Internal degloving injuries are usually associated with high energy trauma and can be devastating. More commonly known as Morel-Lavallee lesions, when in the pelvic or thigh region, a degloving occurs when the superficial fascia separates from the deep fascia in a shearing mechanism. This not only disrupts the vascular and lymphatic channels that span these two layers but creates a potential space for fluid collection. The hemolymphatic fluid that collects is a nidus for infection and may put the overlying skin at risk for necrosis. Management depends on lesion size, severity, and associated injuries.
Internal degloving injuries are uncommon but can have significant associated morbidity, especially if overlooked. Male sex predominates, and a history of a high-speed motor vehicle collision, motorcycle accident, or direct crush to the area is common with motor vehicle collisions being the most common mechanism reported. Such injuries can occur anywhere in the body, but they occur around the hip or in the lower extremity 93% of the time: greater trochanter/hip (30%), thigh (20%), pelvis (19%), knee (16%), gluteal region (6%), lumbosacral area (3%), abdominal area (1%), calf/lower leg (2%), and head (0.5%).
The exact incidence of internal degloving injuries is impossible to determine because small injuries resulting in insignificant or minor fluid collections may not be clinically significant. Furthermore, even large internal degloving injuries are frequently missed due to either delayed presentation or the presence of distracting injuries. Internal degloving injuries do not typically occur in isolation. Morel-Lavallee lesions are frequently associated with and complicate the treatment of fractures of the pelvis, acetabulum, or proximal femur. There is a very wide range of associated rates between pelvic or acetabular fractures and Morel-Lavallee lesions.
Normal skin and musculoskeletal anatomy include the following general layers from superficial to deep: skin, subcutaneous fat, superficial fascia, deep fat, deep fascia, muscle, bone. When a mechanism occurs that causes a tangential shearing of these layers, an internal degloving may take place. Essentially, the bone, muscle, and deep fascia shear one way, and the more superficial layers slide the opposite direction. This event transects the perforating arteries and lymphatics that are traversing the fascial layers and leads to a collection of blood, lymphatic fluid, and necrotic fat in the newly created potential space. In addition, local inflammation and increased cellular permeability of nearby viable cells can add to the expansion. Over time, the body tries to sequester the lesion leading to either resorption of the fluid by nearby cells or a pseudocapsule formation and maturation of the fluid collection. As with any subdermal fluid collection, especially with necrotic tissue present, there is the possibility of infection. Another concern is the viability of the skin overlying the zone of injury. Two mechanisms are considered at fault for the cutaneous injury. First, the destruction of the skin and subcutaneous layers directly from the trauma leading to necrosis and second, the blood flow from the rich vascular plexus in the dermis is interrupted, which allows the skin to become ischemic and eventually die.
Internal degloving injuries have been described to appear in the immediate post-traumatic period or a delayed or chronic fashion. In the polytraumatized patient, there are often distracting, and life-threatening injuries present and the clinical stigmata of the degloving injury are inconsistent and can be delayed for several days. These facts, coupled with a patient population that has an ever-increasing average BMI, results in an injury that is overlooked 33% of the time. Clinically, the practitioner should carefully evaluate the skin overlying a potential internal degloving injury for ecchymosis, edema, fluctuance, skin hypermobility, and decreased cutaneous sensation. With increasing chronicity, the area affected may enlarge, and skin overlying can become firm and painful, indicating the encapsulation of the fluid collection.
If the diagnosis is suspected clinically, large-bore needle aspiration of the area may be attempted to aid in diagnosis.  Additional diagnostic methods include ultrasound, CT, and MRI. Ultrasound may show the collection as anechoic or hypoechoic with or without fluid-fluid levels just superficial to the deep fascia. Often, the trauma or orthopedic workup will include a CT of the pelvis, which can be utilized if the scan encompasses the injury. However, the diagnostic imaging of choice for an internal degloving injury is MRI. Acute lesions appear hypointense on T1- and hyperintense T2-weighted MRI. In more subacute lesions, the lesion is hyperintense on T1- and T2- and the pseudocapsule is identifiable as a hypointense peripheral structure on both T1- and T2-weighted images. Mellado and Bencardino described six types of internal degloving injuries based on the age of the injury, the size and shape of the fluid collection as well as MRI intensity and enhancement patterns. The spectrum ranges from simple seroma to more chronic complex infected fluid collections. The classification system is useful to guide management as the disease manifests.
The management of internal degloving injuries will depend on the overall clinical picture of the patient, including associated fractures, expected surgical course, and planned incisions. Also important is a careful assessment of the extent of devitalized and at-risk tissue, including initial viability of skin and size of the fluid cavity. Management can consist of compressive therapy, needle aspiration, sclerodesis, limited or radical surgical irrigation, and debridement. Several case series demonstrate validity for non-operative management with compressive wrap with occasional serial aspiration. This conservative management is reserved for asymptomatic or minimally symptomatic smaller lesions (<50 mL) with viable overlying skin. In such lesions, which fail to resolve with compression and aspiration alone, sclerodesis has been successful in some trials using several agents, including talc, ethanol, and doxycycline. As the lesion size increases, the probability of non-operative success decreases, and aspirating more than 50 mL of fluid was much more common among lesions that recurred (83%) than among those that resolved (33%). Therefore, it is recommended that an internal degloving injury of more than 50 mL of fluid prompts operative intervention. Shen published a literature review of 21 articles that noted superior outcomes for surgically managed lesions compared with conservative options. Operative incision and drainage is the standard of care in large lesions, especially those with skin necrosis. Hudson reported a prospective series on internal degloving injuries with an average volume of 120 mL. They used a single small incision to drain the hematoma with compression bandages post-operatively. They published good results with only 1 of 16 patients requiring skin grafting. Hak proposed more involved surgical intervention in 1997 after doing a retrospective review of 24 Morel-Lavallee lesions. Their technique involved an incision in the middle of the degloved area, cultures of the cavity, evacuation of hematoma with aggressive irrigation and debridement of necrotic fatty and connective tissue. The authors believed that primarily closing the incision resulted in a higher complication rate and thus proposed leaving wounds open and packed with gauze saturated in dilute Betadine for a few days before changing the dressings to saline-saturated dressings. Nearly all their patients had associated pelvic or acetabular fractures, and the Morel-Lavallee lesion was usually debrided at the time of the orthopedic procedure. In their series, they found 46% of the patients had positive bacterial cultures at the time of debridement with surgery performed on average 13.1 days after the injury. They reported successful healing in all wounds allowed to heal by secondary intention, with only two patients undergoing revisions for cosmetic concerns.  Tseng and Tornetta describe a two or three 2-cm incision technique with incisions at both the proximal and distal ends of the injury for hematoma drainage, brushing of the cavity, pulse lavage irrigation, and placement of a low-pressure drain connected to wall suction to limit reaccumulation of fluid. Over fifteen percent of the patients in their series had bacterial colonization at an average operative date of 3 days after injury, but all patients in their series had complete resolution. The authors attribute their decreased bacteria culture-positive percentage intraoperatively to earlier surgical intervention, averaging 10 days sooner than Hak's study. Various other surgical techniques have been described, but overall, no single surgical technique has been shown to be superior. The decision to close the wound primarily is left to surgeon preference, with negative pressure dressings proving useful in assisting with closure and graft bed preparation in these injuries.
Differential diagnoses for internal degloving injuries include seroma, abscess, vascular injury, compartment syndrome, and deep venous thrombosis. However, history and physical exam, coupled with appropriate imaging, should be able to direct the clinician to the correct diagnosis. In the acute trauma setting, a seroma or abscess should be less likely. A vascular injury, while possible, should be ruled out with a distal neurovascular exam, ankle-brachial index, and CT angiogram if necessary. Likewise, a deep venous thrombosis would most likely have more generalized limb swelling and could be easily evaluated for with duplex ultrasound. Compartment syndrome of the thigh is rare and, while possible, should be ruled out by the physical exam. If in question, compartment pressure measurements can be obtained.
As discussed, most of the literature has demonstrated that with identification and proper surgical management of Morel-Lavallee lesions, complete resolution can be obtained. Recurrence, infection, wound healing issues are the most likely complications.
Specifically, recurrence is the most common complication, and rates differ with treatment modalities. Percutaneous aspiration alone is associated with the highest risk of recurrence at approximately 56%, compared to compression wrapping and observation at 19%. Lower rates of recurrence are reported with proper operative management. Recurrence is more likely with larger lesions, but the location of the degloving injury does not seem to have an impact on the recurrence rate. If there is a return of the fluid collection, management options include repeat surgical drainage, percutaneous drain placement, negative pressure wound therapy, and sclerotherapy. If a patient has a large chronic lesion and operative management is going to be attempted, one should follow the same basic principles as for acute injuries, but more focus should be placed on the eradication of the dead space and thorough excision of the pseudocapsule. Skin necrosis is another stated complication. Risks for developing necrosis of the skin overlying the lesion are delay in identification/treatment and large lesion size. Plastic surgery referral may be necessary for wound coverage, tissue rearrangement, and management of cosmetic concerns that may arise  Bacterial consolidation is common in Morel-Lavallee lesions and is a worrisome issue with prompt evacuation desirable as untreated lesions can progress to infection or even necrotizing fasciitis. Hudson reported an early infection rate of 56%, while another series showed 25% of patients develop an infection. Tseng and Tornetta recommend continuing antibiotic coverage throughout the time any drain is present and had a lower infection rate in their study. Morel-Lavalle lesions complicate the care of orthopedic injuries - one retrospective study reported an 8.4 times increased risk of postoperative infection after acetabular fracture fixation in the presence of a Morel-Lavallee lesion.
Patients that suffer internal degloving injuries may have a host of orthopedic and other injuries at the time of presentation. Discussion with family and patient are paramount in setting expectations for the clinical course. They should be informed that the internal degloving injury is uncommon and may complicate any fractures in the area; however, surgical treatment is usually successful with complete resolution being the goal.
During the hospital and rehabilitation course, these patients will undoubtedly see many different medical teams. The initial evaluation and stabilization efforts are likely to be performed in the emergency department by the trauma service. When a fracture is present, the orthopedic surgeon is also involved early in the care process and responsible for definitive care of the associated orthopedic injury and potential surgical wounds and incisions. A thorough exam by these initial providers may identify concern for internal degloving early in the hospital course and limit complications during treatment as well as decrease the incidence of missing these often overlooked injuries. [Level 3] Radiologists can play an important role by having a high index of suspicion when evaluating the advanced imaging performed on high energy trauma patients. [Level 5]
Plastic surgery consultation may be of use in assisting with wound management. While often not involved in performing the initial drainage of the lesion - they are frequently consulted for wound coverage, chronic lesions, and tissue rearrangement. The plastic surgeon may also assume care in an outpatient setting for contouring or cosmetic procedures after the initial wound is healed. [Level 4] In the setting of infection, particularly septic arthritis or osteomyelitis, infectious disease consultation is of benefit in directing antibiotic choice and duration. Nursing staff often has the most direct patient contact and is typically responsible for daily dressing changes, drain stripping, and volume recording, on top of their standard duties. Physical therapy should be considered when not contraindicated by comorbid injuries. Edema control may improve wound survival, and scar modalities may aid cosmesis, as well as these providers may help patients regain mobility. Internal degloving injuries can cause significant morbidity that can complicate traumatic injuries, and successful treatment requires a collaborative, multimodal effort.
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