Anterior knee pain  is a very common discomfort that can affect people of all ages and activity levels. Among the many possible causes, one less known but important one is the impingement of the knee fat pads.

Although often overlooked, this condition can be a treatable cause of persistent pain and difficulty moving the knee.

What are the knee fat pads?

The fat pads are soft structures made of adipose tissue, well vascularized and innervated. They are located inside the knee joint capsule (but outside the synovial membrane) and perform fundamental functions:

• They act as biomechanical cushions.
• Lubricate and facilitate the sliding of internal structures.
• Adapt to changes in joint shape during movement.

The two main fat pads involved in impingement syndromes are:

1. Infrapatellar Fat Pad (Hoffa's Fat Pad)

Located just below the kneecap, between the distal femur and the patellar ligament. It is the largest and most commonly affected.

2. Suprapatellar or Prefemoral Fat Pad

Located above the kneecap, between the quadriceps tendon and the femur. Although smaller, it can also cause pain when inflamed or abnormally enlarged.

What causes fat pad impingement?

Impingement occurs when these structures become irritated or trapped between bones or tissues during movement. Below are the most frequent causes according to location:

Infrapatellar Impingement (Hoffa’s Syndrome)

Most common causes:

• Direct trauma: blows or falls on the knee.
• Repetitive movements: activities such as running, jumping, kneeling, or deep squatting.
• Knee hyperextension: movements exceeding normal extension range.
• Previous surgeries: such as ACL reconstruction or arthroscopy, which can leave scars or structural changes.
• Patellofemoral alignment abnormalities:
  • High-riding patella (patella alta)
  • Lateralized patella
  • Trochlear dysplasia
  • Poor patellar tracking during movement

Additional risk factors:

• Quadriceps weakness (especially the vastus medialis oblique)
• Biomechanical alterations (such as knock knees, flat feet)
• Overweight
• High-impact sports (soccer, running, CrossFit)

Suprapatellar / Prefemoral Impingement (PFIS)

Structural and mechanical causes:

• Fat pad hyperplasia: abnormal growth of fat tissue, even if histologically normal.
• Mass effect: compression caused by:
  • Intra-articular lipomas
  • Synovial cysts
  • Localized pigmented villonodular synovitis
  • Thickened synovial plicae
• Inflammation without clear mass: edema or inflammation without evident occupying lesion.
• Post-surgical or post-traumatic fibrosis: limiting fat pad mobility and making it prone to trapping.

Other mechanical factors:

• Sudden direction changes (sports like tennis, skiing, soccer)
• Repetitive flexion-extension
• Joint hyperlaxity

Clinical and Imaging Diagnosis

Diagnosis is made through:

Clinical evaluation

• Pain localized in the front of the knee.
• Worsening with full leg extension or certain movements.
• Positive Hoffa sign: pain on compressing the fat pad while extending the knee.
• In PFIS: pain is more proximal or superior, harder to pinpoint exactly.

Magnetic Resonance Imaging (MRI)

• Hoffa’s syndrome: edema in the infrapatellar fat pad (especially superolateral), synovial thickening, fibrosis, and even ossifications.
• PFIS: fat pad hyperplasia, mass effect, or signal alteration without obvious mass.

MRI is key to confirm diagnosis and rule out other causes of anterior knee pain.

Treatment

1. Conservative treatment (first-line)

Highly effective in most cases:

• Specific physical therapy to:
  • Reduce inflammation
  • Improve flexibility
  • Strengthen quadriceps, hamstrings, and hip stabilizers
• Ice application and NSAIDs
• Patellar taping and biomechanical re-education
• Avoid painful activities: such as deep squats, kneeling, or forced extension

2. Ultrasound-guided injections

• Precise administration of corticosteroids or local anesthetics into the affected area.
• Performed under ultrasound guidance to improve safety and effectiveness.
• Useful for controlling pain and reducing inflammation in cases resistant to physical therapy.
• Should be used judiciously, as excessive use can cause fat pad atrophy.

3. Surgical treatment (if conservative treatment fails)

• Indicated after several months without improvement with conservative management.
• Performed through knee arthroscopy:
  • Allows direct visualization and partial resection of the inflamed or hyperplastic fat pad tissue.
  • In Hoffa’s fat pad, preserving as much healthy tissue as possible is crucial.
  • In PFIS caused by hyperplasia, arthroscopic excision effectively relieves symptoms.
• Other concomitant lesions, such as plicae, osteophytes, or cartilage irregularities, can also be addressed.

Prognosis and final considerations

The prognosis is usually good, especially with early diagnosis and proper treatment. It is essential for physicians to consider these syndromes when evaluating anterior knee pain to avoid misdiagnosis and inadequate treatment.

Make an appointment with Dr. Jordi Jiménez. He will see you in the center of Palma de Mallorca and help you regain your quality of life.

Frequently Asked Questions About Anterior Knee Pain and Fat Pad Impingement Syndromes

What is anterior knee pain?

It is pain located at the front of the knee, common in active people and athletes, and can have various causes.

What are the fat pads of the knee?

They are fatty structures inside the joint that act as cushions to protect and lubricate the knee.

What are the most common causes of anterior knee pain?

Direct trauma, repetitive microtrauma, biomechanical alterations, problems with the fat pads, among others.

How are fat pad impingement syndromes diagnosed?

Through clinical history, physical examination, and magnetic resonance imaging to identify inflammation or entrapment.

What symptoms do these syndromes present?

Localized pain, swelling, tenderness, and pain during specific knee movements.

What is Hoffa’s syndrome?

It is the impingement and inflammation of the infrapatellar fat pad, a common cause of anterior knee pain.

What treatments are available for these syndromes?

From physical therapy and ultrasound-guided injections to arthroscopic surgery in severe cases.

What is an ultrasound-guided injection?

A technique that uses ultrasound to precisely direct the application of medication to the affected area.

When is surgery recommended?

When conservative treatment does not improve symptoms after several months.

What exercises help improve anterior knee pain?

Stretching and strengthening exercises for the quadriceps, hamstrings, and iliotibial band are essential.

What role does magnetic resonance imaging play in diagnosis?

It is the best tool to visualize inflammation and changes in the fat pads.

Can anterior knee pain be prevented?

Yes, through appropriate exercise, good biomechanics, and avoiding movements that cause overload.

What complications can arise if impingement is not treated?

Chronic pain, fibrosis, and deterioration of joint function.

Does anterior knee pain affect all ages?

Yes, although it is more common in active people and athletes.

What is the prognosis for these syndromes?

Generally good if diagnosed and treated early.