Ultrasound of Complete Muscle/Tendon Tear - Lower Limb

1. Normal Achilles Tendon (for comparison)

2. Complete Achilles Tendon Rupture

3. Achilles Tendinopathy with Power Doppler (pre-rupture stage for context)

How to Recognize a Complete Tear on Ultrasound

• Discontinuity - complete loss of fibrillar echotexture across the full thickness
• Retraction - proximal tendon stump retracts, often visible as a curled-up echogenic mass
• Hematoma - anechoic or hypoechoic collection filling the gap
• Herniated fat - in Achilles tears, echogenic Kager's fat is seen interposed between the torn ends
• Quadriceps/patellar tendon: complete rupture shows hypoechogenicity over the entire length and thickness of the tendon, with a wedge-shaped separation

Ultrasound of Infective Myositis (Pyomyositis)

Stage 1 - Invasive Stage: Early Muscle Edema

• Diffuse muscle swelling and enlargement
• Loss of normal striated muscle architecture (the usual parallel echogenic fibrillar pattern is disrupted)
• Mildly hypoechoic or heterogeneous muscle echotexture
• No discrete fluid collection yet

Stage 2 - Suppurative Stage: Intramuscular Abscess Formation

Ultrasound Features Summary by Stage

Key Technical Points

• Probe: High-frequency linear array (7.5-15 MHz) for superficial muscles; lower frequency curvilinear (3-5 MHz) for deep muscles (iliopsoas, gluteus)
• Doppler: Power Doppler shows peripheral hyperemia around the abscess wall - distinguishes active infection from old hematoma
• Sonopalpation: Gentle probe compression over the collection reveals movement of pus/debris - confirms liquefaction
• Always compare with the contralateral normal side
• Limitation: Stage 1 (invasive) may be missed on ultrasound; MRI is the gold standard when clinical suspicion is high despite normal/equivocal ultrasound

Ultrasound of Myositis Ossificans

Stage-by-Stage Ultrasound Appearances

Stage 1 (Early / Acute: 0-3 weeks) - Hematoma, No Calcification Yet

Stage 2 (Intermediate / Subacute: 3-8 weeks) - Peripheral Calcification

Stage 3 (Late / Mature: >8 weeks) - Complete "Eggshell" Calcification

Ultrasound Findings Summary by Stage

Key Diagnostic Points on Ultrasound

1. Zone phenomenon - peripheral calcification with a relatively lucent center is the hallmark; calcification always starts at the rim and moves inward (opposite to osteosarcoma)
2. Posterior acoustic shadowing increases progressively as ossification matures - in late stages it can be so dense that the lesion interior is completely obscured
3. No bone continuity - the lesion is separate from the adjacent cortex (important to confirm with orthogonal views); absence of a cleavage plane from bone suggests malignancy
4. Doppler: Active hyperemia in early/intermediate stages; absent flow in mature calcified rim
5. Probe: High-frequency linear 7.5-15 MHz; standoff pad may help for very superficial lesions
6. US is very sensitive to calcific changes - it can detect ossification earlier than plain radiography in some cases

Ultrasound Imaging of Muscle Sarcoma (Soft Tissue Sarcoma)

Image 1 - Undifferentiated Pleomorphic Sarcoma (UPS) / MFH - Thigh

Image 2 - Soft Tissue Sarcoma, Forearm - Heterogeneous Mass with Marked Doppler Vascularity

Image 3 - Large Deep Sarcoma (Abdominal/Retroperitoneal Leiomyosarcoma) with Doppler

Image 4 - Synovial Sarcoma with Abnormal Doppler Flow

Image 5 - Radiopaedia Case: Intramuscular Sarcoma, Right Upper Thigh

Ultrasound Features: Benign vs. Sarcoma

Key Sarcoma Subtypes and USG Characteristics

Role of Ultrasound in Sarcoma - Practical Points

1. First-line triage: Ultrasound can definitively diagnose benign lesions (lipoma, ganglion, haematoma) and refer suspicious ones urgently
2. Biopsy guidance: USG-guided core needle biopsy is the standard method - along the shortest path, avoiding neurovascular structures, with care to keep the biopsy tract within the eventual surgical resection field
3. Always use Doppler: Vascularity pattern is the most discriminating feature
4. Pitfall - myxoid tumors: Can mimic cysts on greyscale - increase the gain to reveal internal echoes indicating solid content (myxoid liposarcoma, intramuscular myxoma)
5. If any doubt: Any mass >5 cm, deep to fascia, or with internal vascularity requires urgent MRI - do not attempt excisional biopsy without imaging staging

Ultrasound of Tennis Leg

Anatomy Relevant to USG

1. Skin / subcutaneous fat
2. Gastrocnemius (hypoechoic with pennate fibrillar pattern)
3. Echogenic fascia / aponeurosis (the triceps surae junction - the key interface)
4. Soleus (deeper, also pennate)

Image 1 - Classic Tennis Leg: Fluid Between Gastrocnemius and Soleus (Labeled)

Image 2 - Extended Field-of-View: Aponeurotic Tear with Hematoma

Image 3 - Focal Disruption at the Musculotendinous Junction

Image 4 - Bilateral Comparison (Affected vs. Normal)

Image 5 - Large Hematoma Between Layers

USG Findings by Injury Grade

Classic USG Checklist for Tennis Leg

1. Fluid between MHG and soleus - the hallmark sign; seen in 90.9% of cases
2. Disruption of the pennate/fibrillar pattern of the distal MHG - loss of the normal echogenic septae
3. Hematoma size - measure thickness; predicts severity and recovery time
4. MHG retraction - retracted proximal stump visible as a hypoechoic bulge
5. Fluid tracking distally along fascial planes - indicates large tear
6. Always check for DVT - coexists in up to 10% of tennis leg cases; DVT appears as a non-compressible thrombosed vein
7. Plantaris tendon - look for it as a separate thin echogenic line between MHG and soleus; discontinuity = plantaris tear (only 1.4% of tennis leg cases)
8. Doppler - hyperemia at the tear margins; helps guide aspiration

Ultrasound of Baker's Cyst and Ruptured Baker's Cyst

PART 1: Intact Baker's Cyst

Image 1 - Classic Simple Baker's Cyst: Transverse View with Measurements

• Large anechoic (completely black/dark) fluid-filled cavity
• Sharply defined walls
• Posterior acoustic enhancement (the area deep to the cyst appears brighter than surrounding tissue - confirms fluid content)
• Well-encapsulated, oval/teardrop shape

Image 2 - Anatomical Position: Baker's Cyst between Semimembranosus and Medial Gastrocnemius (Labeled)

Image 3 - Baker's Cyst with Neck Communication to Knee Joint

• Panel A: Large cyst - yellow arrows show the "neck" communication connecting the cyst to the knee joint; white arrows show the cyst walls
• Panel B: Medium-sized cyst with clear neck visible between SM and MG
• Panel C: Small early cyst - subtle anechoic collection with the characteristic neck

Image 4 - Complex Baker's Cyst with Internal Debris (Thick-Walled)

• Internal echoes / debris (hyperechoic foci within the anechoic fluid)
• Wall thickening and irregularity
• Loss of clean posterior wall definition

Image 5 - Intact Baker's Cyst, Right Popliteal Fossa

PART 2: Ruptured Baker's Cyst

Image 6 - Ruptured Baker's Cyst: Pointed "Beak" Sign + Leaking Fluid Tracking into Calf

• The Baker's cyst body (dark anechoic area upper left)
• A pointed/beaked inferior margin (arrow) - this is the "beak sign" indicating the cyst has ruptured inferiorly
• Fluid tracking distally into the calf (dark hypoechoic fluid extending to the right along fascial planes)

Image 7 - Ruptured Baker's Cyst: Extended Field of View, Popliteal to Mid-Calf

Image 8 - Right Popliteal Fossa: Intact Cyst at Popliteal Level

Image 9 - Complex Cyst: Bilateral Comparison, Right Knee

USG Comparison: Intact vs. Ruptured Baker's Cyst

Practical USG Protocol

• Probe: High-frequency linear (10-15 MHz)
• Position: Patient prone, knee extended; or lateral decubitus
• Start at: Popliteal fossa in transverse plane - look for cyst between SM tendon and MHG
• Identify the neck - trace the connection to the knee joint (goes anterosuperiorly)
• Scan distally if rupture suspected - follow fluid down the calf to the level of the soleus
• Always add Doppler of the popliteal and proximal calf veins to exclude DVT
• Dynamic compression - a simple cyst is compressible; a solid mass is not