Anterior Cruciate ligament Reconstruction – what the Radiologist needs to know?

Young male with history of ACL reconstruction about 1 year back shows good positioning an ligamentization of the  the graft, normal PCL and menisci with subtle free fluid  with too anterior placement of tibial tunnel, post bioabsorbable screws. Case submitted by Dr MGK Murthy, Mr Hari Om, Mr Sahadev Gupta. 

Healthy Graft on MRI should be:

-Low signals if intact unimpinged graft

- Posterior to but not in contact with intercondylar roof

- T1 shows the structure better than T2 because of inherent heterogeneity on T2

-Tibial tunnel should not be too anterior

-Posterior cruciate ligament signals should not be gray/ heterogeneous

(A)        Technical factors evaluation

On X –ray

-fractures/screws integrity or position/union of bony portion/tunnel placement/size of screw tunnel

On MRI

 -Tunnel positioning (common failure is far too anterior placement at tibia )

-Tunnel widening(harmless)

-Graft integrity(heterogeneous signals sign of tear) other soft tissues evaluation

-Femoral insertion  should be at intersection of blumensaat line (intercondylar roof)and extended line from posterior femoral cortex

-Tibial  tunnel should  be posterior and parallel  to tibial intersection of blumensaat line

(B)        Biological factors

-failed ligamentization—not well seen on MRI

-infection

-Arthrofibosis—seen as low signal nodule surrounded by fluid , anterolateral to tibial tunnel called Cyclops lesion on MR (consists of debris of remnant ACL and graft )

-infrapatellar contracture syndrome