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Knee

Patellar Instability

What is Patellar Instability?

Patellar instability refers to a condition where the kneecap (patella) does not stay properly aligned within the trochlear groove of the femur. This can lead to partial dislocations (subluxations) or complete dislocations, causing pain, dysfunction, and an increased risk of further injury. Patellar instability is common among athletes and individuals with anatomical predispositions, such as shallow trochlear grooves, baseline knee alignment and ligamentous laxity.

The medial patellofemoral ligament (MPFL) is a crucial structure in maintaining patellar stability. It is a band-like ligament that extends from the medial femoral condyle to the upper medial aspect of the patella. The MPFL serves as the primary restraint against lateral patellar displacement, preventing the kneecap from dislocating outward. In cases of patellar dislocation, the MPFL is often stretched or torn, leading to recurrent instability.

Several anatomical structures contribute to patellar stability:

  • Patella: The kneecap, a sesamoid bone embedded within the quadriceps tendon, is essential for knee extension
  • Trochlear Groove: The groove in the femur where the patella glides during knee movement. A shallow or dysplastic trochlea increases instability risk.
  • Quadriceps Muscles: The quadriceps group (rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius) provides dynamic stabilization of the patella.
  • Patellar Retinaculum: Soft tissue structures, including the medial and lateral retinacula, contribute to patellar tracking and stability.
  • Medial Patellofemoral Ligament (MPFL): As mentioned, the MPFL is the primary passive restraint against lateral patellar dislocation.
  • Lateral Patellofemoral Ligament (LPFL) and Other Soft Tissues: These structures also contribute to knee stabilization but play a secondary role compared to the MPFL.

Individuals with patellar instability may experience:

  • Recurrent kneecap dislocations or a feeling of the patella “slipping out”
  • Pain around the front of the knee (anterior knee pain)
  • Swelling and inflammation after dislocation episodes
  • Difficulty walking, running, or using stairs
  • A sensation of weakness or giving way in the knee
  • Audible popping or clicking noises during movement

For patients with mild patellar instability or those who prefer conservative treatment, nonsurgical options include:

Physical Therapy

  • Strengthening the quadriceps, particularly the vastus medialis obliquus (VMO), to improve patellar tracking
  • Core and hip strengthening to address biomechanical deficiencies
  • Proprioceptive and balance training to enhance neuromuscular control

Bracing and Taping

  • Knee braces designed to prevent lateral patellar displacement
  • McConnell taping or Kinesio taping can help promote proper patellar alignment during recovery or activity

Activity Modification

  • Avoiding high-impact activities that may provoke dislocation in the early phases of recovery
  • Implementing gradual return-to-sport protocols

Anti-Inflammatory Medications

  • NSAIDs such as ibuprofen or naproxen to reduce pain and swelling

Surgical intervention is considered for individuals with recurrent dislocations, structural abnormalities, or failed conservative treatment. Common procedures include:

Medial Patellofemoral Ligament Reconstruction (MPFL Reconstruction)

The MPFL is reconstructed using a tendon graft (often from the hamstring) to restore medial stability and prevent lateral dislocation.

Trochleoplasty

A surgical reshaping of the trochlear groove in cases of trochlear dysplasia to provide better patellar containment.

Tibial Tubercle Osteotomy (TTO)

The tibial tubercle, where the patellar tendon attaches, is repositioned to improve patellar alignment and tracking.

Lateral Release and Medial Imbrication

Releasing tight lateral structures and tightening medial structures to improve patellar tracking.

Arthroscopic Debridement and Realignment

Minimally invasive techniques to remove damaged cartilage and improve patellar positioning.

Nonoperative treatment

Short-Term Outcomes

  • Many patients experience improvement in pain and swelling within weeks
  • Strength and confidence in the knee often improve with structured physical therapy
  • Most patients can return to normal daily activities

Long-Term Outcomes

  • Success rates vary depending on individual anatomy and compliance with therapy
  • Approximately 50–70% of patients do well without surgery after a first dislocation
  • Some patients experience:
    • Ongoing feelings of instability
    • Recurrent subluxations (partial slipping)
    • Reduced confidence during sports or cutting movements

Risk of Recurrence

The risk of another dislocation is higher in younger patients, especially adolescents and athletes

Recurrent instability rates range from 20–40%, and may be higher in those with:

  • Shallow trochlear groove
  • High-riding patella
  • Ligament laxity

Functional Outcomes

  • Many patients can return to low-impact activities
  • Return to high-level sports is possible, but not guaranteed
  • Recurrent instability may lead to cartilage damage over time

Short-Term Outcomes

  • Pain and swelling improve gradually over the first several months
  • Most patients require structured rehabilitation for 4–6 months
  • Early stiffness and muscle weakness are common but usually temporary

Long-Term Outcomes

  • Surgical treatment has high success rates, particularly for recurrent instability
  • Studies show 80–95% of patients experience improved stability
  • Significant reduction in the risk of future dislocations
  • Improved knee confidence and function in daily and athletic activities

  • Most patients return to normal daily activities by 3–4 months
  • Return to sports typically occurs around 6–9 months, depending on:
    • Type of surgery
    • Rehabilitation progress
    • Sport demands
  • Many patients return to the same or higher level of activity as before injury

  • High overall satisfaction due to improved stability and reduced fear of dislocation
  • Most patients report:
    • Less pain
    • Improved knee trust
    • Better quality of life

  • Mild discomfort with kneeling or prolonged activity may persist
  • A small risk of stiffness or over-tightening exists
  • Recovery requires patience and adherence to rehab

Patellar instability can significantly impact mobility and quality of life. While many cases can be managed with conservative treatments such as physical therapy and bracing, recurrent instability often requires surgical intervention. Many patients do well with nonoperative care, especially after a first dislocation. Surgical treatment offers more reliable long-term stability for recurrent cases, Early and appropriate treatment helps reduce the risk of cartilage damage and arthritis later in life. Outcomes are best when treatment is individualized and rehabilitation is followed closely. Understanding the underlying anatomy and available treatment options allows for informed decision-making and effective management of this condition.

At a Glance

Dr. Hasani Swindell

  • Fellowship-Trained Sports Medicine Specialist
  • Board-Certified Orthopedic Surgeon
  • Summa Cum Laude Graduate from the University of Pittsburgh
  • Medical Degree from Columbia University
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