Patella Alta: Definition, Diagnosis, and Management
Patella alta is an abnormally high-riding patella that significantly increases the risk of patellofemoral instability, anterior knee pain, and other patellofemoral pathologies, requiring precise radiographic measurement and consideration for surgical correction when associated with recurrent instability.
What is Patella Alta?
Patella alta describes a patella positioned abnormally proximal relative to the femur, trochlear groove, or tibia, resulting in decreased bony stability 1, 2. This anatomic variant is clinically important because:
- It reduces patellofemoral contact area during knee flexion, leading to increased stress on the patellofemoral joint
- It delays patellar engagement with the trochlear groove, allowing excessive lateral patellar mobility
- It serves as a major predisposing factor for patellofemoral instability and recurrent patellar dislocations 2, 3
- It associates with anterior knee pain, cerebral palsy, and may predispose to patellofemoral osteoarthritis 1
The condition may be congenital or acquired, though recent literature remains inconclusive about its etiology 1.
Diagnostic Approach
Radiographic Measurement Methods
The field lacks consensus on optimal measurement techniques, with 18 different measurement methods and 27 different cutoff values reported in the literature 3. The most commonly used indices include:
Insall-Salvati Index (ISI) - Most Frequently Used
- Measures patellar tendon length divided by patellar length on lateral radiographs
- Cutoff values for patella alta range from >1.2 to >1.5 (most commonly >1.3) 3, 4
- Used in 75% of review studies 3
Caton-Deschamps Index (CDI) - Second Most Common
- Measures distance from inferior patellar articular surface to anterosuperior tibial plateau divided by patellar articular surface length
- Cutoff values range from >1.2 to >1.3 3
- Originally developed for true lateral radiographs 5
MRI-Based Measurements - Emerging Standard
- Patellar Height Index (PHI): >1.16 indicates patella alta 5
- Sagittal Patellar Engagement (SPE) Index: <0.38 indicates patella alta 5
- Patellar tendon length: >52-56 mm suggests patella alta 3
- "Functional patella alta" defined as PHI >1.16 AND SPE index <0.38, assessing position relative to both tibia and trochlea 5
Critical Diagnostic Pitfalls
The measurement indices are NOT interchangeable 6. A 2024 study found that while BPI, CDI, and ISR showed significant correlations, they identified different numbers of patella alta cases (15, and 25 respectively out of 100 knees), with only 7 knees classified as patella alta by all three methods 6. This variability means:
- You cannot reliably convert between indices
- Different methods may yield conflicting diagnoses in the same patient
- Consistency in measurement technique is essential for longitudinal assessment
Associated Measurements to Evaluate
When patella alta is identified, assess these additional parameters 4:
- Tibial tubercle-trochlear groove (TT-TG) distance - significantly elevated in patella alta
- Lateral patellar tilt angle (LPTA) - increased in patella alta
- Patella-patellar tendon angle (PPTA) - increased in patella alta
- Trochlear dysplasia - independently associated with instability 5
- Quadriceps patellar tendon angle (QPA) - novel measurement, elevated in patella alta 4
Imaging Recommendations
Start with standard lateral knee radiographs at 25-30 degrees of flexion for initial assessment using ISI or CDI 7. Axial radiographs demonstrate patellar tilt or subluxation 8, 9.
For surgical planning or when radiographs are equivocal, obtain MRI with metal artifact reduction techniques if hardware present 8, 9. MRI allows assessment of:
- Patellar height relative to both tibia and femur
- Trochlear morphology
- Soft tissue pathology
- Cartilage status
Management Strategy
Non-Surgical Management
For patella alta with anterior knee pain but without instability, initiate exercise therapy combined with education as the primary intervention 10, 11.
Exercise Prescription
- Combine hip and knee exercises - superior to knee exercises alone for pain reduction and functional improvement in short, medium, and long term 10
- Knee-targeted exercises should be the foundation, with hip strengthening added based on individual assessment 11
Adjunctive Interventions (Select Based on Individual Presentation)
- Prefabricated foot orthoses - recommended for short-term pain reduction 10
- Patellar taping - may provide symptomatic relief 10
- Patellofemoral braces - subjectively helpful, inexpensive component of therapy that may improve patellar tracking through medially directed force 12
- Use elastic material (neoprene) with lateral buttress
- Fit according to manufacturer guidelines (measure 3 inches above and below mid-patella)
- Position buttress to resist lateral displacement
- Must be combined with comprehensive rehabilitation program including strengthening and flexibility 12
- Manual therapy - not recommended in isolation but may be used as part of combined intervention 10
Electrophysical agents and isolated mobilizations are NOT recommended 10.
Surgical Management
Consider surgical correction when patella alta is associated with recurrent patellofemoral instability (>2 documented lateral patellar dislocations) 5. The prevalence of functional patella alta in objective patellar instability is 24% 5.
Indications for Surgery
Only 11 studies have proposed critical patellar height thresholds for surgical intervention, with no established consensus 3. However, surgical correction should be considered when:
- Recurrent patellar instability with documented patella alta
- Failed conservative management
- Significant functional limitation
Surgical Options
Three main approaches exist, with choice depending on associated pathology 13:
Proximal Procedures Alone
- Medial patellofemoral ligament reconstruction (MPFLR)
- Lower risk of major complications compared to distal procedures 13
- May be insufficient if significant patella alta present
Distal Procedures
- Tibial tubercle distalization (with or without patellar tendon tenodesis)
- Tibial tubercle distalization and medialization
- Distal advancement of patellar tendon
- Patellar tendon imbrication
- Better correction of patellar height and TT-TG distance 13
- Higher risk of major complications and subsequent surgery (RR 38.07) compared to proximal procedures alone 13
Combined Proximal and Distal Procedures
- MPFLR with tibial tubercle distalization
- Addresses both soft tissue restraints and bony alignment
Surgical Outcomes
A 2021 meta-analysis of 546 knees demonstrated 13:
- Pooled relative risk of 51.80 for no postoperative dislocation
- Pooled relative risk of 48.70 for no postoperative apprehension or instability
- Mean Kujala score improvement of 31.98 points
- Mean Lysholm score improvement of 35.93 points
- Mean patellar tilt angle improvement of 10.94 degrees
Distal procedures achieved significantly better correction of:
- Insall-Salvati ratio (weighted mean improvement 0.31)
- Caton-Deschamps index (weighted mean improvement 0.24)
- TT-TG distance (weighted mean improvement 6.77 mm)
Post-Total Knee Arthroplasty Context
In the setting of total knee arthroplasty, patella alta can result from patellar maltracking, component malrotation, or extensor mechanism imbalance 8, 9. Radiographic signs include:
- Patella alta on lateral radiographs
- Posterior tibial subluxation
- Localized soft-tissue swelling
- Bony avulsions or dystrophic calcifications
Standard radiographs are usually satisfactory for assessment, with axial views demonstrating degree of tilt or subluxation 8, 9. Weight-bearing axial radiographs better assess patellofemoral kinematics 9. CT with metal artifact reduction may be needed for surgical planning 8.
Key Clinical Pearls
- Patella alta is a spectrum condition - not all cases require intervention
- Measurement method matters - use consistent technique and understand that indices are not interchangeable 6
- Assess the entire patellofemoral joint - patella alta rarely exists in isolation; evaluate for trochlear dysplasia, increased TT-TG, and soft tissue pathology
- Conservative management first for pain without instability - exercise therapy with education as foundation 11
- Surgical correction indicated primarily for recurrent instability - not for isolated patella alta without symptoms 13
- Distal procedures correct height better but carry higher complication risk - weigh benefits against risks 13