FEASIBILITY OF NON-CONTRAST MRI TO DETECT CHANGES IN SYNOVITIS AFTER ACL RECONSTRUCTION SURGERY

Abstract

INTRODUCTION

Synovitis is a recognized risk factor for post-traumatic osteoarthritis post-ACL reconstruction (ACLR). The reference standard for imaging synovitis is contrast enhanced MRI, but this adds time and cost and may be contraindicated in some patients, which may limit evaluation of this important finding. Recently, several non-contrast MRI methods have shown strong agreement with CE-MRI for semiquantitative assessment of synovitis.

OBJECTIVE

To evaluate the feasibility of quantitative double-echo in steady-state (qDESS) as a non-contrast MR technique to detect changes in synovitis in patients pre- and post-ACLR.

METHODS

14 males and 4 females (age:27±6 years, BMI:24±3 kg/m²) with ACL tears underwent ACLR surgery (mean time from injury to surgery 10±5 weeks) and were scanned on a 3T MR scanner at three timepoints: (1) baseline post ACL tear but before reconstruction, (2) 6-weeks and (3) 6-months after ACLR. At each time point, a 3D qDESS acquisition was performed with parameters: TR/TE1/TE2 = 20.5/6.4/34.6 ms; acquisition resolution = 0.4 × 0.4 × 1.5 mm³; 80 slices; Flip Angle = 20. qDESS synovitis hybrid images were created by a weighted subtraction of the 2^nd echo signal from the 1^st echo to null signal from joint fluid in order to provide contrast to the synovium. Synovitis was scored in the knee overall and in 4 regional locations by a blinded radiologist on a scale of 0-3 (0 = none to 3 = severe).

RESULTS

Figure 1 shows a representative case of qDESS synovitis-weighted hybrid images at the three timepoints and their corresponding scores. Figure 2a shows a table of the % of patients (out of 18) that were scored to have improved or worsened synovitis between baseline and 6-weeks post-ACLR and between 6-weeks and 6-months post-ACLR. Overall, there was a clear trend towards synovitis worsening 6-weeks after ACLR and then improving between 6-weeks and 6-months post-surgery. Furthermore, when the 6-week and 6-month timepoints for each patient were compared directly but blinded to order, an improvement in assessed synovitis was observed in a further 82% of overall impressions that were previously scored as no change in blinded and randomized assessments (Figure 2b). Repeated synovitis scoring assessments showed very strong agreement (Gwets AC2>0.80) in overall and sub-region assessments.

DISCUSSION

While ground-truth synovitis measures were not available, the qDESS hybrid method was able to detect both worsening synovitis that is expected after ACLR surgery and improvement in synovitis that is expected during the following 5 months of recovery. The lack of differentiation of synovitis changes between timepoints may partly be attributed to the coarseness of the 4-point semi-quantitative Likert-scale which is based on synovial hypertrophy and nodularity In overall and regional assessments when no change was detected in randomized and blinded datasets on the conventional 4-point scale, subsequent direct comparison of the 6-week and 6-month timepoints for each participant, the radiologist was able to detect improvement in synovitis in the majority of cases despite being blinded to timepoint. The noted exception was in the intercondular notch where the evaluation of synovitis was confounded by surgical alteration along Hoffa’s fat pad, possibly leading to over-estimation of the degree of synovitis in this region. Lastly, reproducibility agreement metrics for overall impression and regional assessments showed strong agreement, further supporting the potential utility of this approach.

CONCLUSION

Non-Contrast MRI of synovitis using the qDESS approach was able to detect changes in synovitis post-ACLR and during recovery, particularly when directly comparing intrasubject timepoints. This approach shows new diagnostic potential to identify patients at risk for PTOA due to chronic inflammation and could potentially be used to monitor treatment effects.