1003 - Rare Posterior Knee Morel-Lavallée Lesion in a 59-Year-Old Female Following Motor Vehicle Crush Injury: A Case Report from Inpatient Rehabilitation

Friday, February 20, 2026

5:00 PM - 6:30 PM AST

Presenting Author(s)

JJ

James Jabara, MD

PM&R Resident Physician
Medical College of Wisconsin
Milwaukee, Wisconsin, United States

Co-Author(s)

DD

David Del Toro, MD

Attending Physician
Medical College of Wisconsin
Wauwatosa, Wisconsin, United States

Submitter(s)

JJ

James Jabara, BS

Western Michigan University Homer Stryker, M.D. School of Medicine
Kalamazoo, Michigan, United States

Case Diagnosis: Posterior knee Morel-Lavallée lesion following slow-velocity motor vehicle crush injury

Case Description: A 59-year-old female sustained lower-extremity–focused polytrauma after being crushed by her own vehicle in her driveway. During inpatient rehabilitation (IPR), she developed progressive pain and swelling, and worsening ecchymosis of the left posterior knee. Initial considerations included hematoma, seroma, or infection. The ecchymotic area subsequently dehisced during therapy, draining copious serous fluid. Imaging confirmed Morel-Lavallée lesion, the popliteal fossa being an uncommon site compared with the more typical greater trochanter or lateral thigh. The lesion became clinically evident only after transfer to IPR and subsequent mobilization in IPR, underscoring the evolving nature of trauma-related complications. Management required coordinated care among PM&R, trauma surgery, and wound care teams.

Discussions: Morel-Lavallée lesions are closed degloving injuries caused by shearing forces that separate subcutaneous tissue from fascia, creating a cavity that fills with blood, lymph, and fat. While classically associated with high-velocity trauma, this case illustrates that they can also occur following slow-velocity crush injury. Posterior knee involvement is exceedingly rare and may be mistaken for more common rehabilitation complications such as DVT, cellulitis, hematoma, or cyst. Delayed or missed diagnosis increases the risk of infection, chronic seroma, or impaired mobility. Recognition in this case required high clinical suspicion, timely imaging, and interdisciplinary collaboration for definitive management.

Conclusions: This case highlights an uncommon posterior knee Morel-Lavallée lesion following slow-velocity crush injury, identified during IPR. It emphasizes the role of PM&R physicians in detecting evolving and rare trauma sequelae. Maintaining a broad differential and vigilance for atypical “zebra” presentations is critical to avoid potential complications and to optimize functional outcomes.