Patellar Instability & Dislocation: Signs, Symptoms, and When to Seek Care

What are the signs and symptoms of patellar instability and dislocations?

Patellar instability refers to a condition where the kneecap (patella) moves abnormally within its groove, often feeling loose or dislocating, while a patellar dislocation is an acute event where the patella completely slips out of its normal position, typically to the outside of the knee.

Understanding Patellar Instability and Dislocation

The patella, or kneecap, is a small, sesamoid bone embedded within the quadriceps tendon. It glides within a groove at the end of the thigh bone (femur), called the trochlear groove, as the knee bends and straightens. This intricate movement is crucial for efficient knee function. Patellar instability occurs when the patella repeatedly moves partially (subluxation) or fully (dislocation) out of this groove. A patellar dislocation is a more severe event where the patella completely displaces, usually laterally (to the outside of the knee). This often results from a direct blow, a sudden twisting motion of the knee, or underlying anatomical predispositions.

Immediate Signs and Symptoms of Acute Patellar Dislocation

When the patella acutely dislocates, the experience is often dramatic and immediately noticeable. The signs and symptoms typically include:

• Sudden, Severe Pain: An intense, sharp pain is usually the first and most prominent symptom, localized to the front of the knee.
• Visible Deformity: The kneecap will appear visibly out of place, often shifted to the outside of the knee. This is a hallmark sign and can be quite alarming.
• Popping Sensation: Many individuals report feeling or hearing a distinct "pop" or "snap" at the moment of dislocation.
• Inability to Straighten or Bend the Knee: The knee may become "locked" in a slightly bent position, making it impossible to fully extend or flex due to pain and mechanical obstruction.
• Rapid Swelling: Significant swelling (hemarthrosis) often develops quickly due to bleeding within the joint capsule, caused by damage to blood vessels and soft tissues.
• Feeling of the Knee "Giving Way": The knee may feel unstable or buckle under weight immediately prior to or at the moment of dislocation.

Signs and Symptoms of Chronic Patellar Instability

Chronic patellar instability refers to recurrent episodes of subluxation or dislocation, or a persistent feeling of the kneecap being loose. These symptoms may be less acute than an initial dislocation but can significantly impact daily activities and quality of life. They include:

• Recurrent "Giving Way" or Buckling: The knee may suddenly feel unstable and buckle, especially during activities involving pivoting, twisting, or changing direction. This is often described as the knee "giving out."
• Feeling of the Kneecap "Shifting" or "Loosing": Individuals frequently describe a sensation that the kneecap is moving out of place, either partially (subluxation) or completely, before it spontaneously reduces back into the groove.
• Anterior Knee Pain: Pain is common, often localized to the front of the knee, particularly during or after physical activity, climbing stairs, or prolonged sitting with bent knees (known as the "Theater Sign").
• Intermittent Swelling: Episodes of swelling may occur, especially after activity that stresses the knee, indicating irritation or minor bleeding within the joint.
• Catching or Locking Sensation: The knee may momentarily "catch" or "lock" if the patella briefly gets stuck out of its groove or if damaged cartilage fragments interfere with joint movement.
• Crepitus: A grinding, crunching, or clicking sound may be heard or felt during knee movement, particularly during activities like squatting or stair climbing, due to abnormal patellar tracking or cartilage wear.
• Apprehension: A psychological symptom where the individual develops a fear or apprehension about certain movements or positions that they anticipate might cause the patella to dislocate.
• Tenderness: Palpation around the edges of the patella, especially on the medial (inner) side where the supporting ligaments may be stretched or torn, can elicit tenderness.

Differentiating Instability from Other Knee Conditions

While some symptoms of patellar instability, such as anterior knee pain and swelling, can overlap with other common knee conditions like patellofemoral pain syndrome (PFPS) or meniscal tears, the key differentiator for instability is the feeling of the kneecap actually shifting or dislocating. PFPS typically involves pain without the sensation of displacement, while meniscal tears are more often associated with mechanical locking, clicking, and pain along the joint line. A thorough clinical examination is crucial for accurate diagnosis.

When to Seek Medical Attention

• Acute Patellar Dislocation: If you experience an acute patellar dislocation, it is a medical emergency. Seek immediate medical attention at an emergency room or urgent care clinic. Do not attempt to reduce the dislocation yourself, as this can cause further damage.
• Chronic Patellar Instability: If you experience recurrent symptoms of patellar instability, such as the persistent feeling of your kneecap shifting, recurrent "giving way," or unexplained anterior knee pain accompanied by apprehension or swelling, consult with a physician or an orthopedic specialist. Early diagnosis and intervention can help prevent further cartilage damage and improve long-term knee health.

Diagnostic Process

Diagnosis of patellar instability and dislocation involves a detailed clinical history, a thorough physical examination (including specific tests like the apprehension test), and imaging studies. X-rays are typically used to confirm dislocation and rule out fractures. An MRI may be ordered to assess soft tissue damage, such as ligament tears (e.g., medial patellofemoral ligament, MPFL) and cartilage injuries, which are common complications of patellar instability.