Background <p>Evidence on prophylactic interventions to prevent heterotopic ossification (HO) around the knee is scarce. We conducted a scoping review to map reported indications, interventions, and outcome reporting.</p> Methods <p>We followed a prospectively developed protocol and searched four major databases (MEDLINE via PubMed, Embase, Cochrane Library, and Web of Science), complemented by searches of trial registries and grey literature using a high-sensitivity strategy. Data extraction was performed in duplicate and summarized descriptively by modality.</p> Results <p>The search yielded 2,958 records. We included 78 unique publications, comprising 18 expert-opinion sources and 62 clinical publications reporting data on 3,321 patients, of whom 1,579 received the evaluated interventions, with two publications contributing to both syntheses. Modalities comprised continuous passive motion (CPM) in 8, pharmacological prophylaxis in 21, radiotherapy (RT) in 18, surgical techniques in 3, and combination therapy in 14 studies. Most identified studies were case reports or case series. Pharmacological data were largely driven by one large ASA cohort, whereas RT and combination-therapy studies were small and mainly addressed recurrence prophylaxis. One late fatal, potentially RT-induced sarcoma was reported. Because of substantial clinical and methodological heterogeneity, crude reported event proportions should not be compared directly across modalities. Outcome reporting was inconsistent, with limited use of standardized patient-reported outcomes and incomplete adverse-event reporting.</p> Conclusions <p>Knee HO prophylaxis evidence is dominated by low-level, heterogeneous studies with substantial reporting gaps. Comparative knee-specific studies with standardized outcome definitions, functional outcomes, and systematic safety reporting are needed.</p> Trial registration <p>This review was prospectively registered on the Open Science Framework (OSF registration ID 5328k).</p> Graphical Abstract <p></p>