Unicompartmental arthroplasty and high tibial osteotomy have become successful standard procedures in the treatment of medial arthritis of the knee. With a more frequent use in young and active patients, bone-sparing procedures have become more important as an alternative to total knee arthroplasty. The instrumentation, implants and surgical techniques have been improved so that very good functional and long-term results can be achieved with both procedures. This article describes the indications, results and complications of both surgical techniques. The aim is to give clear guidelines for indications. In addition, the advantages and disadvantages of hemiarthroplasty and osteotomy are explained regarding clinical results, survival rates, revision options and complications. The focus is on medial unicompartmental arthroplasty and valgus tibial osteotomy.