Irreducible knee dislocation (KD) is a rare high-velocity injury (determined by shear and/or rotational forces) that is associated with the interposition of capsule-ligamentous or muscle structures in the joint space. This condition often requires open reduction. To our knowledge, irreducible KD is not widely reported in the literature. Here, we report the case of a 69-year-old man with a right KD that occurred after falling from a height and entrapment of the leg between concrete blocks. The patient presented to the emergency department with a right knee deformity without distal neurovascular deficit. After two failed attempts of close reduction (under sedation and spinal anesthesia), open reduction was performed. Intraoperatively, there were cruciate ligament tears, wide capsule tears, and intra-articular vastus medialis interposition, preventing reduction. The decision to release the muscle from the notch, suture of the medial capsule, temporary K-wire stabilization, and cast immobilization were taken. After K-wire removal, the patient underwent rehabilitation to regain function and resume activities of daily living. This case report highlights the need for open reduction in some KD cases. Identifying possible soft-tissue interposition can accelerate surgical treatment and minimize the risk of complications.