Pseudotumor Associated with a Bioabsorbable Screw in a Patient with Reconstructed Congenital Absence of the Anterior Cruciate Ligament: a Case report

Abstract

Congenital absence of the anterior cruciate ligament (ACL) is an extremely rare condition associated with a wide spectrum of malformation. Here we describe a rare complication in a patient with congenital absence of the ACL after ACL reconstruction using a bioabsorbable screw. A 35- year-old woman presented a right knee mass that had been slowly growing for several months. Five years previously, she experienced acute right knee pain, locking, and instability after hiking. Images and diagnostic arthroscopy at that time revealed an absence of the anterior cruciate ligament, a hypoplastic lateral distal femoral condyle, a stenotic intercondylar notch, and hypoplastic posterior cruciate ligament along with a bucket handle tear of the medial meniscus. A right anterior cruciate ligament reconstruction was performed, and she did well for the next five years without knee joint instability until she presented a mildly painful subcutaneous pretibial soft tissue mass. Imaging studies demonstrated a 2.4 cm subcutaneous lobulated soft tissue mass protruding from the expanded tibial tunnel. The mass was excised, and the histology showed a solid and cystic lesion composed of a histiocytic and foreign body giant cell reaction to the degraded polymer along with spheres of calcium phosphate particles. At a two-year follow-up after debridement, the patient reported an overall improvement without any knee instability or local recurrence. To the best of our knowledge, this is the first report of a pseudotumor developed after ACL reconstruction in a patient with a congenital absence of the ACL.