Some patients feel persistent discomfort at the front of the knee after a total knee replacement. This discomfort often relates to how the kneecap (patella) moves in its groove on the thigh bone (the trochlea). To improve outcomes, surgeons and researchers need better ways to test how the patellofemoral joint behaves during movement. A recent study by Dr Jobe Shatrov and colleagues, published in SICOT-J, introduces a new laboratory model that keeps the major muscle attachments intact on cadaver knees. This allows more realistic testing of patellofemoral biomechanics and helps us understand what truly supports smooth kneecap motion after knee arthroplasty.

Read the full paper: https://www.sicot-j.org/articles/sicotj/full_html/2025/01/sicotj250074/sicotj250074.html

Why the patellofemoral joint matters

The patellofemoral joint is where the kneecap glides in a shallow channel at the end of the femur. The shape of this channel, the position of the implants, and the tension in the surrounding soft tissues all influence whether the patella tracks centrally or tends to drift. Patients with patellofemoral problems may notice pain when getting up from a chair, going downstairs, squatting, or kneeling. Reducing these symptoms requires a mix of good implant design, accurate alignment, balanced soft tissues, and targeted rehabilitation. To refine each of these elements, researchers need a testing method that behaves more like a real knee.

What was missing from older test models

Traditional lab models often disconnect the key muscles and simulate their pull with simple cables or static loads. These setups are useful for some questions but they do not fully reproduce the coordinated forces from the quadriceps, hamstrings and hip musculature during flexion and extension. Without the native muscle attachments, patella tracking in the lab can differ from tracking in a living knee. That makes it harder to draw firm conclusions about which implant shapes, alignments or soft-tissue adjustments will help real patients.

What this study created

Dr Shatrov and Dr David Parker’s team developed a cadaveric model that preserves the native muscle attachments. In practical terms, the model keeps the quadriceps mechanism and other soft tissues intact so that researchers can apply controlled loads that more closely mimic normal muscle function. The knee can then be taken through a range of motion while sensors and cameras record how the patella tracks, how much pressure it experiences at different angles, and how changes in component positioning or soft-tissue tension alter that behaviour.

This design brings the test environment closer to real life. It is still a laboratory model, but it allows more precise, repeatable experiments with input forces that mirror clinical reality. The model also makes it possible to test the same knee under different scenarios, such as small changes in femoral rotation, tibial slope, or patella resurfacing, without the variability that comes from comparing different specimens.

Why this matters to patients

Better testing leads to better decision-making in the operating theatre and improved implant design over time. Specifically, this model can help researchers and surgeons:

• Measure how small changes in component position influence patella tracking through a full arc of motion.

• Identify implant shapes that reduce peak contact pressures on the patellofemoral joint.

• Understand which soft-tissue releases or balancing steps improve tracking in difficult cases.

• Validate the settings that computer navigation and robotic systems use to guide alignment.

For patients, the downstream benefits include more predictable kneecap motion, lower risk of anterior knee pain, and greater confidence with daily activities that load the patellofemoral joint.

How this evidence fits with modern knee replacement

Modern knee arthroplasty relies on accurate component alignment, appropriate implant selection, and soft-tissue balance. Navigation and robotics help surgeons place components where they were planned. Yet the patellofemoral joint is sensitive to small variations, and traditional rules of thumb do not always suit every knee. A model that can test these variables under realistic muscle forces allows the profession to move from broad assumptions to measured, evidence-based targets.

Examples of practical questions this model can address include:

• How much does a one or two degree change in femoral component rotation alter patella tracking at 30, 60 and 90 degrees of flexion

• Which trochlear shapes better centralise the patella without increasing pressure at higher flexion

• Under what conditions does resurfacing the patella reduce pressure or improve tracking compared with leaving the native patella

Answers to these questions translate into clearer surgical plans and, over time, into implant designs that prioritise patellofemoral comfort.

What patients can expect in care with this approach

While the study is a laboratory advance rather than a clinical trial, it supports the way Dr Shatrov plans and performs knee replacement:

• Detailed pre-operative review of limb alignment, trochlear shape and patella position on imaging.

• Intraoperative checks of component rotation and balance, with adjustments to encourage central patella tracking.

• Selective resurfacing of the patella when cartilage quality, symptoms and implant choice support that decision.

• Early rehabilitation that builds quadriceps and hip strength, restores full extension and progressive flexion, and retrains stair mechanics to manage patellofemoral load.

Patients often ask if technology alone solves kneecap problems. Technology helps measure and execute a plan. This research adds another layer by improving the biomechanical evidence that informs the plan in the first place.

Frequently asked questions

Does this mean my knee replacement will not have kneecap pain
Many patients have no patellofemoral symptoms after surgery. This model does not guarantee outcomes. It helps refine decisions that reduce the risk of discomfort.

Will this change which implant I receive
Implant choice depends on your anatomy, arthritis pattern and goals. Improved biomechanical testing guides manufacturers and surgeons toward features that support smoother patella tracking.

Can rehabilitation improve patella tracking
Yes. Strong quadriceps and good hip control help centralise the patella. Your physiotherapy plan focuses on extension, flexion, strength, balance and gradual return to kneeling and stair work.

Is this the same as robotic surgery
No. This is a laboratory testing model. Its findings can inform how surgeons use planning tools and robotics, but it is not a surgical device.

Key takeaways

• The patellofemoral joint is a common source of symptoms after knee replacement, so understanding its biomechanics is important.

• The study by Dr Shatrov and colleagues presents a cadaveric model that preserves native muscle attachments, producing more realistic patella tracking during tests.

• Better test models allow clearer answers about implant design, alignment targets and soft-tissue strategies that support comfortable kneecap motion.

• The goal is predictable function in day-to-day life, with less anterior knee pain and greater confidence on stairs, slopes and during kneeling.

Read the full paper: https://www.sicot-j.org/articles/sicotj/full_html/2025/01/sicotj250074/sicotj250074.html