Patients with problems after ACL reconstruction - what do help MRI and SPECT/CT?

AIMS AND OBJECTIVES: Magnetic resonance imaging (MRI) and single-photon emission computed tomography/ computed tomography (SPECT/CT) are established diagnostic instruments for symptomatic patients after ACL reconstruction. The purpose of the study was to compare and correlate MRI and SPECT/CT findings of symptomatic patients after ACL reconstruction. MATERIALS AND METHODS: In a retrospective study 30 knees of symptomatic patients complaining about pain and/or instability after ACL reconstruction were investigated using 99mTc-HDP SPECT/CT and MRI. In MRI signs of a graft tear (partial and complete) were noted. Graft signal intensity, bone bruise, cyst formation in proximal, medial and distal femoral and tibial tunnels, roof impingement, roof osteophytes, graft arthrofibrosis, knee joint effusion and synovial thickness were classified. Measurements were performed by two musculoskeletal radiologists. The agreement of the assessed MR signs were calculated using cohen’s kappa coefficient. These showed excellent (kappa >0.75) to good (kappa >0.40) reproducibility between the readings of the two observers. Quantitative grading of bone tracer uptake (BTU) for each anatomical area of a previously validated localisation scheme was done. Tunnel width was assessed in CT at three different levels for femoral and tibial tunnels. The findings in SPECT/CT and MRI were correlated (p<0.05). RESULTS: Increased BTU in most femoral and tibial knee regions was found in patients with MR findings of knee joint effusion, synovial thickening and bone bruise in various knee regions. A reciprocal correlation was shown for cyst formation in the central and distal area of the femoral tunnel and BTU in the femoral tunnel. MR findings such as graft continuity, graft signal intensity in the femoral and tibial tunnel, roof impingement, roof osteophytes did not show a significant correlation. A reciprocal correlation was revealed for tunnel enlargement in the proximal and central femoral tunnel and MR signal intensity in the entire intra-articular graft. Cyst formation in the femoral tunnel significantly correlated with tunnel enlargement in the proximal and central part of the femoral tunnel. Proximal femoral cyst formation also correlated with tibial tunnel enlargement in the central and distal part. BTU did show a positive correlation with tibial tunnel enlargement and a negative correlation with femoral tunnel enlargement. CONCLUSION: Both imaging modalities play an important role in postoperative diagnostics of patients with problems after ACL reconstruction. The results of our study could help in clinical decision-making to accurately identify causes of painful ACL reconstructions. MRI will remain the primary imaging modality, but SPECT/CT could be helpful giving information on in-vivo loading of the knee.