Lower limb amputation techniques in PAOD 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 minor amputations showed a relative increase of 16.7% [1]. Approximately 25,000 major amputations are performed annually in Germany, about 70% of which involve patients with diabetes mellitus, whose risk of amputation is roughly tenfold higher [2, 3].
Etiology
The most common causes of amputation are PAOD stage III with intense pain at rest and stage IV with necrosis and ulceration, provided that perfusion cannot be improved, pain is refractory to therapy, or the patient's general condition does not permit vascular surgical intervention. Critical limb ischemia may cause multiorgan failure and thus also constitutes an indication for amputation. Other indications include acute uncontrollable infections, trauma, osteomyelitis, tumours and congenital malformations [2, 4].
Definitions
In the lower extremity, a distinction is made between 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 amputation; Chopart and Lisfranc amputation; transmetatarsal forefoot amputation; toe amputation
Borderline amputation
- Amputation right at the border to vital tissue
- Common in diabetic and PAOD patients [5]
In the German DRG billing system, transmetatarsal forefoot amputation is already counted among the 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 performed as distal as possible, because the longer the residual limb, the better its biomechanical leverage (exception: bedridden patients). The end-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 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 footdrop, which may result in pressure sores and ulceration [7].
(Partial) toe amputations are often borderline-zone amputations performed after demarcation of the 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 determined by 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 "internal amputations", the affected metatarsal or tarsal bone is resected via an approach on the dorsum of the foot, leaving the toes intact; over time these retract, form false joints, or serve as placeholders [7].
Amputations of the forefoot
In transmetatarsal amputations, the skin incision is usually placed on the dorsum of the foot in order to spare the sole. The aim is to obtain the longest possible plantar flap. After exposing the metatarsal bones, they are transected such that the bone 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 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 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 result in the residual foot assuming a 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 malleolar 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 suitable for 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 impossible 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 for mobilisation. Transtibial amputation is not advisable in bedridden patients with knee joint contractures. The proximal half of the tuberositas tibiae is already adequate for extension of the stump at 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 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 are more common [4, 7]. In PAD, the proximal third has proven to be the level of choice for amputation.
Prosthetic grafts in the wound area should be completely removed if infection is suspected (patch the proximal anastomosis if needed); in the absence of infection, they should be transected 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, the minimised risk of inactivity osteoporosis thanks to the 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 because no muscle or bone is transected. However, there is a higher risk of wound healing disorders and stump necrosis because the stump is covered by full-thickness skin only. 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 cartilage removal, 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 outside the weight-bearing zone as possible. The skin in the knee area 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 through the femoral diaphysis. In terms of functionality, they are inferior to amputations in the knee area, as the prospects for rehabilitation are considerably poorer, which is why they should only be performed if amputation further distad is no longer possible or in cases 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 a single stroke. After ligating the vessels with absorbable sutures, the femur is transected approximately 2 cm distal to the flap angle, the bone edges are smoothed, and the sciatic nerve is ligated and shortened approximately 5 cm more proximally.
For postoperative pain relief, the nerve can 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 infusing a long-acting local anaesthetic onto the nerve stump. However, this does not influence the occurrence of phantom limb pain [11, 12].
Hip disarticulation and ultra-short transfemoral amputation in the femoral neck
Hip disarticulations and ultra-short transfemoral amputations, which are indicated only once the amputation options further distad have been exhausted, are rarely performed in PAD; the main 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 pressure ulcers. Prosthetic management of the ultra-short femoral stump is more difficult because of the preserved trochanteric mass, but sitting is easier for the patient.