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 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. 

The infrapatellar fat pad 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 infrapatellar fat pad 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].

Numerous studies investigated the influence of the fat pad on knee mechanics. 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 fat pad 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[6]. 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[7]. 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.

Diagnosis[edit | edit source]

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% [8]of anterior knee pain cases and 6.8%[9] as a secondary disorder.

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

Examination should aim to exclude any other radiating pathologies particularly from spine and hip.

Inflammed 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 [9] 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].

[10]

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

Acute Fat Pad Syndrome[edit | edit source]

Chronic Fat Pad Syndrome[edit | edit source]

References[edit | edit source]

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 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. ↑ Mellor R, Hodges PW. Motor unit syncronization is reduced in anterior knee pain. The Journal of pain. 2005 Aug 1;6(8):550-8.
  7. ↑ 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.
  8. ↑ 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.
  9. ↑ 9.0 9.1 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.
  10. ↑ 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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