Longitudinal quantitative T2 mapping and SPECT-CT assessment of unloading therapy within a randomized controlled...

Quantitative imaging has great potential for early detection and monitoring effectiveness of potential therapies for osteoarthritis (OA). In this study, we explore whether T2 mapping and quantitative single-photon emission computed tomography-computed tomography (SPECT-CT) can detect early changes in knee articular cartilage composition and subchondral bone turnover after unloading therapy with an unloader brace or a high tibial osteotomy (HTO) in patients with medial knee OA and varus knee malalignment. We also investigated correlations between these imaging modalities and with clinical outcomes.

Patients 18-65 years were enrolled in a multicenter randomized controlled trial (RCT) comparing an unloader brace to HTO. Patients were eligible if they had radiographic medial knee OA Kellgren & Lawrence (K&L) grade I-III and a varus knee malalignment. Magnetic resonance imaging (MRI) with T2 mapping and SPECT-CT using technetium-99m hydroxydiphosphonate (99mTc-HDP) was conducted at baseline and after 1 year. We assessed differences in T2 relaxation times and maximum standard uptake value (SUVmax) between baseline and follow-up scans and compared knee compartments at both time points using a paired t-test. We used linear regression to assess whether changes in imaging outcomes over time were correlated between the two techniques and whether these were correlated with clinical outcomes using the Knee Injury and Osteoarthritis Outcome Score (KOOS). Data were analyzed for the entire group and separately for each treatment arm.

Fifty-one patients were included in the study. In the HTO group (28 patients; 17 males; mean age 55.3 years), T2 relaxation times were statistically significantly increased in the lateral weight-bearing femoral and tibial regions at follow-up (baseline vs. follow-up in ms: 38.4 vs. 40.4, P=0.05 and 35.2 vs. 39.2, P<0.01, respectively). The brace group (23 patients; 14 males; mean age 50.0 years) showed statistically significantly increased T2 relaxation times of the medial weight-bearing femoral condyle (42.5 vs. 44.1 ms, P=0.03). SUVmax values were statistically significantly decreased at follow-up in the medial compartment in the HTO group (baseline vs. follow-up: 13.4 vs. 11.0, P=0.03). No changes were observed in the brace group. The following findings applied to the entire study population as well as separated per treatment. Both techniques showed statistically significant outcomes between the medial and lateral compartments. No correlation was observed between the change in T2 values and the change in SUVmax over time. We did not observe a correlation between the change of the quantitative imaging outcomes and the change in the KOOS subscales between baseline and follow-up measurements.

T2 mapping and SPECT-CT are able to detect changes after unloading therapy. These techniques depict OA processes and monitor OA therapies in a different and complementary way. Our results suggest that HTO accomplishes a load transfer from the medial to the lateral compartment, while the unloader brace does not.

Dutch Trial Register NTR NL4200.