Tibial tunnel and pretibial cysts following ACL graft reconstruction: MR imaging diagnosis

Abstract

Tunnel cyst formation is a rare complication after anterior cruciate ligament reconstruction, usually occurring 1-5 years post-operatively, which may occasionally be symptomatic. There are multiple proposed theories regarding the etiology of tunnel cysts. Theories include necrosis, foreign-body reaction, lack of complete graft osteo-integration, and intravasation of articular fluid. It is important to know if the tunnel cysts are communicating or not communicating with the joint, as surgical management may be different. Imaging characteristics on magnetic resonance images (MRI) include tibial tunnel widening, multilocular or unilocular cyst formation in the graft or tibial tunnel, with possible extension into the pretibial space, intercondylar notch, and/or popliteal fossa. The MR imaging differential diagnosis of tibial tunnel cysts includes infection, foreign-body granuloma, or tibial screw extrusion. Importantly, to the best of our knowledge, graft failure or instability has not been reported in association with tibial tunnel cysts.

Bone tunnel widening following arthroscopic reconstruction of anterior cruciate ligament (Acl) using hamstring tendon autograft and its functional consequences

“…Mechanical factors include the types of graft and devices, the location of the graft, and the presence and degree of stress shielding proximal to the interference screw that results in bone resorption [2,3,4,18] . Although bone tunnel widening with fibrotic tissue proliferation has been known to be a clinically significant finding that may complicate revision surgery, many clinical studies failed to demonstrate an association between bone tunnel widening and instability or prevalence of post-traumatic osteoarthritis after ACL reconstruction [1,2,3,18,20] . In terms of imaging modality, conventional radiographs and CT have been studied [1,12,13,17] .…”

Current Concepts on MRI Evaluation of Postoperative Knee Ligaments

“…55,56 These changes normally stabilize by the first year and decrease during the following 2 years. 57 During the first 18 months postoperatively, a small amount of fluid may be detected normally within the fixation tunnel, which may at the same time enlarge up to 13 mm. 28 Tunnels may enlarge up to 33% in average value, particularly in the distal part, without necessarily any correlation with stability, joint function, and patient satisfaction scores.…”

“…Tunnel widening with cyst formation may result from excess motion of the graft, high position of the graft fixation close to the joint, forced rehabilitation before full graft incorporation, and the presence of synovial fluid cytokines in the graft interface, causing osteolysis. 57 The impaired graft incorporation can be suspected from cyst formation within the tunnel, more commonly the tibial, with widening that may exceed 20 mm (►Fig. 19).…”

“…Cyst formation in grafts is more common with hamstrings, may be related to knee pain and impaired motion, but it is not clear if it has a direct association with graft failure. 57,60,61,89…”

Knee Imaging Following Anterior Cruciate Ligament Reconstruction: The Surgeon's and Radiologist's Perspectives

“…Tunnel widening affects the tibial tunnel more commonly than the femoral tunnel and tends to occur in the first 6 months, stabilizing within 2 years. 56 No correlation was found between tunnel widening and graft failure; however, tunnel widening may cause problems if revision surgery is needed. Although tunnel widening is a frequent phenomenon, little is known regarding its cause or natural history.…”