Concept of Angiosome in the Ischemic Diabetic Foot

Author Vlad-Adrian Alexandrescu, M.D.

Draft by Staff Researcher

Modern life stress has increased to such an extent that it has taken almost 15% Diabetic patient to develop foot ulcers. Out of these 14-43% goes through foot amputation. The survival rate after the limb loss is estimated to be an alarming of 40-60%. In order to reduce the limb loss rate, surgeons have found a way to introduce the concept of angiosome in the treatment of CLI or Critical Limb Ischemic.

Primary Angioplasty has been proven to be the most beneficial treatment in treating Diabetic CLI. Recent clinical study shows that these techniques have other beneficial results. They considerably reduce hospital stay, thus reducing medical expenses. Research has also show that the location of the Ischemic foot wound matters. If the wound is below the knee, the wound can be healed by the use of drug-eluting balloons or DEBs. This is where the concept of adding angiosome comes in. These DEBs are basically small balloons containing drugs, which are released into the blood vessels.

In Type-2 diabetes, where hyperglycemia is present in the metabolism, the treatment procedure becomes quite challenging. Other factors may include built up of excess Calcium in the blood vessels, causing long term blockage. The patient can also develop atherosclerotic diseases, which are mainly caused by blockage of the artery walls, by fats, cholesterols and other substances. In spite of so many advancements, all these complexities in Type-2 and Type-3 diabetes have made the treatment procedure very difficult. The Angiosome Concept, although proven promising, is still very unpredictable.

However, there are some new insights in the angiosome concept. This approach is based on specific angiographic “wound oriented” guidance in the treatment of arteries. This method is often termed as Wound Targeted Revascularization or WTR. WTR is applied to tibial and pedal angioplasty in the diabetic patients, for better tissue recovery and limb preservation.

Reconstruction of the Diabetic Foot

The Angiosome concept was first introduced in 1987, by Taylor and Palmer in the reconstructive plastic surgery field. They analyzed the blood supply to the skin and deep tissues, studied the anatomical data, performed several dissections and studied intricately the structure of vein distribution in the human body. After a research of many years, they came up with impressive results. They recognized a 3D structure of veins and arteries in the human tissue layers, which was also present in other animals as well. These veins and arteries had the power of reproducing themselves.

In their initial study, Taylor used live samples extracted from humans like skin, tissues, bones and many others to study how the arteries are spread in the human body. These samples were carefully studies and later tagged with metal clips with the observations. Subtraction images were additionally used to show the distribution of veins in the muscles. Each branch of the artery was marked from the source to the target tissues. This way Taylor made a whole 3D structure of the affected limb.

Another study conducted by Taylor focused on the venous areas of the human body. This helped identify the vein structure in the same 3D area of the arteries. A radiopaque product was injected into the body, which identified the veins and separated them from the tissues. All of these were studied separately and then radio graphed. The “source veins” and the “source arteries” were traced and marked. Venous perforators, which connect the superficial vein and the deep veins, were clustered in various places of the limb. These were detected and marked. Some of the veins were dissected to locate the valves. The nervous system in this area was also studied and radio graphed. All these helped to form a cross section 3D structure, right from the skin to the deep tissue. This is how Taylor managed to get every detail right. It is said that Taylor studied 538 human and 72 animal muscle specimens.

Modern analysis from living humans and animals has also proved to be helpful. Most of these show great potential in the use of angiosome for CLI treatment. In their studies, Taylor and Palmer found out that the 3D structure of skin and deep tissues were nourished by the source arteries. All the blood supply was done by the source angiosomal arteries. This was helpful in determining how important the location is, in the human body. Each location had a specific source artery and its own 3D structure of tissues and veins. These arteries varied in length, density, caliber in the parts of the body.

In the affected limb area, Taylor noticed that the blood supply was done by two or more source arteries. This proved to be an important finding, since now they knew how to compartmentalize the arteries which were supplying blood to the affected limb. One of the most complex part of the clinical process in the treatment of CLI is the study of the tibial “source artery, which was studied from a variety of angels; different types of intra-compartment muscle and pressure.

The cardiovascular system or CV in the human body creates an efficient network so that one source artery is able to supply blood to several angiosomes. When the “source arteries” are blocked or clogged due to some reason, these cardiovascular systems in the body acts as the rescue center. They redirect the blood flow through other available CVs in the 3D structures. This system of working together is closely associated with wound healing processes. This helps in forming new blood vessels from pre-existing blood vessels; a process known as angiogenesis. Thus, forms an integral part of wound or tissue healing.

The CV system is also closely related to a complex network of tiny blood vessels called collaterals. Previous research showed that these collaterals can be ranked and graded based on the distribution of the tibial angiosomes. These collaterals are also graded based on their size, diameter etc. Large collateral can have diameter up to 1 mm whereas medium sized collateral can range from 0.1 to 0.5 mm and also less. When certain coronary arteries become narrow or clogged, this collateral expands and becomes active.

Further research shows that apart from these collaterals there are also networks of capillaries. Capillaries are extra tiny blood vessels which are responsible for distributing oxygenated blood from the arteries to the tissues of the body. It is said that, “16 collaterals with a 0.25 cm diameter” may equal to “625 collaterals with 0.1 cm diameter”, in order to achieve the accuracy of blood flow, in an unobstructed artery of 0.5 cm diameter.

Thus, it shows that just a few collaterals and capillaries are far more efficient in the regulation of blood flow, than “hundreds of small collaterals and capillaries”. In case of a CLI, foot angiosomes, the CV system together with the collaterals and capillaries can be quite promising in channeling the blood flow thereby increasing the possibility of better tissue healing. The common vascular anatomy has 90% reproduction and regeneration rate in healthy patients. However, in case of any diseases, the other 10% acts as a variant.

Taylor and Palmer also made another discovery when studying these 3D structures. They showed that the primary blood supply to the skin was provided by “direct” cutaneous arteries. Cutaneous arteries are mainly responsible for supplying venous blood to the skin, lungs and the lymphatic system. They showed that these vessels arise from the angiosomal “source arteries”. These arteries too vary in length, diameter and density in various regions of the body. These arteries are assisted by “indirect” tiny branches of arteries called the terminal branches of arteries. They are responsible for nourishing and supplying blood to the deep tissues.

In an average human, these “indirect” arteries include more than three hundred major cutaneous perforators or CP. Perforators are side branches of muscular vessels that supply blood to the skin. These were separately studied by Taylor and his colleagues in the 3D structure. The quality of skin, including its blood flow is majorly dependent on these CPs.

A certain researcher showed that the main angiosomal branches that supply blood to the cardiovascular system and the perforators have a dominant effect in the neighbouring areas of the body. In the Diabetic Foot Syndrome (DFS), this concept is quite evident. Numerous small collaterals together with the nerves present in a particular area affect the plantar surface of the nervous system on the ischemic diabetic foot. The nerves enhance the dilation of the blood vessels and decrease the blood pressure. The plantar surface is basically the sole of the foot, which is supplied by two or more adjacent angiosomes. These angiosomes are dominant in channeling the flow of blood to the tissues.

This aspect also however affects any nerve problems in the ischemic diabetic foot and also causes in a loss of the collaterals in the patients. Since the location of the disease was important to the wound healing factor, Rozen, another researcher proposed the use of “perforator angiosomes”. These were used in designing perforator flaps. Perforator flap is a technique in reconstructive surgery, where the skin is removed from an adjacent part of the body to reconstruct a damaged part. In simple words, we can call it plastic surgery.  This not only helped in the healing of the CLI, but also helped in other skin regeneration treatments.

The veins in the human body are also responsible for regeneration and reproduction. As the “source arteries” supply blood to the 3D structure of the tissues, the corresponding venous system drains the blood in the opposite direction, in the same angiosomal areas. Each angiosome is composed of matching arteriosomes (territories with arteries) and venosomes (venous territories). Venosomes make up a network of arcade-like structure in the tissues of the human body. These arcades are different in different parts of the body. They are also concentrated in the adjacent nerves.

Valves in the adjacent venous territories give the exact location of the oscillating veins.  Similar to the arteries in the cardio vascular system, these oscillating veins enable the balance of blood pressure in the between the neighbouring venosomes. Similar to the perforator angiosomes, most inferior limb venosomes are connected to the underlying skin by “venous perforators”.  Venous perforators are long perforating veins where the blood flow happens in an ascending manner. A thorough knowledge of the venous perforators is necessary for all surgical procedures involving the angiosomes.

As discussed earlier, the topography or the location of any diseases was important in the treatment. Taylor and his colleagues greatly understood the nerves, arteries and the veins in reference to the human topographical system. They observed that the main cutaneous sensory nerves and the muscular motor nerves are constantly associated with specific arteries and nerves. The “source” therefore acted as a building block in the 3D structure and identifying the source was important in any treatment.

After conducting such an elaborate research Taylor and his colleagues found out that there are various factors that may aid a surgeon in the treatment of CLI. Firstly, the angiosome concept can provide a better selection of the perforator flap design in the plastic surgery method. It also provides useful information regarding the most safest and efficient ways of amputation. Secondly, the knowledge of the flow of distribution and re-distribution between the adjacent angiosomes also show how it can be helpful in skin or tissue regeneration. Thirdly, identification of the “source” or the “direct” angiosomal arteries can help a surgeon in better evaluation of the disease and hence effective treatment. Lastly, the existence of adjacent venous and the nervous systems show how the body works together in the distribution of blood. This acts as an added advantage not only to the surgeon, but also the patient because the body acts as the rescuer in case of any diseases.

The study of angiosomes conducted by Taylor, Palmer and other researchers provided a foundation in the field of plastic surgery and also provided major insight in the treatment of CLI and other related conditions.