Acute dislocation of the patella is a common orthopaedic emergency. The dislocated patella commonly reduces spontaneously or is reduced by a physician as an emergency. Rarely, open reduction is needed. Osteochondral fragments that detach from the patella or medial femoral condyle might interfere with patellar reduction, and sometimes osteophytes can interfere with reduction. Therefore, arthroscopic or, rarely, open reduction can be necessary. We present an unusual case of a locked knee related to a tibial plateau fracture. An osteochondral fragment that originated from the tibial plateau inhibited reduction of the patella. Such a fracture related to permanent patella dislocation has not previously been reported.