A patellar dislocation occurs when the kneecap (patella) completely slips out of its normal position. The patella typically tracks within the trochlear groove at the end of the femur, but a sudden force or twisting motion can push it out of this channel. This common and painful injury often requires immediate professional medical intervention to safely realign the joint. The dislocation usually forces the kneecap laterally, toward the outside of the knee.
Identifying the Immediate Signs
The onset of a patellar dislocation is often accompanied by an unmistakable sensation. Many individuals report hearing or feeling a distinct “pop” or tearing sound at the moment of injury, followed instantly by intense, sharp pain. This immediate pain makes it impossible to continue any activity and often causes the knee to buckle and give way.
The most definitive sign is the visible deformity of the knee. Instead of resting centrally, the kneecap appears shifted and lodged to the side, commonly creating a noticeable bump on the outer aspect of the knee. This displacement prevents the knee from functioning normally, resulting in an immediate inability to bear any weight on the injured leg.
Rapid swelling (hemarthrosis) begins almost immediately as blood fills the joint capsule from torn soft tissues. The leg is often held in a slightly bent, fixed position because the quadriceps muscles involuntarily spasm and the displaced patella physically locks the joint. Any attempt to straighten the leg manually or apply pressure will increase the severe pain.
Distinguishing Dislocation from Other Knee Injuries
A complete patellar dislocation is distinct from other common knee traumas, like sprains or fractures, primarily due to the obvious visual displacement. For instance, a patellar subluxation is a partial dislocation where the kneecap slips out of the groove but spontaneously snaps back into place. While subluxation causes transient pain and instability, the visible deformity is momentary, unlike a full dislocation where the patella remains out of alignment.
Distinguishing a dislocation from a ligamentous sprain, such as a tear of the anterior cruciate ligament (ACL) or medial collateral ligament (MCL), is important. Ligament tears also cause severe pain, swelling, and a sensation of the knee giving way, but they lack the hallmark sign of the kneecap resting outside its groove. Most fractures of the long bones around the knee, while painful, do not result in the patella being visibly displaced from its track.
The pain and instability associated with a dislocation are uniquely tied to the kneecap’s non-anatomical position. The medial patellofemoral ligament (MPFL), the primary passive stabilizer preventing lateral dislocation, is almost always torn during a first-time event. This soft tissue disruption, combined with the joint’s mechanical locking, provides a clinical presentation that is more severe and visually obvious than a typical sprain or fracture.
Essential Steps to Take Immediately
The most important step after recognizing a suspected kneecap dislocation is to avoid any attempt to manually push the patella back into place. Trying to reduce the joint without professional knowledge can cause further damage to the cartilage, nerves, and blood vessels surrounding the knee. The danger of bone fragments or soft tissue getting trapped in the joint space makes self-intervention too risky.
The injured leg should be kept as still as possible and immobilized in the exact position it was found. Using pillows, rolled blankets, or clothing to gently support the limb helps prevent inadvertent movement while waiting for assistance. This stabilization minimizes the risk of additional trauma to the compromised soft tissues and surrounding structures.
Applying the principles of R.I.C.E. (Rest, Ice, and Elevation) is appropriate while awaiting medical help. A cold pack, wrapped in a thin towel, should be applied gently to the swollen areas around the joint for 15 to 20 minutes at a time to mitigate rapid swelling and pain. Elevating the injured leg above the level of the heart, if possible without causing more pain, assists in reducing internal bleeding and swelling. Since a dislocated kneecap is a major injury with potential for associated fractures, professional evaluation in an emergency room setting is necessary.
Medical Treatment and Recovery
Once in a medical setting, the diagnosis is confirmed by physical examination, followed by X-rays to check for associated fractures or loose bone fragments within the joint. The definitive treatment for a dislocation is a closed reduction, which is the non-surgical process where a healthcare provider gently manipulates the kneecap back into the trochlear groove. This procedure is performed after administering pain medication or sedation to ensure the muscles are relaxed and the patient is comfortable.
Following successful reduction, the knee is usually immobilized in a brace or splint for a period, often two to three weeks, to allow the torn soft tissues to begin healing. The recovery process centers on physical therapy, which is important for restoring stability and preventing a recurrence. A primary focus of rehabilitation is strengthening the vastus medialis obliquus (VMO) muscle, the innermost part of the quadriceps, as it is a dynamic stabilizer of the patella.
If the dislocation is a recurring issue, or if significant damage such as a large cartilage fragment or a complete tear of the MPFL is present, surgical intervention may be necessary. Procedures like MPFL reconstruction, where a new ligament is crafted to provide lateral stability, are performed for chronic instability. For a first-time dislocation without severe damage, patients can return to sports within three to four months. However, the risk of a future dislocation remains elevated compared to those who have never experienced the injury.