There have been conflicting reports in the literature regarding the results of post high tibial osteotomy knee arthroplasty. This study aims to assess the clinical and radiological results as well as patient satisfaction following post high tibial osteotomy knee arthroplasty and to identify the variables affecting the results. A total of 29 cases of post osteotomy knee arthroplasties were retrospectively analyzed. Preoperative and postoperative range of movement and deformity were recorded with knee scores at latest follow-up. Weightbearing radiographs were taken preoperatively and at latest follow-up. Patients were asked if they were satisfied with their results. Average follow-up was 7.5 years with an average interval between osteotomy and knee arthroplasty of 4.7 years. Average age at osteotomy was 62.5 years. Seventeen patients had Maquet's dome osteotomy and 12 had closing wedge osteotomy. The average knee score was 117.4. Overall 5 (17.2%) patients had a poor result. There was a significantly greater pre-osteotomy subluxation (9 mm) in the failed knees compared to the successful arthroplasties (3.64 mm) with p = 0.033 using the Mann-Whitney U test. This has to be tempered by the fact that numbers were small. Failed arthroplasties had a valgus cut of the tibia (1.5 degrees) compared to either a neutral or slight varus cut in successful arthroplasties (average 2.42 degrees varus). Lateral translation of tibial tray was greater in the failed knees whereas posterior translation was greater in the successful knees. However, differences in tibial tray angle and translation were not statistically significant. Four (21.05%) cases went on to revision of their arthroplasty in less than 8 years, 2 for painful valgus instability. This study concludes that post high tibial osteotomy knee arthroplasty is a technically demanding operation with altered anatomy and significant balancing problems. Results of knee arthroplasty after high tibial osteotomy are inferior to that of primary arthroplasties and the amount of lateral subluxation prior to surgery may adversely affect results.