Understanding Patellar Anatomy

The knee joint is formed by three bones:

• Femur (thigh bone)
• Tibia (shin bone)
• Patella (kneecap)

The patella sits within a groove in the femur called the trochlear groove. As the knee bends and straightens, the kneecap glides smoothly within this track.

Tendons, including the quadriceps tendon and patellar tendon, form the knee’s extensor mechanism and allow the knee to straighten.

Stability of the patella depends on:

• The shape of the trochlear groove
• Surrounding ligaments (especially the medial patellofemoral ligament, or MPFL)
• Quadriceps muscle strength
• Hip and core alignment
• Lower limb biomechanics

If any of these structures are abnormal or injured, the patella may shift out of alignment.

What Is Patellar Instability?

Patellar instability refers to abnormal movement of the kneecap. It may include:

Patellar Subluxation

A partial shift of the kneecap out of the groove that typically returns to position on its own.

Patellar Dislocation

A complete displacement of the kneecap, usually toward the outside (lateral side) of the knee. This often requires manual reduction (a procedure in which a medical provider gently guides the kneecap back into place) or other medical intervention.

Recurrent patellar instability occurs when dislocations or subluxations happen repeatedly.

What Causes Patellar Instability or Dislocation?

Patellar instability may result from traumatic injury or underlying anatomical factors.

Traumatic Injury

• Sudden twisting or pivoting motion
• Direct blow to the knee
• Sports requiring cutting and directional changes (soccer, basketball, football)
• Falls or awkward landings

A first-time dislocation frequently tears the medial patellofemoral ligament (MPFL), a key stabilizer that prevents the kneecap from moving outward.

Anatomical Risk Factors

Some individuals are predisposed to kneecap instability due to:

• Shallow trochlear groove (trochlear dysplasia)
• High-riding kneecap (patella alta)
• Increased Q-angle
• Ligamentous laxity
• Quadriceps or hip muscle imbalance
• Flat feet or abnormal lower limb alignment

Adolescents and young athletes, particularly females, are at increased risk due to anatomical and biomechanical differences.

Symptoms of Patellar Instability

Knee pain is the most common symptom of patellar instability, often felt below or around the kneecap and worsened by activity.

Other symptoms may include:

• Sudden knee pain at time of injury
• A visible shift of the kneecap
• Swelling or joint effusion
• A feeling that the knee “gave out”
• Instability during walking or activity
• Tenderness along the inside of the knee
• Difficulty straightening or bending the knee
• Recurrent slipping or catching sensations

After a dislocation, swelling often develops quickly within hours.

How Patellar Instability Is Diagnosed

Accurate diagnosis is essential to prevent recurrent dislocation and cartilage damage.

At OrthoTexas, evaluation includes:

Comprehensive Clinical Examination

• Detailed injury history
• Assessment of kneecap tracking
• Stability testing
• Range-of-motion evaluation
• Strength and alignment assessment

Imaging Tests

• X-rays to evaluate bone alignment and rule out fractures
• MRI (magnetic resonance imaging) to assess ligament injury (such as MPFL tear), cartilage damage or loose fragments
• CT scan (in select cases) to evaluate bone alignment and structural abnormalities

Imaging helps determine whether conservative treatment is appropriate or if surgical stabilization is necessary.

Treatment Options for Patellar Instability

Treatment depends on:

• First-time vs. recurrent dislocation
• Severity of ligament injury
• Underlying anatomical factors
• Activity level
• Presence of cartilage damage

OrthoTexas prioritizes conservative treatment when appropriate.

Non-Surgical Treatment

Many first-time patellar dislocations can be treated without surgery.

Initial Management

• RICE (Rest, Ice, Compression, Elevation)
• Temporary bracing or immobilization
• Crutches if needed

Physical Therapy

Rehabilitation focuses on:

• Strengthening the quadriceps (especially the vastus medialis obliquus)
• Improving hip and core stability
• Enhancing neuromuscular control
• Correcting patellar tracking mechanics
• Gradual return to sport

Structured physical therapy programs are essential to restore strength, improve range of motion and reduce recurrence risk.

Bracing may also be used during activity for additional support.

Surgical Treatment

Surgery may be recommended if:

• Recurrent dislocations occur
• Significant ligament tears are present
• Cartilage damage or loose bodies exist
• Structural abnormalities predispose to repeated instability
• Non-surgical treatment fails

MPFL Reconstruction

Reconstruction of the medial patellofemoral ligament using a tendon graft restores stability and prevents lateral displacement.

Tibial Tubercle Osteotomy

This procedure realigns the patellar tendon attachment to improve kneecap tracking.

Trochleoplasty

In rare cases of severe trochlear dysplasia, the groove may be reshaped to improve stability.

Arthroscopy

Used to remove loose cartilage fragments or repair cartilage damage.

Your orthopedic surgeon will recommend the most appropriate approach based on your anatomy, activity level and goals.

Prevention of Patellar Instability

Preventive strategies include:

• Strengthening the quadriceps and hip muscles
• Improving flexibility
• Using proper movement mechanics
• Wearing a brace during high-risk activities (if recommended)
• Avoiding sudden increases in training intensity

Strong lower extremity muscles and proper biomechanics significantly reduce recurrence risk.

Potential Complications

If left untreated, patellar instability may lead to:

• Recurrent dislocation
• Cartilage damage
• Osteochondral fractures
• Knee pain
• Early patellofemoral arthritis

Early evaluation and appropriate treatment are key to preventing long-term joint damage.

Rehabilitation and Recovery

Non-Surgical Recovery

• Return to light activity within weeks
• Full return to sports typically within 6–12 weeks

Post-Surgical Recovery

• Brace protection initially
• Progressive physical therapy
• Return to sports often between 4–6 months

A structured rehabilitation program is essential for optimal recovery.

When to See a Knee Specialist

Schedule an evaluation if you experience:

• A kneecap that visibly shifts out of place
• Recurrent “giving out” episodes
• Persistent swelling after injury
• Instability when walking or climbing stairs
• Difficulty returning to sports

Prompt care helps prevent additional joint damage.

Comprehensive Kneecap Instability Care at OrthoTexas

OrthoTexas provides advanced care for patellar instability and kneecap dislocation, including:

• Advanced imaging
• Personalized conservative rehabilitation programs
• MPFL reconstruction
• Tibial tubercle osteotomy
• Arthroscopic cartilage procedures
• Return-to-sport guidance

Our team is committed to restoring knee stability, protecting long-term joint health and helping you return to activity safely and confidently.