Unstable Kneecap Symptoms and Causes

The kneecap (known as the patella) is connected dynamically to the thighbone (known as the femur) via a groove (called the trochlea). Both the patella and this femoral groove are coated in cartilage to reduce friction. If the kneecap stays in this groove, then you hardly even notice that it’s there. You go about your life – sitting, walking, running and squatting – smoothly. If the kneecap should slip out of its groove, though, you become very aware that it is there. It screams out to be paid attention to. The kneecap is a connective link between the thigh muscle (called the quadriceps) and the shinbone (called the tibia). As the quadriceps, along with other muscles, bend and extend your leg, the patella slides up and down accordingly. Because the kneecap is so important for leg bending and extension, if your kneecap becomes unstable, locomotion can be impacted quite negatively. 

Athletes who play very physically demanding sports are most at risk of sustaining an unstable kneecap. The reason that many football players wear knee braces is to protect against injuries like unstable kneecaps. As an unstable kneecap affects one’s balance negatively, it is a hated football injury; falling down is the last thing you want to do in a game of football (especially if you’re carrying the ball). Without proper medical intervention and care, an unstable kneecap can cause permanent damage, such as severe arthritis.

Anatomy of the Kneecap
The kneecap, while seemingly a small part of the human body, bears an outsized burden when it comes to balance and locomotion. It is not merely protection for the knee joint; it is a key connection point between the tibia and the quadriceps and, as such, is vital for leg bending and extending. This area of the body consists of:

  • The patella (the kneecap, which is a flat bone)
  • The patella tendon (attaches the kneecap to the tibia)
  • The femur (the thighbone, a groove in which holds the patella)
  • The tibia (the shinbone, which the patella is connected to via the patella tendon)
  • The quadriceps muscles (located on the front of the thigh, they are connected to the kneecap)

Types of Unstable Kneecap
Unstable kneecap can be divided into two main types:

  • Laterally unstable kneecap – When the kneecap moves out of its groove and toward the leg’s outside, you have a laterally unstable kneecap. This is the more common kind of unstable kneecap.
  • Medially unstable kneecap – When the kneecap moves out of its groove and toward the leg’s inside, you have a medially unstable kneecap, which is less common than having a laterally unstable kneecap.

Causes of Unstable Kneecap
An unstable kneecap can result from a traumatic injury or, if one is very predisposed to sustaining one, from normal, everyday movement. The following are the causes of unstable kneecaps:

  • An intense impact – The kneecap can become dislodged from its groove because of a blow (most frequently associated with sports injuries).
  • Anatomical abnormality – If the femoral groove is not straight or is not sufficiently deep, the kneecap can slip out.      

Symptoms of Unstable Kneecap
The symptoms of unstable kneecaps are pretty consistent, though they, of course, vary in severity. Generally speaking, if you have an unstable kneecap, you will no longer be able to bear your own body weight, and bending your knee will cause you a lot of pain. Additionally, your knee will periodically lock up, swell, stiffen and make “popping” sounds. 

The following are common unstable kneecap symptoms:

  • Pain
  • Locking knee
  • Inability to walk without aid
  • Swelling
  • Stiffening
  • Knee “popping”

The symptoms of an unstable kneecap may be mistaken for the symptoms of other medical conditions (kneecap dislocation, prepatellar bursitis, etc.). Make sure you consult a doctor in order to determine if you have an unstable kneecap and get the appropriate treatment. 

The multidisciplinary team of orthopaedic experts at North Shore-LIJ Orthopaedic Institute in New York treats Unstable Kneecaps as well as a broad range of conditions that affect the bones within the body.

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