Morel-Lavallee Lesion

A Morel-Lavallee lesion is a closed internal degloving injury caused by tangential shear trauma. The skin and subcutaneous fat slide away from the underlying fascia, tearing perforating vessels and lymphatics. The created space fills with a mixture of blood, lymph and necrotic fat. If the cavity persists, inflammation and organisation can form a fibrous pseudocapsule, making spontaneous resolution and simple aspiration less reliable.

This is not simply a bruise. The lesion is a dead-space problem with three risks:

• It can be missed in polytrauma and later present as a painful mass or recurrent seroma.
• It can become colonised or infected, especially around pelvic and acetabular trauma.
• It can threaten the overlying skin because the subdermal vascular supply has been sheared.

The clinical importance is disproportionate to how harmless the initial swelling may look. In the acute phase it may be labelled as a haematoma, contusion, bursitis or soft-tissue swelling. In the chronic phase it may mimic a soft-tissue tumour or persist as a recurrent fluid collection.

The lesion matters most in five situations:

• Pelvic and acetabular fracture surgery: the collection may overlie the planned approach and increase infection risk.
• Skin compromise: necrosis, blistering, cellulitis or threatened flap viability requires urgent soft-tissue planning.
• Large dead space: aspiration alone may recur if the cavity is not obliterated.
• Chronic capsule: the capsule prevents collapse and often needs sclerodesis, quilting or excision.
• Delayed diagnosis: chronic pain, cosmetic deformity, infection and repeated procedures become more likely.

The lesion forms at the interface between the subcutaneous tissue and the deep fascia. The deep fascia is relatively fixed to the underlying muscle, while the skin and fat envelope can slide over it. A tangential force tears:

• perforating blood vessels,
• lymphatic channels,
• small cutaneous nerves,
• fibrous septa tethering the skin envelope to fascia.

The cavity initially contains haemolymphatic fluid and fat globules. Over time, haemoglobin breakdown products, inflammatory tissue and fibrous organisation change the imaging appearance. The pseudocapsule is clinically important because it behaves like a seroma cavity: repeated aspiration may temporarily empty it but does not remove the lining or close the potential space.

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Common sites reflect areas where mobile subcutaneous tissue moves over firm fascia or bony prominences:

• greater trochanter and lateral thigh,
• gluteal and pelvic region,
• flank and lumbosacral region,
• knee and prepatellar region,
• proximal femur and thigh after crush or road trauma,
• less commonly, upper limb, foot, breast or trunk.

The classic mechanism is high-energy blunt shear, such as a road traffic accident, run-over injury, crush injury, motorcycle collision or fall with tangential sliding. Sports mechanisms are described, especially around the hip, pelvis and knee, but a large or recurrent lesion after apparently modest trauma should still be treated seriously if the clinical signs fit.

Mechanism points that change management:

• Crush/run-over injury: higher risk of skin compromise and necrotic fat.
• Associated pelvic or acetabular fracture: plan the incision and timing around the lesion.
• Anticoagulation: may increase collection size and persistence.
• Open wound or skin necrosis: treat as a contaminated soft-tissue problem, not a simple closed seroma.
• Delayed presentation: suspect capsule, organised haematoma or secondary infection.

Presentation depends on timing.

Look specifically for:

• fluctuant swelling after shear trauma,
• skin hypermobility over deep fascia,
• bruising or ecchymosis,
• reduced cutaneous sensation over the lesion,
• central pressure necrosis or blistering,
• expanding size after the initial trauma,
• tenderness, erythema or warmth suggesting infection,
• proximity to planned fracture incision or implant site.

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Examination should define the lesion and the limb, not just confirm a swelling.

Assess the skin first:

• Is the skin viable, blistered, necrotic or cellulitic?
• Is there an open wound or drainage?
• Is the collection under tension?
• Does the skin slide abnormally over the fascia?

Then assess the lesion:

• size and boundaries,
• fluctuance,
• tenderness,
• compressibility,
• recurrence after prior aspiration,
• altered sensation,
• relation to bony prominences and surgical approaches.

Finally assess the associated trauma:

• pelvic, acetabular, proximal femoral or knee injury,
• vascular status,
• neurological status,
• compartment syndrome if swelling is deep or painful out of proportion,
• contamination risk if there is any open wound.

Imaging questions that matter clinically:

• Is the lesion superficial to deep fascia?
• Is it acute and ill-defined, or chronic and encapsulated?
• Are there fat globules, septations, blood products or internal debris?
• Is there gas, rim enhancement or surrounding cellulitis suggesting infection?
• Does the lesion cross or contaminate the planned surgical approach?
• Is there skin thinning or necrosis?
• Is there a tumour mimic that needs specialist imaging review?

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Several MRI-based classifications exist, including the Mellado-Bencardino system, which separates lesions by MRI morphology, signal, capsule, enhancement and sinus formation. The practical value is not memorising every imaging subtype; it is recognising the features that change treatment.

The differential depends on timing and location.

Technique is selected by the lesion biology. A small acute collection may only need aspiration and compression. A chronic encapsulated cavity needs a method that collapses or removes the lining. Necrotic or infected lesions need open debridement, cultures and staged soft-tissue management.

Preoperative planning

Before any procedure, define:

• the exact anatomical extent on ultrasound, CT or MRI,
• whether the lesion is acute fluid, chronic capsule, infected collection or necrotic soft tissue,
• whether the skin is viable enough for compression, quilting or closure,
• whether a pelvic, acetabular, femoral or knee approach will cross the lesion,
• whether plastic surgery input is needed for exposed fascia, necrotic skin or likely flap/graft coverage.

Consent should include recurrence, infection, repeat debridement, persistent drainage, contour deformity, skin loss, delayed fracture fixation and possible need for negative pressure therapy or soft-tissue reconstruction.

Image-guided aspiration and catheter drainage

This is appropriate for selected symptomatic acute lesions with viable skin and no established capsule.

Aspiration steps:

• Confirm the subcutaneous-fascial plane with ultrasound.
• Mark the lesion boundaries and choose a dependent entry point away from planned surgical incisions.
• Prepare the skin using sterile technique and infiltrate local anaesthetic.
• Aspirate the collection completely where possible, documenting volume, colour, fat droplets and clot.
• Send fluid for culture when there is erythema, warmth, fever, necrosis, previous intervention or nearby planned fixation.
• Apply firm compression or a pressure dressing immediately after aspiration.
• Review early; rapid reaccumulation means the cavity has not collapsed and needs a different strategy.

Failure points:

• aspiration without compression,
• aspirating an encapsulated chronic lesion repeatedly,
• placing the needle track through a future fixation approach,
• missing infection because fluid was not cultured.

Catheter drainage is useful when the collection is too large for reliable single aspiration, when it reaccumulates, or when ongoing output needs monitoring.

Drainage steps:

• Insert the catheter under ultrasound or CT guidance into the dependent portion of the cavity.
• Break down simple loculations only if safe and within the planned image-guided technique.
• Connect to suction or dependent drainage according to local protocol.
• Maintain compression to keep the skin-subcutaneous flap opposed to fascia.
• Monitor output, skin viability and inflammatory signs.
• Remove the drain only when output is low and the cavity is clinically collapsing.

If the drain output remains high or the collection reforms after drain removal, reassess for capsule, missed loculations, infection or a need for quilting, sclerodesis or capsulectomy.

Sclerodesis

Sclerodesis is used for recurrent or persistent cavities when skin is viable and uncontrolled infection has been excluded. It is not a substitute for debridement when there is necrotic skin, abscess or gross contamination.

Principles:

• drain the cavity first,
• confirm that the sclerosant can contact the cavity wall,
• protect surrounding skin from leakage or chemical irritation,
• use the agent and dwell time according to local protocol,
• re-drain as required,
• apply compression,
• follow the patient for pain, inflammation, infection and recurrence.

Agents reported in the literature include doxycycline, talc, ethanol, fibrin sealant and povidone iodine. The key teaching point is not the specific agent; it is the indication. Sclerodesis is for a viable, persistent cavity that needs obliteration of the lining.

Percutaneous quilting or progressive tension sutures

Quilting treats the mechanical problem directly: the mobile skin-subcutaneous flap is tacked back to the deep fascia so the cavity cannot refill.

Steps:

• Position the patient so the full lesion and any associated fracture field are accessible.
• Mark the lesion boundaries using clinical examination and imaging.
• Drain the collection through small incisions or percutaneous access.
• Irrigate the cavity and remove loose necrotic fat or debris if accessible through the chosen approach.
• Pass multiple absorbable or non-absorbable sutures from the skin-subcutaneous flap to the deep fascia, spacing them across the cavity to eliminate shear space.
• Avoid excessive tension that compromises skin perfusion.
• Place a closed suction drain when needed.
• Apply a compressive dressing or bolster.
• Review skin viability, drain output and recurrence.

This is most logical when the skin is viable, the lesion is not grossly infected, and the main problem is persistent dead space rather than extensive necrotic tissue.

Open debridement and capsulectomy

Open surgery is required for necrotic skin, abscess, infected collections, large chronic encapsulated lesions, failed less invasive treatment, or lesions that compromise a planned fixation corridor.

Position and setup:

• position according to lesion location and associated fracture surgery,
• prep widely because the cavity may extend beyond the visible swelling,
• mark skin necrosis, fluctuance, prior needle tracks and planned fixation incisions,
• give antibiotics according to infection status, but obtain cultures first when safe and clinically appropriate,
• use a tourniquet only when anatomically relevant and safe for the limb.

Incision planning:

• avoid raising unnecessary flaps in already degloved skin,
• avoid crossing future pelvic, acetabular or femoral fixation incisions if possible,
• place the incision where drainage, debridement and later coverage can be achieved,
• involve plastic surgery early if the skin envelope is marginal.

Cavity management:

• enter the cavity carefully and send fluid/tissue for microbiology if infection is possible,
• evacuate haemolymphatic fluid, clot and necrotic fat,
• irrigate thoroughly,
• excise non-viable skin and subcutaneous tissue,
• in chronic lesions, excise the pseudocapsule when this can be done without destroying viable skin,
• preserve perforators and any remaining soft-tissue vascularity,
• inspect the deep fascia and surrounding tissues for persistent loculations.

Dead-space closure:

• use quilting or progressive tension sutures to tack the flap to fascia when skin is viable,
• place closed suction drains in dependent positions,
• use compression or bolster dressings when the anatomy allows,
• avoid tight closure over compromised skin.

Closure strategy:

• primary closure is reasonable only if the skin is viable, tension is low and contamination is controlled,
• delayed closure is safer when viability is uncertain,
• negative pressure wound therapy is useful after debridement when repeat inspection or staged closure is needed,
• graft or flap coverage may be required after skin necrosis or repeated debridement.

Staged infected or necrotic lesion

When the lesion is infected or the skin is necrotic, treat it like a soft-tissue envelope failure rather than an elective seroma.

Sequence:

• assess sepsis and start resuscitation if required,
• obtain imaging to define the collection and relation to implants/fractures,
• debride necrotic tissue and drain the cavity,
• send cultures and tailor antibiotics,
• use negative pressure therapy if the wound cannot be closed safely,
• reinspect and repeat debridement until the wound is clean and viable,
• coordinate definitive fixation, closure, grafting or flap coverage once the envelope is safe.

The unsafe pattern is definitive internal fixation through an infected or necrotic degloving cavity without a soft-tissue plan.

Follow-up continues until the cavity has resolved, the skin is safe, and any associated fracture surgery is not threatened by soft-tissue recurrence.

Monitor:

• recurrence of fluctuance,
• persistent drainage,
• cellulitis or abscess,
• skin necrosis,
• contour deformity,
• chronic pain or tightness,
• wound breakdown,
• deep infection around implants,
• need for repeat aspiration, drain, sclerodesis or capsulectomy.

Complications:

• missed diagnosis,
• recurrent seroma,
• pseudocapsule formation,
• secondary infection,
• skin necrosis,
• chronic pain,
• cosmetic deformity,
• delayed fracture fixation,
• deep infection after pelvic or acetabular surgery,
• need for flap or graft reconstruction.

After drainage, sclerodesis, quilting or debridement, review focuses on dead-space collapse and skin safety.

Key elements:

• compression or bolster dressing when anatomically possible,
• suction drain care and output monitoring,
• wound review for necrosis, cellulitis and persistent drainage,
• repeat ultrasound if clinical swelling persists,
• antibiotics guided by cultures when infected,
• physiotherapy and mobilisation adapted to associated fractures,
• timing of definitive fixation or reconstruction once soft tissues are safe.

Small acute lesions can resolve with compression or limited drainage. Prognosis worsens when diagnosis is delayed, the cavity becomes encapsulated, the lesion is large, overlying skin is compromised, or the lesion overlies fracture fixation.

The desired endpoint is:

• no recurrent fluctuance,
• healed and viable skin,
• no infection,
• collapsed dead space,
• safe timing for associated fracture fixation or reconstruction,
• acceptable contour and pain control.

Persistent recurrence usually means the treatment has drained fluid but not closed the cavity.

In Australian orthopaedic practice, Morel-Lavallee lesions are most often considered within high-energy road trauma, pelvic trauma, farm or crush injury, and orthoplastic soft-tissue decision-making. Practical priorities are early recognition during trauma assessment, careful documentation of skin viability, timely cross-sectional imaging, culture when infection is suspected, and coordination between orthopaedic trauma, plastic surgery, radiology, infectious diseases and rehabilitation teams when the lesion threatens fixation or coverage.

The relevant clinical issue is whether the soft-tissue envelope is safe for drainage, fixation, debridement, negative pressure therapy or flap/graft coverage.