7 Using the Flap and Angiosome Concepts to Optimize Functional Lower Leg and Foot Amputations
The key factor when considering salvage or amputation of the lower leg or foot is to optimize the functional result appropriate for the age and activity level of the patient. In either case, first, assurance of an adequate blood flow to allow healing and eradication of any residual infection is imperative. This next may require serial radical debridement with removal of any biofilm while retaining any critical interconnections between source vessel angiosomes. Retention of all available viable tissues, especially in the foot, should be routine at the initial debridement, as this may be a source of healthy soft tissue for later wound closure. Once these conditions have been satisfied, and a level of amputation determined, the actual techniques are outlined in necessary detail to allow a toe, transmetatarsal, Lisfranc, Chopart, Syme, or below-knee amputation.
Keywords: toe amputation, transmetatarsal amputation, Lisfranc amputation, Chopart amputation, Syme amputation, below-knee amputation, Ertl modification
When salvaging a limb, it is critical to assess the type of function the reconstructed limb can potentially achieve. The physician has to accurately determine the activities that the patient desires and will be physically capable of eventually. This then determines what best meets those goals: the planned reconstructed limb versus an amputation. Salvaging a limb just to salvage the limb is no longer an acceptable goal. One has to salvage a functional limb that meets the patient’s realistic goals whether it is a reconstructed or an amputated limb. The younger the patients, the more they will demand of their reconstructed leg. As such, the reconstructed limb may not be able to meet the patient’s desired expectations, and the decision to go to an amputation may be more appropriate. However, the older the patient, the less will be demanded of the reconstructed leg as long as it allows them to accomplish their activities of daily living so that they can maintain their independence.
The intent here will not be to discuss the basic amputation techniques of the foot and lower leg. Instead, this discussion will be from a plastic surgery perspective using flaps and myodesis to optimize function. Because plastic surgeons have mastered the art of shaping soft tissue and are comfortable with handling both bone and tendon, they are fully qualified to perform the most functional of amputations. As such, the key factors to consider with every amputation to optimize those functional results will be reviewed. This will be critical if one is to be capable of planning whether to salvage or amputate part of the foot or the lower leg.
7.1.1 Preoperative Preparation
The need for a decision to potentially perform an amputation occurs because of inadequate available soft tissue or bone for reconstruction of a functional limb, uncorrectable blood flow, or presence of overwhelming infection. To assess the leg for possible reconstruction, one has to accomplish three things: ensure adequate blood flow for healing, eradicate any residual infection, and have a functional result in mind.
When presented with a diabetic or irradiated patient, it is often difficult to clinically assess blood flow. The angiosome concept must be kept in mind at all times to be sure that the area in question will be well perfused. Ankle–brachial indices are unreliable in diabetics and renal failure patients because of their calcified vessels. Doppler signals can be misleading, but doppler waveforms are more reliable. The most trustworthy is an angiogram with magnified views of the foot. This actually allows the surgeon to visualize the rate of flow in each artery. This can be done with very little dye (< 10 mL of dye) especially in patients with kidney function at risk. This will demonstrate the contributions of each of the three source arteries to the foot, and the arterial–arterial interconnections between each other.1 The planned amputation may lead to the sacrifice of some of those arterial–arterial connections on which part of the foot may depend as collaterals and could lead to poor outcomes, so that a revision of that plan might be in order.
To ensure the best vascular supply to the impaired limb, it is essential to have a good vascular team to rely upon. They must excel in angioplasty, bypass surgery, and venous surgery. Review of the angiogram with the respective vascular interventionist is critical so that he or she understands exactly what type of blood flow is needed in order for the surgery to be successful. This is especially true if microsurgery is one of the possible reconstructive options. Angioplasties tend to have a shorter half-life when compared to that of a bypass, and that must be considered within the time frame of the required reconstruction. The optimal flow to the downstream foot [as measured by total carbon dioxide (TCO2)] with bypass surgery is 5 to 8 days versus as long as 30 days with angioplasty. Any microsurgical anastomosis to a major artery should always be in an end-to-side fashion so as not to sacrifice distal flow that already may be compromised. The exception is when the recipient site will be a small perforator, where an end-to-end anastomosis using supermicrosurgery is preferable. When doing microvascular surgery, the venous flow also has to be evaluated to make sure that the venous return from the flap travels via the venous system (superficial or deep) that has the least amount of resistance.2
Dealing with an infection can be difficult because the exact diagnosis will be affected by the way the specimen is collected, the way the laboratory handles it, the presence of biofilm, and assessing the PCR (polymerase chain reaction) data. In addition, one has to consider host factors, as the more medically compromised the patient, the more vulnerable they will be for harboring a residual infection.
The quality of debridement can often vary. We recommend removing all exposed tissue after painting the wound with blue dye to accurately demarcate the wound surface.3 Only by excisional debridement to normal red, yellow, and white tissue can one be certain that all the surface bacteria has been removed. The thicker the excision, the more likely will be removed any underlying biofilm, which can be as deep as 4 mm under the surface. The resection of any indurated tissue at the edges of the wound also helps remove all potentially inflamed tissue. Pre- and postdebridement tissue cultures (vs. culture swabs) are essential to assess the quality of that debridement. Once the postdebridement results are available, the surgeon can then make the decision as to whether to close the wound or not. Meanwhile, a close working arrangement with the infectious disease service ensures that the initial broad-spectrum antibiotics and subsequent culture-specific antibiotic coverage are appropriate to minimize the potential toxicity of any antibiotics. If the bone infection has been resected, note that antibiotics are needed for only 1 week as per the guidelines of the Infectious Diseases Society of America (IDSA)4 and the International Society of Infectious Diseases (ISID).
After completion of the preoperative preparation, finally a decision has to be made as to what will be the best type of reconstruction. Remember that if an ulcer does heal in a diabetic foot, the chances of ulcer recurrence at 2 years can be as high as 80%.5 The final result therefore has to be a functional foot that will also minimize the risk of recidivism. If the surgeon believes that the function of a salvaged limb will not meet the physical capacity and expectations of the patient, then amputation has to be considered. That can be either a foot amputation or a below-knee amputation (BKA). The proposed procedure and possible options must be fully discussed with not only the patient but also their entire family or other caregivers. A peer amputee discussion with the patient can be very helpful, as the patient is more likely then to understand the implications of an amputation. Also important is that a prosthetist and orthotist talk to the patient about the consequences of shorter foot amputations versus a BKA. All these factors will permit the patient and their family to make the most intelligent decision as to which option should be chosen.
7.1.2 Toe Amputation
The amputation of toes distal to the metatarsophalangeal (MTP) head should be done either with vertical or horizontal clamshell flaps. The key is to design them so that direct blood flow to the skin is retained, and the closure does not lead to a bulbous toe tip. The diameter of the closure should be the same as that of the more proximal intact toe. One should try to keep part of the proximal phalanx intact to help prevent medial or lateral deviation of the adjacent toes. When only the distal toe is to be amputated, the germinal matrix of the nail bed must be removed to avoid new nail growth in unexpected parts of the line of closure.
When doing a hallux amputation, first determine whether hallux rigidus is present. If it is, it is preferable to amputate the hallux at the MTP joint rather than preserving part of the proximal phalanx. Recurrent ulceration at the distal toe is three or four times higher with partial hallux amputations in patients who have hallux rigidus.6 Otherwise, preserving as much of the hallux as possible works well.
If the metatarsal head is exposed and the neighboring toe is intact, one can consider fillet of the existing or neighboring toe to cover the defect rather than cutting the metatarsal head shorter to close the defect. A filleted toe never creates as much of a flap as one thinks. The key to filleting a toe is to remove bone without damaging the underlying existing blood supply. The incision can be medial or lateral along a line that separates the top one-third of the toe from the bottom third (▶ Fig. 7.1a). A cut is then made around the distal phalanx staying proximal to the germinal matrix to expose the interphalangeal (IP; hallux) or distal IP (DIP) joint (lesser toes; ▶ Fig. 7.1b). A towel clamp used to grasp the distal phalanx allows retraction to flip it from proximal to distal a complete 180 degrees while the soft tissue is dissected off (▶ Fig. 7.1c, d). The same is done for the proximal phalanx (▶ Fig. 7.1e, f). The volar plates under the IP joints are cut by placing a scissor in the flexor tendon sheath (▶ Fig. 7.1g) and splitting it in two. Each hemivolar plate is carefully removed to avoid damaging the plantar digital vessels that pass just lateral and inferior to it. The flexor tendons are then removed (▶ Fig. 7.1h). The filleted toe is ready to be transferred (▶ Fig. 7.1i, j). Using a fillet of toe can be very useful for preservation of the proximal phalanx (▶ Fig. 7.1k) or filling in large forefoot defects that can occur as when doing transmetatarsal amputations (TMAs; ▶ Fig. 7.2).
7.1.3 Transmetatarsal Amputation
When planning a TMA, the surgeon has to establish whether there is arterial inflow in both the dorsal and plantar surfaces. The direction of the flow and its source artery must be known. Any critical arterial interconnections between the dorsal and plantar foot occur just distal to Lisfranc joint. The main one is from the dorsalis pedis artery that dives between the first and second proximal metatarsals to join the lateral plantar artery. If there is good independent inflow from both the dorsalis pedis and the lateral plantar artery, the dorsal and plantar flaps can be designed with impunity as there will be direct inline flow to each. However, if only one of the two arteries is supplying blood flow to the entire foot, then it is imperative to keep the arch between the dorsalis pedis and lateral plantar arteries intact. This is of particular concern when a proximal TMA or Lisfranc amputation is required. Under those circumstances, to avoid damaging this arch, the first metatarsal is removed medially without visualizing the tissue between the proximal first and second metatarsals to avoid damaging it. The second through fifth metatarsals are removed laterally, again without visualizing the connection between the dorsal and plantar circulation.
When initially debriding any foot that is going to later undergo potential amputation, any soft tissue that is viable should be preserved (▶ Fig. 7.2a–d). This means only removing what is necrotic and saving everything else that can then be a possible option for any subsequent reconstructive surgery needed to preserve length. Salvaged toes or even portions thereof can be extremely valuable for closure of forefoot amputations (▶ Fig. 7.2, ▶ Fig. 7.3). At the time of skin closure, the metatarsals are cut to recreate the normal arch of the metatarsal heads (▶ Fig. 7.2e, f). The residual toes are filleted and used to cover the exposed bone to provide an adequate soft-tissue envelope (▶ Fig. 7.2g–j). This allows the foot to be longer so that the plantar surface area will endure a lower pressure in pounds per square inch through the gait cycle (▶ Fig. 7.2k, l).
Fig. 7.1 Great toe fillet flap. (a) A line is drawn along the medial glabrous junction of the toe proceeding circumferentially to the lateral side, and then connecting the sides of this line dorsally just proximal to the germinal matrix of the nail bed. (b) The glabrous junction is incised, and then also the dorsal line proximal to the germinal matrix to expose the interphalangeal joint. (c) With the towel clamp grasping the distal phalanx, that can be flipped 180 degrees toward the surgeon while the bone is freed up from the underlying soft tissue from proximal to distal. (d) The distal phalanx has been removed from the hallux leaving the distal plantar tissue intact. (e) Similarly, the proximal phalanx has been freed from the overlying tissue and the metatarsophalangeal joint entered. (f) With the towel clamp now grasping the proximal phalanx, again it can be flipped 180 degrees toward the surgeon so that the bone can be freed from the underlying soft tissue with minimal damage. (g) Identify the volar plate with scissors by going into the flexor tendon sheath, cut it along its center, and remove both halves while carefully staying on the plantar volar plate surface to avoid damaging the proper digital arteries. (h) The flexor hallucis longus tendon is grasped and removed. (i) The now filleted great toe flap is stretched out and (j) rotated dorsally to cover the preserved hallux metatarsal head. (k) Clinical result of distal filleted hallux flap and concomitant second toe amputation that used a horizontal clamshell skin flap closure.
At a secondary operation for a TMA, after the initial debridement, all exposed tissue is painted with blue dye and re-excised to clean healthy tissue (▶ Fig. 7.3a, b). The metatarsals are then cut in an arch with the second being the longest (as in ▶ Fig. 7.2e, f). The cuts are made generally in a direction perpendicular to the shaft, although some bias is preferable by beveling them so that the plantar side is slightly shorter. The first metatarsal and the fifth distal metatarsal are also cut with a slight proximal/distal bias so the distal end will be less prominent medially and laterally, respectively. The metatarsal heads are then removed by grasping the proximal cut metatarsal with a towel clip and flipping 180 degrees to free them up carefully from the underlying soft tissue that is separated without damaging the blood supply (▶ Fig. 7.3c). Generally, the volar plates are split in the middle and removed with care so as not to damage the underlying plantar metatarsal vessels (Fig. 7.3d). The sesamoids from the hallux are removed. Once the wound has been debrided thoroughly and is ready for closure, it is lavaged with the irrigation of choice, and new instruments are chosen to minimize contamination.
Fig. 7.2 Transmetatarsal amputation with toe fillet coverage. Necrotizing fasciitis involving both (a) the right dorsal and (b) the plantar mid forefoot. During the initial debridement of nonviable tissue, most of the hallux and fifth toe did not appear involved on the (c) dorsal and (d) plantar surfaces. They were preserved for the eventual reconstruction. (e) Radiograph of the right foot following soft-tissue and bony debridement. (f) A transmetatarsal amputation (TMA) was planned. The normal metatarsal head parabola was recreated by cutting across the proximal metatarsals with that of the second toe being the longest. Both the (g) first and (h) fifth toes were filleted so they could be used as soft-tissue flaps to help close the TMA while preserving length. (i) The toe fillet flaps were rotated dorsally to close the TMA defect. (j) A skin graft was placed on the remaining open medial dorsal aspect of the foot. (k) Dorsal and (l) plantar views of the healed TMA 3 months later.
Fig. 7.3 Conventional transmetatarsal amputation (TMA). (a) Open area of debrided right foot has been painted with methylene blue to ensure that the secondary debridement is adequate prior to completion TMA, whose planned incision lines have also been marked. (b) The fourth and fifth toes have been disarticulated. (c) The cut fifth metatarsal head now grasped with a towel clip is freed up by vertically flipping 180 degrees toward the surgeon so that it can be dissected off the plantar soft tissue without destroying any underlying blood supply. Note that the rest of the foot has undergone excisional debridement. (d) The metatarsophalangeal joint volar plate is exposed by going into the flexor tendon sheath with a tonsil or scissor. It is then cut along its center and both halves are removed taking care to stay on the plantar side to avoid the digital arteries. Note that the metatarsals were recut to form a parabola with the second metatarsal being the longest. (e) To restore some dorsiflexion of the foot lost when the toe extensors were amputated, a tenodesis of the flexor and extensor tendon of the fifth toe was planned. Here they were located and placed on gentle traction, and (f) then sewn together to complete the tenodesis with the ankle maintained at 90 degrees or neutral position. (g) The plantar flap will usually have a longer arc than the dorsal flap. This inequality will lead to protruding dog ears on the medial and lateral sides of the stump. That can be circumvented by taking a large wedge from the center of the plantar flat to equalize the arcs. (h) A simple, smooth closure is then possible.
The foot will have lost a significant amount of its capability to dorsiflex because the deep and superficial extensors to the toes have been cut during the necessary debridement. The flexors of the foot, since overpowering, will cause the foot to slowly go into an equinovarus position with eventual breakdown of the lateral plantar foot under the fifth metatarsal. This can be prevented by a tenodesis of the flexor and extensor tendons of the fourth and fifth toes with the foot in neutral to restore some of that lost extension (▶ Fig. 7.3e, f). Alternatively, a percutaneous Achilles tendon lengthening will weaken the plantar flexion forces of the foot. Finally, the plantar flap will frequently have a larger diameter than the dorsal flap, so that when closed, dog-ears occur on either side. A wedge can be taken out of the center of the plantar flap so that the circumferences of both sides will be equal to avoid this (▶ Fig. 7.3g, h). Deep sutures are avoided if possible because they can potentiate infection.7
Postoperatively, the ankle is maintained in neutral with a well-padded posterior splint. Weight bearing is avoided until at least 3 weeks postsurgery. Staples remain for 1 week and sutures until 4 weeks. Only then will the patient be fitted for orthotics and accommodative shoe wear. However, the foot will remain in a cam walker when ambulatory for a total of 6 weeks from the date of surgery to protect the skin closure and the Achilles tendon (if it was percutaneously lengthened) from being overstressed and rupturing.