Bio-interference screw cyst formation in anterior cruciate ligament reconstruction--10-year follow up.

PURPOSE: This study used serial MRI to assess the absorption of a poly l-lactide Bioabsorbable interference screw used in the anterior cruciate ligament reconstruction with a 4-strand hamstring technique. METHODS: A consecutive series of ten patients undergoing anterior cruciate ligament reconstruction a 4-strand hamstring technique were assessed with magnetic resonance imaging (MRI) scans at 1, 2, 4, 7 and 10 years postoperatively. RESULTS: No resorption had occurred after 4 years in any of the patients. By 7 years screw absorption was complete in seven patients and had progressed in three. New cyst formation occurred in 3 patients between 5 and 7 years. Half the patients displayed small fluid collections within the tibial tunnels. At 10 years all screws were fully absorbed; however cyst formation was common, including the development of a new cyst in the period between 7 and 10 years in one patient. None of the patients had instability, persistent effusions, or clinically detectable adverse reactions to the screws. CONCLUSIONS: This study has shown that poly l-lactide bioabsorbable screws take longer to resorb than initial in vitro data suggested. It is unclear whether ganglion formation within the tibial tunnel is related to screw resorption or the hamstring graft. The theoretical advantages of bioabsorbable screws must be weighed against these findings.