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Fat Pad Syndrome

Original Editor - Mariam Hashem

Top Contributors - Mariam Hashem, Tarina van der Stockt, Kim Jackson, Ewa Jaraczewska, Tony Lowe, Simisola Ajeyalemi, Uchechukwu Chukwuemeka, Wanda van Niekerk, Jess Bell, Marleen Moll, Robin Tacchetti, Stacy Schiurring and Rishika Babburu

Introduction

Acute or chronic inflammation of the Infrapatellar Fat Pad (IFP) is a common source of Anterior Knee Pain; also called Hoffa's disease, fat pad syndrome or hoffitis. Fat pad syndrome was first reported by Albert Hoffa in 1904. [1]

Anatomy/Biomechanics

The IFP is found in the anterior knee compartment as a mass of adipose tissue that lies intracapsular but is extra synovial (extra-articular). [1] This fat depot is structured into distinct lobules composed of unilocular adipocytes encapsulated by a layer of connective tissue.[2] Additionally, the IFP contains a rich supply of blood vessels, nerve fibres, and various immune cell populations.

The IFP plays a crucial role in knee joint health by reducing load, enlarging the synovial space, supporting blood supply to the patellar tendon, and distributing lubricant within the joint.[2] It facilitates flexible deformation in the knee joint and supports patellar stability.[3] The relatively high density of nerves within the IFP supports its role as a mechano-receptor/proprioceptor. [4][5]

Boundaries include (1) superiorly by the inferior pole of the patella and alar folds,.[1] (2) inferiorly by the anterior tibia, intermeniscal ligament, meniscal horns and infrapatellar bursa, [6] (3) interiorly by the patellar tendon,[6] patellar ligament and joint capsule, [1]and (4) posteriorly by the femoral condyles, intercondylar notch[6] and the synovial membrane. [1]

Attachments include (1) the intercondylar notch via the ligamentum mucosum, (2) anterior horns of the menisci, (3) the proximal end of the patella tendon, and (4) the inferior pole of the patella[6]

Innervated mainly by the posterior tibial nerve,[7] The IFP can be a source of both localised and severe knee pain. This could be attributed to type VIa nerve endings[8] which could be activated through mechanical deformation or chemical pain mediators.  Substance P-nerve fibres are also present in individuals with anterior knee pain, particularly when the infrapatellar fat pad is inflamed. [9] As a potential source of inflammation and pain, some authors considered the fat pad to be a key structure in patellar tendinopathy[10] and osteoarthritis. [11]

The IFP is a dynamic structure. It alters position, pressure, and volume throughout the knee ROM. [12] When the knee moves into flexion, the superolateral portion of the fat pad becomes relaxed, freely expansive and moves posteriorly. The IFP lies between the lateral patella facet and the quadriceps tendon. Therefore, most commonly observed symptoms are associated with extension. However, it could also be seen in flexion, where pain is provoked by the trapped IFP between the patella tendon and the anterior femur. [6]

IFP facilitates gliding between the femoral condyles and the joint capsule. Knee mechanics can be altered when there is adhesion in the fat pad that changes the position of the patella and patellar tendon. Consequently, the effectiveness of the extensor mechanism is compromised, decreasing the effective moment arm and placing greater demands on the quadriceps to produce the same knee extension force. A shorter patellar tendon length affects patellar mobility and creates resistance to lateral translation at full extension. [12]

A study showed reduced coordination between medial and lateral vastus muscle motor units in anterior knee pain. [13] Another reported a significantly later activation and reduced amplitude of quadriceps contraction during stair stepping following injecting the fat pad with a painful hypertonic saline. [14] The inhibited fat pad resulted in increased patellofemoral loading and reduced quadriceps activation. [6] However, the exact association of fat pad and knee biomechanics needs further investigation.

Metabolic Influence of the Infrapatellar Fat Pad

Early studies reported the fat pad as a lubricant structure that facilitated the flow of synovial fluid inside the joint.[6] Subsequently, it has become clear that the IFP yields more sophisticated functions due to its complex neurovascularity.

The IFP is considered to be a producer of many inflammatory mediators found in association with OA. [15] As an adipose tissue, IFP mainly secretes fatty acids, which are well-known for their pro-inflammatory effects. [16] Adipose tissue also stores immune cells, another potential source of inflammatory mediator substances. [16] In addition, a study showed that IFP actively secretes IL-6 and its soluble receptor sIL-6R, at relatively higher levels compared to other adipose tissues. [17]

IFP has been found to release mesenchymal stem cells with enhanced chondrogenic activity, but this finding requires further investigations. [16]

Regulation of glycosaminoglycan release, [18] a source of reparative cells, [12] release of pro-inflammatory cytokines associated with elevated BMI[19] and collagen release[20] are also reported to be functions of IFP.

Duran et al., [21] studied the IFP volume and found it to be decreased in patellar cartilage defect.

Pathophysiology/Clinical Picture

Little is known about the development of fat pad syndrome, but there is growing evidence that high patellar height, larger tibial tubercle-tibial groove distance, and an increased trochlear angle predispose the development of fat pad syndrome.[22] The anatomical location of IFP exposes it to mechanical load, especially during extension. [1] Overuse or repeated micro trauma from sports or falls leads to hypertrophy. If the fat pad fails to recover, it can become chronically inflamed, which, if not properly managed, may result in fibrosis and ossification. [1]

Predominantly seen in young women, jumping sports and ligamentous laxity are also considered to be risk factors for Hoffa's disease. [1]

There is growing evidence of a connection between fat pad syndrome and knee osteoarthritis (OA), though the exact relationship remains complex and not fully understood. Some authors consider the fat pad to be a key structure in osteoarthritis, as the infrapatellar fat pad secretes multiple endocrine factors and inflammatory cytokines that can regulate joint physiology and disease. Fat pad impingement appears to frequently co-occur with OA and other knee injuries, suggesting these conditions may influence each other through inflammatory pathways and compromised mechanical function of the IFP's normal cushioning role. However, the size of the in IFP does not appear to be related to knee pain[23][24], indicating the relationship between IFP changes and OA symptoms is more nuanced than simple structural alterations, and further research is needed to clarify the precise mechanisms linking these two conditions.

Diagnosis/Physical Examination

The inflamed fat pad is often enlarged, firm in consistency and easy to palpate. Hoffa’s test can be performed. To avoid pain provocation in adjacent structures and incur false results, Krumar et al. [25] suggested a modification of Hoffa’s test. This involves taking the knee into passive forced hyperextension by lifting the heel and keeping anterior pressure on the tibia. This position stimulates pain exclusively in the fat pad if it is inflamed. [6]

[26]

Gliding the patella in all four directions (medially, laterally, superiorly and inferiorly) is important to detect adhesion or movement restriction during knee movement, particularly in hyperextension. Pain in hyperextension is a strong indicator of the presence of inflamed IFP. [12]

Examination should also exclude other radiating pathologies, particularly from the spine and hip.

Differentiation

Fat pad syndrome could be a primary disorder or secondary to other pathologies such as meniscus injuries and or ligamentous tear. Prevalence is not widely investigated; however, two studies reported an isolated fat pad in 1% [27] of anterior knee pain cases and 6.8%[25] as a secondary disorder. Synovitis and fat pad swelling were reported after anterior cruciate ligament (ACL) rupture. [28]

A detailed history and findings on functional assessment are important to discriminate fat pad syndrome from other conditions such as: patellar lateral femoral friction syndrome, impingement of the infrapatellar plica and arthrofibrosis or “cyclops syndrome”. Refer to the discussion in this article to learn about the characteristics of each condition.

Symptoms of fat pad syndrome include (1) anterior knee pain,[29] often retropatellar and infrapatellar; (2) patellofemoral crepitus might be present, with knee loading such as in stairs negotiation, [6] squatting, jumping and running; [12] and (3) effusion and decreased ROM are often seen with inflamed IFP.

Pain and/or discomfort from long walks, flat shoes, and prolonged standing mainly refers to fat pad syndrome. Pain resulting from up- or downhill walking is a characteristic of PFPS.

[30]

Imaging

MRI is the best imaging technique in diagnosing IFP inflammation. [1] Edema of the superior/posterior fat pad, inflamed infrapatellar bursa are easily detected by magnetic resonance. However, it is recommended to refer the patient to an MRI only to exclude any other pathologies, particularly when there is a history of trauma. [6]

Dynamic sonographic assessment revealed superolateral fat pad impingement associated with a perceived tight Iliotibial band.[6]

Management

Conservative treatments that have been reported to relieve symptoms include taping, physiotherapy, non-steroidal anti-inflammatory drugs, injections of local anaesthetics and/or corticosteroids. When these interventions are not effective, surgery may be the next step.[31]

Diagnostic and therapeutic injections of local anaesthetics and steroids into the fat pad resulted in immediate pain relief and reconstruction of movement. [6]

Two studies evaluated the results of arthroscopic resection, which showed an improvement on the Cincinnati rating System  and the Lysholm knee score. [27][25]

The role of IFP in knee osteoarthritis was studied by Liu and Gas, who indicated that a partial excision of the IFP significantly reduced pain, improved function, and promoted cartilage health in patients with knee osteoarthritis. [32]

An average improvement of 4.83 on VAS was reported following ultrasound-guided alcohol ablation by House and Connell. [33]

Refer to the case reports in this article to learn about different management approaches.

Management of Acute Fat Pad Syndrome

The acute symptoms occur as a result of falls, direct knee trauma or after knee surgeries resulting from arthroscopic equipment. Acute symptoms management includes (1) ice massage to relieve acute symptoms, [1] (2) taping following ice massage to alleviate pressure off the fat pad,[34] (3) flat footwear should be avoided to minimise IFP loading.[35], and (4) advise the patient to avoid provocative activities till the acute symptoms resolve.

[36]
[37]
[38]
[39]
[40]

Management of Chronic Fat Pad Syndrome

Fat pad syndrome typically presents without a history of trauma, making biomechanical assessment and correction essential components of management. Addressing biomechanical abnormalities such as excessive hyperextension is crucial to decrease IFP loading, which can be achieved through the use of relatively elevated shoes to correct hyperextension patterns. Movement awareness and education play important roles in treatment, alongside implementing knee straightening exercises and quadriceps and anterior hip stretching[41], which have been found to improve IFP restriction symptoms. Weight management represents a significant factor, as high BMI and obesity have substantial impacts on both knee osteoarthritis and fat pad syndrome - an 18-month randomized controlled trial demonstrated that a weight loss program combining exercise and diet resulted in significant reduction in IFP volume through changes in body fat percentage[42]. Additionally, emerging research suggests that therapeutic modalities may offer promise, as a randomized, single-blind, placebo-controlled study by Ikeda et al. indicated that high-intensity continuous ultrasound improved IFP stiffness and gliding in healthy participants, though further study is needed to evaluate its efficacy in patients with fat pad syndrome.[43]

[44]

References

  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 Larbi A, Cyteval C, Hamoui M, Dallaudiere B, Zarqane H, Viala P. et al. Hoffa's disease: A report on 5 cases. Diagnostic and interventional imaging. 2014;95(11):1079-84.
  2. ↑ 2.0 2.1 Wang MG, Seale P, Furman D. The infrapatellar fat pad in inflammaging, knee joint health, and osteoarthritis. NPJ Aging. 2024 Jul 15;10(1):34.
  3. ↑ Kitagawa T, Ozaki N, Aoki Y. Effect of physical therapy on the flexibility of the infrapatellar fat pad: A single-blind randomised controlled trial. PloS one. 2022 Mar 17;17(3):e0265333.
  4. ↑ Leese J, Davies DC. An investigation of the anatomy of the infrapatellar fat pad and its possible involvement in anterior pain syndrome: a cadaveric study. Journal of Anatomy. 2020 Jul;237(1):20-8.
  5. ↑ Edama M, Otsuki T, Yokota H, Hirabayashi R, Sekine C, Maruyama S, Kageyama I. Morphological characteristics of the infrapatellar fat pad. Scientific Reports. 2022 May 27;12(1):1-9.
  6. ↑ 6.00 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.10 6.11 Mace J, Bhatti W, Anand S. Infrapatellar fat pad syndrome: a review of anatomy, function, treatment and dynamics. Acta Orthopaedica Belgica. 2016;82(1):94-101.
  7. ↑ Macchi V, Stocco E, Stecco C, Belluzzi E, Favero M, Porzionato A et al. The infrapatellar fat pad and the synovial membrane: an anatomo-functional unit. J Anat. 2018;233(2):146-54.
  8. ↑ Bohnsack M, Wilharm A, Hurschler C, Rühmann O, Stukenborg-Colsman C, Wirth CJ. Biomechanical and kinematic influences of a total infrapatellar fat pad resection on the knee. The American journal of sports medicine. 2004;32(8):1873-80.
  9. ↑ Bohnsack M, Meier F, Walter GF, Hurschler C, Schmolke S, Wirth CJ. et al. Distributing substance-P nerves inside the infrapatellar fat pad and the adjacent synovial tissue: a neurohistological approach to anterior knee pain syndrome. Archives of orthopaedic and trauma surgery. 2005;125(9):592-7.
  10. ↑ Culvenor AG, Cook JL, Warden SJ, Crossley KM. Infrapatellar fat pad size, but not patellar alignment, is associated with patellar tendinopathy. Scandinavian journal of medicine & science in sports. 2011;21(6):e405-11.
  11. ↑ Clockaerts S, Bastiaansen-Jenniskens YM, Runhaar J, Van Osch GJ, Van Offel JF, Verhaar JA. et al. The infrapatellar fat pad should be considered as an active osteoarthritic joint tissue: a narrative review. Osteoarthritis and Cartilage. 2010;18(7):876-82.
  12. ↑ 12.0 12.1 12.2 12.3 12.4 Hannon J, Bardenett S, Singleton S, Garrison JC. Evaluation, Treatment, and Rehabilitation Implications of the Infrapatellar Fat Pad. Sports health. 2016;8(2):167-71.
  13. ↑ Mellor R, Hodges PW. Motor unit synchronisation is reduced in anterior knee pain. The Journal of Pain. 2005;6(8):550-8.
  14. ↑ Hodges PW, Mellor R, Crossley K, Bennell K. Pain induced by injection of hypertonic saline into the infrapatellar fat pad and effect on coordination of the quadriceps muscles. Arthritis Care & Research. 2009;61(1):70-7.
  15. ↑ Jiang LF, Fang JH, Wu LD. Role of infrapatellar fat pad in pathological process of knee osteoarthritis: Future applications in treatment. World Journal of Clinical Cases. 2019 Aug 8;7(16):2134.
  16. ↑ 16.0 16.1 16.2 Ioan-Facsinay A, Kloppenburg M. An emerging player in knee osteoarthritis: the infrapatellar fat pad. Arthritis research & therapy. 2013;15(6):225.
  17. ↑ Distel E, Cadoudal T, Durant S, Poignard A, Chevalier X, Benelli C. The infrapatellar fat pad in knee osteoarthritis: An important source of interleukin‐6 and its soluble receptor. Arthritis & Rheumatism: Official Journal of the American College of Rheumatology. 2009;60(11):3374-7.
  18. ↑ Caspar-Bauguil S, Cousin B, Galinier A, Segafredo C, Nibbelink M, Andre M et al. Adipose tissues as an ancestral immune organ: site‐specific change in obesity. FEBS letters. 2005;579(17):3487-92.
  19. ↑ Dragoo JL, Samimi B, Zhu M, Hame SL, Thomas BJ, Lieberman JR, et al. Tissue-engineered cartilage and bone using stem cells from human infrapatellar fat pads. The Journal of bone and joint surgery. British volume. 2003;85(5):740-7.
  20. ↑ Kim CS, Lee SC, Kim YM, Kim BS, Choi HS, Kawada T. et al. Visceral fat accumulation induced by a high‐fat diet causes the atrophy of mesenteric lymph nodes in obese mice. Obesity. 2008;16(6):1261-9.
  21. ↑ Duran S, Akşahin E, Kocadal O, Aktekin CN, Hapa O, Genctürk ZB. Effects of body mass index, infrapatellar fat pad volume and age on patellar cartilage defect. Orthopaedic journal of sports medicine. 2014;2(11_suppl3):2325967114S00159.
  22. ↑ Abelleyra Lastoria DA, Benny CK, Hing CB. Predisposing factors for Hoffa’s fat pad syndrome: a systematic review. Knee Surgery & Related Research. 2023 Jun 9;35(1):17.
  23. ↑ Wang MG, Seale P, Furman D. The infrapatellar fat pad in inflammaging, knee joint health, and osteoarthritis. npj Aging. 2024 Jul 15;10(1):34.
  24. ↑ Pereira Herrera B, Emanuel K, Emans PJ, van Griensven M, Cillero-Pastor B. Infrapatellar fat pad as a source of biomarkers and therapeutic target for knee osteoarthritis. Arthritis Research & Therapy. 2025 Apr 5;27(1):81.
  25. ↑ 25.0 25.1 25.2 Kumar D, Alvand A, Beacon JP. Impingement of infrapatellar fat pad (Hoffa’s disease): results of high-portal arthroscopic resection. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 2007;23(11):1180-6.
  26. ↑ Lenny Macrina. Fat Pad Assessment. Available from: https://www.youtube.com/watch?v=https://youtu.be/kbu9nybRV0M
  27. ↑ 27.0 27.1 Ogilvie-Harris DJ, Giddens J. Hoffa's disease: arthroscopic resection of the infrapatellar fat pad. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 1994 ;10(2):184-7.
  28. ↑ Witoński D, Wągrowska-Danielewicz M. Distribution of substance-P nerve fibres in the knee joint in patients with anterior knee pain syndrome: A preliminary report. Knee Surgery, Sports Traumatology, Arthroscopy. 1999;7(3):177-83.
  29. ↑ Genin J, Faour M, Ramkumar PN, Yakubek G, Khlopas A, Chughtai M et al. Infrapatellar Fat Pad Impingement: A Systematic Review. J Knee Surg. 2017;30(7):639-46.
  30. ↑ Claire Patella. Infographic:Differentiating fat pad and pfj pain. Available from: https://youtu.be/eiwKkb1SulU
  31. ↑ Kim YM, Joo YB. Arthroscopic treatment of infrapatellar fat pad impingement between the patella and femoral trochlea: comparison of the clinical outcomes of partial and subtotal resection. Knee surgery & related research. 2019 Mar;31(1):54.
  32. ↑ Liu Y, Gao Q. Partial excision of infrapatellar fat pad for the treatment of knee osteoarthritis. J Orthop Surg Res. 2024 Oct 7;19(1):631.
  33. ↑ House CV, Connell DA. Therapeutic ablation of the infrapatellar fat pad under ultrasound guidance: a pilot study. Clinical radiology. 2007;62(12):1198-201.
  34. ↑ Park Y-C, Kim Y-M, Joo Y-B. Arthroscopic Resection of Infrapatellar Fat Pad Impingement Syndrome: Long-Term Clinical Results at Minimum 10-Year Follow-Up. Medicina. 2025; 61(6):997.
  35. ↑ Mazzella N, Trowell D, Fox A, Saunders N, Vicenzino B, Bonacci J. Patellofemoral joint loads are lower when adolescents with patellofemoral pain run in flat, flexible shoes compared to traditional athletic shoes. Phys Ther Sport. 2025 May;73:165-170.
  36. ↑ How to ice massage for knee tendonitis, my Physio SA Adelaide Physiotherapist. Available from: https://www.youtube.com/watch?v=6CRarRzStrU
  37. ↑ Claire Patella. Ice-It-Away Instructions-Fat Pad Available from: https://www.youtube.com/watch?v=aE6-EGAFkfI
  38. ↑ Union Physical Therapy. McConnel fat pad taping. Available from: https://www.youtube.com/watch?v=Xy7CibqEUtQ
  39. ↑ McConnell Physiotherapy Group. MCCONNELL KNEE TAPING (OFFICIAL). Available from: https://youtu.be/WbHXYnwUwws
  40. ↑ Motion Guidance. infrapatellar fat pad mobilization. Available from: https://www.youtube.com/watch?v=KR_peakgyi4
  41. ↑ Dragoo JL, Johnson C, McConnell J. Evaluation and treatment of disorders of the infrapatellar fat pad. Sports medicine. 2012;42(1):51-67.
  42. ↑ Murillo AL, Eckstein F, Wirth W, Beavers D, Loeser RF, Nicklas BJ. et al. Impact of diet and/or exercise intervention on infrapatellar fat pad morphology: secondary analysis from the intensive diet and exercise for arthritis (IDEA) trial. Cells Tissues Organs. 2017;203(4):258-66.
  43. ↑ Ikeda N, Fukaya T, Sezaki Y, Toyoshima S, Yokoi Y, Morishita K. Effects of High-intensity Continuous Ultrasound on Infrapatellar Fat Pad Stiffness and Gliding in Healthy Participants: A Randomized, Single-blind, Placebo-controlled Crossover Trial. Ultrasound Med Biol. 2025 Jan;51(1):49-56.
  44. ↑ Infrapatellar Fat Pad Knee Pain (Hoffa's Syndrome) Clinical Treatment - Dr Mandell. Available from: https://www.youtube.com/watch?v=xPouEzBmVJk
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