Large Infected Femoral Cystic Swelling after Anterior Cruciate Ligament Reconstruction through Transportal Technique

INTRODUCTION: Large cystic swellings in the knee are a rare complication of anterior cruciate ligament (ACL) reconstruction surgery. Most cystic swellings in the literature arise from the tibia; femoral cystic swellings which are clinically significant and infected are thus extremely rare. Little is known about the etiology of such cystic swellings post-ACL reconstruction, and there are no standardized protocols for their treatment. CASE PRESENTATION: Our patient presented 6 months post-ACL reconstruction, with a large swelling over the lateral aspect of the femur in the operated knee. His presentation presented a clinical dilemma: On the one hand, he presented with a large cystic swelling adjacent to the knee, but had only vague knee pain with no significant joint effusion and no fever or other constitutional symptoms; while on the other, his swelling was significantly large and his imaging findings were worrisome. This cystic swelling turned out to be an infected cyst arising from the tissue adjacent to the femoral tunnel. We present a rare complication of ACL reconstruction and discuss the possible causes of such large cystic swellings. We also discuss the management of large infected cysts post-ACL reconstruction. CONCLUSION: Large, infected femoral cyst post-ACL reconstruction is rare and requires appropriate clinical assessment and management. It is important to ascertain whether they are associated with intra-articular infections/septic arthritis. If there is no septic arthritis, these swellings can be treated with simple surgical debridement and antibiotics and retention of ACL graft. The long-term outcomes of graft retention in these patients are excellent.