Allograft Reconstruction of ACL-Deficient Knee

Updated: Dec 24, 2015
  • Author: Bart Eastwood, DO; Chief Editor: Thomas M DeBerardino, MD  more...
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Overview

Background

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. This article deals with the grafts available and is aimed at providing the reader with an increased confidence in choosing from various materials. This article does not cover surgical indications or techniques; other articles in this publication address these issues.

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Anatomy

The anatomy of the knee is reflective of its function in ambulation. Knee stability and pain-free range of motion 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:

  • Patellar ligament
  • Medial collateral ligament (MCL)
  • Lateral collateral ligament (LCL)
  • Oblique popliteal ligament
  • Arcuate popliteal ligament

The intra-articular ligaments are as follows:

  • ACL
  • Posterior cruciate ligament (PCL)
  • 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.

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Pathophysiology

An image depicting ACL injury can be seen below.

Anterior cruciate ligament reconstruction aims to 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.
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Prognosis

Long-term published clinical studies comparing allografts to autografts are few. Indelicato [4] and Shelton [5] 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. [6] In another study, an overall trend of fewer patellofemoral symptoms and better range of motion 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, they all 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. [7]

Beynnon theorized that the initial and 2- to 3-year outcome studies may not accurately assess longer-term results. [8] He showed that reestablishing anteroposterior (AP) stability is not a predictor of future graft behavior. Using strain gauges in autograft reconstructions, he showed that strain characteristics established at the time of surgery was 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 recent 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 [4] and Shelton [5] achieved all predated the era of accelerated rehabilitation protocols popularized by Shelbourne. [9] In fact, the allograft protocols included limited arcs and crutch weightbearing for up to 12 weeks.

With all of this in mind and knowing 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 recent trends in accelerated rehabilitation? Although Shelbourne has not suggested 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 due to the decreased morbidity compared with autografts. [10, 11, 12]

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. [13, 14] Allograft use in younger and more athletic populations have also shown higher failure rates in studies. [15]

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. [16]

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