。
I broke my leg as a result of a horse fall.
Literal
Horse-fall [possessive-の] result leg [object-を] broke.
落馬 ('falling from a horse') is a specific one-word compound for that particular mishap — Japanese packs concepts English phrases. ~の結果 ('as a result of') is a fixed causal frame. 折る ('to break') is transitive — the speaker broke their own leg via the fall.