Written by Dr Sean Leo, a consultant orthopaedic surgeon whose clinical focus is the knee, sports injuries and the lower limb.

Last updated: 9 October 2026.

Patella alta is a kneecap that sits higher than usual, and patella baja is a kneecap that sits lower than usual.^[1] Patella alta is described as a risk factor for kneecap dislocation.^[1] It is also described as contributing to pain at the front of the knee, although how much this matters clinically remains uncertain.^[2]

What are patella alta and patella baja?

In patella alta, the kneecap sits further up than usual in relation to the thigh bone.^[1] In patella baja, it sits lower than usual.^[1]

In patella alta, the kneecap engages the groove it glides in later than usual as the knee starts to bend.^[1]
Patella baja is a recognised X-ray finding after total knee replacement, and how often it occurs, what predicts it and how much it matters are still debated.^[3]

What’s covered on this webpage

What are patella alta and patella baja?
Is a high or low kneecap linked with knee problems?
What symptoms can go with a high or low kneecap?
How are patella alta and patella baja assessed?
What is the surgical option for a high-riding kneecap?
What is known about patella baja?
When is urgent help needed?
What should I do next?

Is a high or low kneecap linked with knee problems?

Patella alta is described as a risk factor for kneecap dislocation.^[1] It is also described as contributing to maltracking (the kneecap not gliding smoothly in its groove) and to pain at the front of the knee, although how well the height measures agree, and how much they matter clinically, remain uncertain.^[2]

In a study of 609 people after a first kneecap dislocation, patella alta was associated with repeat dislocation.^[4]
In a study of 250 people aged 18 to 38 who had both a knee X-ray and an MRI, patella alta was more frequent in people with Hoffa’s fat-pad impingement (pinching of the fat pad at the front of the knee) and in people with advanced chondromalacia (softening of the cartilage under the kneecap).^[2]
These are associations, and they do not show that patella alta causes either condition.^[2]

More on patella baja after a knee replacement

In one study of 178 people followed for at least 5 years after a total knee replacement, patella baja was found in 61 (34.3%), including 33 true and 28 pseudo cases.^[3] Clinical outcomes did not differ significantly between people with and without patella baja.^[3] A lower kneecap showed only weak links with front-of-knee pain and with WOMAC scores (a questionnaire score for knee pain, stiffness and function).^[3]

Pseudo-patella baja is a low-looking kneecap after a knee replacement in which the kneecap is in its normal position relative to the thigh bone, because the joint line has moved up instead.^[5] The Blackburne-Peel and Caton-Deschamps ratios (measures of kneecap height) are affected by the position of the joint line, so they are not reliable for detecting true patella baja in a knee replacement.^[5]

A young volleyball player lands with bent knees during practice in a bright community sports hall.

What symptoms can go with a high or low kneecap?

Patella alta is described as contributing to pain at the front of the knee, although how much this matters clinically remains uncertain.^[2] Patella alta is a risk factor for kneecap dislocation, and complaints of instability, such as a feeling that the kneecap may slip, are part of the assessment of kneecap instability.^[1][6]

How are patella alta and patella baja assessed?

The doctor asks about your symptoms and about any previous kneecap dislocations or partial slips (subluxations).^[6] The doctor examines the alignment of the leg and checks how the kneecap tracks as the knee moves.^[1][6] A side-on (lateral) X-ray shows kneecap height, and MRI can also be used.^[6][2]

Kneecap height is worked out from a ratio, such as the Insall-Salvati ratio (the length of the patellar tendon divided by the length of the kneecap) or the Caton-Deschamps index (the distance from the lower end of the kneecap to the front edge of the top of the shin bone, divided by the length of the kneecap’s joint surface).^[6][1]
Different sources and measurement indices give different cut-off values for patella alta ^[1][6], and how often it is found depends on the measurement method ^[2].

More on how measurement changes the result

In one study of 250 people aged 18 to 38 who had both a knee X-ray and an MRI, patella alta was found in 13.2% on the Insall-Salvati ratio on X-ray, in 10.8% on the same ratio on MRI, and in 1.6% or fewer on a modified version of the ratio.^[2] Agreement between the X-ray and MRI results was moderate.^[2] The authors advise that the findings should not be extrapolated to acute injury or to people without symptoms.^[2]

What is the surgical option for a high-riding kneecap?

For a high-riding kneecap that goes with kneecap instability, one surgical option is tibial tubercle distalisation, an operation that moves the attachment of the kneecap tendon on the shin bone downward.^[1]

In one set of published guidelines, this operation is performed when measurements of kneecap height, of how well the kneecap engages the groove, or both, fall outside set limits.^[1]
How the operation works, and when it is chosen, is explained on the kneecap realignment surgery page.

A young woman performs a controlled step-up while a physiotherapist watches beside her.

What is known about patella baja?

StatPearls describes patella baja as “commonly seen after a patellar ligament rupture repair, patellar fracture, or high tibial osteotomy”.^[7]

For treatment, StatPearls states that treatment of symptomatic patella baja “usually involves surgical intervention to proximalize the patella. There is no gold standard patella baja treatment.”^[7] In plain terms, the surgery moves the kneecap up.

When is urgent help needed?

The list below covers the signs that should not wait for a routine appointment, including a knee that is stuck and will not straighten.

Signs that need urgent help

Some symptoms should not wait for a routine appointment. Each item below says where to go.

After an injury

The leg looks twisted or bent, a bone is showing, there is a deep cut, or the foot or leg turns cold, pale, numb, blue or white. Go to an emergency department or call 995.
You cannot lift your leg up with the knee kept straight, and you may feel a gap just above or just below the kneecap. Arrange an urgent same-day assessment.

At any time

The knee is stuck and will not straighten, or it is very painful and you cannot move it or put weight on it. Arrange an urgent same-day assessment.
The knee is suddenly very painful, hot, red and swollen, especially with a fever or feeling generally unwell. Go to an emergency department or call 995.
One calf or thigh is newly painful and swollen. Arrange an urgent same-day assessment. If you also feel short of breath or have chest pain, go to an emergency department or call 995.

After knee surgery

The operated knee becomes more painful, swollen or red, a wound is leaking, or you develop a fever. Go to an emergency department or call 995, or contact your surgical team straight away.

If you are admitted by the doctor at the urgent care centre of one of these private hospitals, the Parkway Pantai hospitals (Mount Elizabeth Orchard, Mount Elizabeth Novena, Gleneagles and Parkway East), Farrer Park Hospital and Thomson Medical Centre, you may ask for Dr Sean Leo to be your attending orthopaedic surgeon. If you are instead discharged and referred for orthopaedic follow-up, you may contact the clinic to arrange an appointment. Both are subject to the hospital’s admission processes and to Dr Leo’s availability.

What should I do next?

For anyone with kneecap pain, a kneecap that feels unstable, or a diagnosis of patella alta or patella baja, an assessment is a sensible next step. It brings together the patient’s story, an examination and any tests that help, so that the patient and clinician can decide what to do next. An appointment supports an informed decision. It is not a commitment to surgery.

Read about MPFL reconstruction and about kneecap realignment surgery for kneecap instability.
Read about kneecap dislocation and about knee fat pad syndrome.
Arrange a knee assessment when you are ready.
Browse the Knee Hub for other knee problems, or more articles.
Read more about Dr Sean Leo, who is named as the author of this page.

Arrange a knee assessment

Explore knee treatment options

This page provides general information and cannot diagnose an individual condition. OrthoKinetics does not provide emergency or urgent care through this webpage or its WhatsApp contact.

References

Dejour DH, Mesnard G, Giovannetti de Sanctis E. Updated treatment guidelines for patellar instability: “un menu à la carte”. J Exp Orthop. 2021;8:109. doi:10.1186/s40634-021-00430-2. PMID:34837157.
Almohideb, Felemban, et al. Patella Alta on X-Ray and MRI: Diagnostic Agreement and Clinical Correlations. Diagnostics (Basel). 2026;16(15):2444. doi:10.3390/diagnostics16152444. PMID:42587681.
Darilmaz MF, Bulut M, Yolaçan H, Güler S, et al. Incidence, predictors, and clinical impact of patella baja after primary total knee arthroplasty. BMC Musculoskelet Disord. 2026;27(1):212. doi:10.1186/s12891-026-09577-4. PMID:41668090.
Sanders TL, Pareek A, et al. Incidence of First-Time Lateral Patellar Dislocation: A 21-Year Population-Based Study. Sports Health. 2018;10(2):146. doi:10.1177/1941738117725055. PMID:28795924.
Grelsamer RP, et al. Patella baja after total knee arthroplasty: is it really patella baja? J Arthroplasty. 2002;17(1):66-69. doi:10.1054/arth.2002.28728. PMID:11805927.
StatPearls. Patellar Instability. Bookshelf ID NBK482427. PMID:29494034. https://www.ncbi.nlm.nih.gov/books/NBK482427/
StatPearls. Anatomy, Bony Pelvis and Lower Limb, Knee Patella. Bookshelf ID NBK519534. https://www.ncbi.nlm.nih.gov/books/NBK519534/

Understanding patella alta and patella baja