One of the reasons patients can remain unhappy after total knee replacement is pain at the front of the knee. A 2025 study co-authored by Dr Jobe Shatrov looked at one possible reason for this: patellar obliquity, which means the resurfaced kneecap has been cut unevenly so that one side is thicker than the other.

The study found that this kind of asymmetry can change the way the kneecap moves and increase pressure in specific parts of the patellofemoral joint.

Why the shape of the kneecap matters

When the patella is resurfaced, the aim is generally to create a balanced, symmetric surface that glides smoothly through the trochlear groove. If one side is left thicker, the kneecap may no longer sit and move centrally.

That can lead to:

• altered tracking

• abnormal pressure on one part of the kneecap

• front-of-knee discomfort

• a knee that feels less natural during movement

What the study set out to test

The researchers compared three different conditions:

• a neutral resurfacing

• a medial-thick oblique resurfacing

• a lateral-thick oblique resurfacing

They then measured kneecap movement and joint pressure during passive flexion and a stair descent simulation.

The question was whether an uneven patellar cut would produce measurable changes in biomechanics.

What the study found

The study showed that patellar obliquity does alter patellofemoral biomechanics. In particular, a medial-thick oblique resurfacing increased pressure along the central ridge of the kneecap and changed the way the patella tracked.

Interestingly, these changes happened even though the total force across the joint did not rise dramatically. That means a patient can still develop focal pressure overload and symptoms even when the overall mechanics may look acceptable at first glance.

What this means for patients

For patients, the message is simple: details matter. A knee replacement is not just about putting implants in the right place. The shape and symmetry of the resurfaced kneecap also influence how comfortable the joint feels afterwards.

This research suggests that keeping the patella as symmetric as possible may help reduce the risk of pain and maltracking after surgery.

Why this matters in everyday life

Patellofemoral pain is often most noticeable during:

• stairs

• getting up from a low chair

• squatting

• kneeling

• walking downhill

That is why some patients may feel their knee is generally good but still not comfortable during more demanding movements. This study helps explain how even small asymmetries in kneecap resurfacing can contribute to that.

Where this fits into surgical planning

This paper supports careful patellar resurfacing technique and reinforces the importance of checking patellofemoral tracking during surgery. It also shows that not all front-of-knee pain after knee replacement is random or unexplained. Sometimes it can be traced back to very specific biomechanical factors.

How Dr Shatrov applies this evidence

This study supports:

• symmetric kneecap resurfacing where appropriate

• careful intraoperative tracking checks

• attention to details that reduce focal overload in the front of the knee

Key takeaways

• An uneven kneecap cut can change patellofemoral tracking after knee replacement.

• Medial-thick asymmetry appears particularly important in increasing pressure on the kneecap.

• Front-of-knee pain may sometimes relate to focal overload, not just overall joint force.

• Symmetric resurfacing may help improve comfort after total knee replacement.

Read the full paper: https://esskajournals.onlinelibrary.wiley.com/doi/full/10.1002/ksa.70201