Lower limb amputation techniques in PAD patients
Epidemiology
Between 2005 and 2011, the number of inpatients treated for amputation-threatened extremities in Germany increased from 110,345 to 132,889 cases. With the increase in open and endovascular vascular reconstructions, major amputations decreased by a relative 32.4%, while the relative increase in minor amputations was 16.7% [1]. Roughly 25,000 major amputations are performed annually in Germany, about 70% of which involve diabetic patients, whose risk of amputation is approximately tenfold higher [2, 3].
Etiology
The most common causes of amputation are stage III PAD with intense pain at rest and stage IV PAD with necrosis and ulceration, if perfusion cannot be improved, pain is refractory to therapy, or the patient's general condition does not permit vascular surgical intervention. Critical leg ischemia potentially results in multiorgan failure and thus is also an indication for amputation. Other indications include acute uncontrollable infections; trauma; osteomyelitis; tumors; and congenital malformations [2, 4].
Definitions
Amputations of the lower extremity are divided into major, minor, and borderline amputations:
Major amputation
- Amputation proximal to the ankle
- e.g., hip disarticulation; above-the-knee amputation; through-the-knee amputation; below-the knee amputation; Syme amputation
Minor amputation
- Amputation in the foot region
- e.g., Pirogoff-Spitzy; Chopart and Lisfranc amputation, transmetatarsal forefoot amputation, toe amputation
Borderline amputation
- Amputation right at the border to vital tissue
- Common in diabetic and PAD patients [5]
In the German DRG billing system, major amputation already includes transmetatarsal forefoot amputation, and only toe amputations and ray amputations are grouped as minor amputations [2, 6].
Determining the amputation level
The amputation level depends on the vascular situation, tissue damage and patient mobility. Good wound healing requires enough vital tissue, hence the amputation level often has to be decided during surgery The goal is a definitive solution - as much as necessary and as little as possible. Transcutaneous pO2 measurement may help determine the amputation level.
Amputation should be as distal as possible because the longer the residual limb, the better its biomechanical leverage (exception: bedridden patients). The weight-bearing capacity of the stump is important for the transmission of proprioceptive information, which is best achieved by amputation through cancellous bone or by disarticulation [4,7].
Minor and borderline amputation
Due to the preserved sole, amputations in the region of the foot have the benefit of a high weight-bearing capacity of the residual foot. This is because the more area of the sole is preserved, the lower the increase in pressure per square centimeter and the better the proprioception and associated stable walking and standing. However, partial foot amputation may result in muscle imbalance and thus malposition of the foot, especially varus position and footdrop, which may result in pressure sores and ulceration [7].
(Partial) toe amputations are often borderline amputations performed after demarcation of necrosis in healthy tissue with appropriate shortening or disarticulation of the bones. Here, the resection line may be based on given anatomical amputation lines (e.g., disarticulation) or on the extent of necrosis without specific anatomical correlation. Bone splinters, resection rims and bradytrophic tissue (e.g. tendon remnants) must be removed, and the capsule of adjacent joints must be spared. Whether primary wound closure is indicated depends on the infection situation in question [7].
In " inner amputations," the affected metatarsal or tarsal bone is resected via an approach on the dorsum of the foot, leaving the toes intact which will retract over time, form false joints, or serve as placeholders [7].
Amputations of the forefoot
To spare the sole in transmetatarsal amputations, the skin incision is usually placed on the dorsum of the foot. The aim is to obtain the longest plantar flap possible. After exposing the metatarsal bones, they are transected such that their stumps will align harmoniously with each other. To obtain a weight-bearing tip, the shorter the stump, the more the bones must be rounded.
In Lisfranc amputation, the incision line is fishmouth-shaped. For the plantar flap, the sole is detached from the bone and disarticulation is performed between the tarsus (cuneiform and cuboid bones) and the base of the metatarsal bones. After drain placement, the wound is closed with tension-free interrupted sutures [7].
Amputations of the hindfoot
These include the Chopart, Pirogoff-Spitzy and Syme techniques. The common principle is to preserve the heel skin so that the stump maintains a functional sole and can bear weight [8].
In Chopart amputations, the resection is performed distal to the calcaneus and talus via a skin incision across the hindfoot about 1 cm distal to the malleoli. The incision is continued toward the sole of the foot such that a sufficiently large flap is fashioned for tension-free wound closure. A disadvantage is the subsequent muscle imbalance, which may result in the stump assuming varus and supination malposition [7, 8].
In the Pirogoff-Spitzy technique, the talus and malleoli are resected and the calcaneus is fused by osteosynthesis with the tibia and fibula. Because of the osteosynthesis it requires, this technique should not be undertaken in patients with PAD [7, 9].
The Syme amputation, which is technically quite challenging, involves disarticulation of the ankle joint in the manner of a supramalleolar amputation with rounding of the ankle tips. Its great advantage is the full weight-bearing capacity of the end of the stump with long leverage of the lower leg and an almost undisturbed gait pattern with good fitting of the prosthesis. Unlike the Pirogoff technique, no osteosynthesis is performed, making it particularly useful in patients with PAD and diabetics [7, 9].
Below-the knee amputation
Transtibial amputation requires a sufficiently large posterior myocutaneous flap for stump coverage. While small necroses in the area of the posterior flap do not rule out transtibial amputation, it is contraindicated in large-scale necrosis, regardless of the arterial blood supply.
In addition to the weight-bearing capacity of the end of the stump, the length of the residual limb and preservation of the knee joint are important in ambulation. Transtibial amputation in bedridden patients with contracted knee joints is not recommended. The proximal half of the tibial tuberosity is already adequate for extension of the stump in the knee joint, and a short stump of 3-5 cm length can be fitted with a prosthesis. Nevertheless, a longer stump of the lower leg is preferred because the larger the possible contact area of the prosthesis, the better the pressure distribution. A tibial stump length of 12-13 cm is ideal. Further distad, the slender musculature is not sufficient for adequate coverage of the stump, and wound healing disorders and hypothermic stumps are more common [4, 7]. In AVK, the proximal third has proven to be the level of choice in below-the-knee amputation.
Prosthetic grafts in the wound area should be completely removed if infection is suspected (patch proximal anastomosis if needed); in the absence of infection, they should be removed as far proximally as possible.
Through-the-knee amputation (knee disarticulation)
Advantages of through-the-knee amputation include the weight-bearing capacity of the end of the stump, minimized risk of inactivity osteoporosis thanks to the preservation of the cartilaginous surface, and ideal transmission of sensorimotor information from the end of the stump. Unlike in transfemoral amputation, postoperative bleeding, hematomas, and exostoses are less common because no muscle or bone is transected. However, there is a higher risk of wound healing problems and stump necrosis because the stump is only covered by full-thickness skin. If the present soft tissues are not enough to cover the stump, transcondylar amputation with patellar resection may be an option. The disadvantage is that blood loss and the risk of infection are greater than with disarticulation because of cartilage removal [7].
Choose the skin incisions for the flaps such that the scar is as far outside the weight-bearing zone as possible. The skin around the knee area is highly elastic and retracts more than usual. The easiest way is to make a circular skin incision 5-7 cm distal to the tibial plateau. The scar comes to lie between the condyles in longitudinal direction. With long posterior soft tissue flaps, the scar is anterior as in transtibial amputation.
Transfemoral amputation
Transfemoral or above-the-knee amputations are amputations through the diaphseal femur. In terms of functionality, they are inferior to through/below-the-knee amputations because the prospects for rehabilitation are poorer, which is why they should only be performed if amputation further distad is no longer possible or in case of patient confinement to bed [7].
To achieve a tension-free stump, two symmetrical skin-muscle flaps are usually fashioned in the anterior plane, meeting at an angle of 70-90° ("fishmouth"). After skin incision, the flaps are fashioned with the amputation knife in one swift motion. After ligating the vessels with resorbable sutures, the femur is transected about 2 cm distal to the flap angle, the rims of the bone are smoothed, and the sciatic nerve is ligated and shortened about 5 cm proximally.
For postoperative pain relief, a local anesthetic (e.g., 5-10 ml bupivacaine 0.5%) can be instilled into the nerve [6, 10]. In the first 48 hours, postoperative pain can also be significantly reduced by infusion of a long-acting local anesthetic onto the nerve stump. However, this does not affect the development of phantom limb pain [11, 12].
Hip disarticulation and ultra-short above-the-knee amputation in the femoral neck
Hip disarticulations and ultrashort transfemoral amputations, which are indicated only when amputation options further distad have been exhausted, are rarely performed in PAD; the main causes are tumors and trauma. In PAD patients, soft tissue coverage can be challenging because the pelvic circulation is usually occluded, resulting in extensive necrosis and decubitus. Prosthetic management of the ultrashort femoral stump is more difficult because of the preserved trochanteric mass, but sitting is easier for the patient.