Prepatellar Bursitis - Ultrasound (USG)

Anatomy

USG Technique

• Transducer: High-frequency linear probe - 7.5 to 10 MHz (maximum resolution for superficial structures)
• Position: Longitudinal orientation, indicator pointing toward the patient's head, placed over the anterior aspect of the knee
• Key landmark: The patella appears as a brightly echogenic (white) arcing line with posterior acoustic shadowing just beneath the surface

"Locating the patella is key to distinguishing prepatellar bursitis, which will appear as a dark, fluid-filled collection superficial to the patella, and a joint effusion, which will appear as a dark, fluid-filled collection deep to the patella."

• Roberts and Hedges' Clinical Procedures in Emergency Medicine

USG Findings in Prepatellar Bursitis

1. Fluid Collection (Anechoic/Hypoechoic)

• Appears as a dark gray to black (anechoic/hypoechoic) fluid-filled collection located superficial to the patella
• This is the hallmark finding distinguishing it from a joint effusion (which is deep to the patella)
• Simple uncomplicated fluid = anechoic (purely black)

2. Septic / Infective Bursitis Findings

• Excess fluid in the bursa (may appear more echogenic/complex due to debris, pus, or fibrin)
• Wall thickening of the bursal sac
• Increased colour Doppler flow within and around the bursal wall - due to hyperaemia and inflammatory changes
• The image below shows infective bursitis with colour Doppler:

3. Chronic / Traumatic Bursitis Findings

• Bursal wall thickening and synovial proliferation
• Fluid may contain internal echoes (fibrin strands, debris)
• Possible nodules within the bursa (fibrotic synovial nodules)
• Compressibility of the collection on pressure

4. Calcific Bursitis

• Presence of hyperechoic foci (bright spots) with or without posterior shadowing within the bursa
• Associated with chronic or crystal-related disease (gout, CPPD)

USG Differential Diagnosis at the Patella

USG-Guided Aspiration

• Guides needle aspiration of bursal fluid for Gram stain, culture, and crystal analysis (to distinguish septic from non-septic bursitis)
• Approximately one-third of patients with prepatellar bursitis have septic bursitis, making this distinction clinically important
• Aspiration fluid should be sent for: WBC count, Gram stain, culture, and polarized microscopy for crystals
• Colour Doppler can identify vascular supply before needle placement
• Real-time guidance reduces risk of inadvertent joint penetration

Key Points Summary

• Roberts and Hedges' Clinical Procedures in Emergency Medicine, Knee USG section
• Grainger & Allison's Diagnostic Radiology, p. 1187
• Harrison's Principles of Internal Medicine 22E (2025), Bursitis
• Campbell's Operative Orthopaedics 15th Ed (2026), p. 593
• Rosen's Emergency Medicine, Olecranon and Prepatellar Bursitis

Prepatellar Bursitis - USG Images

IMAGE 1: Anatomy - Location of the Prepatellar Bursa

IMAGE 2: Clinical Appearance - Septic Prepatellar Bursitis

IMAGE 3: USG Appearance - Infective Bursitis (Greyscale + Colour Doppler)

• (A) Greyscale B-mode: Irregular, predominantly hypoechoic/anechoic fluid collection within the bursa. Wall thickening is visible at the margins.
• (B) Colour Doppler: Markedly increased colour Doppler flow in the bursal wall and peribursal tissue - indicates active inflammation/infection (hyperaemia). This is the key feature distinguishing infective from simple traumatic bursitis.

IMAGE 4: Step-by-Step Aspiration Procedure

1. Anterior knee swelling confined to the prepatellar space, passive ROM preserved
2. Antiseptic prep + lidocaine infiltration of entry site
3. Knee extended, needle inserted into the fluctuant prepatellar space (medial or lateral approach)
4. Aspiration - use large syringe (substantial fluid volume possible)
5. "Milk" the bursa during aspiration - the prepatellar bursa is multiloculated, not a single cavity
6. Aspirate may be hemorrhagic (post-trauma) or purulent (septic)
7. Knee regains normal contour post-aspiration
8. Apply compressive dressing to reduce recurrence

USG Key Findings Summary (What to Look for on Scan)

"The patella can be seen as a brightly echogenic (white) object with posterior shadowing. Prepatellar bursitis will appear as a dark, fluid-filled collection superficial to the patella, and a joint effusion will appear as a dark, fluid-filled collection deep to the patella."

• Roberts and Hedges' Clinical Procedures in Emergency Medicine

Infrapatellar Bursitis - USG Images & Findings

Types of Infrapatellar Bursae

IMAGE 1: Anatomy - Both Infrapatellar Bursae in Context

IMAGE 2: USG - Normal Patellar Tendon with Trace Deep Infrapatellar Fluid (Longitudinal View)

• Green arrows = patellar tendon - appears as multiple hyperechoic (bright) fibrillar bundles running longitudinally
• White arrow = patella (at left/proximal end) - brightly echogenic with acoustic shadowing
• Brown arrow = tibial tuberosity (at right/distal end) - echogenic bony landmark
• Purple arrows = Hoffa's infrapatellar fat pad - intermediate echogenicity, sits deep to the tendon
• Blue arrows = trace fluid in the deep infrapatellar bursa - small anechoic/hypoechoic collection at the posterior aspect of the distal patellar tendon, just above the tibial tuberosity

"The patellar tendon is visible as multiple hyperechoic bundles extending from the patella toward the tibial tuberosity. Hoffa's infrapatellar fat pad and trace fluid in the deep infrapatellar bursa are also present." (Imaging Anatomy: Bones, Joints, Vessels and Nerves)

IMAGE 3: Fat Pads and Normal Deep Infrapatellar Bursa - MRI Reference

• Yellow arrows = suprapatellar fat pad
• Orange arrows = prefemoral fat pad
• Purple arrows = infrapatellar (Hoffa's) fat pad
• Blue arrows = normal deep infrapatellar bursa - the small potential space that becomes distended in bursitis

IMAGE 4: Superficial Infrapatellar Bursitis - MRI

• (a) Sagittal PD: fluid collection anterior to the mid-portion of patellar tendon, with internal septations visible
• (b) Sagittal STIR: bright high-signal fluid confirms active bursitis with septations

"When large, this bursitis can be indistinguishable from prepatellar bursitis."

IMAGE 5: Deep Infrapatellar Bursitis - MRI

• (a) Axial PD-FS: thin, low-signal capsule containing bright high-signal fluid with septations - located posterior to the patellar tendon at the tibial insertion
• (b) Sagittal T2FS: well-defined fluid collection between the posterior distal patellar tendon and anterior tibia, with an internally-septated pattern

• Hypoechoic/anechoic fluid collection posterior to the distal patellar tendon
• Thin echogenic capsule
• Internal septations in chronic cases
• Located in the space between patellar tendon and tibial tuberosity (Hoffa's fat pad may appear compressed or displaced)
• No communication with the knee joint

USG Technique for Infrapatellar Bursae

USG Findings Summary

Clinical Notes for USG

• The infrapatellar bursa lies deeper and more distal than the prepatellar bursa - the patellar tendon itself acts as the anterior boundary
• In Osgood-Schlatter disease, USG will also show: pretibial soft-tissue swelling, fragmentation of the tibial ossification center, and insertional thickening of the patellar tendon alongside bursal distension
• The deep infrapatellar bursa is separated from the knee joint synovium by Hoffa's fat pad - a sterile effusion of the knee joint may coexist but should not be confused with infrapatellar infection
• A distended deep infrapatellar bursa "obliterates the normal depression on each side of the patellar tendon" - this is the clinical sign that USG confirms

• Imaging Anatomy: Bones, Joints, Vessels and Nerves (Thieme), Figs. 21.34, 21.35, 21.38, 21.39
• Campbell's Operative Orthopaedics 15th Ed (2026), p. 595
• Grainger & Allison's Diagnostic Radiology
• Rosen's Emergency Medicine, Osgood-Schlatter Syndrome
• Goldman-Cecil Medicine, Bursitis and Tendinitis