## 1 Introduction
Furthermore, OA treatment reportedly controls subchondral bone remodeling and improves the trabeculae [13]. We previously performed MRI on patients with knee OA whose symptoms (pain and swelling) did not improve even after intra-articular injection of hyaluronic acid. As ESWT acts directly on the bone, it is effective against BMLs of the subchondral bone [17]. Conversely, APS is absorbed through the synovial membrane and acts primarily on the synovial membrane; thus, it is an effective treatment for synovitis. Therefore, ESWT is recommended for patients with BMLs based on MRI findings and APS therapy is recommended for patients with synovitis and intra-articular hydrops. Some patients had both BML and synovitis, and they were treated with a combination of APS and ESWT to improve their condition. For the first year, we used both APS and PRP, but APS therapy was overwhelmingly better at improving intra-articular edema, and thus, we now recommend APS therapy to most patients, except for those who strongly hope to receive PRP. There are three reasons why we used a combination of APS and ESWT for severe knee OA. First, we thought that a single treatment would not be sufficient to deal with both synovial pain and subchondral bone pain, which are the causes of knee pain. In other words, APS is effective for synovitis, but ESWT is effective for BML, and thus, we thought that severe knee OA with both synovitis and BML must be treated with both APS and ESWT. Second, many cases of severe knee OA, such as Kellgren-Lawrence classification grade 4 (KL4), have fewer synovitis symptoms, such as joint fluid, which may reduce the effectiveness of APS than KL2 or KL3. This was because we thought that applying some kind of stimulus to ESWT would make it easier for APS to respond. Third, for severe KOA, such as KL4, there are some reports that ESWT and APS alone were inefficient, and thus, we thought that it would be better if we combined both of them. In 2013, [PERSON] et al. reported that ESWT was effective for KL2 and KL3 knee OA [8]. Moreover, in 2022, [PERSON] et al. reported that APS therapy was administered for KL4 knee OA; the effectiveness rate was 47.4% after 6 months of follow-up [18]. In addition, [PERSON] et al. performed APS on KL4 knee OA and reported that a few cases improved after 3 months [19]. APS and ESWT alone were reported to be effective for mild-to-moderate knee OA, such as KL2 and KL3, but were less effective and short-lasting for more severe OA, such as KL4. [PERSON] et al. performed a 12-month follow-up study of 148 knees with KL2, 3, and 4 OA that received APS injections and reported that the Knee Injury and Osteoarthritis Outcome Score (KOOS) was significantly lower in KL4 than KL2 [20]. These reports showed that both ESWT and APS were less effective for KL4 severe knee OA. Since 2019, a combination of APS therapy and ESWT for knee OA has been used to increase the success rate and duration in cases with synovitis and BML on MRI. The effectiveness of these combination treatments for severe knee OA has not been reported. Therefore, this study aimed to examine the effects (success rate and duration) of a combination of APS and ESWT on knee OA by severity.