Is the etiology of pretibial cyst formation after absorbable interference screw use related to a foreign body reaction?
BACKGROUND
Arthroscopically assisted anterior cruciate ligament reconstruction using a bioabsorbable tibial fixation screw is occasionally complicated by pretibial cyst formation. The few case reports describing pretibial cyst formation noted several graft types and fixation techniques, making it difficult to establish one etiology. Some literature suggests cysts form from communication between the joint and pretibial area leading to extravasation of joint fluid, maturing into a cyst. We propose the development of cysts after PLLA screw use may be related to a foreign body reaction.


OBJECTIVE
We propose this foreign body reaction (1) relates to the biochemical breakdown of bioabsorbable materials; and (2) differs from cystic formations resulting from joint communication.


METHODS
We retrospectively reviewed seven patients who developed pretibial cysts at least 2 years after original primary ACL reconstruction surgery. MRI was used to visualize the extent of cystic formation. Cysts were treated by débridement with specimens sent for histologic analysis. Cyst appearance had a 3-year incidence of 5%.


RESULTS
No cyst had an infectious etiology. In all cases, the tibial screw outline was present on MRI, although intraoperatively, the screw was substantially decomposed. Grafts were well incorporated and none of the knees demonstrated anterior laxity. Histologically, cyst material contained fragments of PLLA surrounded by foamy histiocytes, suggesting a foreign body reaction. No cysts recurred.


CONCLUSIONS
Tibial cysts occur in a subset of patients undergoing ACL reconstruction using a bioabsorbable PLLA interference screw. We suspect they arise from a foreign body response to the screw breakdown. Removal is well tolerated.


METHODS
Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
Gonzalez-Lomas
Guillem
G
Center for Shoulder, Elbow and Sports Medicine, 622 W 168th Street, PH-1117, New York, NY 10032, USA.
Cassilly
Ryan T
RT
Remotti
Fabrizio
F
Levine
William N
WN
D000328:Adult; D016118:Anterior Cruciate Ligament / Q000000981:diagnostic imaging / Q000601:surgery*; D000070598:Anterior Cruciate Ligament Injuries; D001182:Arthroscopy / Q000009:adverse effects* / Q000295:instrumentation; D001672:Biocompatible Materials; D001863:Bone Screws / Q000009:adverse effects*; D003646:Debridement; D005548:Foreign-Body Migration / Q000209:etiology* / Q000473:pathology / Q000601:surgery; D006801:Humans; D007718:Knee Injuries / Q000000981:diagnostic imaging / Q000601:surgery*; D019344:Lactic Acid; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D009519:New York City; D011091:Polyesters; D011108:Polymers; D011474:Prosthesis Design; D011859:Radiography; D012086:Reoperation; D012189:Retrospective Studies; D013581:Synovial Cyst / Q000209:etiology* / Q000473:pathology / Q000601:surgery; D013710:Tendons / Q000637:transplantation*; D013977:Tibia / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D013997:Time Factors; D014182:Transplantation, Autologous; D014184:Transplantation, Homologous; D016896:Treatment Outcome; D055815:Young Adult
D001672:Biocompatible Materials; D011091:Polyesters; D011108:Polymers; D019344:Lactic Acid; C033616:poly(lactide)