Soft Tissue Coverage

Surgery

January 17, 2023

≈21 min

Introduction

Soft tissue injuries represent a heterogeneous constellation of surgical problems. Given the numerous roles of the integument, musculature, connective tissues and neurovascular structures, a spectrum of injuries from simple to complex may occur following trauma.

To achieve optimal form and function, prompt triage is required to mitigate downstream complications including pain, bleeding, infection, and impaired wound healing. Goals of reconstruction must include strategies to mitigate these sequelae of injury. After any life-saving needs are addressed following acute trauma, the plastic surgeon will optimize the recipient site for a given reconstruction. Once the wounds have been optimized, and the type and extent of soft tissue loss have been established, the surgeon can select the appropriate reconstructive strategy.

Historically, the “reconstructive ladder” has been the central paradigm within reconstructive plastic surgery. It is comprised of rank-ordered surgical options in increasing surgical complexity, where the simplest option to achieve reconstructive goals was often considered the best. Our current model is more like an “elevator” where the correct floor is selected based upon the recipient site requirements, donor site morbidity, patient preference as well as surgeon’s preference, skill and resources^[1].

Soft tissue deficits can result from direct tissue loss due to sharp or high-velocity trauma or as a manifestation of local ischemia and/or hypoxia. This often is accompanied by concomitant or resulting necrosis and protein denaturation that requires debridement to eradicate dead tissues that may serve as loci for infections and generate an interface of healthy tissue that can support reconstruction efforts. Crush or burn mechanisms of injury are often associated with possible life-threatening processes including compartment syndrome or under-resuscitation due to insensible losses and hypermetabolic states requiring fascio-/escharotomies and aggressive fluid repletion, respectively^[2].

After stabilization, as in the other mechanisms of soft tissue damage, regions of injury are optimized to minimize the degree of necrosis: gross contamination is irrigated, displaced but available tissues from lacerations or avulsions are generally secured to their original locations, and any residual soft tissue deficits are covered with sterile dressings for serial evaluation and preoperative planning as necessary.

This article could not encompass the entirety of reconstructive options; however, governing principles and common reconstructive options will be discussed.

Acute Resuscitation: Advanced Trauma Life Support Protocol (ATLS)

In settings of acute trauma, it is imperative that ATLS principles are first implemented to ensure stabilization of the patient with a focus on mortality over morbidity^[3].

Code leaders direct teams to ensure (A)irway patency, intact (B)reathing mechanics, sufficient (C)irculatory system function to support sufficient perfusion pressures to critical organ systems, management of any other life-threatening systemic (D)isability, and full examination and (E)xposure. After initial resuscitation, plastic surgeons are essential contributors in the transition to the secondary survey.

Burn resuscitation

In settings of patients with greater than or equal to 20% total body surface area (TBSA) burns of deep partial thickness (white, leathery, non-blanching), patients require substantive fluid resuscitation to compensate for acute insensible losses. The total need for crystalloid resuscitation in the first 24 hours may be calculated using the Parkland formula: 4cc/kg (3cc/kg in children) * weight (kg) * %TBSA (Total Body Surface Area).

The total volume is divided in half, with the first half delivered over 8 hours (from the time of the burn, not on arrival to medical care) and the second half delivered in the remaining 16. Subsequent fluid requirements are then titrated to end organ parameters, namely urine output between 0.5-1cc/kg/hr in adults and 1.0-1.5 cc/kg/hr in children in conjunction with other vital signs to assess current intravascular volume status^[4].

Compartment Syndrome

In settings of severe burn or musculoskeletal polytrauma, teams must exercise a high index of suspicion for restrictive physiology i.e. compartment syndromes within the trunk or extremities. In the setting of circumferential burns, the necrotic and desiccated tissues lose significant compliance creating increased internal pressures in the setting of inflammation and edema.

In crush injuries, ischemia-reperfusion, high-velocity trauma, or arterial disruption can also lead to markedly elevated tissue pressures below the deep fascia. These elevated compartment pressures ultimately lead to a predictable cascade of venous congestion, arterial insufficiency, and critical ischemia/hypoxia leading to irreversible death of connective tissues and vital structures leading to disastrous disability^[5].

Furthermore, dying muscle can also release critical amounts of free myoglobin causing acute kidney injury and potassium that may cause aberrant cardiac conduction and severe cardiovascular collapse. Circumferential burns and compartment syndrome require emergent surgical attention with escharotomy or fasciotomies, respectively.

Open fractures

Open fractures add an additional layer of complexity due to the exposure and contamination of bone. Subsequent infection can lead to impaired bone healing, loss of skeletal stability and secondary limb loss. Open long bone injuries require antibiotic prophylaxis, typically a first- or second- generation cephalosporin (Gustilo grade I and II) with addition of aminoglycosides in more severe injuries (Gustilo grade III) with frank contamination^[6].

In addition, aggressive acute serial debridement of contamination and devitalized tissue should be immediately following by fixation and coverage. In general, this should ideally occur once the wound is adequately prepared and within the first week following injury.

The Reconstructive Ladder/Elevator

After ensuring adequate patient resuscitation and wound preparation, reconstruction may truly begin. The reconstructive ladder provides a conceptual framework to approaching soft tissue deficits in increasing levels of surgical complexity: secondary intention, primary closure, delayed secondary closure, graft, tissue expansion, local tissue rearrangement/random pattern flaps, pedicled/axial flaps, and free tissue transfer. Contemporary paradigms more resemble an elevator that may “skip” certain rungs to best optimize function and aesthetics.

The selection of a reconstruction strategy is governed in part by the degree and extent of tissue deficit along with the quality of wound bed. In regions of vast tissue loss with loss largely limited to skin, skin grafts can provide extensive superficial coverage. Grafts, however, are entirely reliant on the recipient site for their perfusion and are particularly vulnerable to local infection.

In contrast, flaps are volumes of tissue perfused either by a presumed network of small vessels underneath the skin and underlying tissues (random pattern) or a named blood vessel and its venae commitantes (axial pattern), constituting a vascular supply, a pedicle, to the mobilized tissue. They can be constituted by a single or multiple tissue types and mobilization of the flap along with its pedicle allows for coverage of defects that is independent of local vascularity. Although these flaps may provide a hardier form of coverage, they are limited by the dimensions of tissue perfused by the pedicle, the extent to which they can be mobilized, as well as the expense of increased donor site morbidity. In situations where an appropriate flap does not have a sufficiently long pedicle to allow local or regional transfer, free tissue transfer can be performed using microsurgery to reestablish perfusion using an artery and venous source near the wound.

In addition to wound characteristics and available reconstruction options, the realities of patient preferences with regards to considerations such as recovery time, quality and durability of reconstruction and donor site morbidity should always be considered. Similarly, surgical experience, time and resources introduce realities into decision-making that may affect the reconstructive approach.

Healing by secondary intention vs. primary closure: Lacerations/Avulsions

Lacerations and avulsions should be examined for depth of injury (epidermis, dermis, subcutaneous fat, muscle, connective tissues) and involvement of vital structures (ligaments, tendons, veins, arteries, and nerves). In sensitive regions including the face and extremities, examination for intact nerve function and adequate distal to wound must also be carefully performed. In the absence mitigating vital structure injuries, hemostasis should be achieved, and the wound thoroughly irrigated with normal saline.

If the wound is acute and clean, it may be repaired with a focus on reducing tension to minimize scarring and wound healing delay: depending on the degree of contamination and local tissue tension a 3-0/4-0 absorbable suture can be used for subcutaneous tissue approximation and a smaller caliber monofilament used to reapproximate the skin edges.

If the wound or a portion of the wound cannot be closed without undue tension, it may be best to allow the wound to simply heal secondarily with regular dressing changes. Avulsion injuries should be assessed to determine whether they are in fact viable. If the avulsed segment of skin is not viable, it should be removed, thinned out as much as possible and then placed over the wound as a skin graft.

If the avulsed segment is viable, it may be tacked down in place, approximating the wound edges. In settings where the viability of affected soft tissues is in question, it may be best to observe the wound assess over several days with regular dressing changes. At this point, the wound can either be debrided and the reconstruction options reassessed, or a delayed wound closure performed.

Special considerations for the face

Facial injuries require meticulous examination to exclude injuries to vital structures such as the facial nerve as well as the parotid duct. Not only do some of these injuries have long time functional implications, but some may impair wound healing when missed on the secondary survey.

It should also be noted that facial soft-tissues are very well perfused and even severely damaged structures such as the nose and ear, may be repaired directly despite complex injury. As such, debridement of specialized facial tissues at the time of presentation should be undertaken with caution or withheld until viability or necrosis is absolutely clear.

Special considerations for the hand

The forearm and hand have numerous vital structures that are often exposed to both blunt and penetrating trauma. Similar to the face, the distal hand and fingers should undergo careful assessment for neurovascular and musculoskeletal status as identification and repair of vital structures is integral to long term successful function of the limb. Although injuries to major vascular structures and tendons are typically clear, the extent of peripheral nerve injuries can be more subtle.

Vascular injuries compromising hand perfusion require prompt repair within hours to minimize necrosis and maximize functional outcomes. In the case of lacerations, major nerve repairs can similarly be performed with the caveats of minimal tension at the repair site and mobilization of the nerve endings only as much as necessary to achieve a protected, tension free repair.

In the case of crush injuries or penetrating high velocity missile injuries, the type and extent of nerve injury may be unclear. In these situations, it may be wise to withhold exploration (unless otherwise indicated) and reassess for return of nerve function as the nerve may be intact but in a state of neuropraxia. In addition, these types of nerve injuries may induce local injury proximally and distally along the nerve even if the nerve is no longer in continuity. If a major nerve disruption is discovered during initial wound exploration following these types of injuries, marking the nerve endings may be followed by secondary exploration, resection, and repair to avoid repairing injured nerve to injured nerve.

Skin Grafting

For soft tissue wounds primarily limited to the skin, skin grafting is an excellent reconstructive option. The technique is simple and generally familiar to all surgeons. However, successful grafting does require a non-contaminated field that is able to form granulation tissue. As such, exposed bone and tendon, missing periosteum and paratenon, are classically unable to support skin grafts. Split thickness skin grafts (STSG) are suitable to acutely covering greater surface areas due to less elastin and correspondingly reduced primary contraction^[7].

These grafts are also further stretched and expanded with meshing that minimizes the amount of donor tissue required and facilitate higher rates of survival. However, these grafts also inherently demonstrate greater secondary contraction as they heal. These grafts are typically harvested from lateral thighs, buttocks, or back due to their flat planes and thicknesses amenable to repeat harvest if necessary. In more cosmetically sensitive areas that require minimal secondary contracture (e.g., hand) at the expense of increased primary contracture or must withstand higher mechanical loads, full thickness grafts may provide better outcomes. For non-face recipients, groin is a typical donor. For specific regions of the face, pre/post-auricular and sometimes preclavicular donor sites can provide better color-matching^[8].

Grafts survive and heal in three distinct stages: diffusion of nutrients from the underlying wound bed (imbibition), anastomoses between donor site and graft vessels (inosculation), and ingrowth of nascent vessels (neovascularization). Grafts fail in the acute phase by several mechanisms that impair these stages of healing: separation of graft from wound bed via intervening fluid collection (seroma/hematoma), disruption of wound bed/graft contact and inosculating vessels(trauma/shear), and ongoing inflammation resulting in impaired proliferation and differentiation (infection). These graft sites must be carefully bolstered to apply consistent pressure.

Negative pressure wound therapy (NPWT) involve the use of porous sponges, overlying impermeable tape, and negative pressure via machines that can generate compression that is form-fitting and evenly distributed across even complex contours. These devices have routinely replaced bolsters for this post-surgical care. Fresh grafts that are placed over regions of active motion across joint spaces or muscle bellies are correspondingly immobilized and routinely also managed with a short-term course of antibiotics for infectious prophylaxis.

Random Pattern Flaps (Local Tissue Rearrangement)

For smaller soft tissue deficits without a suitable wound bed for graft survival, several strategies for local tissue rearrangement can be employed to cover any vital structure or mechanically stressed anatomical locations. These rearrangements primarily rely on random, scattered blood vessels that primarily course deep to the dermis i.e. the subdermal plexus. This “random pattern flap” thus is “pedicled” or derives its blood flow from the part of soft tissue that remains connected to its native anatomy. Furthermore, any liberated tissue that carries with it a known blood supply is termed a “flap”.

Each of the following local tissue rearrangements, or skin flaps, incorporates non-circumferential incisions, extensive undermining, and exhibit a different variety of pedicle to facilitate specific geometrical manipulations that will, with exploitation of the inherent elasticity of dermis, permit coverage of an adjacent defect: extensive undermining, Z-plasty^[9] (in series and combinations), advancement flaps (simple, VY, Moberg ^[10]), rotational flaps^[11], and transpositional flaps (Rhomboid/Limberg^[12], bilobed, propeller), (Figure 1).

**Figure 1:** Simple advancement flap; VY advancement flap; transpositional flap ( Rhomboid / Limberg )

One final iteration of this strategy includes the delayed flap, most commonly the abdominal or groin flap where a pedicled skin flap is lifted, and an extremity (often the hand) is covered with this abdominal tissue^[13].

Other similar examples include thenar flap for distal finger defects. The arm is immobilized to protect this coverage and subsequently after 2-3 weeks, the pedicle is transected and the abdominal flap is inset into the remaining defect with the donor site closed primarily.

Axial Pattern Flap

Larger soft tissue deficits or those with extensive depth involving the exposure of frank bone or critical neurovasculature, indicate a need for more robust coverage with thicker tissues. These coverage options are characterized by their axial pedicle, typically a named vessel or immediately downstream perforator and thus carry their own blood supply that has far more degrees of freedom and mobility than their aforementioned subdermal-pedicle counterparts.

“Pedicled flaps,” referring to these axial flaps with named source blood vessels incorporate a heterogeneous combination of tissues. The thinnest and most pliable are fasciocutaneous flaps that contain skin and the underlying fascia. Underlying muscle can be also included yielding a myocutaneous flap. And in certain instances, muscle alone can be mobilized as a muscle flap with an additional skin graft if superficial coverage is also needed; an intermediate option that can limit donor site morbidity by leaving the native skin behind.

The options for pedicled flaps are primarily restricted by the length of the perforating blood vessels and as such are defined by the spatial relationships between the defect location and the neighboring anatomy [Table 1].

Table 1: Anatomically derived flap options for defect coverage

	Local Tissue Rearrangement	Fasciocutaneous flaps (pedicle)	Muscle flaps (pedicle)
Head/neck	• Cervicofacial • Bilobed • Propeller • Nasolabial • Abbe/Estlander	• Forehead (supraorbital and supratrochlear aa) • Temporoparietal fascial (superficial temporal aa)	• Trapezius (transverse cervical aa)
Trunk	• Propeller • Transposition	• Thoracodorsal artery perforator (TAP) flap • Deep inferior epigastric perforator (DIEP) flap • Scapular flap (transverse branch of the circumflex scapular artery) • Superior gluteal artery perforator flap • Trapezius (dorsal scapular artery and superficial cervical artery)	• Pectoralis major (pectoral branch of thoracoacromial vs. internal mammary aa ) • Rectus abdominis (superior and inferior epigastric aa) • Latissimus (thoracodorsal vs. posterior intercostals) • Omental (gastroepiploic aa)
Upper extremity	• Propeller • Moberg • Finger crossover • Abdominal	• [Reverse] Radial forearm (radial artery) • Posterior interosseus artery • Lateral arm (posterior radial collateral) • Perforator • First dorsal metacarpal artery	• Flexor carpi ulnaris pedicle flap (ulnar artery/posterior ulnar recurrent artery) • Brachioradialis (radial artery/radial recurrent artery)
Lower extremity	• Propeller	• Reverse sural artery • ALT (descending branch of lateral circumflex artery off of SFA)	• Sartorius (branches off of SFA) • Gracilis (medial circumflex artery PFA) • Gluteus maximus (superior and inferior gluteal) • Gastrocnemius (medial and lateral sural aa) • Soleus (posterior tibial)

Options for coverage are anatomically restricted. In the lower extremity, the proximal and middle two-thirds are classically treated with pedicled gastrocnemius^[14] (medial/lateral sural artery) or soleus^[15] (perforators off of the posterior tibial artery). Smaller defects of the distal lower extremity and foot must be selected judiciously including medial plantar flap^[16] (medial plantar artery) for heel and lateral plantar defects and reverse sural artery^[17] (peroneal vessels) flap for the distal foot. Of note some of these flaps may have tenuous vasculature and can be utilized in a delayed fashion for more robust mobilized tissue.

Common upper extremity and hand flaps include the lateral arm flap^[18] (posterior radial collateral artery), posterior interosseus artery^[19] (PIA) flap, Littler flap^[20] and first dorsal metacarpal artery^[21] (FDMA). In significant defects of the face, especially the nose, a paramedian flap^[22] (supratrochlear artery) can be lifted and mobilized with subsequent division after delay.

Free flap

In situations where there is no ideal pedicled option typically in the distal segments of the appendicular skeleton and the face, a flap can have its pedicle transected with the whole flap and vessel transported to a distant recipient site and the donor pedicle subsequently anastomosed to new blood vessel at the recipient site with microsurgery, representing the pinnacle of the reconstructive ladder. Several common examples in the setting of acute trauma include extremity injuries, particularly with the lower limbs. Large and multi-layer defects in the distal third of the foreleg are a classic indication for free flap coverage, often with workhorse flaps from the anterior lateral thigh^[23] (ALT) based on the descending branch of the lateral circumflex artery or latissimus dorsi based on the thoracodorsal artery.

Other applications also include facial reconstructions, particularly of the mandible that require a vascularized portion of bone via free fibular flap^[24] (peroneal artery) or reconstructions of nasal segments with the radial forearm^[25] free flap in settings that make local options like the paramedian forehead flap untenable.

Special consideration

Acute trauma resulting in nerve injury or amputations infers an elevated risk of chronic pain and possible neuroma formation. In these types of injuries, as a part of reconstruction or revision, targeted muscle reinnervation^[26] (TMR) or regenerative peripheral nerve interfaces^[27] (RPNI) should be considered. Resection of neuroma and coaptation to donor distal motor branch (TMR) or free muscle graft (RPNI) mitigate neuroma formation or recurrence. These procedures may markedly reduce or prevent the genesis of peripheral pain.

Summary

Especially in the setting of trauma, the first priority is hemodynamic stabilization per ATLS
After adequate resuscitation and ruling out of compartment syndrome, wounds can be typically temporized with irrigation and conservative wound care
Optimize zone of injury which facilitates wounds to declare extent of damage
Diagnose the missing soft tissues and degree of deficits
Surgical planning with reconstruction goals encompass function and form
Select soft tissue coverage option per the reconstructive ladder/elevator
Miscellaneous considerations include extremity polytrauma and increased patient risk for developing neuroma

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