Identification of non-physiologic load on osteoarthritic knees with varus alignment using knee SPECT/CT before and after realignment surgery

Introduction: Osteoarthritis is one of well-known cause of painful knees. One of effective treatment option is high tibial osteotomy (HTO) as realignmetnt surgery. Knee surgeons have expected that the realignment could redistribute the non-physiologic load of medial tibiofemoral compartment to lateral or whole joint. Although radiographic assessment demonstrated the change of coronal and sagittal alignments, it could not directly present the change of load on the joint. To assess the change after realignment surgery, we identified the sites of active lesions and evaluated the changes in their activities on knee single photon emission computed tomography/computed tomography (SPECT/CT) before and after HTO in patients with osteoarthritis.

Methods: Osteoarthritic patients who underwent HTO from January 2012 to December 2021 were recruited retrospectively. All the patients underwent knee SPECT/CT both before and after HTO within the interval of 24 months . Finally, seventy-seven osteoarthritic knees were enrolled in this study. Radiographic assessment including coronal mechanical alignment and posterior tibial slope was performed using teleradiogram and knee radiographs. Visual assessment was done for knee SPECT/CT. All the knee joints were divided into 4 compartments; three tibiofemoral (TF) compartments as medial, central lateral, and one patellofemoral (PF) compartment. The activity of lesions was graded as a three-point score (no active lesion, moderate, and intense lesion). Due to high prevalence of active lesions, the medial tibiofemoral compartment was sub-devided into 4 segments; anteromedial, anterocentral, posteromedial, and posterocentral areas. We defined the meaningful change of non-physiologic load as the decrease in the extent of active lesion at knee SPECT/CT by more than 50%, including complete resolution. To find affecting radiographic variables for the meaningful change in knee SPECT/CT, multivariate logistic regression analysis was performed.

Results: Seventy-seven medial TF compartments had active lesions in all preoperative knee SPECT/CT, whereas, 8 lesions in central (10%) and 9 in lateral compartment (12%). There was no knee with increased extent of medial TF uptake after HTO. Completely resolved medial compartment lesion after HTO reported in 21 knees (27%). Other 56 knees have residual medial TF compartment uptake. Fourty-five (58%) knees show meningful decrease in medial tibiofemoral joint. At multvariate logistic regression analysis, posterior tibial slope (OR=1.18; 95% CI=1.05-1.32, p=0.004) was the only significant factor for the meaningful decrease in the extent of active lesion at medial tibiofemoral compartment. In the segmental analysis, active lesions at anteromedial and posteromedial segments of medial tibiofemoral compartment were found in 74 (96%) and 46 (60%) knees before HTO, which were changed to 51 (66%) and 14 (18%) knees after HTO, respectively. In posteromedial segment, posterior tibial slope (OR=1.33; 95% CI=1.10-1.62, p=0.004) was the significant factor for the decrease in the extent of active lesion.

Conclusions: All osteoarthritic knee with varus alignment show various degrees of decrease in the extent of active lesions after surgery. After realignment surgery, 58% of cases showed significant decrease in extent of active lesions including 27% of cases showed complete resolution at medial tibiofemoral compartment. Posterior tibial slope was found as a significant factor for meaningful decrease in the extent of active lesion at medial tibiofemoral compartment. The segment presents the biggest meaningful decrease is posteromedial segement of medial TF joint. Hence, correction of posterior tibial slope should be considered when we get proper knee alignment. Considering normal knee joint dose not present active lesion, significant reduction of active lesion in osteoarthritic knee with varus alignment could be correlated to unloading of non-physiologic load.