Tibial Tunnel Cyst

About diagnostic imaging of postoperative complication of anterior cruciate ligament (ACL) reconstruction.

This is the case of a patient the came to my observation for a palpable mass into the anterior-medial pretibial region, two years after ACL reconstruction.

Tunnel cyst formation is a rare complication after ACL reconstruction, usually occurring 1-5 years post-operatively, which may occasionally be symptomatic. The ultrasound exam in this case is not enough. The study is completed with MRI and Cone-Beam CT examination.

Tibial Tunnel Cyst MRI

MRI-Cone-Beam CT

Why Cone-Beam CT? Same diagnostic capability of total-body CT but low radiation dose!

Low Radiation Dose

The computed tomography dose index (CTDI) is a commonly used radiation exposure index in X-ray computed tomography (CT); in this case 4,74 mGy was the value detected. 16.98 mGy is the estimated absorbed dose by using a total-body CT scan for the same examination.

Total-Body CT

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Dynamic Mri of ACL Reconstruction

ACL (anterior cruciate ligament) reconstructions usually are performed with bone-patellar tendon-bone (BPTB) or hamstring (distal semimembranosus and gracilis) autografts. The Mri imaging appearance of an ACL reconstruction varies depending on the type of graft used and on the timing of imaging relative to graft placement. Mri examination is the best choice of imaging modality to study the complications of ACL reconstruction that usually are graft failure, graft impingement, and arthrofibrosis. acl.jpgThe location of the femoral and tibial tunnels and graft position play a central role in the avoidance of impingement; the femoral tunnel should lie posterior to the intersection of Blumenstaat’s line (BL) with a line parallel to the posterior femoral cortex. This measure is well seen with conventional radiography but Mri imaging also allow to appreciate the integrity of the graft. I use all of the imaging modality in my daily practice but now my preference goes to dedicated systems; I think it’s very important to see what happens during knee flexion-extension to the reconstructed ACL.

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Same patient scanned with dedicated Mri system (0.3 T) and 1.5 T Mri scan – Sagittal T2w and Stir sequences.

Dynamic evaluation of a normal reconstructed ACL.

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Sagittal T2w and Xbone-T1w Mri scan of suspected graft-impingement.

Sagittal dynamic Mri scan of the same patient.