Even when a knee replacement is technically well performed, some patients still experience discomfort at the front of the knee. One reason for this may be the final thickness of the kneecap after resurfacing. A 2026 study co-authored by Dr Jobe Shatrov explored what happens when the patella is made slightly thicker or thinner than the patient’s original anatomy during total knee replacement.

The findings are important. Even small increases in patellar thickness changed the way the kneecap moved and increased the forces through the patellofemoral joint. In other words, a few millimetres can make a meaningful difference.

Why patellar thickness matters

The patella sits in a groove at the front of the femur and glides through that groove as the knee bends and straightens. If the resurfaced patella becomes too thick, the front of the knee can become “overstuffed.” This may change how the kneecap tracks, increase pressure in the joint, and contribute to pain with activities such as stairs, squatting, or getting up from a chair.

This matters because front-of-knee pain remains one of the more common reasons some patients feel that their knee replacement never quite feels natural.

What the study set out to test

The research team tested cadaveric knees under three different conditions:

• an understuffed patella

• a neutral patella that matched native thickness

• an overstuffed patella

They then measured how the kneecap moved and what forces were generated during passive knee bending and a stair descent simulation.

The question was simple: does changing patellar thickness by just a few millimetres alter patellofemoral biomechanics in a meaningful way?

What the study found

The clearest issues appeared in the overstuffed knees. When the patella was made thicker than normal, the researchers found:

• altered kneecap movement

• increased patellofemoral joint force

• a shift in loading towards the lateral side of the kneecap

• changes in alignment that may make tracking less natural

This suggests that making the patella too thick does not just change the shape of the joint. It changes how the knee actually functions.

What this means for patients

For patients, this study highlights how much attention is paid to small details during surgery. Restoring the kneecap to something close to its original thickness may help reduce unnecessary pressure in the front of the knee.

This does not mean every case of pain after knee replacement is caused by patellar thickness. But it does show that this is one of the factors surgeons think carefully about when trying to optimise the result.

Why this matters in everyday life

The patellofemoral joint is loaded during many ordinary movements:

• climbing and descending stairs

• rising from a chair

• squatting

• kneeling

• walking downhill

If the kneecap is overstuffed, these common movements may become more uncomfortable. This helps explain why some patients describe their knee replacement as “fine on flat ground” but not as good on steps or slopes.

How modern planning can help

This research supports a more individualised approach to knee replacement. Rather than treating every patella the same way, surgeons can aim to restore anatomy as accurately as possible and avoid unnecessary thickening.

As implant design and planning tools continue to improve, the goal is to recreate a front-of-knee anatomy that feels more natural and loads more evenly.

How Dr Shatrov applies this evidence

Research like this reinforces the importance of:

• checking patellar thickness carefully during resurfacing

• assessing kneecap tracking during surgery

• using detailed planning to reduce avoidable patellofemoral overload

Key takeaways

• Small increases in patellar thickness can significantly alter knee replacement mechanics.

• Overstuffing the patella increases pressure in the front of the knee.

• These changes may contribute to pain with stairs, squatting, and similar activities.

• Careful restoration of native anatomy may help improve comfort after total knee replacement.

Read the full paper: https://esskajournals.onlinelibrary.wiley.com/doi/full/10.1002/ksa.70282