Dislocated Patella: Understanding, Causes, Symptoms, and Treatment

What is a Dislocated Patella in the Knee?

A dislocated patella, commonly known as a dislocated kneecap, occurs when the patella bone slips out of its normal position within the trochlear groove at the end of the thigh bone (femur), most often moving laterally (outward) from the center of the knee.

Understanding the Patella and Knee Anatomy

To grasp what a dislocated patella entails, it's essential to understand the basic anatomy of the knee joint. The knee is a complex hinge joint formed by the articulation of three bones: the femur (thigh bone), the tibia (shin bone), and the patella (kneecap).

The patella is a sesamoid bone, meaning it's embedded within a tendon—specifically, the quadriceps tendon, which connects the powerful quadriceps muscles of the thigh to the tibia via the patellar tendon. Its primary role is to enhance the leverage of the quadriceps muscles, allowing for more efficient extension of the knee.

The patella normally glides smoothly within a V-shaped groove on the end of the femur, known as the trochlear groove. Stability of the patella within this groove is maintained by:

• Bony Anatomy: The depth and shape of the trochlear groove.
• Soft Tissues: The quadriceps and patellar tendons, and the medial and lateral retinaculum (ligamentous structures that hold the patella in place), with the medial patellofemoral ligament (MPFL) being particularly crucial for preventing lateral dislocation.
• Muscle Balance: The coordinated action of the quadriceps muscles, particularly the vastus medialis obliquus (VMO), which helps pull the patella medially.

What Constitutes a Dislocation?

A patellar dislocation occurs when the patella completely leaves the trochlear groove. While it can theoretically dislocate in any direction, the vast majority (over 90%) involve a lateral dislocation, where the kneecap shifts towards the outside of the leg.

It's important to distinguish between a dislocation and a subluxation:

• Dislocation: The patella completely exits the trochlear groove.
• Subluxation: The patella partially slips out of the groove but then spontaneously returns to its normal position. While less severe, subluxations indicate instability and can also cause significant pain and damage.

Common Causes and Mechanisms of Injury

Patellar dislocations can result from direct trauma or non-contact mechanisms, often influenced by underlying predisposing factors.

• Direct Trauma: A direct blow to the kneecap, especially when the knee is slightly bent, can force the patella out of its groove. This is common in contact sports or falls.
• Indirect Trauma / Non-Contact Injury: This is the more common mechanism, particularly in athletes. It typically involves:
  • Sudden twisting or pivoting movements: Especially when the foot is planted and the body rotates over a slightly flexed knee.
  • Rapid deceleration: Stopping suddenly from a run.
  • Awkward landings: From a jump.
  • These actions can create a valgus (knock-kneed) force on the knee, combined with external rotation of the tibia, which predisposes the patella to dislocate laterally.

Predisposing Factors (Risk Factors): Certain anatomical or biomechanical factors can increase an individual's susceptibility to patellar dislocation:

• Shallow Trochlear Groove (Trochlear Dysplasia): A less defined groove provides less bony restraint for the patella.
• Patella Alta (High-Riding Patella): When the patella sits higher than normal in the trochlear groove, it has less bony engagement, especially in full extension.
• Genu Valgum (Knock-Knees): This alignment increases the lateral pull on the patella.
• Generalized Ligamentous Laxity: "Double-jointedness" can mean the knee ligaments are less stable.
• Muscle Imbalances:
  • Weakness of the Vastus Medialis Obliquus (VMO): This inner quadriceps muscle helps pull the patella medially. Imbalance with the stronger vastus lateralis can lead to lateral tracking.
  • Tightness of the Iliotibial Band (IT Band): A tight IT band can exert a lateral pulling force on the patella.
• Previous Patellar Dislocation: Once dislocated, the MPFL (medial patellofemoral ligament) is often stretched or torn, making subsequent dislocations more likely.

Recognising the Symptoms

A dislocated patella is usually an acutely painful and obvious injury. Key symptoms include:

• Sudden, Sharp Pain: Often described as excruciating at the moment of injury.
• Visible Deformity: The kneecap will appear visibly displaced, usually to the outside of the knee.
• Popping Sensation: Many individuals report feeling or hearing a "pop" as the patella dislocates.
• Inability to Straighten or Bend the Knee: The knee may be "locked" in a bent position.
• Swelling (Effusion): Rapid swelling due to bleeding within the joint (hemarthrosis) from stretched or torn tissues.
• Feeling of Instability or "Giving Way": Even if the patella spontaneously reduces, the knee will feel unstable.
• Tenderness to Touch: Especially along the medial (inner) side of the kneecap where the MPFL may be injured.

Diagnosis and Initial Management

If a patella dislocation is suspected, immediate medical attention is crucial.

• Diagnosis: A healthcare professional will perform a physical examination. X-rays are typically taken to confirm the dislocation, check for any associated fractures (e.g., osteochondral fractures, where a piece of bone and cartilage breaks off), and assess the bony alignment. An MRI may be used to evaluate soft tissue damage, such as tears to the MPFL or articular cartilage.
• Initial Management (Reduction): The primary immediate step is reduction, which is the process of gently manipulating the patella back into its groove. This should only be performed by a trained medical professional to avoid further damage to the joint or surrounding structures. Attempting to reduce it yourself can cause more harm.
• Immediate Steps After Injury (Before Medical Help): While awaiting medical assistance, apply the RICE protocol:
  • Rest: Avoid moving the knee.
  • Ice: Apply ice packs to reduce swelling and pain.
  • Compression: Gently wrap the knee with a bandage if possible.
  • Elevation: Keep the leg elevated above heart level.

Treatment Approaches

Treatment for a dislocated patella depends on various factors, including the severity of the injury, the presence of associated damage, and whether it's a first-time or recurrent dislocation.

Non-Surgical Treatment

Most first-time patellar dislocations, especially those without significant associated fractures, are initially managed non-surgically.

• Immobilization: A knee brace or immobilizer is often used for a few weeks to allow initial healing and reduce pain.
• Pain Management: Over-the-counter pain relievers or prescription medication.
• Physical Therapy: This is a cornerstone of recovery. A progressive rehabilitation program focuses on:
  • Restoring Range of Motion: Gradually increasing knee flexion and extension.
  • Strengthening: Targeting the quadriceps (especially the VMO), hip abductors, glutes, and core muscles to improve dynamic knee stability.
  • Flexibility: Addressing any muscle tightness (e.g., hamstrings, IT band).
  • Proprioception and Balance Training: Re-educating the knee's sense of position and movement.
  • Activity Modification: Gradual return to activities and sports.

Surgical Treatment

Surgery may be considered for:

• Recurrent Dislocations: If conservative treatment fails to prevent repeated dislocations.
• Significant Osteochondral Damage: Fractures of the cartilage and bone within the joint.
• Persistent Instability: Despite extensive physical therapy.
• Specific Anatomical Abnormalities: That predispose to dislocation.

Common surgical procedures include:

• Medial Patellofemoral Ligament (MPFL) Reconstruction: The MPFL is often torn during a lateral dislocation. This procedure reconstructs or repairs this crucial ligament, using a graft (from the patient or a donor) to stabilize the patella.
• Tibial Tubercle Osteotomy: In cases where the patellar tendon attaches too far laterally on the tibia, a section of bone where the tendon attaches (tibial tubercle) is cut, moved medially, and reattached, improving patellar tracking.
• Trochleoplasty: Less common, this procedure involves reshaping a shallow trochlear groove to provide more stability for the patella.

Rehabilitation and Prevention

Regardless of whether treatment is surgical or non-surgical, a structured rehabilitation program is vital for optimal recovery and reducing the risk of future dislocations.

• Rehabilitation: A physical therapist will guide you through stages of recovery, progressing from pain and swelling management to regaining full range of motion, strength, balance, and sport-specific movements. This typically involves:
  • Early Phase: Reducing pain and swelling, gentle range of motion exercises.
  • Mid Phase: Strengthening exercises for the quadriceps, hamstrings, glutes, and core. Proprioceptive exercises (e.g., balancing on one leg).
  • Late Phase: Agility drills, plyometrics, and sport-specific training to prepare for return to activity.
• Prevention: While not all dislocations can be prevented, especially those from high-impact trauma, addressing modifiable risk factors can significantly reduce recurrence:
  • Address Muscle Imbalances: Consistent strength training for the VMO, hip abductors, and glutes.
  • Improve Flexibility: Regular stretching for hamstrings, quadriceps, and IT band.
  • Proprioceptive Training: Incorporate balance and agility exercises into your fitness routine.
  • Proper Warm-up and Cool-down: Prepare muscles for activity and aid recovery.
  • Gradual Training Progression: Avoid sudden increases in intensity or volume.
  • Appropriate Footwear: Ensure shoes provide adequate support.
  • Sport-Specific Biomechanics: Work with coaches or trainers to refine movement patterns that might predispose to injury.

When to Seek Medical Attention

You should seek immediate medical attention if you suspect a dislocated patella. Even if the kneecap appears to have spontaneously returned to its place, it's crucial to be evaluated by a healthcare professional to:

• Confirm the diagnosis.
• Rule out associated fractures or cartilage damage.
• Receive proper guidance on initial management and a rehabilitation plan to prevent recurrence.
• Any persistent pain, swelling, instability, or inability to bear weight after a knee injury warrants medical evaluation.