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Benefits of bioabsorbable screws 'not sufficient' for regular use in ACL reconstruction
Drogset JO. Knee Surg Sports Traumatol Arthrosc. 2011. doi: 10.1007/s00167-010-1353-4.
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The results of a level 1 study comparing ACL reconstructions using bone-patellar tendon-bone grafts fixed with either bioabsorbable or metal interference screws shows good functional and clinical outcomes for both groups at 7-year follow-up.
“The potential advantages of using PLLA screws compared to metal screws are not sufficient to warrant the routine use of PLLA-screws in ACL reconstructions,” the investigators wrote in their abstract.
The investigators followed 22 women and 19 men who underwent ACL reconstruction performed during a 1-year period with bone-patellar tendon bone grafts fixed with bioabsorbable poly-L-lactic acid (PLLA) or metal interference screws. The metal screw group included 20 patients, and the PLLA group had 21 patients.
The investigators found that the groups had similar postoperative outcomes using the following measures: Lysholm score, Tegner activity score, Knee injury and Osteoarthritis Outcome Score, Lachman test and KT-1000 arthrometer examination. However, they found that the PLLA group had better outcomes using pivot shift testing. Using MRIs, the investigators found bioscrew degradation. Of the 16 patients in the PLLA group who had an MRI, a residual screw tract that looked threaded was visible in the tibias of 11 patients.
The main purported benefit of absorbable interference screws is easier revision surgery. In a study of 41 patients, it is unlikely that many, if any, went on to revision surgery. Therefore, the main potential benefit is not being evaluated.
It is interesting to note that the PLLA screws had a better pivot shift. This doesn't make a whole lot of sense. Studies like this are often simply a comparison of one surgeon who uses PLLA screws and another that uses metal. If the two surgeons place their tunnels in different positions, you can end up with differences in pivot and other outcomes. It is important to know this, but I cannot gather it from the abstract.
The purpose stated is to compare the clinical outcomes of these two groups. If this is the case, we need validated outcome scores (IKDC, Tegner, Lysholm, etc.) and objective measures (KT-1000, Lachman, and pivot) also spelled out in the results. Also, if this is their true aim, this study is almost certainly underpowered with an n=41 to detect significant differences.
If the true purpose of this study is to explore the potential benefits of PLLA screws vs. metal screws, it would be more beneficial to look at a study of revision surgery of say, 100 ACLs. Then look at the outcomes, operative time etc of the revisions where PLLA was used the first time vs. revisions where metal was used the first time. Then, correlate these things with screw types.
I applaud the authors for attempting to address these problems, but think there are some issues with this study as I have mentioned.
– Vishal Mehta, MD
Fox Valley Orthopedic Institute
Fox Valley Orthopedic Research Foundation
Geneva, Ill.
Disclosure: Mehta receives honoraria from Arthrex for teaching courses and sits on the scientific advisory board for Allosource.