Infrapatellar fat pad syndrome is when your fat pad becomes pinched (impinged) between your kneecap and thigh bone, or your thigh and shin bones. It’s also known as infrapatellar fat pad impingement. Your infrapatellar fat pad has a rich supply of nerves, so impingement can be very painful. Infrapatellar fat pad impingement can occur for many reasons, including the Overload of the extensor (quadriceps) mechanism such as when running and when kicking a ball during football. Hyperextension of the knee (over straightening of the knee), e.g. in gymnastics/dance. Symptoms of fat pad syndrome are anterior knee pain, often retropatellar and infrapatellar. Patellofemoral crepitus might be present, with knee loading such as in stairs negotiation, squatting, jumping, and running. Effusion and decreased ROM are often seen with inflamed IFP. This is often hard to pinpoint and there has been no clear injury. Activities such as climbing the stairs, or even sitting with the knee bent are painful. In some cases, there is a background ache and occasional jolts of sharp pain. Treatment for Hoffa’s fat pad syndrome involves reducing inflammation and controlling nerve pinching in your knees. The first line of treatment involves rest and medications. Other conservative treatments include taping the knee, performing strengthening exercises, and anti-inflammatory injections.
Other Names
- Infrapatellar fat pad impingement
- Fat Pad Syndrome
- Hoffa’s Syndrome
- Hoffa’s Fat Pad Syndrome
- Hoffa’s disease
- Fat pad herniation
Pathophysiology
- General
- The disease process suffers from a paucity of literature
- The IFP is an intracapsular, extra synovial adipose tissue structure in the anterior knee
- An important source of anterior knee pain
Causes
- Overall, poorly understood
- IFP impingement has been termed ‘an impingement of the hypertrophic fat pad between the articular surfaces of the knee’
- Specifically, the IFP impinges between the Patella and Medial Femoral Condyle
- Alternatively may impinge between the femur and tibia during extension
- This leads to inflammation, hypertrophy, chronic inflammation with necrosis, and fibrosis
- Pathology is thought to be caused due to
- Inflammation and fibrosis associated with trauma
- Trauma may be a direct blow, acute hyperextension, chronic irritation or postsurgical scarring
- Pediatric population
- IFP can herniate through a defect in the lateral retinaculum
- Will present as a painless, atraumatic mass in the anterolateral infrapatellar region
- Infrapatellar Fat Pad
- Intracapsular and intrasynovial adipose tissue structure
- Heavily vascularized, highly innervated
- Largest soft tissue structure in the knee joint
- Function
- Biochemical: reservoir rich in stem cells, may contribute to healing response after injury
- Biomechanical: dynamic structure which can change in shape during knee motion, stabilizing patella and patellar tendon
- Borders
- Anterior: Patellar Tendon, joint capsule
- Superior: the inferior pole of the Patella
- Inferior: proximal Tibia, deep infrapatellar bursa, intermeniscal ligament, meniscal horns and infrapatellar bursa
- Posterior: joint synovium, femoral condyles, and intercondylar notch.
- Attachments
- intercondylar notch via the ligamentum mucosum
- Anterior horns of the menisci
- The proximal end of the patella tendon
- Inferior pole of the patella
- Description
- Consists of a central body with medial and lateral extensions
- There is a vertical cleft in the superior aspect of the fat pad
- The horizontal cleft in the posteroinferior aspect of the fat pad
- Vascular Supply
- Upper and lower geniculate arteries create an abundant peripheral anastomotic blood supply
- Supromedial and superolateral geniculate arteries provide 2 vertical arteries
- 2 or 3 horizontal arteries connect the vertical arteries
- Innervation
- The predominant nerve supply to the fat pad is the Posterior Tibial Nerve
- Female > Male (need citation)
- Sports that require a forceful extension of the knee
- Dance
- Gymnastics
- Swimming
- Martial arts
- Jumping events (high jump, long jump, triple jump)
Differential Diagnosis
- Fractures
- Distal Femur Fracture
- Patellar Fracture
- Tibial Plateau Fracture
- Dislocations & Subluxations
- Patellar Dislocation (and subluxation)
- Knee Dislocation
- Proximal Tibiofibular Joint Dislocation
- Muscle and Tendon Injuries
- Quadriceps Contusion
- Iliotibial Band Syndrome
- Quadriceps Tendonitis
- Patellar Tendonitis
- Popliteus Tendinopathy
- Extensor Mechanism Injury
- Patellar Tendon Rupture
- Quadriceps Tendon Rupture
- Patellar Fracture
- Ligament Pathology
- ACL Injury
- PCL Injury
- MCL Injury
- LCL Injury
- Meniscal Pathology
- Posterolateral Corner Injury
- Multiligament Injury
- Arthropathies
- Knee Osteoarthritis
- Septic Arthritis
- Gout
- Bursopathies
- Prepatellar Bursitis
- Pes Anserine Bursitis
- MCL Bursitis
- Infrapatellar Bursitis
- Patellofemoral Pain Syndrome (PFPS)/ Anterior Knee Pain)
- Chondromalacia Patellae
- Patellofemoral Osteoarthritis
- Osteochondral Defect Knee
- Plica Syndrome
- Infrapatellar Fat Pad Impingement
- Patellar Instability
- Neuropathies
- Saphenous Nerve Entrapment
- Other
- Bakers Cyst
- Patellar Contusion
- Pediatric Considerations
- Patellar Apophysitis (Sinding-Larsen-Johansson Disease)
- Patellar Pole Avulsion Fracture
- Tibial Tubercle Avulsion Fracture
- Tibial Tuberosity Apophysitis (Osgood Schalatters Disease)
Diagnosis
- History
- Patients typically endorse anterior knee pain
- Duration of symptoms can range from weeks, months to even years
- Symptoms are worse with activity
- Some patients may have a history of mild or repetitive trauma, usually related to activity or sports
- Physical Exam: Physical Exam Knee
- The joint effusion may or may not be present
- Pain, tenderness around the patella especially at the inferior pole
- Range of motion may be restricted
- Pain at terminal extension
- Special Tests
- Hoffa’s Test: pain with pressure on the medial or lateral side of the patella with the knee in extension
Radiographs
- Standard Radiographs Knee
- May be normal
- Findings
- Small effusion
- Case reports have shown calcifications, opacity
MRI
- Findings[6]
- Hypointensity lesions
- Ossified lesion
- Solitary unossified lesions
- Localized edema of the superior and/or posterior part of the infrapatellar fat pad
- Deep fluid-filled infrapatellar bursa
- Non visualization of vertical and/or horizontal clefts
- Fibrosis or calcification of the fat pad
- Clinical correlation with MRI findings
- Specific edema locations do not correlate with clinical infrapatellar fat pad impingement
- Patients with clinical symptoms do have more regions of edema
- The second group only 4/47 patients with fat pad edema had symptoms of IFP impingement
Ultrasound
- Findings
- Enlargement and/or decreased echogenicity within the IPFP
- Color doppler: increased vascularity suggesting inflammation
- Dynamic ultrasound
- Can demonstrate impingement of fat pad during terminal extension
- Useful to evaluate suspected herniating IFP (see inflection, absent in extension)
Treatment
Nonoperative
- Indications
- First-line therapy in all cases
- Relative rest
- NSAIDS
- Brace
- Ice Therapy
- Physical Therapy
- Emphasis on strengthening quadriceps
- Corticosteroid Injections
- Fat Pad Sclerosis and Ablation[8]
- House and Connell injected the IFP of 12 patients with alcohol and bupivacaine under US guidance
- The injections were repeated at 3-week intervals for an average of 4 times per patient
- Patients had an average of 62% decrease in symptoms at 6 weeks of follow up
Operative
- Indications
- Failure of conservative measures
- Technique
- Arthroscopic resection of IFP
- Repair of lateral retinaculum (for herniating IFP)
