PLLA Screw-Related Foreign Body Reaction and Role in Pretibial Cyst Formation after ACL Reconstruction

Pretibial cyst formation is an uncommon but clinically significant complication following anterior cruciate ligament (ACL) reconstruction using bioabsorbable poly-L-lactic acid (PLLA) interference screws. This study reviews six cases of pretibial cyst formation after ACL reconstruction to evaluate its etiology, clinical presentation, and treatment outcomes. A retrospective analysis was conducted on six patients from a cohort of 446 ACL reconstructions performed with PLLA screws. Patients presented 2-4 years postoperatively with pretibial swelling and tenderness without systemic infection or allergic manifestations. Radiographs and magnetic resonance imaging demonstrated multiloculated cystic lesions and tibial tunnel widening adjacent to degrading screws. All patients underwent cyst debridement and screw removal, and histopathological specimens were analyzed. Histological examination revealed granulomatous inflammation characterized by macrophages, foreign body giant cells, and focal necrosis, supporting a foreign body reaction to PLLA degradation. Clinical evaluation showed preserved knee stability, with stable Lysholm, IKDC, and Lachman scores, although Tegner activity scores demonstrated mild postoperative decline. No communication between the cyst and joint space was identified, supporting the hypothesis that cyst formation results from localized inflammatory reactions rather than synovial fluid leakage. These findings suggest that PLLA screw degradation may induce foreign body reactions leading to pretibial cyst formation after ACL reconstruction. Surgical excision of the cyst and removal of the bioabsorbable screw resulted in symptom resolution without recurrence. Further investigation into alternative bioabsorbable materials with improved biocompatibility and degradation profiles is warranted to reduce inflammatory complications following ACL reconstruction.