Pretibial Cyst Formation after ACL Reconstruction. A series of 14 cases with different etiologies

OBJECTIVES: Among complications following an ACL reconstruction, the formation of a pre-tibial cyst in the site of the tibial tunnel is rare and might happen even years after surgery. The purpose of this study was to analyze 14 patients with pretibial cyst after ACL reconstruction. METHODS: We retrospectively evaluated patients between 2008 and 2016. The inclusion criteria were patients who underwent an ACL reconstruction, and developed an extra-articular cyst at the tibial tunnel level. For recurrence evaluation, patients with less than one-year follow-up were excluded. A pre and postoperative clinical and radiological evaluation was performed. We analyzed the graft selection and surgical technique for ACL reconstruction, the time between primary surgery and onset of symptoms, and the clinical presentation. A pre and postoperative radiological evaluation was performed for every patient. Surgical technique for cyst excision, histological analysis and culture results were also analyzed. The recurrence rate was evaluated at final follow-up. RESULTS: Nine patients were male, with an average age of 38 years. The average follow-up was of 35 months. All ACL reconstructions were performed using hamstrings graft and a trans-tibial technique. Tibial fixation was performed with a biodegradable screw in 9 patients, three of them associated with the use of a staple. In four patients hamstrings tibial insertion was left in situ with an open stripper and fixed in the tibia using non-absorbable Ethibond 2 sutures. The average time between primary ACL surgery and onset of the cyst was 29 months. All patients presented a palpable tumor at proximal tibia and a stable knee. The cyst size varied between 1 and 3 cm. In all cases, Rx and MRI showed a widening of the tibial tunnel, though no articular communication could be confirmed. The arthroscopic evaluation revealed no graft loosening. All cysts were approached through the previous tibial incision and staples or screws where removed. In all cases curettage of the tibial tunnel walls was performed, filling the space with cancellous bone in 7 of them (5 obtained from proximal tibia and 2 from the lateral femur condyle). Pathological anatomy reported 14 synovial cysts, 5 associated with remaining suture. No infection was informed. At final follow-up, 13 out of 14 patients returned to normal activities with no pain or recurrence. One patient required three open surgeries to achieve definitive treatment using bone allograft chips to fill the tibial tunnel. Despite the tunnel widening, no graft loosening was observed. CONCLUSION: Although most authors attempt to define an etiology for this complication, there is not enough evidence to support a unique conclusion. It has been traditionally associated with a foreign-body reaction. Though we believe the etiology to be multifactorial, cysts can be defined as communicating or non-communicating. If patients present with an onset of pain, surgical resection is indicated. When no articular communication is suspected, cyst resection and hardware removal might be sufficient. Otherwise, treatment must include debridement, hardware removal and local bone grafting. In case of a recurrence, aggressive curettage and extensive bone grafting is recommended. None of the patients revealed signs of instability.