Patellar Instability

What is Patellar Dislocation and Instability?

The patella (kneecap) normally glides up and down within a groove at the front of the femur (thigh bone) called the trochlear groove. Patellar instability occurs when the kneecap does not track properly and tends to move out of this groove. A patellar dislocation is when the kneecap fully comes out of the groove, almost always towards the outer (lateral) side of the knee.

After a first dislocation, some people go on to experience recurrent dislocations or a persistent sense of the kneecap being unstable. This is more likely when there are underlying anatomical factors that predispose the kneecap to slip out of place.

Causes and Risk Factors

Dislocation may follow a specific injury, such as a twisting movement or a direct blow, but it often occurs in people whose anatomy makes the kneecap more prone to instability. Contributing factors can include:

• A shallow or underdeveloped trochlear groove (trochlear dysplasia)
• A high-riding patella (patella alta)
• Malalignment of the lower limb
• Looseness of the soft tissues that stabilise the kneecap, including injury to the medial patellofemoral ligament (MPFL)
• Generalised ligament laxity

Symptoms

• The kneecap visibly slipping out of place, or a sensation that it does
• Pain at the front of the knee
• Swelling, particularly after a dislocation
• A feeling of the knee giving way or being unstable
• Apprehension or reluctance with certain movements

Diagnosis

Diagnosis is based on the history and a clinical examination assessing kneecap tracking, stability, and alignment. Imaging is important: X-rays assess bony alignment and the shape of the groove, while MRI evaluates the stabilising soft tissues (including the MPFL), cartilage, and any associated injury. Measurements from imaging help identify the underlying anatomical factors contributing to instability.

Treatment Options

Treatment depends on whether this is a first-time or recurrent dislocation, the underlying anatomical factors, and the impact on your activities.

Non-surgical treatment

A first-time dislocation without significant associated injury is often managed non-surgically:

• A period of relative rest and protection
• Physiotherapy to strengthen the muscles that control the kneecap
• Bracing or taping in some cases
• Activity modification

Surgical treatment

Surgery may be considered for recurrent dislocations, ongoing instability, or where there are significant anatomical risk factors or associated injuries. Procedures are directed at the underlying cause and may include reconstruction of the medial patellofemoral ligament (MPFL) or procedures to correct bony alignment. The most appropriate option will be discussed with you at your consultation. (See also the Patella Stabilisation page.)

Recovery

Recovery varies according to whether treatment is non-surgical or surgical and the specific procedure performed. Rehabilitation focuses on restoring movement, strength, and control of the kneecap, progressing gradually back to activity. Your specific plan will be tailored to your circumstances.

Frequently Asked Questions

Will my kneecap dislocate again?

The risk of further dislocation is higher in younger patients and in those with underlying anatomical risk factors. Some people have a single dislocation and no further problems, while others develop recurrent instability. Imaging helps identify which factors are present in your case.

Do I need surgery after a kneecap dislocation?

Many first-time dislocations are managed without surgery, focusing on physiotherapy and strengthening. Surgery is more commonly considered for recurrent dislocations, ongoing instability, or where significant anatomical risk factors or associated injuries are present.

What is the MPFL?

The medial patellofemoral ligament (MPFL) is a key soft-tissue restraint that helps hold the kneecap in place against displacement towards the outer side of the knee. It is commonly injured during a dislocation, and reconstructing it is one of the procedures used to address recurrent instability.

Medical Disclaimer
The information on this page is intended as general patient education and does not constitute medical advice. Every patient is different, and treatment decisions should always be made in consultation with a qualified medical professional based on your individual circumstances, health history, and imaging. Outcomes from treatment vary between patients and cannot be guaranteed. If you have concerns about your knee health, please contact Dr Slattery’s rooms to arrange a consultation.