Introduction Unicompartmental knee arthroplasty (UKA) and valgus high tibial osteotomy (HTO) are two options for isolated medial femorotibial osteoarthritis in genu varum. In the absence of registries for osteotomies and for arthroplasty in the knee, epidemiological data are hard to obtain in France. We therefore performed a retrospective study, with the aims of: 1) estimating UKA and HTO survival without revision by total knee arthroplasty (TKA), and 2) assessing risk factors for revision according to treatment group. Hypothesis Medium-term survival is better with HTO than UKA in under-70-year-olds. Materials and method All elderly patients undergoing HTO or UKA in the French National Hospitals Database for the period 2011–2020 were included: i.e., 108,007 patients; 43,537 HTO (29,330 male, 14,207 female; mean age 49.7 years, 95% CI 49.6–49.8) and 64,470 UKA (31,181 male, 33,289 female; mean age 60.5 years, 95% CI 60.5–60.6). Results Survival free of revision by TKA was 75.8% (95% CI = 75.2–76.4) for UKA and 80.6% (95% CI = 80.0–81.3) for HTO (p < 0.00001). In UKA, revision risk factors comprised: low annual center volume (< 17 UKAs per year) (HR = 1.50; 95% CI = 1.41–1.59), obesity (HR = 1.25; 95% CI = 1.18–1.32), and age < 60 years, with maximum risk for 50–59 years (HR = 2.41; 95% CI = 1.83–3.16 in 50–59 year-olds). In HTO, revision risk factors comprised: obesity (HR = 1.42; 95% CI = 1.31–1.53), rheumatoid arthritis (HR = 2.75; 95% CI = 1.37–5.51), joint chondrocalcinosis (HR = 2.01; 95% CI = 1.18–3.39), and age > 60 years (HR = 8.81; 95% CI = 7.23–19.73 in 60–69-year-olds). Male gender was a protective factor against revision in both groups: UKA, HR = 0.75 (95% CI = 0.72–0.79); HTO, HR = 0.73 (95% CI = 0.69–0.77). The number of UKAs increased over the years, matching the increase in arthroplasty in France, with a decrease in HTOs until 2019. Conclusion HTO showed better medium-term survival than UKA in under-70-year-olds in France. Even so, indications decreased in favor of UKA, although the respective risk factors differ. These findings suggest that conservative surgery still has a role, depending on osteoarthritis stage.