Fat Pad Syndrome (Hoffa's)

Lower Limb

Overview

Hoffa's fat pad syndrome is an inflammatory condition affecting the infrapatellar fat pad located beneath the patellar tendon in the knee joint. This highly innervated and vascularised structure becomes irritated, impinged, or inflamed, causing anterior knee pain that is often exacerbated by extension activities. The condition is commonly seen in athletes and individuals with patellofemoral dysfunction or recent knee trauma.

Pathophysiology

The infrapatellar fat pad (ligamentum mucosum) is a highly sensitive structure rich in nociceptors and blood vessels. Repetitive microtrauma, direct compression, sudden hyperextension, or chronic irritation from patellofemoral joint dysfunction can cause the fat pad to become inflamed, hypertrophic, or impinged between the femoral condyle and tibia. Synovitis and inflammatory mediator release perpetuate pain and swelling. Postural dysfunction and quadriceps weakness allow increased anterior knee translation, compressing the fat pad further.

Patient Education

Hoffa's fat pad syndrome typically responds well to activity modification, reducing deep knee bending movements, and addressing underlying biomechanical issues such as quadriceps weakness or altered patellar tracking.

Typical Presentation

Site

Anterior knee, deep to the patellar tendon, often localised to the infrapatellar region just below the patella

Quality

Sharp, catching, or pinching sensation; may describe as deep knee pain rather than surface pain

Intensity

Mild to moderate (4-7/10), variable depending on activity level

Aggravating

Deep knee bending (stairs, squats, lunges), activities requiring knee extension against resistance, kneeling, prolonged sitting with knee bent, activities causing sudden hyperextension

Relieving

Rest, ice application, anti-inflammatory medications, knee extension in relief position, avoiding deep flexion activities

Associated

Mild swelling around infrapatellar region, slight warmth, catching sensation, functional limitation with stairs, difficulty with sports or running, stiffness after rest

Orthopaedic Tests

Hoffa's Test (Fat Pad Impingement Test)

Procedure

Patient supine or seated with knee extended. Palpate medial and lateral gutters of the patellofemoral joint, then apply gentle pressure into the fat pad while passively flexing and extending the knee through 20–30 degrees.

Positive Finding

Reproduction of sharp, localized anterior knee pain beneath the patellar tendon, typically worse at terminal extension or early flexion

Sensitivity / Specificity

71% / 76%

Ferretti et al., 1992, American Journal of Sports Medicine

Interpretation

Suggests mechanical irritation or impingement of the infrapatellar fat pad; supports diagnosis of Hoffa's syndrome when pain is reproduced with palpation and movement

Prone Knee Flexion Test (Hoffa's Pinch Test)

Procedure

Patient prone with knee flexed to 90 degrees. Examiner palpates the fat pad on either side of the patellar tendon in the infrapatellar space and applies gentle medial and lateral pinching pressure while moving the knee through flexion–extension.

Positive Finding

Sharp, well-localized pain in the infrapatellar fat pad region with minimal radiation; pain often diminishes with slight knee flexion or posterior knee capsule stretch

Sensitivity / Specificity

null / null

Interpretation

Directly provokes fat pad compression; consistent with mechanical impingement; helps differentiate fat pad syndrome from patellar tendinopathy or patellofemoral pain

Knee Extension Lag with Fat Pad Palpation

Procedure

Patient supine with knee extended. Examiner palpates the infrapatellar fat pad bilaterally while patient actively extends the knee against gravity or mild resistance.

Positive Finding

Reproduction of sharp anterior knee pain localized to the fat pad area; patient may demonstrate guarding or inability to complete full active extension due to pain

Sensitivity / Specificity

null / null

Interpretation

Pain with active quadriceps contraction and knee extension suggests dynamic impingement of the irritated fat pad; supports mechanical diagnosis

Suprapatellar Effusion Reduction Test (Ballottement with Fat Pad Compression)

Procedure

Patient supine with knee slightly flexed (15–20 degrees). Examiner applies gentle compression to the fat pad region in the infrapatellar notch while observing for fluid displacement or pain reproduction during passive knee extension.

Positive Finding

Sharper anterior knee pain or apprehension when fat pad is compressed and knee moved into extension; may indicate swelling or irritation compressing the pad

Sensitivity / Specificity

null / null

Interpretation

Suggests reactive inflammation or effusion contributing to fat pad mechanical irritation; indicates need for imaging to rule out meniscal or chondral pathology

Medial-Lateral Fat Pad Discrimination Palpation

Procedure

Patient supine or seated with knee extended and quadriceps relaxed. Examiner carefully palpates the medial and lateral borders of the patellar tendon in the infrapatellar space, systematically moving from proximal to distal and noting tenderness.

Positive Finding

Focal, reproducible tenderness directly deep to the patellar tendon, typically in the central or superolateral infrapatellar fat pad; pain is localized and does not radiate diffusely

Sensitivity / Specificity

null / null

Interpretation

Confirms localized fat pad irritation; tenderness isolated to the fat pad helps differentiate from patellar ligament pathology, synovitis, or meniscal injury

⚠ Red Flags

  • •Severe acute swelling with inability to bear weight following traumatic injury
  • •Signs of acute ligamentous injury (ACL/MCL/PCL damage)
  • •Fever with joint swelling suggesting septic arthritis
  • •History of cancer with new knee symptoms
  • •Severe redness and warmth suggesting acute infection
  • •Mechanical locking suggestive of meniscal tear

⚡ Yellow Flags

  • •High fear-avoidance behaviours regarding knee movement
  • •Excessive catastrophising about symptoms
  • •Poor compliance with activity modification recommendations
  • •Secondary gain factors related to injury
  • •Significant psychological distress affecting function
  • •Unrealistic expectations for rapid recovery

Osteopathic Techniques

Region

Infrapatellar fat pad and anterior knee joint

Technique

Soft Tissue

Rationale

Direct soft tissue mobilisation reduces muscle tension in surrounding musculature (vastus medialis obliquus, vastus lateralis) and promotes circulation to the inflamed fat pad, facilitating resolution of inflammation and reducing compression.

Region

Patellofemoral joint

Technique

Articulation

Rationale

Gentle patellofemoral gliding and mobilisation improves joint mechanics, reduces abnormal patellar tracking, and decreases compression forces on the infrapatellar fat pad during range of motion.

Region

Quadriceps muscle group

Technique

MET

Rationale

Muscle energy techniques improve quadriceps strength and balance, enhancing dynamic patellar stability and reducing anterior knee translation that compresses the fat pad.

Region

Knee joint capsule and synovium

Technique

Functional

Rationale

Functional technique positions the knee in a pain-free position while gently releasing restrictions, reducing fat pad irritation and synovial inflammation without aggressive mobilisation.

Region

Tibial and femoral structures

Technique

Articulation

Rationale

Tibiofemoral mobilisation in pain-free ranges restores normal knee mechanics and reduces aberrant movement patterns that contribute to fat pad impingement.

Region

Lymphatic drainage pathways around knee

Technique

Lymphatic

Rationale

Lymphatic drainage technique promotes resolution of local inflammatory swelling and reduces fluid accumulation in the infrapatellar region, decreasing pressure on the fat pad.

Add-On Approaches

Chinese Medicine

Acupuncture to points around the knee (Ex-LE7 Xiyan, ST34, ST35) combined with moxibustion to warm and promote circulation, particularly beneficial for chronic cases with qi stagnation and blood stasis patterns.

Chiropractic

Patellar tracking assessment and correction with lateral release techniques if patella alta is present; adjustment of tibiofemoral alignment to reduce aberrant biomechanics.

Physiotherapy

Progressive quadriceps strengthening (VMO emphasis), patellar taping for dynamic stabilisation, proprioceptive training, and weight management to reduce knee joint loads.

Remedial Massage

Deep tissue massage to quadriceps, vastus medialis obliquus, and IT band to release myofascial tension; soft tissue release techniques to reduce muscular guarding around the knee.

Rehabilitation Exercises

Supine Knee Extension with Towel Roll

Range of MotionBeginner

Quadriceps Stretch (Standing or Prone)

StretchingBeginner

IT Band and Hip Flexor Stretch

StretchingBeginner

Quadriceps Setting (Isometric VMO Contraction)

StrengtheningBeginner

Straight Leg Raise (Supine)

StrengtheningIntermediate

Short Arc Quadriceps Strengthening

StrengtheningIntermediate

Terminal Knee Extension (TKE) with Resistance Band

StrengtheningIntermediate

Step-Ups (Low Height, Progressive)

StrengtheningIntermediate

Single Leg Stance on Stable Surface

BalanceIntermediate

Hip Abduction in Standing (Clamshells or Side-Lying)

PosturalIntermediate

Lateral Lunge (Controlled Depth)

StrengtheningAdvanced

Single Leg Squats or Pistol Squat Progression

BalanceAdvanced

Referral Criteria

  • •Failure to improve after 6-8 weeks of conservative treatment
  • •Signs of meniscal pathology (mechanical locking, giving way)
  • •Suspected ligamentous injury (ACL/MCL/PCL)
  • •Imaging evidence of significant osteoarthritis or loose bodies
  • •Persistent swelling despite treatment
  • •Suspected infection or septic arthritis (fever, severe warmth, redness)
  • •Functional limitation preventing return to work or daily activities
  • •Consideration for injection therapy (corticosteroid injection) or surgical intervention if fat pad impingement confirmed on imaging