The patella or kneecap is a small, triangular-shaped bone at the front of your knee. Although it seems insignificant, it has an important function. The kneecap increases the lever arm of your quadriceps muscle. This enables your thigh muscle to generate more force so that you can jump higher or kick harder.  The real value of the kneecap is recognised when it cannot perform its function. Patella dislocation is the movement of the kneecap out of the groove on the thigh bone. Faulty tracking and decreased lever arm equals loads of pain when bending or straightening your knee. Physiotherapy can help you recover from a patella dislocation.

Dislocation is when the kneecap is locked and stays hooked out of position, which needs a specialist to return it to its normal position, without injuring any of the delicate structures around the knee. A subluxation is a less severe form of a patella dislocation there the patella pops back into position as the knee is straightened.

Where does my patella fit into my knee joint?

Bones

Your patella is a sesamoid bone, which means it is completely embedded in a tendon. The knee is actually two different joints. The joint a three-year-old points to when asked “where is your knee?” is the tibiofemoral joint. The tibiofemoral joint is formed by the thigh bone (femur) above and shin bone (tibia) below. The second joint is the patellofemoral joint, between the femur and the patella (kneecap).

Ligaments

The knee joint relies on ligaments for stability (ligaments connect bone to bone in our bodies). The ligaments in your knee work in pairs to prevent movement of the thigh bone on the shin bone. The cruciate ligaments avoid front-to-back gliding, and the collateral ligaments avoid sideways gliding of the thigh on the shin.

The patellofemoral joint has the retinaculum and patellar tendon for stability. The patellar tendon is the spot a doctor will hit with a reflex hammer when testing your knee reflex.

The meniscus is specialised joint cartilage on top of the tibia, within the joint capsule. The meniscus acts as a shock absorber or buffer that absorbs some of the forces that pass through the knee. Think jumping and jogging. This function protects the joint surfaces from damage.  The meniscus also aids in joint lubrication and nutrition.

Muscles & Nerves

Different muscles cross the knee joint to allow movement. The hamstring muscles pass behind the knee, from above to attach below the knee on either side. The calf (gastrocnemius) muscle passes behind the knee, from below to connect above the knee on either side. Deeper underneath this criss-cross lies the popliteus and plantaris muscles. The quadriceps muscles (rectus femoris, vastus medialis, vastus lateralis and vastus intermedius) at the front of the thigh merge to form a tendon (quadriceps tendon) that crosses in front of the knee. The patella sits snugly within this tendon, which attaches below the knee joint on the tibia. The iliotibial band (ITB) attaches on the outside of the leg, below the knee. A group of three tendons, the pes anserinus (sartorius, gracilis, semitendinosus), attach on the inside of the thigh, below the knee.

The sciatic nerve splits into the tibial and common peroneal nerve above the knee, at the back of the leg. The popliteal artery and vein pass behind the knee.

Your knee is a hinge joint. Like a door can open and close as it moves at the hinges, the knee also allows movement in only one direction. Bending or flexing the knee, to bring the calf to the back of the thigh, and straightening or extending the knee to kick a ball.

The kneecap increases the leverage of the quadriceps muscle up to 50%! This unique lever arm enables greater force generation. More leverage, more power. Which comes in handy when kicking a ball or jumping to lift the entire body weight to shoot a goal or clear a hurdle.  

The femur has a special groove wherein the patella slides when bending or straightening the knee.  Patellar tracking describes this smooth gliding of the patella within the femoral groove. In full extension (with the knee straight) the kneecap lies below the femoral groove towards the outside. When the knee reaches 20-30 degrees of flexion, the kneecap moves into the femoral groove. As the knee bends the kneecap glides up and in within the groove. The shin bone then rotates slightly in too. At 130 degrees flexion, the patella has almost completed its “up and in” journey to sit at the top towards the inside of the femoral groove.

What’s going on on a tissue level?

The excruciating pain you feel because of a patella dislocation is driven and maintained by the structures around the kneecap. The retinaculum of the knee is stretched and injured when the kneecap moves out of the trochlear groove. This starts an inflammatory process that the body needs to initiate healing.

The damaged cells within the retinaculum release chemicals like histamine, bradykinin, and prostaglandins. These chemicals are the first responders to the scene of the accident, they cause local blood vessels to leak fluid into the tissue that causes swelling. That is why your knee can almost double in size when injured. These chemicals, together with the added pressure from the swelling, stimulates nociceptor nerves. These are the messages that our brains interpret as pain.

Self or on-site assisted reduction, that means getting, guiding or forcing the patella back into the groove by straightening your knee ASAP is crucial. This is not for the faint-hearted. But the benefit of quick reduction means that you don’t reinjury tissue that you would with a delayed reduction.

Traumatic

The most common cause of dislocation is traumatic and the result of external forces. Either from a blow from sports equipment (hockey stick, a boot of another player) or twisting action of the knee, landing from a jump where the knee suddenly gives way from under you.

In some cases, the patella will relocate to the patellofemoral groove when you straighten your knee. However, this is extremely painful. If this relocation does not happen by itself, you will need assistance from a doctor.

Atraumatic (spontaneous)

Atraumatic patella dislocation mostly happens in young female athletes because of ligamentous laxity or hypermobility. You may be predisposed to patella dislocation because of:

• Insufficient quadriceps strength (on the inside of the knee)
• Overpronation of the feet (excessive subtalar pronation), where the feet roll in or flatten too much when running. This causes the leg to turn inwards which leaves the patella susceptible to moving outwards as the quadriceps contract. Increased Q angle of the knee (commonly referred to as knock knees).
• Shallow femoral groove
• Ligamentous laxity/ general hypermobility (this is not a party trick!!!)
• Patella Alta describes an anatomical variation where the kneecap sits higher in relation to the femur than usual

How bad is my patella dislocation?

A patellar dislocation/subluxation should always be assessed to determine the extent of damage to the surrounding structures. The injury to the other soft tissue structures will be different for each person and situation. An atraumatic dislocation in a hypermobile joint may have less swelling than a traumatic dislocation on the sports field. However, repeated dislocation can lead to permanent damage of the retinaculum and patellar tendon. 

As physiotherapists, we are able to assess the joint, muscles, ligament and tendon to determine the extent of injuries. In most cases, an acute, traumatic patella dislocation would force you to visit the emergency room. Here a doctor would have reduces the patella back to the femoral groove. Hopefully, your doctor would have encouraged you to seek physiotherapy treatment. We can establish the presence of other injuries. If there is an injury to the ligaments, meniscus, muscles or nerve, we will find it. Because each injury scenario is unique, each degree of damage is unique to each person. Depending on the accompanying problems, we will custom fit your treatment program to your injury.

• Firstly the amount of swelling may be measured using a good old measuring tape to compare to the other side.
• The range of motion (available movement) will be assessed using a goniometer.
• Ligament integrity/laxity and meniscus injury will be assessed using special orthopaedic tests.

X-ray show images of the bone. The position of the kneecap is assessed by X-ray. It will also rule out the possibility of a patella fracture. We can make some deductions from the structures surrounding the knee joint & patella. There is a specific group of X-rays that need to be done when we want a clear picture of what’s going on around your knee cap.

Diagnostic Ultrasound shows superficial soft tissue. This would be the best scan to do if the patella reduced immediately after it dislocated, considering there was no direct blow to the knee. The soft tissue injury takes priority. If our objective assessment requires soft tissue visualisation, a sonar is needed. The meniscus will not be visible on a sonar.

Magnetic resonance imaging shows bone, ligament, nerves, blood vessels and the meniscus. It is a costly procedure and needs a specialist referral. If X-rays ruled out a fracture, and the kneecap reduced (returned to the patellar groove) MRI would not be necessary, unless gross damage is suspected.

Ongoing pain after a single incident of traumatic patella dislocation is due to subchondral swelling, swelling of the bone itself. You need adequate rest and treatment for ALL injured structures before you consider returning to play.

Repeated atraumatic patella dislocation, when your patella dislocates with small movements, needs further investigation. You may be predisposed to this injury because of your anatomy/biomechanics. Hypermobility and lax ligaments can make you more prone to dislocation. We are able to dig deeper, find the problem and solve it. Repetitive patella dislocation may cause chronic knee pain. The reason for repeated incidents needs treatment. In this case, you can expect a more lengthy treatment period to include strength training and improve your movement patterns.

Due to the misdiagnosis of the contributing factors or inadequate rehabilitation, pain can become chronic after patella dislocation. That is why thorough assessment and committing to a complete rehabilitation program are so important. You only have two knees to carry you through life.

Trying too many treatments, but not finishing any will address, but not all of your problems.

Medication makes the pain bearable by changing your sensitivity to nociceptive information from your nervous system. Tablets can’t make structural changes to your knee. You only mask the symptoms by taking pills.

Generic braces or long term use of any type of brace can cause general weakness and instability. A brace should be used responsibly. After complete rehabilitation, there is no need for a brace in the long run. Do not get addicted to external stability. Your knee was made to carry your load.

We are skilled to evaluate and diagnose your patella dislocation. Our physiotherapists can identify other contributing factors and address that through your treatment to enable you to get back to what you love doing in as little time as possible. We will guide you through your rehabilitation and implement an effective, progressive plan to lessen your fear and give you confidence in your knee again. Your rehabilitation program will address muscle strength, range of motion, flexibility, and stability.

All dislocations are specific to the mechanism of injury. Therefore all dislocations will heal within a different time frame. In general, you can expect 6 weeks for soft tissue healing, and then the strength training can intensify. You will need to see your physio twice a week for the first 2 weeks and then weekly as you progress. The pace of your recovery is largely up to how compliant you are with your rehabilitation exercises. 

Many sports disciplines teach players how to relocate a patella on the field, like soccer and rugby. It is best to get a professional to reduce your dislocated patella. You will need to go to the emergency room and use a brace and crutches.

Remember that other structures get injured too and a single manipulation will not solve your problem.

Analgesics and anti inflammatory medication will assist with pain relief in the initial phases of healing but use responsibly. Prolonged use of these medications may cause gastrointestinal symptoms, like diarrhea, indigestion and constipation.

If you participate in high-level sport a biokineticist can collaborate in your final rehabilitation.

Surgery may be necessary after a patella dislocation, especially if you have repeated incidents of dislocation.

With a traumatic injury, where other structures are also injured, a surgical debridement may be done and a repair of the injured tissue. Most commonly the medial side of your patella femoral ligament is repaired or reconstuctered with a graft.

Where anatomical abnormalities are causing repetitive patella dislocations bone realignment may be considered. Here your trochlear groove can be deepenend or  tibial tubercle moved.

Remember that surgery is just the first step to your recovery. Postoperatively you will need rehabilitation to regain movement, strength and endurance. Rhabilitatin after surgery will be specific to the procedure you underwent and can take 6 weeks to 4 months.

Patella fracture

Usually the result of direct trauma (fall onto the knee, blunt force from a hockey stick). This can happen due to excessive force from the muscles, in this case, there would be an accompanying muscle tear of the quadriceps.

Knee dislocation (tibiofemoral joint)

Patella dislocation is not the same as a dislocation of the knee joint itself which is a much more severe traumatic injury, which will probably require surgery. In this instance, the thigh and shin bone dislocate, leading to severe deformation.

ACL rupture

A rupture or tear of one or both of the cruciate ligaments may have the same mechanism of injury as a patella dislocation. In most cases when you landed and then twisted your knee and it immediately gave way. An ACL rupture may cause an audible pop sound.

• Patella subluxation
• Kneecap dislocation