Patellofemoral Dysplasia: Understanding, Causes, Symptoms, and Treatment

What is Patellofemoral Dysplasia?

Patellofemoral dysplasia refers to a congenital or developmental abnormality in the shape or alignment of the patellofemoral joint, specifically involving the trochlear groove of the femur and/or the patella, leading to instability and often pain.

Understanding the Patellofemoral Joint

The patellofemoral joint is the articulation between the kneecap (patella) and the groove at the end of the thigh bone (femur), known as the trochlear groove. This joint is crucial for efficient knee extension, allowing the quadriceps muscles to exert their force effectively. The patella acts as a fulcrum, increasing the leverage of the quadriceps. For optimal function, the patella must track smoothly within the trochlear groove as the knee bends and straightens. Any deviation from this precise tracking can lead to pain, dysfunction, and long-term joint issues.

What Exactly is Patellofemoral Dysplasia?

Patellofemoral dysplasia is a condition characterized by an atypical development or malformation of the structures within the patellofemoral joint. It primarily involves the trochlear groove (the V-shaped groove on the femur where the patella slides) and/or the patella itself. These structural abnormalities compromise the stability and tracking of the patella, predisposing individuals to recurrent patellar subluxation (partial dislocation) or dislocation, chronic anterior knee pain, and accelerated cartilage degeneration.

Key characteristics of dysplasia include:

• Shallow or Flat Trochlear Groove: Instead of a well-defined V-shape, the groove may be too shallow, flat, or even convex, providing insufficient bony containment for the patella.
• Hypoplastic Lateral Femoral Condyle: The outer ridge of the trochlear groove may be underdeveloped, further reducing stability.
• Patella Alta: A condition where the patella sits too high on the femur, causing it to engage the trochlear groove later in knee flexion, increasing its instability at the beginning of movement.
• Patellar Tilt or Maltracking: The patella may not sit centrally or track smoothly, often tilting laterally due to the abnormal bony anatomy and associated soft tissue imbalances.

Types and Classifications

Patellofemoral dysplasia is often classified based on the specific anatomical abnormalities observed, particularly concerning the trochlea. The Dejour classification is widely used, categorizing trochlear dysplasia into four types (A, B, C, D) based on features like trochlear spur, crossing sign, and double contour, which are identified through imaging. These types reflect increasing severity of the trochlear malformation. Other related conditions often present alongside or are considered forms of patellofemoral dysplasia, such as patella alta (high-riding patella) and excessive lateral tilt of the patella.

Causes and Risk Factors

Patellofemoral dysplasia is primarily a developmental or congenital condition, meaning individuals are born with these structural variations or they develop during growth. While the exact genetic and environmental factors are still under investigation, several elements are believed to contribute:

• Genetic Predisposition: A family history of knee instability or patellar dislocation suggests a genetic component.
• Developmental Anomalies: Errors in the growth and formation of the femur and patella during childhood and adolescence.
• Biomechanical Factors: While not direct causes of the dysplasia itself, certain biomechanical factors can exacerbate symptoms or increase the risk of instability in an already dysplastic joint:
  • Muscle Imbalances: Weakness of the vastus medialis obliquus (VMO) relative to the vastus lateralis can pull the patella laterally.
  • Increased Q-angle: A larger angle between the quadriceps tendon and the patellar tendon, often due to wider hips, can increase lateral pull on the patella.
  • Ligamentous Laxity: Generalized joint hypermobility can contribute to patellar instability.
  • Foot Pronation: Excessive inward rolling of the foot can alter lower limb alignment and knee mechanics.

Common Symptoms

Symptoms of patellofemoral dysplasia can vary widely in severity, from mild discomfort to debilitating instability. They often become apparent during adolescence or early adulthood, particularly with increased physical activity.

• Anterior Knee Pain: Pain around or behind the kneecap, often worsened by activities that load the patellofemoral joint, such as climbing stairs, running, squatting, or prolonged sitting with bent knees ("movie theater sign").
• Patellar Instability: A feeling that the knee is "giving way" or that the patella is shifting out of place. This can range from subtle subluxations to full dislocations, which are often very painful and may require manual reduction.
• Clicking, Popping, or Grinding Sensations (Crepitus): These sounds and sensations can occur during knee movement due to abnormal tracking and friction within the joint.
• Swelling: May occur after episodes of subluxation or dislocation, or in cases of significant inflammation.
• Apprehension: A feeling of fear or reluctance to perform certain movements (e.g., knee flexion) due to the anticipation of instability or pain.

Diagnosis

Diagnosing patellofemoral dysplasia involves a thorough clinical evaluation combined with advanced imaging.

• Clinical Examination: An orthopaedic surgeon or sports medicine physician will assess the patient's medical history, symptoms, and perform a physical examination. This includes evaluating knee alignment, patellar tracking, muscle strength, ligamentous stability, and palpating for tenderness. Specific tests, such as the patellar apprehension test, may be performed to elicit instability.
• Imaging Studies:
  • X-rays: Used to assess the bony alignment, patellar height (patella alta), and the overall shape of the patella and trochlea. Specific views, such as a Merchant's view, are useful for assessing patellar tilt and subluxation.
  • Magnetic Resonance Imaging (MRI): Provides detailed images of soft tissues (cartilage, ligaments, tendons) and bony structures. It is excellent for visualizing the depth and morphology of the trochlear groove, assessing cartilage damage, and identifying other associated injuries (e.g., medial patellofemoral ligament tear).
  • Computed Tomography (CT) Scan: Often used to precisely measure the trochlear depth, patellar tilt, and the tibial tuberosity-trochlear groove (TT-TG) distance, which is a critical measurement indicating the lateral offset of the patellar tendon insertion relative to the trochlear groove.

Management and Treatment Strategies

Treatment for patellofemoral dysplasia aims to reduce pain, improve stability, restore function, and prevent further joint degeneration. The approach is highly individualized, starting with conservative measures.

Conservative Management

For many individuals, particularly those with mild dysplasia and without recurrent dislocations, non-surgical treatment is effective.

• Physical Therapy: This is the cornerstone of conservative management. A skilled physical therapist will design a program focusing on:
  • Strengthening: Quadriceps (especially VMO), hip abductors, hip external rotators, and core muscles to improve dynamic knee stability and control.
  • Stretching: Hamstrings, quadriceps, and IT band to address muscle tightness that may contribute to maltracking.
  • Proprioception and Neuromuscular Control: Exercises to improve balance and coordination, enhancing the body's ability to sense and respond to joint position.
  • Patellar Taping or Bracing: Can provide temporary support and improve patellar tracking during activity.
• Activity Modification: Avoiding activities that provoke pain or instability, such as deep squats, lunges, or high-impact sports, until symptoms improve.
• Medications: Over-the-counter non-steroidal anti-inflammatory drugs (NSAIDs) can help manage pain and inflammation.
• Orthotics: Custom shoe orthotics may be recommended to correct foot biomechanics if excessive pronation is a contributing factor.

Surgical Intervention

Surgery is considered when conservative measures fail, especially in cases of recurrent patellar dislocations, severe pain, or significant structural abnormalities that predispose to ongoing instability. Surgical procedures aim to stabilize the patella by altering bony anatomy or soft tissue tension.

• Medial Patellofemoral Ligament (MPFL) Reconstruction: The MPFL is a primary stabilizer against lateral patellar displacement. Reconstruction involves using a tendon graft to create a new ligament, providing static stability.
• Trochleoplasty: This procedure reshapes the trochlear groove to make it deeper and more defined, providing a better track for the patella. It is typically reserved for severe trochlear dysplasia.