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Anatomy

The knee joint consists of three bones:

  • The patella (kneecap), a small, triangular bone at the front of the knee.
  • The femur (thigh bone), which has a groove (trochlear groove) where the patella moves as the knee bends and straightens.
  • The tibia (shin bone), which supports the patella through the patellar tendon.

The quadriceps muscles, located at the front of the thigh, play a crucial role in stabilising the patella. The vastus medialis obliquus (VMO) pulls the patella inward (medially), while the vastus lateralis pulls it outward (laterally). Soft tissues such as the medial patellofemoral ligament (MPFL), patellar tendon, and lateral retinaculum also help keep the patella in place.

What is Patellar Instability?

Patellar instability refers to a range of conditions where the kneecap does not stay properly aligned within the femoral groove. It can present as:

  • Patellar subluxation: A partial displacement where the patella shifts but returns to its normal position.
  • Patellar dislocation: A complete displacement where the patella moves entirely out of its normal position, typically laterally (to the outer side of the knee).

Patellar dislocations may reduce spontaneously or require manual manipulation. Individuals with recurrent instability often experience a sensation of their knee “giving way,” leading to activity limitations and, in some cases, long-term joint damage.

Signs & Symptoms

  • Sudden, severe pain in the knee, particularly after a twisting movement or direct blow.
  • Visible deformity if the patella remains dislocated.
  • A feeling of the knee giving way or being unstable.
  • Swelling and bruising around the knee.
  • Difficulty bending and straightening the knee.
  • A “popping” sensation at the time of dislocation or subluxation.
  • Tenderness around the kneecap, especially medially (inner side of the knee).
  • Recurrent episodes of instability, particularly during activities involving twisting or pivoting.

Causes and Contributing Factors

A few key things can make someone more prone to patellar instability—sometimes it’s due to an injury, but often, it’s a mix of anatomy and muscle function. Here’s what can increase the risk:

  • Direct trauma: A strong impact to the knee, like falling or getting hit during sports, can knock the patella out of place.
  • Twisting injuries: A sudden change in direction, especially with the foot planted, can force the patella to shift out of alignment. This is common in sports like soccer, basketball, and netball.
  • Muscle weakness: The VMO (vastus medialis obliquus)—a key muscle on the inner thigh—helps pull the patella into the right position. If it’s weak, the patella is more likely to shift laterally.
  • Loose ligaments: Some people naturally have more flexible joints (also known as ligamentous laxity), which can make their patellae more prone to slipping out of place. Conditions like Ehlers-Danlos or Marfan syndrome can contribute to this.
  • Patella alta (high-riding patella): If the patella sits too high in the knee joint, it may not engage properly with the trochlear groove, making it easier to dislocate.
  • Trochlear dysplasia: The groove in the femur (trochlear groove) is supposed to guide the patella during movement. If the groove is too shallow, the patella doesn’t have a stable track to follow, making it easier to slip out.
  • Increased Q angle: The Q angle is the angle between the hip and the knee. A larger Q angle—more common in women due to a wider pelvis—can put extra lateral force on the patella, increasing the risk of instability.
  • Tight lateral structures: If the iliotibial (IT) band or lateral retinaculum (the connective tissue on the outer side of the knee) is too tight, it can pull the patella sideways, making it harder for it to stay in place.

While some of these factors—like muscle strength—can be improved through training, others, such as anatomical differences, may require more targeted treatment approaches, including physiotherapy or, in severe cases, surgery.

Prognosis

First-time dislocations often recover well with non-surgical treatment, but there is a 15-60% risk of recurrence. Recurrent dislocations or significant anatomical abnormalities may require surgical intervention to restore stability. If untreated, long-term complications may include cartilage damage and early-onset osteoarthritis.

Treatment

Immediate Management

  • Reduction: If the patella remains dislocated, a medical professional will carefully manipulate it back into place.
  • Rest, Ice, Compression, Elevation (RICE): Helps to manage swelling and pain in the acute phase.
  • Pain management: Non-steroidal anti-inflammatory drugs (NSAIDs) may be recommended.
  • Immobilisation: A brace or knee immobiliser may be used for 2–4 weeks to allow soft tissue healing.

Physiotherapy Rehabilitation

Physiotherapy is essential in both non-surgical management and post-surgical rehabilitation. The goal is to restore joint stability, strength, movement, and neuromuscular control while minimising the risk of recurrence.

Stage 1: Pain, Swelling, and Inflammation Management

  • RICE protocol (Rest, Ice, Compression, Elevation).
  • Isometric quadriceps exercises: Engaging the quadriceps without moving the knee.
  • Patellar bracing or taping: Provides stability and encourages correct alignment.
  • Avoid: High-impact activities, deep squats, and twisting movements.

Stage 2: Recovery of Joint Motion and Flexibility

  • Gentle range-of-motion exercises: Passive and active knee flexion and extension within pain-free limits.
  • Soft tissue release techniques: Stretching of tight lateral structures (e.g., IT band, lateral retinaculum).
  • Cycling or hydrotherapy: Low-impact activities to encourage knee mobility.
  • Avoid: Sudden weight-bearing without support and excessive knee flexion (>90°).

Stage 3: Strengthening of Key Muscles

  • Quadriceps strengthening: Focus on VMO activation through closed-chain exercises (e.g., mini squats, leg presses, step-ups).
  • Gluteal and core activation: Strengthening hip abductors and external rotators (e.g., side-lying leg lifts, resistance band exercises).
  • Neuromuscular retraining: Proprioceptive training using balance exercises (e.g., single-leg stance on an unstable surface).
  • Avoid: Open-chain knee extension exercises in mid-range (30-60°), which place excessive stress on the patellofemoral joint.

Stage 4: Motor Pattern and Coordination Training

  • Functional exercises: Controlled movements that mimic daily activities and sports-specific movements.
  • Single-leg control drills: Step-downs, lunges with proper knee alignment.
  • Sport-specific drills: Light jogging, controlled cutting, and agility training.
  • Avoid: Plyometric exercises (jumping) until strength and control are adequate.

Stage 5: Return to Sport and High-Level Activity

  • Plyometric training: Progressive jump training and landing mechanics.
  • Running progression: Gradual return to running and sport-specific agility drills.
  • Strength and endurance maintenance: Ongoing strength and flexibility training.
  • Functional performance tests: Tests such as single-leg hop tests ensure adequate recovery before returning to full activity.

Surgical Options

Surgery may be recommended for individuals with recurrent dislocations, significant cartilage damage, or anatomical abnormalities predisposing them to instability. Common procedures include:

  • MPFL reconstruction: Rebuilding the medial patellofemoral ligament.
  • Tibial tuberosity osteotomy (TTO): Adjusting the position of the patellar tendon attachment to improve tracking.
  • Trochleoplasty: Deepening the femoral groove for better patellar stability.
  • Lateral release: Loosening tight lateral structures (not recommended as an isolated procedure).

Information is provided for education purposes only. Always consult your physiotherapist or other health professional.

References

1. Hayat, Z., El Bitar, Y., & Case, J. L. (2023). Patella dislocation. In StatPearls [Internet]. StatPearls Publishing. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK538288/

2. ScienceDirect. (n.d.). Patella dislocation. Retrieved from https://www.sciencedirect.com/topics/nursing-and-health-professions/patella-dislocation

3. PubMed. (2023). Patella dislocation research article. National Library of Medicine. Retrieved from https://pubmed.ncbi.nlm.nih.gov/36692346/

4. Journal of Orthopaedic Surgery and Research. (2023). Patella dislocation study. BioMed Central. Retrieved from https://josr-online.biomedcentral.com/articles/10.1186/s13018-023-03867-6

5. National Center for Biotechnology Information (NCBI). (2015). Patella dislocation: Clinical overview. Retrieved from https://pmc.ncbi.nlm.nih.gov/articles/PMC4295683/