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Taking a Closer Look at ACL Reconstructions

Can you believe it? Out of 5,000 studies published since 1990, only one compared the results of autograft to allograft reconstruction surgery for an anterior cruciate ligament (ACL) tear. That’s what orthopedic surgeons report after conducting an extensive systematic review of studies on ACL reconstruction surgery.

When a patient tears or ruptures the ACL ligament inside the knee, surgery is often needed to restore the stability that the anterior cruciate ligament (ACL) provides the knee. The best way to do this is to take tissue (usually a tendon) from some place else around the patient’s own knee (that’s an autograft) or from a donor bank (allograft) and stitch it in place.

The question these surgeons asked was, which one is better: autograft or allograft? They used measures of joint stability (e.g., the Lachman test, pivot-shift test, and KT-1000 arthrometer) as one way to look at results. They also looked at knee function and failure rates as measures of outcome.

Before starting their search, they identified a specific subset of patients to study. Only studies using live humans were included. The patients in these studies had only one knee involved and only the ACL ligament was damaged. Many times, an acute traumatic injury powerful enough to rupture the ACL will also tear other soft tissue structures in the knee. None of the patients had a previous history of other surgeries on the involved knee.

Studies included had to include only patients with a mean age of less than 41 years. The age restriction was to select out younger patients less likely to have additional arthritic changes to contend with. The studies had to follow them for at least two years after surgery.

With more than a quarter of a million ACL reconstruction surgeries performed in the United States each year, and 80 per cent of those using autografts, you would think the question of allograft versus autograft would be settled. In fact, the authors thought they would find no differences in results or outcomes between the two graft choices.

But what they found was that more time and money has been invested in studying the differences in results between two types of autografts (bone-patellar tendon-bone vs. hamstring). Second to that, surgeons have been working hard to improve and refine the way these grafts are attached, a process called graft fixation.

There were only three studies on allografts that fit the criteria used for including studies in this analysis. More of the acceptable studies were focused on autografts (a total of 54 included). Because there weren’t enough direct studies comparing one to the other, it was necessary to look at the studies for each type of graft separately and compare them that way instead. Without enough studies using a direct comparison, the level of evidence to support one or the other is less.

Given all the ifs, ands, or buts, the authors reported that allografts tend to produce a knee that isn’t as stable as joints treated with autografts. In other words, there’s greater joint laxity (looseness) with allografts when using joint stability tests described.

The KT-1000 assessment is probably the most objective way to measure stability. The device shows in millimeters how much the joint moves (slides and glides) when pressure or force is applied to the joint. The other tests (Lachman, pivot-shift) are performed by an examiner and are therefore more subjective.

There were no significant differences based on the other outcome measures (graft failure, function). The authors thought that the lack of significant differences might be more a reflection of how studies are conducted than the fact that there really aren’t differences in results between autograft and allograft.

For example, the study size (number of patients included) varies greatly from one study to the next. That factor alone can affect the results. There is also a wide range of differences among patients included based on age, activity level, and surgical technique used. Without a set standard approach with more similarities than differences in how studies are conducted, results can’t be compared from study to study.

The final conclusion from this meta-analysis was that researchers may need to direct future studies toward comparing autograft to allograft ACL reconstructive surgeries. This is important before continuing to choose autografts over allografts. Autografts have the disadvantage of causing problems at the donor site such as infection, persistent pain, and possible deformity. Allografts eliminate those problems but have their own issues with potential tissue rejection by the patient.

The authors suggest it would be helpful if comparative studies select patients carefully so that other factors don’t cloud the results. Outcome measures using valid tests like the Tegner activity score, Cincinnati knee score, Lysholm score, and International Knee Documentation Committee (IKDC) score should be used in all studies to allow for more accurate comparisons of results.

Lisa M. Tibor, MD, et al. Clinical Outcomes After Anterior Cruciate Ligament Reconstruction: A Meta-Analysis of Autograft Versus Allograft Tissue. In Sports Health. January/February 2010. Vol. 2. No. 1. Pp. 56-72.

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