The posteromedial corner of the knee has intricate anatomical and biomechanical relationships critical to the function of the tibiofemoral joint. Missed or late diagnosis of pathomechanical disorders of the region, such as anteromedial rotary instability, in individuals with knee pain, may result in long-term decreased functional mobility and predisposition for degenerative disorders. This case report describes the chronological history and experience of a 35-year-old male with late diagnosis of anteromedial rotary instability and the subsequent surgical reconstruction and rehabilitation. Difficulties with clinical recognition of the underlying pathology and the postoperative course of rehabilitation are also discussed.