Anterior cruciate ligament (ACL) tears are common orthopaedic injuries and are frequently treated with surgical reconstruction. Post-operatively, biologic and mechanical factors influence graft incorporation and tunnel morphology. Enlargement of tibial and femoral tunnels can lead to delayed graft incorporation, loss of fixation, increased knee laxity, and a difficult revision surgery. PET imaging has been used to assess ACL graft metabolic activity. The purpose se of this study is to assess if 18FDG PET tracer activity after ACL surgery is associated with tunnel lysis and how time effects this relationship.
A retrospective review of 44 patients who underwent an ACL reconstruction (ACLR) was performed. Demographic information collected included age, sex, height, weight, smoking status, concomitant procedures, and laterality of repair. Computed tomography and plain radiographs were used to evaluate the size of the tibial and femoral tunnels and the change in tunnel diameter from the initial drilled size was calculated. PET tracer uptake was measured in a semiquantitative way using SUVmax based on region of interest analysis compared to the original tunnel size.
The initial mean tunnel size was 8mm (Range: 7-10mm). The femoral tunnel widened by a mean of 2.2mm (Range: 0.6-5.1mm) and the tibial tunnel by a mean of 3.8mm (0.8-13.4). The tibial tunnel diameter increased the most in the sagittal orientation in the superior 2/3 of the tunnel, with a mean increase of 2.5mm proximally (T1), 2.8mm centrally (T2), and 1.9mm distally (T3). In the first 12 months after surgery, 18FDG uptake was high in both the tibial and femoral tunnels in most patients. Beyond 12 months, increased 18FDG uptake is associated with a mean wider tibial and femoral tunnel.
PET tracer uptake decreases with time after ACLR surgery. Persistent uptake after one year is associated with tibial and femoral tunnel widening. Further work is required to elucidate the mechanism and implications of this finding