17 Supermicrosurgery Approach to the Lower Limb

Joon Pio Hong

Summary

Supermicrosurgery is manipulating vessels with diameters less than 0.8 mm. In flap surgery, this approach will allow an increase in the selection of recipient pedicles by using a perforator-to-perforator anastomosis approach. Decreased time of surgery, elevation of the flap by taking just a short segment of the perforator pedicle, minimization of any risk for major vessel injury, and utilizing collateral circulation in ischemic diabetic foot are some of the apparent advantages.

supermicrosurgery – perforator-to-perforator microsurgery – diabetic foot reconstruction – freestyle reconstruction

17 Supermicrosurgery Approach to the Lower Limb

17.1 Introduction

Reconstruction of the lower extremity using free flaps remains a difficult procedure. Although limb salvage rates have greatly improved over the past 20 to 30 years, major hurdles regarding single artery limb, atherosclerosis, involvement of hardware, frequent spasm, chronic infections, edema, complexity of lower limb trauma, and diabetes still make it very challenging even for experienced surgeons. ¹ In this age of reconstruction, we are faced with the challenge of achieving not only successful soft-tissue coverage but also functional recovery, chronic infected wound control, and cosmetic improvement. Evolutions in microsurgery have been noted from the days of experimental surgery, finger replantation, and now to perforator flaps and supermicrosurgery, and it has allowed achieving complex goals. These evolutions aim for better results and to minimize complications despite the innate risks of lower extremity soft-tissue reconstruction. The use of perforator-to-perforator supermicrosurgery has reduced complications in high-risk lower extremity reconstructions.

Lower extremity can be extremely difficult to reconstruct with poor outcome. Frequently the lower extremity reconstruction involves major vessel injury leaving only one major vessel to the leg, requires long pedicle length to reach the recipient vessel, may have severe arthrosclerosis in diabetic or elderly patients limiting the choices for recipient vessels, has lower perfusion, being furthest from the heart, and is very difficult to isolate the recipient vessels in the mid and upper leg as it is lying very deep to the skin. How can we overcome these difficult situations without compromising the outcome of reconstruction while maintaining a robust distal flow? This is the key challenge.

The supermicrosurgery technique is defined as microsurgical anastomosis of vessels, with a diameter less than 0.8 mm. ² ^, ³ ^, ⁴ ^, ⁵ This technique, although reported frequently on lymphaticovenous shunting to treat lymphedema, fingertip replantation, finger/toe reconstruction, and sporadically in soft-tissue reconstruction with specific indications, is a relatively new concept for lower extremity reconstruction. ³ ^, ⁶ ^, ⁷ ^, ⁸ ^, ⁹ ^, ¹⁰ ^, ¹¹ ^, ¹² ^, ¹³ As lymphedema supermicrosurgery will be covered in another chapter, this chapter will focus on soft-tissue reconstruction. For the lower extremity soft-tissue reconstruction, one of the applications can be seen in the perforator-to-perforator anastomosis approach or using small-diameter pedicles of perforator flaps to anastomose on a lager vessel end to side. ⁴ ^, ⁵ ^, ¹⁴ ^, ¹⁵ This concept deserves to be recognized as a new paradigm in microsurgery as it has been mentioned that vessel size less than 1 mm may significantly increase the risk of flap failure. ¹⁶ However, with advances in technology and skills, the overall success rate for using supermicrosurgery technique for lower extremity reconstruction compares similar to other reports using vessels larger than 1 mm. ² ^, ¹⁶ ^, ¹⁷ ^, ¹⁸

The evolution into this new concept and paradigm shift came naturally as the understanding of single perforasome (perforator angiosome) unfolded as well as the establishment of free styling of perforator flap elevation. ¹⁹ ^, ²⁰ ^, ²¹ ^, ²² ^, ²³ ^, ²⁴ The successful survival of the skin flap based on a single perforator led the hypothesis of using a single perforator artery and veins as a recipient pedicle. ⁴ ^, ⁵ ^, ¹⁴ Thus, using the perforator as a recipient vessel may overcome the difficult challenges that the surgeons face during lower extremity reconstruction. Introduction of supermicrosurgery, especially perforator to perforator, also led to true free style free flaps as any perforator-based skin flaps even the one with short pedicles now can be used to reconstruct the defect. ⁴ ^, ¹⁰ ^, ¹⁴ ^, ²⁵ ^, ²⁶ ^, s. Literatur

Another possibility that perforator-to-perforator supermicrosurgery showed was in treating ischemic diabetic foot patients. Patient with ischemic diabetic limb develop multiple collaterals as atherosclerosis develops. It is these collateral vessels that can supply the skin perforators to maintain the vascular flow despite of major artery obstruction. Using these collateral arteries and perforators supplied from these collaterals is essential for the application of supermicrosurgery in ischemic diabetic limb. ¹⁵ ^, ²⁸ ^, ²⁹ The details of this approach is described in the chapter for diabetic foot reconstruction.

In this chapter, we will focus on how the perforator-to-perforator supermicrosurgery can help surgeons to overcome some of the challenges seen in lower extremity reconstruction.

17.2 Attributes and Detriments

17.2.1 Attributes

Perforators or small end vessels can be used as recipient vessels.
Perforator-to-perforator supermicrosurgery alleviates the use of major vessels and maintains the distal flow to the leg without disruption.
Pulsatile perforator or an end vessel is a good indication for use.
This approach can be minimally invasive, thus minimizing the need for extensive dissection to isolate the recipient.

17.2.2 Detriments

Special instruments may be required for supermicrosurgery.
There is a steep learning curve.
Perforator as a recipient has a limit in providing perfusion to the tissue.
Volume depletion must be avoided during post-op care.

17.3 Anatomical Consideration

There are more than 420 perforators that are over 0.5 mm in diameter throughout our body. ³⁰ While these perforators can be seen as potential sites for perforator-based flaps, they can be considered as recipient vessels as well. In the lower extremity, there are on average 184 perforators from luteal, hip, thigh, knee, leg, and foot. ³⁰ The abundance of these potential recipient sites truly allows us to approach in free style in not only elevating the flaps, but also selecting the recipient source. ⁴ ^, ⁵ The perforator is an end vessel that is the sum of all supplies not only from major vessels but also from all the branches and collaterals heading toward the end vessel perforator. ¹⁵ ^, ²⁸ Thus, using these perforator or end vessels becomes possible despite the major artery being insufficient from atherosclerosis, trauma, or other relevant causes. ⁴ Even in legs with single artery, the risk of steal phenomenon or distal flow reduction can be avoided as using perforators will not disturb the flow of this major vessel.

Preoperative CT scans will allow us to view the vascular details of the lower extremity. In the cases where foreign body effect deters from obtaining appropriate images, conventional angiograms can be obtained as well. These images can also show the possible recipient sites as well as give information on potential donor flap sites. Preoperative duplex can be used to enforce the findings from Doppler as this can give you objective measurement such as velocity of flow and the diameter of the vessel as well as more detailed anatomical findings.

In the lower extremity, there are relatively constant and large perforators coming out from the three major vessels. The findings of the study by Schaverien and Saint-Cyr are shown in Fig. 17‑1, which depicts the relatively constant regions where the perforator emerges from the three major arteries. ³¹ The perforators from the posterior tibial artery are found between the flexor digitorum longus and soleus in all three intervals, with the largest perforators found in the middle cluster. The constant perforators from the anterior tibial artery are located within two clusters. The proximal perforators, 21 to 25 cm from the intermalleolar line, are in the anterior peroneal septum between the extensor digitorum longus and the peroneus longus, and the distal perforators, 4 to 9 cm from the intermalleolar line, are found between the tibia and the tendon of the tibialis anterior muscle. The constant perforator for the peroneal artery is found 13 and 18 cm from the intermalleolar line emerging from various muscles. ³¹ Using these relatively constantly located perforators will allow the surgeon to approach with some degree of reliability when considering the perforator as a recipient.

**Fig. 17.1** This illustration depicts the relatively constant perforators originating from the three major arteries. If the defect is near these perforators, these are relatively easier to find and use as a recipient.

17.4 Anatomical Variants and Pitfalls

The first and foremost important factor in using a perforator as a recipient is a visual pulse. With an evident pulse on the perforating artery, it can be successfully used as a recipient vessel to supply a sizable flap. A perforator can be located during the debridement or resection as a projectile bleeding from the artery is encountered at this time. One can dissect these small vessels further toward the source vessel and clamp it temporarily after obtaining a comfortable length for anastomosis. However, as mentioned earlier, there are relatively constant perforators from the three major arteries and can start by examining these clusters using Doppler or duplex examination. Nevertheless, any perforator with a visible pulse and a pulsatile flow can be chosen as a recipient source. This free style of searching perforators as recipient vessels embraces any variants possible.

The biggest pitfall of this approach is the flow of the recipient perforator, as manipulation of the perforator during dissection may cause constriction and vasospasm that may not be irreversible. Meticulous dissection is an absolute prerequisite to maximize the chance for success. Finer instruments and better microscope will help but is not an absolute requirement. In most of the cases, the constriction or vessel spasm will recover. Therefore, before ligating the pedicle of the flap, it is prudent to check the flow (pulsation) of the recipient perforator first. If the recipient perforator has not recovered from the spasm, one can search for a different nearby perforator or dissect the original perforator toward the source vessel. Once the recipient is confirmed with pulsatile flow, the pedicle flap should be ligated accordingly with the length required.

17.5 Surgical Approach

Any reconstructive procedure involves debridement or resection of unwanted tissue. During this time, one can come across bleeders that have strong pulsatile flow. This small bleeding artery can also be considered a potential recipient perforator or end vessel and saved for later use. If the wound is chronic, often the small vessels in the zone of injury will be difficult to use due to scarring of the tissue, which makes the dissection difficult, hence the concept of avoiding the zone of injury. However, with better microscope and equipment, one can dissect the recipient perforator with care and will be able to use it as such.

After complete debridement, recipient vessels should be explored while the second team starts elevating the flap. Then the recipient perforator or end vessel can be located within the defect or adjacent to the defect. Preoperative search using duplex, Doppler, and CT angiogram can help you identify potential recipient sites (Fig. 17‑2, Fig. 17‑3). The search for such perforators can begin by examining at high-clustered sites from the three major arteries. ³¹ During the operation, the exploration begins by searching the marked region. Usually recipient perforators can be easily identified by dissecting the plane between the fascia and subcutaneous fat like the suprafascial elevation of a DIEP (deep inferior epigastric artery perforator) flap under loupe magnification. Once the perforating vessels are noted, further dissection using the microscope makes it easier to prepare the vessels and confirm the flow of the recipient perforator. A firm pulse from the artery of the perforator is a sign of good perfusion despite the location being within or near the zone of injury. Accompanying veins are used for primary venous drainage, but if superficial veins are found while exploring the recipient pedicle, it is prudent to save and isolate it. In fingers or toes, digital arteries can be used to connect the artery in an end-to-side manner to maintain the flow distal to the anastomosis. In regions where major vessels are lying shallow from the skin, one can use the branch from the major vessel or connect the artery or vein in an end-to-side manner. However, one must consider the inflow volume when doing an end-to-side inflow to a major vessel as the increased volume of inflow overwhelming the small flap may cause congestion of the flap. There have been reports considering the metabolic demand of the flap, but further research is needed in regard to supermicrosurgery and flap physiology. ⁴

**Fig. 17.2** Doppler can be used to mark the potential perforators around or within the defect. The selection of recipient can be started from these potential sites. However, definitive selection of the recipient vessel must rely on the actual pulsation of the perforator.

**Fig. 17.3** CT angiogram also provides images to locate potential recipient perforators.

Upon securing an adequate recipient vessel, various factors should be considered in relationship to the harvesting flap especially the length of the pedicle. If the intended recipient perforator has poor flow, one can look for a different perforator or trace the initial perforator toward the source vessel until an adequate flow is noted.

Once the flap is ready for final ligation of the pedicle, one should recheck the status of the recipient perforator. Usually, the vasoconstriction recovers by the time flap elevation is finished. If there is no adequate pulse or if the recipient does not recover from the spasm, one can ask the anesthesiologist to increase the perfusion pressure by increasing the blood pressure. If this does not work, one should look for an alternative recipient as mentioned earlier. Ligation of the pedicle flap should be performed only after the adequate recipient vessel has been obtained.

The anastomosis begins by the surgeon’s preference. The author usually prefers to do the vein first or whatever recipient vessel is located deeper and is more difficult to anastomose. Once the artery or vein is aligned for anastomosis, the critical step is dilating the vessel to a sufficient diameter, which makes microanastomosis easier. The vessels are dilated using dilators (Fig. 17‑4). After dilation, for diameters less than 0.8 mm but greater than 0.5 mm, an 11–0 or 12–0 nylon with a 50- to 30-μm needle can be used. If the diameter is less than 0.5 mm, a 12–0 nylon with a 50- to 30-μm needle is used. The anastomosis is the same as any microsurgery anastomosis. A minimum of six stitches and average of nine stitches were performed. ⁴ After anastomosis, brisk bleeding from the margin of the flap is confirmed and the flap is set over the defect.