Fat Pad Syndrome

Original Editor - Mariam Hashem

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

Anatomy and Biomechanics[edit | edit source]

Infrapatellar fat pad (IFP) has been considered as a source of anterior knee pain. A differentiated diagnosis came later as symptoms and diagnostic modalities showed clear evidence of a distinctive pathology yielding practical application to its management. 

Found in the anterior knee compartment, the IFP is an intra-articular extra synovial structure occupying the whole anterior part of the knee joint in all joint positions[1].

Boundaries:

  • Superiorly by the inferior pole of the patella,
  • Inferiorly by the anterior tibia, intermeniscal ligament, meniscal horns and infrapatellar bursa,
  • Anteriorly by the patellar tendon
  • Posteriorly by the femoral condyles and intercondylar notch

Attachments:

  • The intercondylar notch via the ligamentum mucosum,
  • Anterior horns of the menisci
  • The proximal end of the patella tendon
  • The inferior pole of the patella

Supplied mainly by the posterior tibial nerve. The IFP can be a source of both localized and sever pain this could be attributed to the presence of type VIa nerve endings[2] which could be activated through mechanical deformation or chemical pain mediators.  Substance P-nerve fibers is also present in individuals with anterior knee pain, particularly when the infrapatellar fat pad is inflamed[3]. As a potential source of inflammation and pain, some authors considered the fat pad to be a key structure in patellar tendinopathy[4] and osteoarthritis[5].

IFP facilitates gliding between the femoral condyles and joint capsule. The knee mechanics is altered when there is adhesion in the fat pad by changing the position of the patella and patellar tendon. consequently, the effectiveness of the extensor mechanism is compromised, decreasing the effective moment arm. This places greater demands on 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[6].

Earlier studies reported fat pad to be a lubricant structure that facilitated the flow of synovial fluid inside the joint[1]. Later, it became clear that the role of the IFP yields more sophisticated functions due to the complex neurovascular supply of the structure. A study showed reduced coordination between medial and lateral vastus muscle motor units in anterior knee pain[7]. Another reported a a significantly later activation and reduced amplitude of contraction of quadriceps during stair stepping following injecting the fat pad with a painful hypertonic saline[8]. The inhibited fat pad resulted in increased patellofemoral loading and reduced quadricpes activation[1]. However, the exact association of fat pad and knee biomechanics needs further investigations.

The IFP is believed to be a dynamic structure. It alters position, pressure, and volume throughout the knee ROM[6]. When the knee moves into flexion, the superolateral portion of the fat pad becomes relaxed, freely expansive and moves posteriorly. In extension, the IFP lies between the lateral patella facet and quadriceps tendon. Therefore, most commonly observed symptoms are associated with extension. However, it could also be seen in in flexion, where the pain is provoked by the trapped IFP between the patella tendon and anterior femur[1].

Diagnosis and Physical Examination[edit | edit source]

IFP is an extremely sensitive structure. 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 isolated fat pad in 1% [9]of anterior knee pain cases and 6.8%[10] as a secondary disorder. Synovitis and swelling of the fat pad were reported after anterior cruciate ligament (ACL) rupture[11].

Symptoms are anterior knee pain, often retropatellar and infrapatellar. Patellofemoral crepitus might be present, with knee loading such as in stairs negotiation[1], squatting, jumping and running[6].

Examination should aim to exclude any other radiating pathologies particularly from spine and hip. Gliding the patella in all four difrections (medially, laterally, superiorly and inferiorly) is important to detect adhesion or movement restriction and during knee movement, particularly hyperextension. Pain in hyperextension is a strong indicator of the presence of inflamed IFP [6].

Inflamed fat pad is often enlarged, firm in consistency and easy to palpate. Hoffa’s test can be performed. To avoid pain provacation in adjacent structures and end up with false results, Krumar et al [10] suggested a modification of hoffa’s test. Instead they recommend a passive forced hyperextension by lifting the heel keeping pressure on the anterior tibia, believing if the fat pad is pathological pain will be reproduced without any direct pressure[1]. They suggested taking the knee into passive forced hyperextension by lifting the heel and keeping pressure on anterior tibia. This position stimulate pain exclusively in the fat pad, if inflamed[1].

[12]

Findings on functional assessment are important and could possibly discriminate fat pad syndrome from other conditions.

Imaging[edit | edit source]

IFP is clear on MRI. 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 MRI only to exclude any other pathologies , particularly when there is a history of trauma MRI can detect fragment IFP [1].

Dynamic sonographic assessment revealed superolateral fat pad impinegement associated with association with a perceived tight Iliotibial band[1].

Metabolic Role of the Infrapatellar Fat Pad[edit | edit source]

In extreme starvation, IFP was found to be preserved[13]. IFP is considered to be a producer of many inflammatory mediating substances found in association with OA. IFP, as an adipose tissue, mainly secretes fatty acids which are well-known for their pro-inflammatory effects[13]. Adipose tissue stores immune cells, a potential source of inflammatory mediator substances[13]. In addition, a study showed that IFP actively secretes IL-6 its soluble receptor, sIL-6R, at relatively higher levels compared to other adipose tissues[14].

Interestingly, mesenchymal stem cells are found to be derived from IFP and displayed an enhanced chondrogenic activity. This could yield promising results which requires further investigations in the future[13].

Other roles investigated in the literature range from regulation of glycosaminoglycan release[15], a source of reparative cells[6], release of pro-inflammatory cytokines associated with elevated BMI[16] and collagen release[17].

Duran et al [18] studied the IFP volume and found it to be decreased in patellar cartilage defect.


Management[edit | edit source]

Diagnostic and therapeutic injections of local anaesthetic and steroid into the fat pad resulted in immediate pain relief and reconstruction of movement[1].

Arthroscpoic resection In two studies resulted in improvements on both Cincinnati rating System  and Lysholm knee score[9][10].

An average improvement of 4.83 on VAS was reported following Ultrasound guided alcohol ablation by House and Connell[19]

Acute Fat Pad Syndrome[edit | edit source]

Chronic Fat Pad Syndrome[edit | edit source]

Quadriceps and anterior hip stretching is found to improve IFP restriction symptoms[20].

AN 18-month RCT investigated the effect of a weight loss program (Exercise and/or diet) on the IFP. The study reported significant reduction in the IFP volume as a result of weigh loss and changes in body fat percentage, mostly achieved by combining exercise and diet[21].


References[edit | edit source]

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 Mr James MA, Bhatti W, ANAND MS. Infrapatellar fat pad syndrome: a review of anatomy, function, treatment and dynamics. Acta Orthopaedica Belgica. 2016;82:1-2016.
  2. ↑ Bohnsack M, Wilharm A, Hurschler C, Rühmann O, Stukenborg-Colsman C, Joachim Wirth C. Biomechanical and kinematic influences of a total infrapatellar fat pad resection on the knee. The American journal of sports medicine. 2004 Dec;32(8):1873-80.
  3. ↑ Bohnsack M, Meier F, Walter GF, Hurschler C, Schmolke S, Wirth CJ, Rühmann O. Distribution of 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 Nov 1;125(9):592-7.
  4. ↑ 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 Dec;21(6):e405-11.
  5. ↑ Clockaerts S, Bastiaansen-Jenniskens YM, Runhaar J, Van Osch GJ, Van Offel JF, Verhaar JA, De Clerck LS, Somville J. The infrapatellar fat pad should be considered as an active osteoarthritic joint tissue: a narrative review. Osteoarthritis and Cartilage. 2010 Jul 1;18(7):876-82.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 Hannon J, Bardenett S, Singleton S, Garrison JC. Evaluation, Treatment, and Rehabilitation Implications of the Infrapatellar Fat Pad. Sports health. 2016 Mar;8(2):167-71.
  7. ↑ Mellor R, Hodges PW. Motor unit syncronization is reduced in anterior knee pain. The Journal of pain. 2005 Aug 1;6(8):550-8.
  8. ↑ 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 Jan 15;61(1):70-7.
  9. ↑ 9.0 9.1 Ogilvie-Harris DJ, Giddens J. Hoffa's disease: arthroscopic resection of the infrapatellar fat pad. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 1994 Apr 1;10(2):184-7.
  10. ↑ 10.0 10.1 10.2 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 Nov 1;23(11):1180-6.
  11. ↑ Witoński D, Wągrowska-Danielewicz M. Distribution of substance-P nerve fibers in the knee joint in patients with anterior knee pain syndrome A preliminary report. Knee Surgery, Sports Traumatology, Arthroscopy. 1999 May 1;7(3):177-83.
  12. ↑ Infrapatellar Fat Pad Knee Pain (Hoffa's Syndrome) Clinical Treatment - Dr Mandell. Available from: https://www.youtube.com/watch?v=xPouEzBmVJk
  13. ↑ 13.0 13.1 13.2 13.3 Ioan-Facsinay A, Kloppenburg M. An emerging player in knee osteoarthritis: the infrapatellar fat pad. Arthritis research & therapy. 2013 Dec;15(6):225.
  14. ↑ 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 Nov;60(11):3374-7.
  15. ↑ Caspar-Bauguil S, Cousin B, Galinier A, Segafredo C, Nibbelink M, Andre M, Casteilla L, Penicaud L. Adipose tissues as an ancestral immune organ: site‐specific change in obesity. FEBS letters. 2005 Jul 4;579(17):3487-92.
  16. ↑ Dragoo JL, Samimi B, Zhu M, Hame SL, Thomas BJ, Lieberman JR, Hedrick MH, Benhaim P. Tissue-engineered cartilage and bone using stem cells from human infrapatellar fat pads. The Journal of bone and joint surgery. British volume. 2003 Jul;85(5):740-7.
  17. ↑ Kim CS, Lee SC, Kim YM, Kim BS, Choi HS, Kawada T, Kwon BS, Yu R. Visceral fat accumulation induced by a high‐fat diet causes the atrophy of mesenteric lymph nodes in obese mice. Obesity. 2008 Jun;16(6):1261-9.
  18. ↑ 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 Nov 19;2(11_suppl3):2325967114S00159.
  19. ↑ House CV, Connell DA. Therapeutic ablation of the infrapatellar fat pad under ultrasound guidance: a pilot study. Clinical radiology. 2007 Dec 1;62(12):1198-201.
  20. ↑ Dragoo JL, Johnson C, McConnell J. Evaluation and treatment of disorders of the infrapatellar fat pad. Sports medicine. 2012 Jan 1;42(1):51-67.
  21. ↑ Murillo AL, Eckstein F, Wirth W, Beavers D, Loeser RF, Nicklas BJ, Mihalko SL, Miller GD, Hunter DJ, Messier SP. 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.
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