What Do Patella Alta and Patella Baja Mean on Your Report?
Patella alta means your kneecap sits higher than normal on the thighbone. Patella baja means it sits lower than normal. Both are measured on a side-view image of the knee, using ratios such as the Insall-Salvati ratio. Where the kneecap sits affects how well it moves in its groove. So an abnormal position can explain ongoing knee pain or instability.
Key points
- Patella alta = a high-riding kneecap that may slip or dislocate more easily.
- Patella baja = a low-sitting kneecap that can limit bending and cause stiffness.
- Kneecap height is measured with the Insall-Salvati ratio on a lateral (side-view) image.
- Standing imaging shows the knee under real load. This gives a more accurate reading of kneecap position.
- Neither condition is a diagnosis on its own. It is a finding that helps explain symptoms and guide the right next steps.
What does patella alta actually mean?
Patella alta is a high-riding kneecap. Normally the kneecap sits snugly in the groove at the front of your thighbone (the trochlea). In patella alta, it rides higher than expected. This means it does not sit as deeply in the groove when you start to bend your knee. That makes it less stable.
Patella baja is the opposite. The kneecap sits lower than normal, often because the patellar tendon has shortened. This can make the knee feel stiff and limit how far you can bend it.
How is kneecap height measured?
Radiologists use the Insall-Salvati ratio. It compares the length of the patellar tendon with the length of the kneecap itself. It is measured on a lateral (side-view) image. A ratio of around 1.0 is considered normal. A ratio above roughly 1.2 suggests patella alta. A ratio below roughly 0.8 suggests patella baja. Other ratios, such as the Caton-Deschamps index, are sometimes used alongside it.
You do not need to remember these numbers. What matters is whether the finding fits the symptoms you have.
What are the symptoms of patella alta and patella baja?
The symptoms depend on which way the kneecap has shifted. They also depend on how much it affects the way the joint works under load.
What causes patella alta or patella baja?
Several factors can lead to the kneecap sitting too high or too low. Some people are born with this anatomy. Others develop it after an injury or surgery.
Your body works as a connected chain. Alignment at the hip and ankle affects the angle of pull through the kneecap. A problem that starts somewhere else, like a subtle pelvic tilt, can change how the knee is loaded. This can make a borderline kneecap position cause more symptoms.
How is kneecap position assessed on a standing scan?
Kneecap position is best measured on a standing lateral (side-view) image of the knee. It is taken while the joint carries your full body weight. This shows where the kneecap naturally sits when your muscles are working and gravity is acting on the joint. That is the position that matters most for everyday life.
Standing lateral view. Your muscles are active, the joint is compressed under load, and the kneecap sits in its real working position. The Insall-Salvati ratio measured here reflects what your knee goes through when you walk, climb stairs and play sport. ScanAlign standing EOS imaging captures this view with about 90% less radiation than a standard X-ray, around ten times less.
Lying-down imaging. When you lie on a table, your muscles relax. The kneecap may shift slightly from its loaded position. This can make a borderline alta or baja reading look normal. Lying-down scans are still useful in many situations. But for assessing kneecap height in real-life conditions, standing tells you more.
The EOS system captures the full leg, from hip to ankle, in one standing image. So your specialist can also see whether alignment elsewhere, such as a rotated tibia or a tilted pelvis, is adding to an abnormal kneecap position.
Want to see your kneecap position under real load? A standing lateral view gives the clearest picture.
Book a free video consultationWhat are the next steps if you have patella alta or patella baja?
The right approach depends on how severe the finding is and how much it affects your daily life. An accurate measurement on standing imaging helps your treating specialist decide which path suits you.
- Physiotherapy. Targeted strengthening of the quadriceps and the muscles that stabilise the hip can improve how the kneecap tracks, particularly in mild patella alta.
- Bracing or taping. Some people find a patellar strap or taping helpful for reducing symptoms during activity.
- Surgical review. If the kneecap dislocates again and again, or if patella baja is causing significant stiffness after earlier surgery, a specialist may discuss options such as tibial tubercle transfer or MPFL reconstruction.
ScanAlign is a diagnostic imaging clinic. We provide the detailed standing measurements that help your surgeon or physiotherapist plan the right course of action. We do not offer treatment ourselves.
Before you start treatment, or change the one you are on, it is worth getting a detailed diagnosis. Knowing whether the cause sits in the pelvis, the legs or the spine changes what will actually help.
When MRI is the better tool. EOS shows bones, joints and alignment clearly. For soft-tissue detail, such as cartilage damage, ligament tears or nerve compression, MRI is usually the better choice. Your treating specialist may recommend both to build the full picture.
Frequently asked questions
It is a measurement taken on a side-view image of the knee. It compares the length of the patellar tendon with the height of the kneecap. A ratio close to 1.0 is considered normal. Values above about 1.2 suggest patella alta. Values below about 0.8 suggest patella baja.
Not exactly. Patella alta is one risk factor for kneecap dislocation, because the kneecap enters the groove later as the knee bends. But not everyone with patella alta will have a dislocation. It depends on other factors, like the depth of the groove and the strength of the ligaments.
Yes. It is one of the more common causes. Scar tissue can form around the patellar tendon during healing. This in effect shortens the tendon and pulls the kneecap down. It is sometimes called "infrapatellar contracture syndrome."
No. Many people have a mildly high-riding kneecap without any symptoms. Treatment is considered when patella alta is adding to pain, instability or cartilage damage. Accurate imaging helps show whether the finding is clinically significant.
When you stand, your muscles are active and your joint is under real load. The kneecap sits in its true working position. Lying down relaxes the muscles and can shift the kneecap. This can make a borderline alta or baja reading look normal. Standing imaging gives a more accurate measurement.
No. ScanAlign accepts self-referrals, so you do not need a letter from your doctor. You can book a free video consultation first to talk about whether a standing scan is right for your situation.
An EOS scan uses about 90% less radiation than a standard X-ray, around ten times less. This makes it suitable for detailed whole-leg or whole-body imaging with a very low dose.
It can increase the risk. A high-riding kneecap changes the area of contact between the kneecap and the groove. This concentrates pressure on a smaller patch of cartilage. Over time, this may add to softening or wear of the joint surface.
For patients travelling from abroad, the price is confirmed during the free video consultation. You can also visit the ScanAlign FAQs page.
Patella alta describes the vertical position of the kneecap, meaning whether it sits too high. Patellar maltracking describes abnormal side-to-side movement, where the kneecap drifts sideways. The two often occur together, but they are separate findings. You can read more about patellar maltracking on our dedicated page.
See your kneecap position under real load
A standing lateral view measures where your kneecap actually sits when you are on your feet. Start with a free video consultation from home to find out if a scan in London is the right next step for you.
Book a free video consultationWritten by Abbas Dhami (Specialist Diagnostic Radiographer)
Sources
- Insall J, Salvati E. Patella position in the normal knee joint. Radiology. 1971;101(1):101-104.
- Verhulst FV, van Sambeeck JDP, Olthuis GS, van der Ree J, Koëter S. Patellar height measurements: Insall-Salvati ratio is most reliable method. Knee Surgery, Sports Traumatology, Arthroscopy. 2020;28(3):869-875.
- NHS. Knee pain. nhs.uk. Available at: https://www.nhs.uk/conditions/knee-pain/ (Accessed 2024).
This page is general information and not a diagnosis.
ScanAlign is the trading name of CoreMed Solutions Ltd and operates under The Harley Street Hospital's CQC licence.