In a monocenter randomized controlled trial, 45 patients with isolated malleolar fracture type OTA/AO 44 A1-B2 undergoing ORIF were allocated randomly to a postoperative treatment either with a vacuum-stabilized orthesis with prescribed full weight bearing after the second week (23 patients) (orthesis group -- OG) or with functional aftertreatment with partial weight bearing of 15 kg for 6 weeks (22 patients) (control group -- CG). Outcomes were compared at 6- and 10-week follow-up examinations. The Olerud and Molander ankle (OMA) score, ankle swelling, usage of crutches, range of motion, Short Form 12, patient-reported visual analogue scales (VAS) (pain, comfort, walking confidence) and time to return to work were evaluated. All patients of OG showed reduced swelling at discharge. The median OMA scores after 6 weeks were 42 and 42.5 (p = 0.46) and after 10 weeks 69 and 72 (p = 0.55) in the OG and CG, respectively. The time to achieve secure walking capacity was reduced by 1 day (p = 0.03) in the OG. After ORIF of simple malleolar fractures, patients with a vacuum-stabilized orthesis can bear full weight 2 weeks postoperatively. This group experienced no adverse events. Postoperative swelling was significantly reduced and of the ability to walk on stairs confidently was shorter as compared to a functional aftertreatment without any external stabilization of the ankle.