The various causes of knee locking are torn medial meniscus, mis-aligned knee cap, osteoarthritis, knee arthritis, torn lateral meniscus, osteochondritis dissecans, recurrent patella dislocation, chondromalacia patella, knee alignment problem, knee fragment or knee cartilage disorder. True knee locking is caused by either a torn piece of cartilage, or a loose bone fragment due to a bone disorder called osteochondritis dissecans. Sometimes misalignment of the bones and muscles around the knee cause this obstruction. True locking is fairly rare. A person can experience an inability to move the knee after an injury which feels like a locking of the knee. However, this is not due to something physically interfering with the movement of that knee. This is called a pseudo-lock. Hence you may need X-rays and MRIs of the knee to find the exact cause. Please consult an orthopedic specialist. Take care!