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 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 for 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 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 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).

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.

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.

7.1.4 Lisfranc Amputation

If infection or tissue necrosis is proximal enough that a Lisfranc amputation will be necessary, again, the blood flow must be assessed to ensure that both the dorsal and plantar tissue have independent inflow. If that is not the case and either side depends on the arterial arch being open, then it is all the more important not to damage the arch during any dissection. To reiterate, that must be done by removing the first metatarsal medially without disturbing the arch, and then removing the second through fifth metatarsals laterally while also avoiding the arch soft tissues.

When determining which flap (dorsal or plantar) to trim to get an adequate closure, one should always preserve the tissue from the better vascularized side and trim the less well-vascularized side. The circumferences of the dorsal and plantar flaps may vary and create dog-ears at either side if closed directly. This can be circumvented either by removing the dog-ears in routine fashion or by taking a central wedge from the plantar flap wide enough so that the circumference of both sides is equal.

As should always be the case in the foot, all available viable tissue is preserved at the time of the initial debridement to provide the surgeon with the most possibly healthy soft tissue for later closure (Fig. 7‑4). The longest possible dorsal and plantar flaps are created, and the metatarsals are disarticulated at Lisfranc joint. A proximal-to-distal approach is used to remove the metatarsal and thus minimize damage to the underlying tissue. The keystone proximal second metatarsal can be cut at the level of the cuneiforms for stability. Great care with that cut has to be taken if the vascular arch is to be preserved. When the flaps are brought together to close the amputation, always remove the less vascularized tissue in favor of the better vascularized tissue. Since obviously the glabrous plantar tissue is more resistant to repetitive trauma, that if at all feasible should be brought up to cover as much of the Lisfranc joint as possible.

The Achilles tendon with a Lisfranc amputation can be a real problem. Because it will be unopposed, it will cause an equinovarus deformity and lead to eventual skin breakdown over the distal cuboid. A frank tenectomy by removing 1 to 2 cm of the distal Achilles tendon just above its insertion will be a solution for two reasons (Fig. 7‑5). The first is to prevent the equinovarus deformity from occurring at all. The second is to prevent the Achilles tendon from healing back together later and causing a delayed equinovarus deformity. In patients who are not infected, one can also consider reinserting the anterior tibial tendon by splitting it and attaching it to the lateral aspect to the cuboid using an anchor. This would strengthen dorsiflexion of the foot sufficiently to possibly help counterbalance the overwhelming plantar deflecting force from the Achilles tendon.