Patellar Maltracking: Why Does Your Kneecap Shift to the Side?
Patellofemoral maltracking means the kneecap does not glide along the centre of the groove at the front of the thigh bone. Instead, it drifts, tilts or catches, usually towards the outside. This causes pain at the front of the knee, especially on stairs, when squatting or after sitting for a long time. It often involves the alignment of the whole leg, not just the knee.
Key points
- The kneecap sits in a shallow groove. It relies on muscles, ligaments and leg alignment to move in a straight line.
- Patellofemoral maltracking is a common cause of pain at the front of the knee in adults.
- Problems higher up (hip rotation, pelvic tilt) or lower down (flat feet, shin twist) can pull the kneecap off course.
- Lying-down scans relax the muscles, so the kneecap may sit normally. Standing, weight-bearing imaging can show the real tracking problem.
Your kneecap (patella) is the small, rounded bone at the front of the knee. It sits inside the tendon of your quadriceps muscle. Each time you bend or straighten your leg, it slides up and down in a groove on the thigh bone (femur). When everything lines up well, you hardly notice it working.
With a patellar tracking disorder, the kneecap pulls to one side, usually the outer (lateral) side. It may tilt, shift slightly out of its groove (subluxation), or catch and grind as you move. Over time, this can wear down the cartilage on the underside of the kneecap and cause persistent pain.
What does patellar maltracking feel like?
Most people notice a dull, aching pain around or behind the kneecap. It gets worse with activity. The pain usually builds slowly, rather than starting with one injury.
Going down stairs often hurts more than going up. This is because the kneecap presses harder into the groove.
A grating feeling or a click you can hear when you bend the knee. This is sometimes called crepitus.
Pain or stiffness after sitting with your knees bent for a long time. This is sometimes called "cinema sign".
The knee may feel as if it is about to give way, especially on uneven ground or when turning.
Important. If your knee locks completely, gives way suddenly, or you notice significant swelling after an injury, get medical help promptly from your doctor or the emergency department. These may point to a different, more urgent problem.
What causes the kneecap to track incorrectly?
There is rarely a single cause. Patellofemoral maltracking usually comes from a mix of structural shape and muscle or alignment imbalances. Together, these pull the kneecap off centre.
A kneecap that sits higher than usual has less contact with the groove. It is more likely to shift.
Some people are born with a flatter trochlear groove. This gives the kneecap less of a channel to follow.
Weak inner quadriceps or tight outer structures can pull the kneecap laterally.
Knock knees, a twisted shin bone or flat feet change the angle of pull on the kneecap.
Can hip or foot problems cause kneecap pain?
Yes. Your body is a connected chain, from your feet to your spine. When one link is out of position, other areas compensate. The knee is often the place that pays the price.
If your hip turns inward too far, the thigh bone turns with it. This changes the angle between your thigh muscle and the kneecap tendon, and pulls the kneecap outward. Flat feet or too much ankle rolling can have a similar effect from below. A tilted pelvis can change the load on one leg compared with the other.
This is why treating kneecap pain on its own sometimes fails. The kneecap is just the point where the forces meet. Unless you see how the whole leg lines up under load, you may miss the real driver.
How is patellofemoral maltracking assessed when standing?
Standing, weight-bearing imaging shows the kneecap under real-life load, which is when tracking problems actually happen. Lying-down scans relax the muscles and remove the effect of gravity. So the kneecap may sit perfectly in its groove on the scan, even when it does not in daily life.
An EOS scan captures the full length of both legs while you stand naturally. It shows the kneecap position, leg rotation, joint angles and overall alignment from hip to ankle in a single, low-dose image. The scan uses about 90% less radiation than a standard X-ray, around ten times less.
Your muscles are active and gravity is acting on your joints. So the image reflects how your body actually works. If the kneecap drifts laterally under load, it will show up.
Standard X-rays, CT and MRI are usually taken lying down. Without body weight pressing the joints together, and without your muscles working, the kneecap often centres itself in the groove. The result can look normal, even when the patient has clear symptoms while standing or walking.
These scans are still valuable for checking bone shape and cartilage (MRI), and for ruling out other problems. But they may not catch a tracking problem that only appears under load.
At ScanAlign, the EOS system captures your whole leg alignment in one standing image. Your specialist or physiotherapist can then see exactly where the chain breaks down: at the hip, the knee, the shin or the foot. Read more about how standing imaging helps with knee problems.
When MRI is the better tool. EOS shows bones, joints and alignment clearly. For soft-tissue detail, such as cartilage damage, ligament tears or swelling inside the joint, MRI is usually the better choice. In many cases, both types of imaging together give the fullest picture.
What can be done about patellar maltracking?
Treatment depends on the cause and how severe it is. It is always guided by a clinician, not an imaging clinic. ScanAlign provides the diagnostic imaging that informs those decisions. Common approaches include the following.
- Physiotherapy. Strengthening the inner quadriceps and stretching tight outer structures is often the first step.
- Orthotics or footwear changes. If flat feet or too much foot roll play a part, correcting foot position can change how forces reach the kneecap.
- Taping or bracing. Patellar taping can guide the kneecap during exercise and rehabilitation.
- Surgery. In persistent cases, surgery may be considered. This includes cases where the groove is very shallow, the kneecap sits too high (patella alta), or non-surgical options have not helped. Procedures include lateral release or tibial tubercle transfer.
All of these work best when the clinician understands the full alignment picture, not just how the kneecap looks on its own.
So 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.
Not sure whether standing imaging would help your kneecap problem? Speak to us first, at no cost.
Book a free video consultationFrequently asked questions about patellar maltracking
It is a condition where the kneecap does not glide along the centre of the groove on the front of the thigh bone. Instead, it shifts, tilts or catches, usually towards the outer side. This causes pain at the front of the knee, especially when climbing stairs, squatting or sitting for a long time.
They are related but not the same. Maltracking means the kneecap does not follow its groove properly. Subluxation means it partly slips out of the groove. Subluxation is a more severe form of maltracking. Both can cause pain and instability.
Common reasons include muscle imbalance (weak inner quadriceps, tight outer structures), a shallow groove on the thigh bone, a kneecap that sits too high (patella alta), or alignment problems in the hip, shin or foot that change the angle of pull on the kneecap.
Yes. When the foot rolls inward too much (overpronation), the shin bone can rotate. This changes the forces that act on the kneecap, and can contribute to lateral maltracking.
When you lie down, gravity no longer presses your joints together and your muscles relax. The kneecap may settle back into its groove, so the image looks normal. Standing, weight-bearing imaging captures the kneecap under real-life load, when tracking problems actually happen.
An EOS scan captures the full length of both legs while you stand. It shows kneecap position, leg rotation, joint angles and overall alignment from hip to ankle. This helps show whether a problem elsewhere in the chain is contributing to the kneecap problem.
Yes. The EOS system uses about 90% less radiation than a standard X-ray, around ten times less. You can find more details on our safety and FAQs page.
No. ScanAlign is a private, self-pay clinic. You can refer yourself. We offer a free video consultation first, so we can check whether standing imaging is right for your situation.
The price for patients travelling from abroad is confirmed during the free video consultation. You can also visit our FAQs page.
Many people improve with physiotherapy, taping and footwear changes. The right approach depends on the cause. Accurate imaging helps your clinician decide what is most likely to work for you. ScanAlign provides the imaging, not the treatment itself.
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A free video consultation lets us understand your kneecap problem and explain whether standing imaging could help. No referral needed, no obligation.
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- NHS. "Patellofemoral pain syndrome." nhs.uk, National Health Service.
- Post WR, Teitge R, Amis A. "Patellofemoral malalignment: looking beyond the viewbox." Clinics in Sports Medicine, 2002; 21(3): 521-546.
- Defined Diagnostic. "Standing weight-bearing imaging in lower limb alignment assessment." European Journal of Radiology, EOS imaging clinical literature.
Written by Abbas Dhami (Specialist Diagnostic Radiographer)
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.