A 29-year-old woman arrives after her SUV rolled onto its side, one hand pressed against a broad, tender swelling over her left hip. Her jeans are torn and damp with road grit; the skin is bruised but intact, and the mass shifts subtly beneath her fingertips when she moves. She can wiggle her toes, but every attempt to stand produces deep lateral-hip pain. The question is whether this is merely a contusion—or something separating skin from fascia.

— What’s your move? Read on.

Before you read
  • Which findings determine observation versus drainage, sclerodesis, or surgery?
  • Why do apparently “simple” aspirations frequently fail?

When to Think of It

Enter this diagnosis after high-energy tangential trauma—especially motor-vehicle collision, motorcycle crash, pelvic/acetabular fracture, or contact sports—with a fluctuant, compressible swelling over the greater trochanter, thigh, pelvis, knee, or lumbar region. Clues include skin hypermobility, decreased cutaneous sensation, bruising that evolves over hours, and a fluid wave disproportionate to the visible injury.

Sick or Not Sick

The key call is stable closed soft-tissue lesion versus unstable trauma patient or threatened skin. Hypotension, expanding swelling, severe pain, tense skin, open wound, neurovascular deficit, compartment syndrome, or associated pelvic/femoral fracture mandates trauma-level evaluation and urgent specialty involvement.

The First Fifteen Minutes

  • Apply trauma priorities: monitoring, two large-bore IVs, serial vital signs, and hemorrhage assessment; the lesion may represent meaningful closed blood loss.
  • If severe pain is present but the patient is hemodynamically stable: fentanyl 25–50 mcg IV, repeated every 5 minutes to effect, because rapid titration provides analgesia with limited hemodynamic effect. Reduce doses in frail or hypoventilation-prone patients.
  • If pain is moderate and the patient can take oral medication: acetaminophen 1,000 mg PO, because it provides nonopioid analgesia without increasing bleeding risk; limit to 3,000 mg/day in older adults or liver-risk patients and 4,000 mg/day maximum in selected healthy adults.
  • If there is no renal disease, GI bleeding, anticoagulation concern, or major hemorrhage: ketorolac 15 mg IV once, or 30 mg IV in a younger adult with normal renal function, because prostaglandin inhibition reduces inflammatory pain. Check institutional dosing guidance; avoid it when bleeding or renal risk is significant.
  • Do not routinely needle-aspirate a stable lesion in the first minutes; aspiration alone often leaves the shearing cavity and promotes recurrence.

Definitive Care & Disposition

Obtain radiographs or CT when fracture, dislocation, or pelvic injury is possible. Ultrasound can confirm a superficial fluid collection, but MRI best defines the lesion, its chronicity, capsule, and relationship to fascia. Small acute lesions may receive compression and close follow-up; larger, symptomatic, recurrent, or chronic lesions require orthopedic/plastic-surgery consultation for image-guided drainage, drain placement, compression, sclerodesis, or open debridement/capsulectomy. Admission is appropriate for unstable trauma, large/expanding collections, skin compromise, infection, major associated fracture, or inability to ambulate safely.

How This One Kills

The classic failure is treating the swelling as a hematoma, aspirating it once, and discharging without sustained compression or follow-up. Persistent dead space then reaccumulates, forms a capsule, becomes infected, and compromises overlying skin.
The Differential — What Else Looks Like This
  • Simple hematoma — no shearing-plane mobility or persistent fluctuant cavity; confusing them leads to inadequate management of a recurrent closed degloving injury.
  • Abscess — fever, erythema, and purulence favor infection; confusing it with a sterile lesion delays antibiotics and source control.
  • Compartment syndrome — pain with passive stretch and a tense compartment, not merely a mobile superficial collection; confusion risks limb ischemia.
  • Seroma — typically follows surgery or blunt tissue disruption without major shearing; confusion may miss traumatic blood loss or capsule formation.

The Second-Day Story

In obese patients, older adults, or patients presenting days after trauma, the lesion may look like diffuse bruising or dependent edema rather than a discrete fluctuant mass. Analgesics can blunt pain, and intact skin does not exclude extensive separation. Ask specifically about tangential force, skin mobility, numbness, and delayed enlargement; examine standing and supine when safe, and use ultrasound or MRI when the physical examination is equivocal.
Back to Our Patient
Back to the 29-year-old woman: the tangential rollover mechanism, delayed fluctuant lateral-hip swelling, mobile skin, and intact distal neurovascular examination make a Morel-Lavallée lesion the leading diagnosis. She is hemodynamically stable without tense skin or fracture deformity, so the priority is analgesia, trauma imaging, focused ultrasound, compression, and urgent orthopedic/plastic-surgery follow-up rather than reflexive bedside aspiration. MRI is arranged because the collection is large and deep; she is discharged only after safe ambulation, a compression plan, and reliable next-day reassessment, with admission if the collection expands or skin perfusion worsens.
Patient Presentation to Attending
How you’d present this patient on the floor — tight, pertinent positives and negatives, no rambling
“This is a 29-year-old woman after a rollover MVC with progressive painful swelling over the left lateral hip. The swelling is fluctuant and mobile beneath bruised but intact skin, with decreased sensation over the area; she has no open wound, pelvic instability, distal neurologic deficit, or loss of pulses. She is hemodynamically stable and has no peritoneal findings or signs of compartment syndrome. My leading diagnosis is a traumatic Morel-Lavallée lesion, though I am assessing for pelvic or femoral fracture and occult hemorrhage. I would provide titrated analgesia, obtain trauma-directed radiographs or CT and ultrasound, apply compression, and consult orthopedics or plastics for MRI and definitive drainage strategy. She needs admission if the collection is expanding, the skin is threatened, or an associated fracture is found; otherwise she requires close specialty follow-up.”

Study Directive

  • Draw the anatomy of skin, subcutaneous tissue, perforators, and deep fascia, then label where the lesion forms.
  • Review three ultrasound examples and identify simple fluid, hematoma, and a fascial-plane collection.
  • Practice a disposition algorithm: stable/small versus large/recurrent versus skin-threatening.
  • Memorize the analgesic doses above and rehearse a 30-second trauma consult presentation.

Recent Literature