What is the management approach for a lesion on Kager's fat pad?

Management of Lesions in Kager's Fat Pad

The management of lesions in Kager's fat pad should begin with ultrasound diagnosis followed by ultrasound-guided hydrodissection and scar release if tethering to the Achilles tendon is identified. 1

Diagnostic Approach

Initial Imaging

• Ultrasound evaluation is the first-line diagnostic tool for Kager's fat pad lesions
  • Perform the "Kager's squeeze" technique: a dynamic maneuver that identifies tethering by observing deformation and bowing of the deep fibers of the Achilles tendon during compression of Kager's fat pad 1
  • Look for asymmetry of Kager's fat pad in relation to the Achilles tendon during complete passive dorsiflexion (David's sign), which has shown 85.71% sensitivity and 100% specificity for Achilles tendinopathy 2

MRI Assessment

• MRI should be used when ultrasound findings are inconclusive or to better characterize the lesion
• On MRI, evaluate for:
  • Edema patterns within Kager's fat pad (diffuse, confined anteriorly, confined posteriorly, or confined externally) 3
  • Connections between Kager's fat pad and surrounding structures, including the Achilles tendon paratenon, flexor hallucis longus, and ligamentous structures 4
  • Presence of bursal fluid, which may be associated with confined edematous patterns 3

Treatment Algorithm

1. For Kager's Fat Pad Tethering to Achilles Tendon

• First-line treatment: Ultrasound-guided hydrodissection and scar release 1
  • This office-based procedure restores normal motion between Kager's fat pad and the Achilles tendon
  • Technique involves injection of fluid to separate adhesions between the fat pad and tendon
  • Patients typically experience significant clinical improvement shortly after treatment 1

2. For Inflammatory Conditions

• Anti-inflammatory medications
• Activity modification
• Physical therapy focusing on eccentric exercises for the Achilles tendon
• Consider corticosteroid injections only if inflammation is not involving the Achilles tendon directly (to avoid tendon weakening)

3. For Mass Lesions

• For lesions <2 cm: Follow-up with serial ultrasound assessment to monitor for growth 5
• For lesions >2 cm or showing growth: Consider biopsy/excision due to higher risk 5
• For suspicious lesions: Core needle biopsy is preferred over fine needle aspiration 5

Anatomical Considerations

Understanding the functional anatomy of Kager's fat pad is crucial for proper management:

• Kager's fat pad has three specialized regions 6:

  1. FHL part: Contributes to moving the bursal wedge during plantarflexion
  2. Achilles part: Protects blood vessels entering the Achilles tendon
  3. Bursal wedge: Minimizes pressure changes in the retrocalcaneal bursa

• The fat pad moves into the retrocalcaneal bursa during plantarflexion and retracts during dorsiflexion 6

• Fibrous connections linking the fat pad to the Achilles tendon anchor and stabilize it proximally 6

Follow-up Recommendations

• For patients who undergo hydrodissection: Clinical reassessment at 4-6 weeks
• For patients with mass lesions under observation: Follow-up ultrasound every 3-6 months
• Consider MRI for persistent symptoms despite appropriate treatment

Pitfalls and Caveats

• Kager's fat pad scarring with Achilles tendon tethering may mimic or exacerbate Achilles tendinosis symptoms 1
• Consider this diagnosis when conservative treatments for Achilles tendinosis fail
• The double fascial layer surrounding Kager's fat pad may contain edema that affects this region, potentially leading to misdiagnosis 3
• Avoid aggressive surgical intervention before attempting less invasive options like hydrodissection

By understanding the complex anatomy and function of Kager's fat pad and using appropriate diagnostic techniques, clinicians can effectively manage lesions in this region while minimizing morbidity and preserving function.