A patellar dislocation refers to a painful knee injury where the patella (kneecap) slips out of its normal position. Often the knee is partly
The patella is also often felt and seen out of place. Complications may include a patella fracture or arthritis.
A patellar dislocation typically occurs when the knee is straight and the lower leg is bent outwards with a twisting force. Occasionally it occurs when the knee is bent and the patella is hit.
The most commonly associated sports with patellar bone dislocation includes
Dislocations nearly always occur away from the midline and diagnosis is typically based on symptoms and supported by X-rays.
Reduction is done by pushing the patella towards the midline while straightening the knee. Then, after corrective reduction, the patient's leg is generally splinted in a straight position for a few weeks. This is then followed by knee physiotherapy.
Surgery after a first patellar dislocation is generally of unclear benefit. Surgery may be indicated in those who have broken off a piece of bone within the joint or in which the patella has dislocated multiple times.
Statistically, patellar dislocations occur in about 6 per 100,000 people per year and make up about 2% of painful knee injuries. This condition is most common in those 10 to 17 years old. Rates in males and females are about the same.
Unfortunately, patients who have an initial dislocation recurs in about 30% of people.
People often describe patellar pain as being "inside the knee cap."
Their leg tends to flex even when relaxed. In some cases, the injured ligaments involved in patellar dislocation do not allow the leg to flex at all.
A predisposing factor is tightness in the tensor fasciae latae muscle and iliotibial tract in combination with a quadriceps imbalance between the vastus lateralis and vastus medialis muscles can play a large role, found, mainly, in women with higher level the physical activity.
To add to that, women with patellofemoral pain may show increased Q-angle compared with women without patellofemoral pain.
Another cause of patellar symptoms is lateral patellar compression syndrome, which can be caused from lack of balance or inflammation in the joints.
The pathophysiology of the kneecap can be complex, and deals with the osseous soft tissue or abnormalities within the patellofemoral groove. The patellar symptoms cause knee extensor dysplasia, and sensitive small variations affect the muscular mechanism that controls the joint movements.
24% of people whose patellas have dislocated have relatives who have experienced patellar dislocations, so genetics may have a large part to play as well.
Patellar dislocation occurs in sports that involve rotating the knee. Direct trauma to the knee can knock the patella out of joint.
People who have larger Q angles tend to be more prone to having knee injuries such as dislocations, due to the central line of pull found in the quadriceps muscles that run from the anterior superior iliac spine to the center of the patella.
The range of a normal Q angle for men ranges from <15 degrees and for females <20 degrees, putting females at a higher risk for this injury. An angle greater than 25 degrees between the patellar tendon and quadriceps muscle can predispose a person to patellar dislocation.
In patella alta, the patella sits higher on the knee than normal. Normal function of the VMO muscle stabilizes the patella. Decreased VMO function results in instability of the patella.
When there is too much tension on the patella, the ligaments will weaken and be susceptible to tearing ligaments or tendons due to shear force or torsion force, which then displaces the kneecap from its origination.
Another cause that patellar dislocation can occur is when the trochlear groove that has been completely flattened is defined as trochlear dysplasia.
Not having a groove because the trochlear bone has flattened out can cause the patella to slide because nothing is holding the patella in place.
Patellar dislocations can happen due to:
Anatomy of the knee
The patella is a triangular sesamoid bone which is embedded in tendon. It rests in the patellofemoral groove, an articular cartilage-lined hollow at the end of the thigh bone (femur) where the thigh bone meets the shin bone (tibia).
Several ligaments and tendons hold the patella in place and allow it to move up and down the patellofemoral groove when the leg bends.
The top of the patella attaches to the quadriceps muscle via the quadriceps tendon, the middle to the vastus medialis obliquus and vastus lateralis muscles, and the bottom to the head of the tibia (tibial tuberosity) via the patellar tendon, which is a continuation of the quadriceps femoris tendon.
The medial patellofemoral ligament attaches horizontally in the inner knee to the adductor magnus tendon and is the structure most often damaged during a patellar dislocation.
Finally, the lateral collateral ligament and the medial collateral ligament stabilize the patella on either side. Any of these structures can sustain damage during a patellar dislocation.
To assess the knee, a clinician can perform the patellar apprehension test by moving the patella back and forth while the people flexes the knee at approximately 30 degrees.
The people can do the patella tracking assessment by making a single leg squat and standing, or by lying on his or her back with knee extended from flexed position.
A patella that slips laterally on early flexion is called the J sign, and indicates imbalance between the VMO and lateral structures.
Two types of treatment options are typically available:
Due to the risk that patellar knee surgery may impede normal growth of structures in the knee, so doctors generally do not recommend knee operations for young people who are still growing. There are also risks of complications, such as an adverse reaction to anesthesia or an infection.
When designing a physiotherapy program, our senior physiotherapists and surgeons consider associated injuries such as chipped bones or soft tissue tears. Clinicians take into account the patient's
generally only recommend surgery when other structures in the knee have
sustained severe damage, or specifically when there is:
Supplements like glucosamine and NSAIDs can be used to minimize bothersome symptoms.
An effective rehabilitation program reduces the chances of re-injury and of other knee-related problems such as patellofemoral pain syndrome and osteoarthritis.
Typically patella dislocations are initially immobilized for the first 2–3 weeks to allow the stretched structures to heal.
Rehabilitation focuses on maintaining strength and range of motion to reduce pain and maintain the health of the muscles and tissues around the knee joint.
The objective to any good rehabilitation program is to
A common physiotherapy plan is to strengthen the
Commonly used exercises include isometric quadricep sets, side lying clamshells, leg dips with internal tibial rotation, etc.
The idea is that because the medial side is most often stretched by the more common lateral dislocation, medial strengthening will add more stabilizing support.
With progression more intense range of motion exercises are incorporated.
Our senior physiotherapists will also use treatment modalities such as