April 28, 1999
Dear Dr P.
To the editor:
In the March edition of Arthroscopy Martinek and Friederich describe a patient in whom a tibial and pretibial cyst occured 8 months after reconstruction of the anterior cruciate ligament (ACL) using a biodegradable poly-D,L-lactide interference screw for fixation of the tibial bone plug of the autograft. 1 Arthroscopy showed a normal ACL without macroscopic signs of inflammation. Histological examination of the cyst demonstrated neither the presence of screw material within the fluid nor signs of an inflammatory reaction in the cyst wall. The authors did not state which method was used how conclusively the presence of a communication to the joint was excluded e.g. pure observation or methylene blue injection. The authors conclude that the cyst was caused by an adverse reaction of the bone to the biodegradable screw material.
Between 1995 and 1999 a total of 1181 biodegradable poly-D,L-lactide interference screws (Sysorb; Sulzer Orthopedics, Baar, Switzerland) were implanted by several surgeons at our institution. Patellar tendon or hamstring tendon autografts were used to reconstruct the cruciate ligaments in either an endoscopic, open, single incision, double incision or all-inside technique. To date we have not encountered a single case of osteolysis causing patient discomfort or necessitating a repeat operative intervention.
There are numerous case reports of cyst formation similar to that described by Martinek and Friederich in patients in whom metallic devices were used for the fixation of allografts or autografts. Although the exact pathogenesis of cyst formation is not fully understood, it is generally thought that in most cases there is some degree of necrosis of the graft material or the tunnel wall.2,3 The gelatinous cystic content is thought to originate from joint fluid similar as is the case of large Bakers cyst.4,5 Benign cysts have even been found in the vicinity of normal ACLs which had sustained neither previous injury nor operation.6-10
In our opinion the data presented by Martinek and Friedrich do not support the conclusion that the cyst formation in their patient was caused by an adverse reaction of the bone to the biodegradable screw material.