptive properties of the limb. However, the patients who underwent allograft ACL reconstruction returned to normal sport activity earlier than the patients who underwent autograft reconstruction (11.7 ± 10.3 vs 17.9 ± 14.6 weeks).
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Anterior cruciate ligament reconstruction aims to reduce instability episodes in an attempt to preserve the meniscus. When meniscal injury has occurred, the knee becomes degenerate with time.
