What is Patella Dislocation (Knee Dislocation)?
Patellar instability includes a variety of conditions, from intermittent subluxations (partial dislocations) to full dislocations. Usually, patients show visible irregularities and struggle to straighten out their knee. A first-time dislocation has a 15-60% chance of happening again. General patellar instability is estimated to account for 3% of knee-related clinical cases. Most instances can be treated with physiotherapy and bracing, unless a fracture is involved or the dislocations are happening repeatedly.
What Causes Patella Dislocation (Knee Dislocation)?
Acute patellar dislocations, also known as knee cap dislocations, usually happen due to trauma. This might be a twisting injury to the knee when no other body comes into contact or a forceful hit to the inside of the knee. Knee cap dislocations can also happen when your knee rotates to the outside while your foot is stuck to the ground. Some people might have inherently loose ligaments who can experience patellar dislocations; they often experience the knee cap slipping out of place rather than entirely dislocating.
Certain anatomical differences, like having a high-riding kneecap (patella alta) or malformation of the knee groove (trochlear dysplasia), can make a person more prone to knee cap dislocation. Females or those with tissue disorders such as Marfan Syndrome or Ehlers-Danlos often exhibit loose ligaments, which also increases the risk of dislocation. Additionally, an imbalance in the muscles around the knee cap, especially weakness in the inner thigh muscle (the vastus medialis oblique), can lead to knee cap instability.
Some people experience habitual dislocations- these are painless dislocations each time the knee bends, resulting from abnormal tightness of the outer thigh muscle (the vastus lateralis) and the iliotibial band, a ligament that extends from the hip to the shin.
Lastly, newborns can also have knee cap dislocations, and it is most common in children with Down syndrome. This happens due to a combination of a small knee cap and underdeveloped thighbone end, which usually requires surgery to fix.
Risk Factors and Frequency for Patella Dislocation (Knee Dislocation)
Patellar dislocation, or a dislocated kneecap, makes up about 2 to 3% of all knee injuries. It often happens to young and active people, especially teenage girls and athletes. The number of people who dislocate their kneecap is about 5.8 out of every 100,000, but this could rise to 29 out of every 100,000 among teenagers. Though this type of knee injury can happen to both men and women, it’s most common in people who are in their twenties and thirties.
Signs and Symptoms of Patella Dislocation (Knee Dislocation)
If you twist your knee or suffer a direct blow to the front or inside, you might experience knee pain and a change in its shape. This kind of injury may make your knee feel like it’s unable to support you, and you might feel a ‘pop’. In immediate cases, your knee could swell. For long-term cases, you might feel pain at the front or the inside of the knee, and experience moments when your knee fails to support you, clicks, or gets stuck. Kneeling or bending your knee could make these symptoms worse.
If a doctor examines your knee soon after the dislocation, they’ll often find that it’s swollen. However, this is less common in long-term cases. They might also find that your knee isn’t lined up correctly, or that the knee and the structures around it are tender or bumpy. They’ll also check if the range of movement in your knee is normal and whether it makes a grating noise when you bend it. The doctor will also check the ligaments in your knee for any damage.
- Twist or direct blow to the knee
- Knee feels like it gives way, feels a ‘pop’
- Swelling (immediate cases)
- Pain at the front or inner area of the knee (long-term cases)
- Knee incapable of support, clicking, or getting stuck
- Worsening symptoms during kneeling or bending
In some scenarios, a patient may show a positive J sign where the kneecap moves excessively to the side while bending and stretching the knee. Generally, a kneecap should be able to move around 25%-50% its width from the center in either direction. In recurrent dislocators, the kneecap may exhibit a wider range of movement. Another test performed is the apprehension test. Here, the knee is kept loosely bent and the kneecap is pushed outwards. If you feel anxious or tense up in this scenario, it marks a positive test result.
Testing for Patella Dislocation (Knee Dislocation)
If you’re having problems with your knee, your doctor will likely take different types of x-rays to figure out what’s wrong. You’ll most likely have front-to-back and side-on photos of your knee taken, along with certain angles of your knee cap. These can help your doctor see if there are fractures, loose pieces of bone or tissue, any unevenness, or arthritic changes.
Fractures or loose pieces in your knee often come from the inner side of the knee cap, and sometimes involve the outer area of your thigh bone. X-rays can also show whether certain features of your knee anatomy increase your risk for dislocation. For example, the position of your knee cap may be unusual, which can be seen on x-rays. The length of your knee cap compared to the length of the tendon below it can also be measured.
A normal ratio is 1.0; a ratio greater than 1.2 suggests a high-riding kneecap, while less than 0.8 suggests a low-riding kneecap. In addition, certain x-rays can show whether the groove in your thigh bone where the knee cap sits is flatter than it should be or if the thigh bone is not as developed as it should be. Certain angles can be measured to learn more about the tilt of the kneecap.
Your doctor may also use a CT scan to measure the distance between a specific point on the knob on your shin bone and the deepest part of the groove in your thigh bone where your knee cap sits. A normal measurement is less than 20mm, anything more is considered abnormal. A CT scan can also show more detail about any bone fractures and help decide if surgery is needed.
An MRI scan is great for investigating the soft parts of your knee. If the kneecap has fully dislocated, a unique pattern of bruising is often seen on the outer thigh bone and inner knee cap. Disruption of an essential ligament (MPFL) is also typical in such cases. The MRI scan can also help detect damage to the cartilage on the inner side of the knee cap and identify any bone bruises. It’s also very useful for assessing the groove in the thigh bone for conditions like trochlear dysplasia.
Treatment Options for Patella Dislocation (Knee Dislocation)
The immediate treatment for a sudden kneecap dislocation, which typically occurs in the emergency department, is to put the kneecap back into place. This can be done by bending the hip, applying gentle pressure to the side of the kneecap, and slowly extending the knee. The patient can be sitting up during this procedure with their legs hanging off the edge of the bed.
The conventional treatment for first-time dislocators, if there’s no evidence of loose fragments or damage inside the joint, involves pain management, cold therapy, and anti-inflammatory drugs to reduce pain and swelling. It also includes physical therapy and changes in activity. A special kind of knee brace or sleeve may be useful in the short term (2 to 4 weeks) to allow the injured tissues to heal. After this, physical therapy should be started, focusing on strengthening the thigh muscles, core muscles, and improving balance. The patient can bear weight on the knee as it’s comfortable for them.
There’s an ongoing debate about surgical treatment for first-time dislocations. Recent reviews suggest that although there is evidence supporting surgery, the quality of this evidence is not strong enough to change current practice. However, some surgeons recommend using a tiny camera to examine the knee joint in cases of bone and cartilage fractures, and repairing the damage if possible.
Surgery could be considered in several cases, including initial dislocation with bone or cartilage fractures, MRI showing injury to the knee’s medial ligament, dislocation with a normal knee on the other side, failure to improve with nonsurgical treatments, or frequent dislocations. Research suggests that early surgical interventions can decrease the chances of future dislocations, but it’s unclear if there are long-term benefits.
Surgical treatment usually involves realigning the knee in two steps— around the kneecap and along the knee joint. There are different surgical options depending on the patient’s specific circumstances. These include:
* Knee scope procedure with or without removal of loose fragments: These treatments may be needed for displaced bone and cartilage fractures or loose fragments. If enough bone is present, repairing them is usually the first choice.
* Medial ligament repair or reconstruction: The medial ligament, which is often damaged during kneecap dislocations, can be repaired or reconstructed. If the patient has had frequent dislocations, then the ligament might need to be fully reconstructed.
* Lateral release: This procedure involves cutting the stretchy tissue on the outside of the knee joint to help realign the kneecap. It’s generally done alongside other realignment procedures.
* Bone realignment: This is necessary when the kneecap’s tracking is influenced by abnormal anatomy. This procedure, known as a Fulkerson osteotomy, involves cutting the shinbone to reposition the patellar tendon, which helps reduce the risk of recurrence. It’s not suitable for patients still growing.
* Groove deepening: This treatment option is used for patients with repeat dislocations. It involves creating a deeper groove for the kneecap to move through and is usually done alongside ligament reconstruction. It’s not common but can be considered in severe cases.
What else can Patella Dislocation (Knee Dislocation) be?
Injuries to the knee can happen for many reasons and may involve damage to various parts of the knee. Here’s a simplified list of potential injuries that doctors might consider:
- Injury to the anterior cruciate ligament (a key ligament that helps to stabilize the knee)
- Injury to the medial collateral ligament (another important ligament in the knee)
- Injury to the meniscus (a type of cartilage in the knee that acts as a shock absorber)
- Patellofemoral syndrome (issues that cause kneecap pain)
- Medial synovial plica (an inflammation or enlargement of the synovial membrane inside the knee)
- Chondromalacia (a condition where the cartilage on the undersurface of the kneecap deteriorates and softens)
It’s crucial that doctors accurately identify which of these issues may be causing a patient’s knee problems in order to treat it properly.
What to expect with Patella Dislocation (Knee Dislocation)
People may need physiotherapy for up to two to three months after their initial dislocation. This therapy is crucial because if the medial retinaculum (a band of tissue) doesn’t heal properly and the VMO muscle isn’t appropriately strengthened, the dislocation can happen again. Studies indicate there’s a 20 to 40% chance of a dislocation happening again, with even higher chances after a second dislocation.
It’s typical for patients to still have symptoms after the first dislocation. Research has shown that six months later, 58% of patients have difficulty with demanding activities. Although they regain their range of motion, their participation in sports is usually lessened in the first six months after the injury; actions like kneeling and squatting can be notably difficult. More than half didn’t return to their sports.
Another study found that more than half of patients experience some issues after their first dislocation, such as dislocation happening again, subluxation (partial dislocation), or knee pain.
Patients who had dislocations because of anatomical abnormalities in their bodies might also have a dislocation in the opposite kneecap, which would also need treatment. However, a patient’s stability usually improves as they get older.
Possible Complications When Diagnosed with Patella Dislocation (Knee Dislocation)
After a sudden dislocation of the kneecap, problems can include related breaks or chips in the bone, an increased chance of it happening again, and a type of wear-and-tear joint disease.
There are some general risks related to surgical procedures, such as infection, damage to the nerves or blood vessels, and serious conditions such as a deep vein thrombosis or a pulmonary embolism, which are types of blood clots.
Some complications are specific to MPFL surgery, a type of procedure to repair knee injuries, which include damage to a specific nerve (the saphenous nerve) and rupture.
After a specific type of surgical procedure called an osteotomy, people often experience pain over the area where a screw has been inserted. This might make it uncomfortable to kneel, and there’s also a chance of breaking a bone near your knee (proximal tibial fracture).
Even after surgery, there’s still a risk of experiencing instability in the kneecap, causing it to potentially dislocate again.
Complications From Acute Patellar Dislocation:
- Associated osteochondral fracture
- Risk of recurrence
- Progressive degenerative arthritis
General Surgical Complications:
- Infection
- Neurovascular injury
- Deep vein thrombosis or pulmonary embolism
Complications Specific to MPFL Surgery:
- Saphenous nerve neuritis
- Rupture
Complications Following Osteotomy:
- Pain over the screw site
- Loss of ability to kneel comfortably
- Risk of proximal tibial fracture
Additional Risk:
- Recurrent lateral patellar instability even after surgery
Recovery from Patella Dislocation (Knee Dislocation)
The recovery process after surgery depends on the type of operation performed. For example, it’s fastest to recuperate from a lateral release, whereas healing from osteotomies takes significantly longer. The post-surgery recovery period can span anywhere between 6 months and a year, during which physical therapy is essential, especially after a period of stillness or immobilization.
Preventing Patella Dislocation (Knee Dislocation)
Patients should be advised against participating in contact sports until they have completed enough physiotherapy. This therapy helps strengthen the core and muscles around the injury. Using slip-on knee braces can be helpful during the early stages of recovery. It’s crucial for patients to stick to the physiotherapy plan after an initial dislocation. Doing so can help reduce the risk of additional dislocations and the potential need for surgery.
