Patellofemoral Instability

What is patellofemoral instability?

Patellofemoral instability refers to a condition where the kneecap (patella) does not move normally within its groove at the front of the knee.

In more severe cases, the patella can:

• Partially slip out of place (subluxation)
• Fully dislocate, usually to the outside of the knee

This can be a one-off injury or a recurrent problem, particularly in younger and active individuals.

Why does it happen?

Patellofemoral instability is often due to a combination of factors affecting the alignment and stability of the kneecap.

Common contributing factors include:

• MPFL injury: The medial patellofemoral ligament (MPFL) is the main soft tissue restraint preventing the patella from dislocating. It is often torn during a first dislocation.
• Shallow trochlear groove (trochlear dysplasia): The groove the patella sits in may be underdeveloped.
• High-riding patella (patella alta): The patella sits higher than normal, reducing stability.
• Abnormal alignment: Increased lateral pull on the patella due to limb alignment or muscle imbalance.
• Increased femoral or tibial rotation: This can alter the tracking of the patella and contribute to instability.

Often, several of these factors are present together.

Symptoms

Patients with patellofemoral instability may experience:

• A feeling of the kneecap “slipping” or “giving way”
• Episodes of dislocation
• Pain at the front of the knee
• Swelling after an episode
• Apprehension or lack of confidence in the knee
• Difficulty with activities such as stairs, squatting, or sport

Assessment and diagnosis

A detailed assessment is essential to understand the underlying causes.

This includes:

• Clinical examination
• MRI scan to assess ligament injury, cartilage damage, and anatomy
• X-rays or CT scans to assess alignment and bony structure

Careful evaluation allows treatment to be tailored to the individual, rather than a one-size-fits-all approach.

Do all cases need surgery?

Not all patients require surgery.

After a first-time dislocation, treatment is often non-surgical:

• Physiotherapy to improve strength and control
• Activity modification
• Bracing in some cases

However, surgery may be recommended if:

• There are recurrent dislocations
• There is significant underlying anatomical abnormality
• Non-surgical treatment has not been successful
• There is associated cartilage damage

Surgical treatment

Surgery is tailored to address the specific causes of instability. In many cases, more than one procedure is required.

MPFL reconstruction

The medial patellofemoral ligament (MPFL) is the primary restraint preventing the patella from dislocating.

• Often torn during the first dislocation
• Reconstructed using a graft (commonly hamstring or quadriceps tendon)
• Restores soft tissue stability

This is one of the most commonly performed procedures for recurrent instability.

Tibial tuberosity distalisation (and/or medialisation)

The tibial tuberosity is the bony attachment of the patellar tendon.

In patients with:

• Patella alta (high-riding patella)
• Abnormal lateral pull

The tuberosity can be surgically repositioned to:

• Improve alignment of the patella
• Reduce the risk of further dislocation
• Optimise tracking within the groove

This is performed as an osteotomy (controlled bone cut) and fixed with screws.

Rotational osteotomy

In some patients, abnormal femoral or tibial rotation contributes significantly to instability.

A rotational osteotomy involves:

• Cutting the bone (femur or tibia)
• Correcting the rotational alignment
• Fixing the bone in a more optimal position

This is typically reserved for:

• More complex or severe cases
• Patients with significant underlying malalignment

Combined procedures

It is common to combine procedures, for example:

• MPFL reconstruction + tibial tuberosity osteotomy
• MPFL reconstruction + correction of rotational alignment

The aim is to address both soft tissue and bony factors to achieve a stable and well-functioning knee.

Recovery and rehabilitation

Recovery depends on the procedures performed.

Typical rehabilitation includes:

• Early controlled movement
• Use of a brace in some cases
• Gradual progression of weight bearing
• Physiotherapy focusing on strength and control

Return to activities:

• Daily activities: 6–12 weeks
• Higher level activity: 4–6 months
• Return to sport: around 6–9 months once clinically cleared

More complex procedures (e.g. osteotomy) may require a slightly longer recovery.

Outcomes

With appropriate treatment:

• Most patients achieve a stable kneecap
• Recurrence rates are low
• Many return to an active lifestyle

Outcomes depend on:

• Addressing all contributing factors
• Surgical technique
• Rehabilitation

Some patients may experience:

• Ongoing anterior knee pain
• Stiffness
• Risk of cartilage wear over time

Research and evidence

At University Hospitals Coventry and Warwickshire NHS Trust, ongoing research is helping to improve our understanding of patellofemoral instability.

The REPPORT trial is a current study aiming to better understand the role of surgery in patients with this condition, including which patients benefit most from surgical intervention and which may be successfully managed without it.

This type of research helps ensure that treatment decisions are:

• Evidence-based
• Individualised
• Focused on achieving the best long-term outcomes

Why choose specialist care?

Patellofemoral instability can be multifactorial and technically demanding to treat.

Specialist care ensures:

• Detailed assessment of all contributing factors
• Individualised surgical planning
• Expertise in both soft tissue and bony procedures
• Structured rehabilitation

Summary

• Patellofemoral instability occurs when the kneecap does not track normally and may dislocate
• It is often caused by a combination of soft tissue and anatomical factors
• Not all cases require surgery, but recurrent instability often does
• Surgical options include MPFL reconstruction, tibial tuberosity osteotomy, and rotational osteotomy
• Good outcomes are achievable with tailored treatment and rehabilitation