Clinical Usefulness of SPECT/CT for Assessing Postoperative Outcomes After Medial Opening-Wedge High Tibial Osteotomy

Background: Qualitative studies have explored changes in Tc-99m hydroxymethylene diphosphonate (HDP) uptake on single-photon emission computed tomography and computed tomography (SPECT/CT) as a result of offloading after medial opening-wedge high tibial osteotomy (MOWHTO) in patients with medial compartment knee osteoarthritis. However, whether changes in the Tc-99m HDP uptake on SPECT/CT reflect the degree of clinical improvement in postoperative outcomes, especially when using minimal clinically important differences (MCIDs), has not been investigated. Purpose: To investigate the association between changes in Tc-99m HDP uptake on SPECT/CT and MCID-based improvement on the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score in patients who underwent MOWHTO. Study Design: Cross-sectional study; Level of evidence, 3. Methods: The study included 35 knees in 31 patients who underwent MOWHTO. SPECT/CT was performed preoperatively and 3 years postoperatively with clinical and radiological assessments. On SPECT/CT, the knee joint was divided into 10 regions, and the radiotracer uptake amount of each region was divided by the uptake amount of the reference zone. Patients were divided into 2 groups based on whether they achieved the MCID of 16.1 points on the WOMAC at 3 years postoperatively, and changes in uptake amount on SPECT/CT were compared between the groups. Results: At 3 years postoperatively, 22 patients achieved the MCID on the WOMAC (62.9%; above-MCID group) and 13 patients did not (37.1%; below-MCID group). In the above-MCID group, significant improvement was observed in the WOMAC after MOWHTO (from 55.8 to 19.6; P < .05); however, significant improvement was not observed in the below-MCID group (from 38.8 to 32.3; P = .100). Based on mean change of uptake on SPECT/CT in each region, the above-MCID group showed significantly greater reduction of uptake on SPECT/CT than the below-MCID group in the femoral anteromedial compartment (P = .004), tibial anteromedial compartment (P = .009), and tibial anterolateral compartment (P = .031). Conclusion: Reduction in radiotracer uptake on SPECT/CT of the knee joint reflected clinical improvement in patient-reported outcomes following MOWHTO.