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]. Approximately 25,000 major amputations are performed annually in Germany, about 70% of which involve patients with diabetes mellitus, who have an approximately tenfold increased risk of amputation [2, 3].
Etiology
The most common causes of amputation are PAD stage III with intense pain at rest and stage IV with necrosis and ulceration, provided that improvement of perfusion is not possible, the pain is refractory to therapy, or the patient's general condition does not permit a vascular surgical intervention. Critical limb ischemia may cause multiorgan failure and thus also represents 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-knee amputation; through-knee amputation; below-knee amputation; Syme amputation
Minor amputation
- Amputation in the foot region
- e.g., Pirogoff-Spitzy, Chopart and Lisfranc amputation, transmetatarsal forefoot amputation, toe amputations
Borderline amputation
- Amputation right at the border of the necrosis within vital tissue
- Common in diabetic and PAOD patients [5]
In the German DRG billing system, transmetatarsal forefoot amputation is already classed among major amputations, and only toe amputations and ray resections are grouped as minor amputations [2, 6].
Determining the amputation level
The amputation level depends on the vascular situation, the tissue damage and the patient's mobility. Good wound healing requires sufficient vital tissue, hence the amputation level often has to be decided intraoperatively. 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 end 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 end 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 centimetre 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 equinus foot, which may result in pressure sores and ulceration [7].
(Partial) toe amputations are often borderline amputations performed after demarcation of the necrosis within vital 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 the 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 performed depends on the respective infection situation [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; over time they retract, 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 possible plantar flap. After exposing the metatarsal bones, they are transected such that the bony stumps are harmoniously aligned 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 bones and cuboid bone) and the base of the metatarsal bones. The wound is closed over drains with tension-free interrupted sutures [7].
Amputations of the hindfoot
These include the Chopart, Pirogoff-Spitzy and Syme techniques. The common principle is preservation of the heel skin, so that the stump maintains a functional sole and can bear weight [8].
In Chopart amputation, the resection line runs distal to the calcaneus and talus via a skin incision across the hindfoot about 1 cm distal to the malleoli. The incision is continued towards 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 lead to a varus and supination malposition of the residual foot [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 technically quite demanding Syme amputation corresponds to a disarticulation of the ankle joint in the sense of a supramalleolar amputation with rounding of the malleolar tips. Its great advantage is the full end-weight-bearing capacity with a long lower-leg lever arm and an almost undisturbed gait pattern with good prosthetic fitting. In contrast to the Pirogoff technique, no osteosynthesis is performed, so that it is particularly suitable also for patients with PAD and diabetics [7, 9].
Below-the-knee amputation
Below-the-knee amputation requires a sufficiently large posterior myocutaneous flap for stump coverage. While small areas of necrosis in the region of the posterior flap do not preclude a below-the-knee amputation, it is impossible in the presence of 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 for mobilisation. Transtibial amputation is not advisable in bedridden patients with knee joint contractures. The proximal half of the tuberositas tibiae is already sufficient for extension of the stump at the knee joint, and a short stump of 3-5 cm can be fitted with a prosthesis. Nevertheless, a longer transtibial stump is preferable, as the largest possible contact area of the prosthesis leads to better pressure distribution. A tibial stump length of 12-13 cm is ideal. Further distally, the slender musculature is not sufficient for adequate coverage of the stump, and wound healing disorders and hypothermic stumps occur more frequently [4, 7]. In PAOD, the proximal third has proven to be the level of choice for amputation.
Prosthetic bypass grafts in the wound area should be completely removed if infection is suspected (fashion the proximal anastomosis with a patch if needed); in the absence of infection, they should be divided as far proximally as possible.
Knee disarticulation
Advantages of knee disarticulation include the weight-bearing capacity of the end of the stump, the minimised risk of inactivity osteoporosis thanks to preservation of the cartilaginous surface, and the optimal transmission of sensorimotor information from the end of the stump. Compared with transfemoral amputation, postoperative bleeding, haematomas and exostoses are less common, as no muscle or bone is transected. However, there is a greater risk of wound healing disorders and stump necrosis, as the stump is covered only by full-thickness skin. If the present soft tissues are not sufficient to cover the stump, a transcondylar amputation with patellar resection may be performed. The disadvantage is that, owing to removal of the cartilage, the risk of infection and blood loss are greater than with disarticulation [7].
Choose the skin incisions for the flaps such that the scar comes to lie as far as possible outside the weight-bearing zone. The skin in the knee region is highly elastic and retracts more than usual. The simplest approach is a circular skin incision 5-7 cm distal to the tibial plateau. The scar comes to lie longitudinally between the condyles. With a long posterior soft tissue flap, the scar lies anteriorly, as in transtibial amputation.
Transfemoral amputation
Transfemoral amputations are amputations at the level of the femoral diaphysis. In terms of functionality, they are inferior to amputations at the knee, as the prospects for rehabilitation are considerably poorer, which is why they should only be performed when amputation further distally is no longer possible or in case of confinement to bed [7].
To achieve a tension-free stump, two symmetrical skin–muscle flaps are usually fashioned in the frontal plane, meeting at an angle of 70–90° ("fishmouth"). After the 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 bone edges are smoothed, and the sciatic nerve is ligated and shortened about 5 cm more proximally.
For postoperative pain relief, the nerve may be infiltrated with a local anaesthetic (e.g. 5–10 ml bupivacaine 0.5%) [6, 10]. During the first 48 hours, postoperative pain can also be significantly reduced by infusion of a long-acting local anaesthetic onto the nerve stump. However, this does not affect the occurrence of phantom limb pain [11, 12].
Hip disarticulation and ultra-short above-knee amputation in the femoral neck region
Hip disarticulations and ultra-short transfemoral amputations, which are indicated only once amputation options further distally have been exhausted, are rarely performed in PAD; the principal causes are tumours and trauma. In PAD patients, soft tissue coverage can become a challenge, as the pelvic circulation is usually occluded, resulting in extensive necrosis and decubitus ulcers. Prosthetic fitting of the ultra-short femoral stump is more difficult because of the preserved trochanteric mass, although sitting is easier for the patient.