In a female patient with years of severe knee pain, popping/twisting on standing, hyperesthesia, swelling, instability, normal MRI of the spine, hip, and knee, and a sensation of a floating patella (patellar alta), what are the next appropriate diagnostic and management steps?

Obtain Comprehensive Knee Radiographs with Specific Patellar Views

Given the clinical presentation of severe knee pain with instability, popping/twisting, swelling, hypersensitivity, and a sensation of a "floating" patella despite normal MRI, the next step is to obtain comprehensive knee radiographs including anteroposterior, lateral, and specifically a tangential patellar (sunrise/Merchant) view to evaluate for patellofemoral pathology, particularly patella alta and patellar maltracking. 1

Rationale for This Approach

The patient's description of a "floating kneecap" combined with instability and popping/twisting strongly suggests patellofemoral pathology, specifically patella alta (abnormally high-riding patella) or patellar instability that may not have been adequately assessed on standard MRI.

Why Radiographs First

• Standard knee radiographs should include at minimum: anteroposterior, lateral, and tangential patellar views 1
• The lateral view allows measurement of patellar height using the Caton-Deschamps index (normal ≤1.16) 2
• The tangential patellar view demonstrates patellar tilt or subluxation that may explain the instability 3, 4
• Radiographs can identify subtle bony abnormalities, trochlear dysplasia, or signs of chronic patellar maltracking missed on MRI

Critical Pitfall: Standard MRI Limitations

Standard static supine MRI has significant limitations in diagnosing patella alta and patellofemoral instability. Recent evidence shows that static MRI measurements of patellar height are 28% lower than dynamic weight-bearing assessments, meaning patella alta is frequently missed on standard MRI 5. The patellotrochlear index (PTI) measuring cartilage overlap is significantly different between supine and weight-bearing positions, with the distal patellar cartilage margin being 3.3mm more proximal during quadriceps contraction 5.

Subsequent Diagnostic Algorithm

If Radiographs Show Patella Alta or Patellar Maltracking:

1. CT without IV contrast is indicated to evaluate:

   • Patellofemoral anatomy in detail
   • Trochlear morphology and dysplasia
   • Tibial tubercle-trochlear groove (TT-TG) distance
   • Precise measurements for surgical planning if needed 1

2. Consider dynamic weight-bearing imaging (cone-beam CT if available) for more accurate assessment of patellar engagement during functional loading 5

If Radiographs Are Normal:

Given the severity and chronicity of symptoms with hypersensitivity (suggesting possible central sensitization or complex regional pain syndrome features), consider:

1. Referral to specialized patellofemoral pain clinic for comprehensive assessment
2. Evaluation for non-structural causes including:
   • Complex regional pain syndrome (hypersensitivity is a red flag)
   • Inflammatory arthropathy (though less likely with normal imaging)
   • Referred pain sources already ruled out with normal spine/hip imaging

Management Considerations Based on Findings

If Patellofemoral Pathology Confirmed:

Exercise therapy targeting both hip and knee musculature combined with education should be the primary intervention 6, 7. This includes:

• Knee-targeted strengthening exercises
• Hip-focused exercises (particularly hip abductor and external rotator strengthening)
• Education about activity modification and pain neuroscience

Supporting interventions to consider based on specific findings:

• Prefabricated foot orthoses if biomechanical factors identified 6, 7
• Patellar taping for short-term symptom relief during rehabilitation (though evidence is mixed) 7
• Manual therapy as adjunct, not standalone treatment 7

Key Clinical Pearls:

• Patella alta is associated with patellofemoral instability and may require surgical correction (tibial tubercle distalization) if conservative management fails and measurements exceed thresholds (Caton-Deschamps >1.2-1.3) 8, 9
• Both absolute (relative to tibia) and relative (relative to trochlea) patellar height measurements are necessary in moderate-severe trochlear dysplasia 10
• The sensation of a "floating patella" with normal MRI is a classic presentation that requires functional assessment, not just static imaging 5
• Hypersensitivity to touch suggests possible central sensitization that may require pain neuroscience education and graded exposure therapy alongside mechanical interventions

What NOT to Do:

• Do not rely solely on standard supine MRI for patella alta diagnosis 5
• Do not use isolated manual therapy, electrophysical agents, or mobilizations as primary treatment 7
• Do not perform repeat MRI without first obtaining proper radiographic views 1