Patellofemoral instability more commonly occurs in younger population (teens > twenties, and female > male) following trauma such as twisting on a loaded flexed knee. There may be tearing of the medial soft tissue with deformity of the knee. Patella often reduces spontaneously with knee extension.
Patient reported symptoms: history of trauma, rapid onset of swelling, reports of the knee to feel loose or knee cap to slip out, audible pop, knee giving way with pain, severe pain around knee cap.
Clinical signs: effusion, possible deformity, full but painful active and passive movement and positive apprehension test.