Causes of Diffuse Suprapatellar and Infrapatellar Pain
Diffuse suprapatellar and infrapatellar pain is most commonly caused by patellofemoral pain syndrome (PFP), which presents as gradual onset diffuse retropatellar and/or peripatellar pain during activities like squatting, stair climbing, and running 1.
Primary Cause: Patellofemoral Pain Syndrome
PFP is the predominant etiology for this pain pattern and affects both adolescents and adults 1. The condition is characterized by:
- Gradual onset diffuse pain around and behind the patella
- Activity-related symptoms particularly with squatting, stair ambulation, and running
- Poor prognosis with >50% reporting persistent pain beyond 5 years despite treatment 1
Infrapatellar Region-Specific Causes
When pain localizes more to the infrapatellar area, consider these distinct pathologies 2:
Fat Pad Pathology
- Hoffa's disease (infrapatellar fat pad fibrosis/inflammation) - causes burning or aching anterior knee pain 3
- Deep infrapatellar bursitis - inflammation of the bursa beneath the patellar tendon 2
- Fat pad impingement syndromes - mechanical irritation during knee motion 2
- Infrapatellar contracture syndrome - fibrotic scarring causing pain and extension limitation 3
Tendon and Soft Tissue
- Patellar tendinopathy - overuse injury of the patellar tendon 2
- Medial plicae - synovial fold irritation 2
- Adhesive capsulitis - capsular fibrosis 2
Suprapatellar Region-Specific Causes
Suprapatellar pain can arise from:
- Suprapatellar fat pad pathology - though oedema-like changes are more commonly related to fat pad configuration than pain 4
- Vascular lesions or lipomatous tumors affecting the suprapatellar fat pad (rare) 5
- Quadriceps tendinopathy - proximal to the patella
Bone and Cartilage Pathology
These conditions cause more diffuse peripatellar pain 2:
- Patellofemoral cartilage loss - associated with bone marrow lesions (BMLs) 2
- Chondromalacia patellae - cartilage softening and degeneration 6
- Subchondral insufficiency fractures - particularly medial femoral condyle in middle-aged to elderly females 2
- Bone marrow lesions - new or increasing BMLs correlate with increased knee pain 2
Biomechanical and Structural Causes
- Patellofemoral maltracking/subluxation - abnormal patellar tracking 2
- Trochlear dysplasia - developmental abnormality of the femoral groove 6
- Lateral patellofemoral friction syndrome - excessive lateral pressure 2
Less Common Causes
When the above are excluded, consider 2:
- Iliotibial band syndrome - lateral knee pain that can radiate
- Discoid meniscus - congenital meniscal variant
- Ganglion cysts - fluid-filled masses
- Pigmented villonodular synovitis - proliferative synovial disorder
- Tumors - benign or malignant masses (rare)
- Osteonecrosis - bone death from vascular compromise
Clinical Pitfalls
Important caveat: The infrapatellar fat pad is richly innervated and can produce referred pain extending proximally, even to the groin region when severely inflamed 7. This means infrapatellar pathology can masquerade as suprapatellar or more diffuse anterior knee pain.
Do not assume that diffuse pain automatically means PFP - experimental studies show that nociceptive stimulation of the infrapatellar fat pad produces deep aching pain that is not necessarily confined locally, particularly when severe 7.
Diagnostic Approach
Start with plain radiographs (AP, lateral, and tangential patellar views) as the initial imaging 2. When radiographs are normal or show only effusion but pain persists, MRI without contrast is the next appropriate study 2. MRI can identify:
- Cartilage abnormalities and BMLs
- Fat pad inflammation/fibrosis (enhancing synovitis >2mm in Hoffa's fat correlates with peripatellar pain) 2
- Tendon pathology
- Structural abnormalities
Contrast-enhanced MRI may be more accurate for diagnosing Hoffa's disease, deep infrapatellar bursitis, and patellofemoral friction syndrome 2.