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Soft Tissue Reconstruction 

Soft Tissue Reconstruction
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Soft Tissue Reconstruction
DOI:
10.1093/med/9780198849360.003.0008
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date: 29 November 2020

Summary

  1. 1. All open fractures must be covered with well-vascularised soft tissue within 72 hours of the injury to achieve infection-free bony union.

  2. 2. If internal fixation is used, definitive soft tissue coverage should be achieved at the same time.

  3. 3. Dressings, including negative pressure wound therapy, can temporise for cover following wound excision but should not be used as a substitute for definitive flap coverage.

  4. 4. The medial fasciotomy incision is used to raise local fasciocutaneous flaps or to access the posterior tibial vessels for microsurgical anastomosis in free flap reconstruction.

  5. 5. Local fasciocutaneous flaps are usually best reserved for patients with relatively low-energy injuries and a limited zone of injury.

  6. 6. Experimental data suggest that coverage with muscle leads to improved healing of fractures. However, there is currently little clinical evidence to support the use of one form of soft tissue cover over another for open fractures of the lower limb. When choosing a flap, careful consideration should be given to donor site morbidity.

Types of soft tissue coverage

Soft tissue coverage may be in the form of local or free flaps, and may comprise muscle, fasciocutaneous tissues, or both. Flap selection depends on multiple factors, including the size and location of the defect following wound excision, availability of flaps, and donor site morbidity. Additionally, there is increasing evidence to support the biological contribution of soft tissue flaps in fracture repair by providing the optimal availability of growth factors as well as a source of regenerative stem and progenitor cells (1).

Planning and incisions

We recommend that the incisions used to raise local fasciocutaneous flaps as well as to access vessels for microsurgical anastomosis of free flaps are based on the medial fasciotomy incision (see Figure 3.1, Chapter 3). The same incision will have been used to provide access for wound excision of the open fracture. This minimises the risk of damaging the perforating vessels that supply the overlying skin whilst providing good access to the posterior tibial vessels. The medial incision is placed 1.5 cm posterior to the medial subcutaneous border of the tibia and lies anterior to the posterior tibial artery. Placement of the incision too anteriorly risks exposure of the tibia in the tense, swollen limb. Conversely, if the incision is too posterior, it will lie behind the fasciocutaneous perforators and hence preclude the use of flaps based on them. Therefore, accurate placement is essential and we recommend marking the anatomical landmarks before making the incisions.

Local flaps

In general, local flaps are best suited for defects with a limited zone of injury from low-energy trauma. The flap chosen should lie outside the zone of injury to minimise complications such as partial or complete necrosis. A common cause of failure is raising fasciocutaneous flaps in areas where the skin has been degloved. Care must also be taken to ensure the fracture is covered and the entire flap survives. Partial or tip necrosis is equivalent to complete flap failure as this would mean conversion back to an open fracture with the associated risks of poor outcomes. Therefore, local flaps should be reserved for relatively low-energy injuries where the zone of injury is limited. For higher energy injuries and those with degloving free tissue transfer is necessary.

Local fasciocutaneous flaps

An understanding of the topography of lower limb angiosomes together with accurate mapping of perforating vessels has enabled the reliable use of local fasciocutaneous flaps (2, 3) (Figure 8.1). The most commonly used are based on the septocutaneous perforators that arise reliably from the posterior tibial artery with at least one vena commitans on the medial aspect of the tibia (4, 5, 6, 7). Proximally based flaps extending as far distal as the ’15 cm perforator’ (located about 15 cm proximal to the tip of the medial malleolus) can be raised reliably, especially if incorporating the saphenous vein and the artery that runs with the saphenous nerve about 1 cm behind. The anterior border of the flap lies 1.5 cm posterior and medial to the medial subcutaneous border of the tibia, coinciding with the medial fasciotomy incision. The posterior margin can extend to the posterior midline, taking care to avoid injuring the sural nerve. The deep fascia is included within the flap to protect the delicate vascular plexus that lies just superficial to the fascia. It is important to preserve the filmy vascularised tissue overlying the proximal part of the Achilles tendon so as to leave an adequately vascularised bed for a split skin graft to cover the flap donor site.

Figure 8.1 The angiosome concept: an angiosome is a block of tissue (skin, muscle, bone, or a combination) supplied by an artery and the accompanying veins. It can survive when isolated on this pedicle. (a) The posterior tibial artery is an example of an axial artery along which a series of perforators arise to supply the overlying fascia and skin. Each perforator supplies an angiosome. (b) When the perforator to an angiosome is occluded, ‘choke’ or ‘variable resistance’ vessels, which connect to the adjacent angiosome, dilate to maintain the blood supply of the affected angiosome. (c) Usually, a perforator will only reliably perfuse one adjacent angiosome through opening of the intervening choke vessel. Therefore, it is possible to raise a fasciocutaneous flap comprising two angiosomes based on a single perforator to cover local defects. (d) However, attempts to capture more than a single adjacent angiosome risk necrosis of the distal part of the flap.

Figure 8.1 The angiosome concept: an angiosome is a block of tissue (skin, muscle, bone, or a combination) supplied by an artery and the accompanying veins. It can survive when isolated on this pedicle. (a) The posterior tibial artery is an example of an axial artery along which a series of perforators arise to supply the overlying fascia and skin. Each perforator supplies an angiosome. (b) When the perforator to an angiosome is occluded, ‘choke’ or ‘variable resistance’ vessels, which connect to the adjacent angiosome, dilate to maintain the blood supply of the affected angiosome. (c) Usually, a perforator will only reliably perfuse one adjacent angiosome through opening of the intervening choke vessel. Therefore, it is possible to raise a fasciocutaneous flap comprising two angiosomes based on a single perforator to cover local defects. (d) However, attempts to capture more than a single adjacent angiosome risk necrosis of the distal part of the flap.

Flaps should not be based on the fallacious length:width ratio (8), but instead should be based on rational design to incorporate no more than one adjacent perforator (Figure 8.2). Distally based fasciocutaneous flaps are based on relatively constant septocutaneous perforators that arise from the posterior tibial artery and venae commitans around 10 and 15 cm proximal to the tip of the medial malleolus (9) (see Figure 3.1, Chapter 3). Like the proximally based flaps, the anterior border of the flap coincides with the medial fasciotomy incision, 1.5 cm posterior to the medial subcutaneous border of the tibia in adults. Extensive degloving precludes the use of these local flaps due to damage to the perforators as well as the supra- and sub-fascial vascular plexuses. The dominant perforator is directly visualised and, if suitable, the flap is then planned in reverse to ensure that it can be transposed without undue tension. The long saphenous vein should either be excluded from the anterior border of the flap or, if this is not possible, ligated at the base of the flap to prevent venous congestion of the flap as the venae commitans of the perforator will struggle to cope with the venous drainage from the medial side of the foot. Like the proximally based flaps, the deep fascia is included to protect the prefascial vascular plexus. Islanding of the flaps to create the so-called propeller flaps allows turning through a greater angle and a neater inset but may be associated with increased complication rates. In a multicentre prospective study, the Lower Extremity Assessment Project (LEAP) Study Group found that use of local fasciocutaneous flaps for tibial defects following high-energy injuries was associated with higher complication rates compared with free flaps (10). Whilst there were no significant differences between the free and local flap groups with respect to overall complication rates, among those with the most severe grade of underlying bone injury, limbs treated with a local flap were 4.3 times more likely to have a wound complication requiring intervention than those treated with a free flap. In a systematic review and meta-analysis of 40 studies on perforator-pedicled propeller flaps in lower limb defects, of which 55.2% were post-traumatic, complications were found in 25.2%, with a partial necrosis rate of 10.2% and complete necrosis rate of 3.5% (11). The authors identified age of over 60 years, diabetes, and arteriopathy were significant risk factors.

Figure 8.2 Local fasciocutaneous flap options. (a, b) Proximally based flap based on the medial inferior genicular artery/saphenous artery and proximally based perforators to cover defects around the knee. (c, d) Distally based flap based on the 10 cm perforator to cover distal third anterior tibial defects. Both flaps are planned so that the anterior border coincides with the medial fasciotomy incision. The donor site is then resurfaced with a split thickness skin graft.

Figure 8.2 Local fasciocutaneous flap options. (a, b) Proximally based flap based on the medial inferior genicular artery/saphenous artery and proximally based perforators to cover defects around the knee. (c, d) Distally based flap based on the 10 cm perforator to cover distal third anterior tibial defects. Both flaps are planned so that the anterior border coincides with the medial fasciotomy incision. The donor site is then resurfaced with a split thickness skin graft.

The sural artery flap, based on the sural artery and venae commitans that accompany the sural nerve, has been advocated to cover defects in the lower third of the leg. The supplying perforator arises from the peroneal artery, which is often injured when the fibula fractures. A systematic review and pooled analysis of 907 patients with mixed indications including trauma (39.4%), ulcers (16.3%), and open fracture (10.5%) found a complication rate of 26.4%, with a total flap loss rate of 3.2% (12). However, a retrospective review of 70 sural artery flaps utilised for various indications including acute trauma reported an overall complication rate of 59%, with partial or tip or complete necrosis in 35% of all cases (13). Therefore, we do not recommend this flap for patients with open fractures.

Local muscle flaps

There are limited options for local muscle coverage in the lower limb (14). The medial or lateral heads of the gastrocnemius provide limited coverage around the knee but do not extend to cover the proximal pole of the patella or distally to the proximal third of tibia. The larger medial head can reach further and is therefore more commonly used. Whilst normal gait is possible following use of one head of the gasctronemius, functional deficit, including peak force generated during push-off, can be detected during more demanding tasks such as fast or uphill walking (15).

The soleus muscle flap has been used for coverage of middle third tibial defects if based proximally, or even distal third if based distally. However, in addition to the proximal pedicle, the muscle relies on multiple segmental perforators, some of which require division for mobilisation. This precarious blood supply together with its close proximity to the posterior surface of the tibia and inclusion in the zone of injury mean that it is an unreliable option for the reconstruction of open fractures (16).

A tibialis anterior muscle turnover flap can cover long narrow defects over the tibial crest but only for defects up to 1 cm wide (17).

Free flaps

Free tissue transfer has revolutionised the management of open fractures. Free flaps are preferred to local flap reconstruction for patients with multiple co-morbidities such as diabetes, venous insufficiency, and peripheral arterial disease. This subgroup of patients is at high risk of local flap failure and is often erroneously considered to be unsuitable for free flaps. Careful optimisation of the patient and techniques can result in free flap success rates in open fracture of over 90% and similar to those for elective reconstructive surgery (18). Microsurgical free tissue transfer also provides a wide choice for reconstruction of the defect. Flap selection depends on the size and location of the defect, location of the recipient vessels (which are ideally outside the zone of injury), as well as the biological contribution of the constituent tissues.

Fasciocutaneous versus muscle flaps

Every flap option is associated with its own advantages and disadvantages. Muscle flaps easily conform to complex defects. Although initially bulky, the oedema can be controlled with a pressure garment once the overlying skin graft is stable and any external fixator has been removed, and the denervated muscle soon atrophies and does not require thinning. A disadvantage of muscle flaps is that the overlying skin graft may be susceptible to minor trauma especially around the foot and ankle, and the flap can be difficult to raise and re-inset if further open surgery at the fracture site is required. Fasciocutaneous flaps have the advantage of replacing ‘like with like’ without sacrificing muscle function. They can be debulked by liposuction and can therefore provide a good contour and are more resilient to shear forces than a split skin graft.

There is no clinical evidence currently to support the use of one form of soft tissue cover over another for open fractures of the lower limb. Published evidence consists almost entirely of descriptive, retrospective, underpowered observational case series (level IV evidence) with major discrepancies in outcomes measures, thus precluding any meaningful meta-analysis. Few of these studies have compared muscle flaps with fasciocutaneous flaps specifically and those that did were limited by a lack of statistical power and case heterogeneity. A retrospective review of muscle and fascial flaps, both local and free, in lower extremity trauma found that complications were related to the severity of injury rather than the type of soft tissue coverage (19). Another study comparing muscle and fasciocutaneous flaps found that donor site morbidity was similar in both groups at around 4% (20). Comparison of free muscle and fasciocutaneous flaps for lower extremity reconstruction found no difference in major or minor complication rates (21), although patients who underwent fasciocutaneous flap reconstruction were more likely to require revision surgery to improve cosmesis. A retrospective review of patients with open tibial fractures treated with either free muscle or fasciocutaneous flaps showed that equivalent numbers went on to achieve bony union and could walk unaided by 2 years and there was no difference in the rates of complete flap survival and chronic osteomyelitis (22). The authors found that muscle conformed better to complex defects but fasciocutaneous flaps better tolerated secondary surgical procedures. Another recent retrospective review found similar rates of limb salvage and functional recovery when comparing muscle versus fasciocutaneous free flaps in acute traumatic injuries as well as chronic traumatic sequelae, with overall rates of flap loss and limb amputation of 8% and 6%, respectively (23). In patients with grade IIIB injuries and/or exposed defect hardware, fasciocutaneous flaps were more likely to require bone grafting for non-union compared with muscle flaps. It is not possible to determine whether this is due to differences in undocumented primary injury characteristics, the biological effect of the flap on bone repair, or other confounders.

In contrast, there is increasing experimental evidence to show that muscle coverage of diaphyseal fractures leads to superior fracture repair compared with fasciocutaneous tissue (24, 25, 26, 27, 28). Both fasciocutaneous and muscle flaps serve as a vascular supply to the fractured bone ends that have been stripped of periosteum and undergone disruption of the endosteum (24, 25, 28). Therefore, whilst vascularity is essential for fracture repair, other biological factors become limiting once the adequate blood supply threshold has been crossed. Although both fasciocutaneous tissue and muscle harbour mesenchymal stromal cells, human muscle-derived stromal cells exhibit significantly greater osteogenic potential than those from fasciocutaneous tissue, including both skin and adipose, and are equivalent to those from bone marrow (29). Therefore, muscle in direct apposition with diaphyseal fractures may promote repair by providing a readily available pool of mesenchymal stromal cells, which can undergo osteogenic differentiation into bone-forming osteoblasts especially in the post-traumatic inflammatory environment (29, 30, 31). Furthermore, muscle also provides an anabolic environment to bone through the expression of growth factors (32). Studies comparing bacterial clearance found superior elimination under muscle compared with fasciocutaneous tissue, despite a higher blood flow in the latter (33, 34).

In the absence of robust clinical evidence and based on the available experimental data, consideration may be given to the use of chimeric flaps, such as the free anterolateral thigh flap including a segment of vastus lateralis, to cover tibial shaft fractures (35). This would provide the advantage of avoiding the unsightly skin grafted donor site below the knee whilst retaining the biological benefits of muscle in direct apposition to the fracture site.

Recipient vessels for microsurgical anastomoses

The site of anastomoses to the recipient vessels should be selected ideally outside the zone of injury and preferably proximal to the defect. Intimal injury can be difficult to recognise from external inspection and anastomoses just proximal to a patent small vessel supplying the adjacent muscle ensures that the surgeon is outside the zone of injury. The posterior tibial vessels are less likely to have been injured during the initial trauma (36, 37) and are more reliable and accessible as recipient vessels than the anterior tibial vessels. In a retrospective review of 68 patients with open tibial fractures requiring free tissue transfer, 18 patients had 22 vascular injuries (4 patients had injuries to 2 vessels) that were diagnosed using pre-operative computed tomography (CT) angiography (38). In another series of severe open tibial injuries (37), 80.6% of 191 patients underwent vascular imaging. A total of 57.1% had abnormal findings on imaging compared with 11% on initial evaluation and there was a false positive rate of 7.8%. In a randomised controlled trial in 157 patients with isolated open tibial fractures and initially adequate circulation (39), the authors compared the outcomes of patients who underwent conventional wound excision and primary skeletal stabilisation with those who had routine exploration and repair of the major vessels and nerves. In the second group, 28.2% of patients were found to have occult major vascular injuries, and outcomes at both intermediate and long-term follow-up were superior. These studies suggest that preoperative vascular imaging can assist in preoperative planning. However, imaging of the vasculature should not delay operative intervention particularly when there is the limb is devascularised (see Chapter 10). In the UK, many emergency units now offer full body CT scans for trauma patients, hence CT angiogram should not cause excessive delays and is recommended.

We recommend that the artery is anastomosed end-to-side to preserve the distal vascular supply and a single vessel leg is not a contraindication to it being used as a recipient. At an incidence of 7.2%, venous insufficiency was the commonest cause of re-exploration in free tissue transfers to the lower extremity, and anastomoses to the superficial venous system group were associated with a higher rate of venous insufficiency and partial flap loss compared with the deep venous system group (40). The number of venous anastomoses that should be performed remains controversial. In elective free tissue transfer, the use of two venous anastomoses has been found to result in a significant reduction in the rate of venous congestion without significantly impacting on either complication rate or operative time (41). Two retrospective reviews of over 300 free flaps each for lower limb reconstruction found that anastomosis of one rather than two veins did not significantly reduce the rate of surgical complications including total flap loss (40, 42). However, a recent retrospective study of 361 free flaps for Gustilo–Anderson grade IIIB and IIIC injuries (43) found that two venous anastomoses demonstrated a four-fold decrease in complication rates compared with a single venous anastomosis. Furthermore, venous size mismatch of over 1 mm (when anastomosing large to small) was an independent predictive factor for total flap failure.

Many patients suffer from postoperative oedema of the lower limb and the flap. Various dangling protocols and compression stockings have been advocated to aid lymphatic and venous drainage. A recent systematic review of dangling regimes after free flap surgery to the lower limb (44) found that a 3-day flap training regime is sufficient for physiological training and that it may be appropriate to start dangling as early as postoperative day 3. However, robust evidence for dangling and compression is currently lacking (45, 46).

Conclusion

Definitive soft tissue coverage for open fractures should be achieved within 72 hours of the injury if it cannot be performed at the time of wound excision (47). If internal fixation is used, definitive coverage should be achieved at the same time (47). An understanding of the topography of angiosomes of the leg permits raising of local fasciocutaneous flaps reliably; these should be reserved for low-energy injuries where the flap donor site has not been degloved and, in the case of distally based flaps, direct visual inspection of the supplying perforator confirms suitability. High-energy fractures with a wide zone of injury suitable for reconstruction are best covered with free flaps, with the posterior tibial vessels as the preferred recipient vessels for defects over the leg.

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