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Causes & Symptoms of Patellar Dislocation or Kneecap Dislocation

What is Patellar Dislocation or Kneecap Dislocation?

An injury to the knee joint which is caused by a sudden twist or a direct blow is typically Patellar Dislocation or Kneecap Dislocation1. The condition occurs with the slipping of the kneecap (patella) out of its normal position at the patellofemoral groove, causing pain that is intense with effusion generally.

If the patella or kneecap does not slide back into its normal position, then an orthopedic reduction can be done by a medical professional. Patient has swelling and reduced mobility after Patellar Dislocation or Kneecap Dislocation and one should undergo a rehabilitation2 program of six to sixteen weeks irrespective of whether the patient undergoes surgery or not. Surgical options for patellar dislocation or dislocated kneecap consist of open or arthroscopic surgery3 for repairing the damage.

Patellar Dislocation or Dislocated Kneecap

What is Subluxation of the Kneecap?

Knee joint tendons and ligaments hold in place the patella (kneecap). If a strong force hits the knee joint the knee cap slides to the side of the knee. Dislocation occurs if the side is severe. The knee cap does not move too far away so much during a subluxation.

What is the Function of Patella?

The other name given to patella is the kneepan or kneecap. This is a thick, circular-triangular bone articulating with the thigh bone (femur) and protects the front part of knee joint by covering it.

Who is at Risk for Patellar Dislocation or Kneecap Dislocation?

People who are likely to suffer Patellar Dislocation4 or Kneecap Dislocation are young athletes than any other group and the age range that are affected are 16 to 30 years. Sports involving the twisting of the leg suddenly are associated with the involvement of the injury. Soccer, ice hockey and gymnastic are such examples. The occurrence of the same can be when a person slips on a slick surface or tripping over an object, especially a person having predisposing factors.

Causes of Patellar Dislocation or Kneecap Dislocation

The protective bone present in front of the knee joint is called as patella or the kneecap. In healthy individuals, upon flexion of the knee, the patella glides up and down a groove called the patellofemoral groove. It is attached to the quadriceps muscle through the quadriceps tendon. Its function is to increase the leverage from quadriceps muscle when straightening/extending the knee.

The normal position of the patella (kneecap) is within the patellofemoral groove. It is structured to slide vertically within the groove. When the patella slips or moves outside this groove into the bony head of the femur (lateral femoral condyle), then it is called as Patellar Dislocation or Kneecap Dislocation.

A Patellar Dislocation or Kneecap Dislocation is different and much less serious than a knee joint dislocation. Patellar Dislocation or Kneecap Dislocation often results from a severe blow or from a twisting action of the knee. Most of the times the patella (kneecap) will move back to its normal position into the patellofemoral groove upon straightening the knee, but this can be very painful.

Patellar position  in Dislocated  knee and Normal knee

Athletes and women are often seen having Patellar Dislocation or Kneecap Dislocation. When a sudden change of direction is planted on your knee joint is its usual occurrence.

Direct trauma can also give rise to dislocation. With the occurrence of a Patellar Dislocation or Kneecap Dislocation you can easily slip side ways towards the outside of your knee. Patellar Dislocation or Kneecap Dislocation occurrence is due to:

  • Knocking of patella out of the joint with a direct impact.
  • A motion that twists the ankle or the knee.
  • A lateral cut that is sudden.

Signs and Symptoms of Patellar Dislocation or Kneecap Dislocation

You will feel pain after the injury instantly. Displacement of the cap will occur obviously and the likelihood of the knee joint to swell. Despite the fact that swelling and pain will always be present, the knee cap can return to its former normal position after being dislocated briefly.

  • Knee joint swelling
  • Pain around the kneecap
  • Reduced mobility in the knee
  • Noticeable dislocation of the knee cap
  • Patient’s leg tends to flex even when relaxed.

What should you do in Case of Emergency?

An ambulance should be called if you think that your knee have been dislocated for the first time and has not corrected itself. Be still while you have sat with your legs stretched. As support from someone to lift the foot up or you straighten the knee. The pain usually fades rapidly after the kneecap has corrected itself.

It might not be necessary for you to go to hospital if you have dislocated your knee previously and managed to manipulate the knee back to its position gently.

Hold an icepack for 10-15 minutes each hour on the knee, in order to prevent swelling. Do it in the day that you have the injury and do it after a few hours on the subsequent days.

Risk Factors for Patellar Dislocation or Kneecap Dislocation

Patellar Dislocation or Dislocated Kneecap- Normal vs Dislocated Knee

Below mentioned are the possible risk factors for Patellar Dislocation or Kneecap Dislocation:

  • Sports involving rotating the knee give rise to Patellar Dislocation or Kneecap Dislocation.
  • The palate can be knocked out of the joint due to direct trauma.
  • 24 percent of Patellar Dislocation or Kneecap Dislocation’s patients have had relative whose patella has been dislocated.
  • Patella’s misalignment on the knee: the patella will be positioned higher than normally, patella Alta
  • Compression syndrome is another causing factor of Patellar Dislocation or Kneecap Dislocation, usually owed to inflammation or lack of balance in the joints. It is complex to conduct the knee pathology and deals with patellofemoral groove abnormalities or osseous soft tissues. Knee extension dysplasia is caused by the symptoms of the patellar, and the muscular mechanism controlling the joint movement will be affected by the sensitive small variation.

Other Risk factors include:

  • Insufficient VMO Strength. The function of the VMO (vastus medialis obliquus)5 is to maintain the patella (kneecap) in its normal position within the patellofemoral groove by pulling it towards the centre of the knee joint at the time of knee movements. This is known as ‘tracking’. If the muscles or its fibers are not strong or sufficiently oriented, then the patella (kneecap) becomes more prone to dislocation.
  • Overpronation of the feet.
  • Q-angle – Individuals having large femoral angle (Q-angle) usually have a ‘knock-kneed‘ appearance (genu valgum), and when these individuals straighten their leg, the kneecap will be pushed towards external side of the knee. So, when excessive force is applied to the inside of the knee, it results in patellar dislocation or dislocated kneecap.

Complications in Patellar Dislocation or Kneecap Dislocation

Patellar Dislocation or Kneecap Dislocation complications8 include:

  • Tendons, ligaments and muscles tearing which usually help in reinforcing the injured joint.
  • Damage of blood vessels and the nerves surrounding the joint.
  • Reinjure susceptibility if severe dislocation has occurred or dislocation that has repeated.
  • Arthritis development in the affected joint as the age increases.
  • If tearing has occurred on the tendons or ligaments supporting the injured joint or if damaged has resulted on the blood vessels or nerves surrounding the joint, surgery may be needed for the repair of these tissues.

Tests to Diagnose Patellar Dislocation or Kneecap Dislocation

The below mentioned tests are conducted to accurately diagnose Patellar Dislocation6 or Kneecap Dislocation:

  • Plain radiography: The most common most performed diagnostic imaging study done for pallofemoral dysfunction is plain radiography, it is cheap at least.
  • CT (computed tomography) scanning: The sensitivity of CT scanning was found to be more sensitive significantly after being tested against the standard radiography. The fact that it can image patellar cartilage makes CT scan more advantageous than plain radiography.
  • Soft tissue anomalies in the knee can be identified through an MRI (magnetic resonance imaging) due to its extreme sensitivity. MPFL (medial patellofemoral ligament) is an injury occurring following an acute Patellar Dislocation or Kneecap Dislocation was formerly detected by doctor by using MRI, according to a study. The presence of joint laxity and if bony deformities are absent, can be determined with the help of MRI. The help of MRI extends to the patellofemoral apparatus’ relationship and the extensor mechanism. In the determination of the volume and thickness of the cartilage, and when determining the presence of patellar chondral lesions, the effectiveness of MRI outlast those of a CT. When assessing osteoarthritis, determination of the volume and the thickness of the patellar cartilage are important, and it is essential in the preoperative calculation of the effect on load transmission and joint contact following surgical procedures.
  • Ultrasonography: Use of ultrsonsography is typically non-existent. When distinguishing congenial defects, mucinoid degeneration, metaplasia, granulation tissue and cyst, using ultrasonography is viable than CT. it is important to know the availability of ultrasonography for helping in determination of what causes pain in the anterior knee.


Watch 3D Video of Patellar Dislocation or Subluxation

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Team PainAssist
Team PainAssist
Written, Edited or Reviewed By: Team PainAssist, Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:October 5, 2020

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