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Abstract & Commentary
Synopsis: This study prospectively evaluated the long-term effects of bioabsorbable (copolymer) screws. At an average 5-year follow-up, MRI scans demonstrated remodeling and new bone formation at the site of the implants.
Source: Lajtai G, et al. Bone tunnel remodeling at the site of biodegradable interference screws used for anterior cruciate ligament reconstruction: 5-year follow-up. Arthroscopy. 2001;17(6):597-602.
Bioabsorbable interference screws are a popular method for fixation of ACL grafts. Recent experience with revision ACL reconstruction has demonstrated that PLLA screws often take an exceedingly long time to degrade (more than 2-3 years). Concerns over cystic or osteolytic changes in the surrounding bone have also been suggested. Other case reports have suggested that PLLA screws, although they may have long resorption times, do not have adverse tissue reactions. The present paper is the first study of a copolymer screw that contains both lactide and glycolide (85/15 D,L Lactide/Glycolide, Biologically Quiet Screw, Instrument Makar, Okemos, Mich).
In a prospective study, these devices were used in 32 cases of isolated ACL reconstruction using a patellar tendon autograft and fixed with a 9 ´ 25 mm bioabsorbable interference screw. A total of 28 of the original 32 patients were evaluated clinically, with plain radiographs, and with MRI at an average 5.2 year follow-up (range, 4.1-6.4 years). The clinical outcome was good to excellent in more than 90% of cases, and plain radiographs showed no osteolysis or cystic bone formation. MRI scans showed no evidence of residual screws and no edema. Thus, the screws had completely resorbed and were replaced by bone. Lajtai et al did report some tunnel widening on MRI, particularly in the femur, but it was of no apparent consequence.
Comment by Mark D. Miller, MD
This is a good prospective study with mid- to long-term follow-up. Lajtai and colleagues emphasize in their discussion (and I think it is important as well) that their results are only applicable to this particular screw. Additional studies need to be done on other screws that are in clinical use. This copolymer has a quicker absorption profile than more commonly used screws, with absorption within 6 months in an animal study cited by Lajtai et al. The use of plain radiographs and MRI to evaluate bone changes is good, but unfortunately not as good as a gross and histologic evaluation, which simply isn’t possible in a clinical study. This is good news for those who use this particular screw—I hope to see similar studies of other screws in the near future.
Dr. Miller, Associate Editor of Sports Medicine Reports, is Associate Professor, UVA Health System, Department of Orthopaedic Surgery, Charlottesville, Va.