Morel-Lavallée lesion of the knee in a soccer player.

Abstract

First described in 1853 [1], the Morel-Lavallee lesion is a closed, post-traumatic, soft tissue degloving injury [1–3], characterized by an accumulation of blood, lymph, and other breakdown products between the subcutaneous tissue and underlying fascia [4] (Fig. 1). It is due to shearing stress with disruption of perforating blood vessels and the creation of potential spaces. Morel-Lavallee is most commonly associated with pelvic and acetabular fractures, but it may also occur at various locations [4]; the lesion has been reported occurring over the flank, buttock, lumbar spine, scapula, knee, and elsewhere. Fig. 1 Morel-Lavallee lesion. Morel-Lavallee lesion is a post-traumatic injury characterized by an accumulation of fluid (arrows) between subcutaneous tissue and underlying fascia Clinical presentation of the lesion is pain, swelling, and stiffness at the site of injury. Upon examination, there is an area of tissue swelling that is soft to palpation [4]. Radiological investigations, especially ultrasound imaging and magnetic resonance imaging, are highly valued in the traumatic pathology of soft tissue [5] and so for the diagnosis of this condition [6]. The sonographic appearance is characterized by acute lesions that tend to be heterogeneous and lobular, with irregular margins. The chronic lesions are anechoic with well-defined margins, separating the subcutaneous tissue from the underlying fascia [7, 8]. Additionally, the magnetic resonance imaging appearance depends on the age and amount of blood, fat, and lymph [9]. The differential diagnosis is with muscle and soft tissue hematomas and with bursitis [10], more rarely with neoplasms. There is a lack of consensus regarding the management of these lesions, including non-operative therapies and operative techniques [11–13]. An 18-year-old male presented with left medial knee pain and swelling, 26 days following an injury occurred while playing soccer. Clinical examination showed a fluctuant swelling on the medial aspect of the right knee, without any surrounding cutaneous laceration or edema. Ultrasound of the medial aspect of the right knee, using a linear transducer at 18 MHz (Fig. 1), showed a longitudinal homogenous fluid lesion, located between the subcutaneous tissue and muscle (Morel-Lavallee lesion) (Fig. 2). Magnetic resonance imaging of the lesion (Fig. 3) confirmed, on the medial aspect of the right knee, the presence of a homogenous collection of fluid, between the subcutaneous tissue and the underlying muscle. A conservative approach to treatment was preferred. After 3 months of simple resting of the knee, no significant effusion could be appreciated on sonographic examination. The patient is currently asymptomatic. Fig. 2 Morel-Lavallee lesion. Extended field-of-view sonograms a, b shows a fusiform homogeneous anechoic fluid collection (arrows) with smooth margins, located between subcutaneous tissue and muscle Fig. 3 Morel-Lavallee lesion. Axial and sagittal proton density fat suppressed images confirm the presence of fluid collection (arrows) with smooth margins, located between subcutaneous tissue and muscle Morel-Lavallee lesions [1] are rare but should be suspected in high inertia trauma of the knee, commonly developing secondarily to blunt trauma separation of subcutaneous tissue from the underlying fascia. The diagnosis remains primarily a clinical diagnosis [2], but there is a wide range of differential diagnoses, including hematomas, abscesses, bursitis, fat necrosis, and neoplasms; particularly, the clinical presentation of a post-traumatic hematoma and an acute Morel-Lavallee lesion are similar. Ultrasound and MRI must be used to confirm the diagnosis [2, 4] and for the differential diagnosis. The sonographic and magnetic resonance imaging characteristics of Morel-Lavallee lesions are variable: lesions less than 1 month of age tend to be heterogeneous and irregularly marginated. When they evolve, they became more regularly marginated and homogeneous, but only the anatomic features are typical: a fluid lesion, located between subcutaneous tissue and muscle [6, 8]. The Morel-Lavallee lesion has a specific anatomic location and pathophysiological process that make it more prone to complications and chronicity. No clear best management is known, but the options can be narrowed based on location, age, and size of the lesion [2].