Cyclops and cyclopoid formation after anterior cruciate ligament reconstruction: clinical and histomorphological differences.

Prospectively, 119 patients were pursued clinically and by follow-up-arthroscopy for the occurrence of a "cyclops syndrome" after ACL reconstruction with a patellar tendon autograft, augmented by LAD. Twenty-one patients showed nodular formations. Ten of these (group 1) developed early clinical evidence of a "cyclops syndrome" with a mean extension deficit of 19 degrees before follow-up-arthroscopy, on average 5.9 months after the index operation. The nodular formations found and excised during débridement had a hard consistency. Histomorphological undecalcified microtome section evaluation of six specimens revealed fibrocartilagineous tissue with active bone formation in the center. The other 11 patients showed no clinical symptoms (group 2). A similar but soft nodulous scar formation was detected at follow-up-arthroscopy, on average 9.5 months after the index operation. Histomorphologically these so-called "cyclopoid" formations were only built-up fibrocartilagineous islands surrounded by granulation tissue. Neither remnants of tendon graft fibers nor old bone particles were found in specimens of either group. It can be concluded that both the hard cyclops and the soft "cyclopoid" are de novo scar formations.