Debridement is critical to wound healing as it removes necrotic tissue, decreases bioburden, disrupts biofilm and converts a hard-to-heal (chronic) wound into an acute wound.1, 2 Devitalised tissue impedes cell migration and is a favourable environment for bacterial proliferation that frequently leads to bacterial wound colonisation and infection.2
The principles of wound bed preparation are characterised by the TIME acronym:3
Non-advancing, rolled or undermined edges stall wound closure, and little has been reported on how to overcome this critical problem. The two main recommendations are to either resect rolled edges or to cauterise them using silver nitrate. A study of three patients described the successful use of polymeric membrane dressings.4 Topical oxygen and electrical stimulation were also found in one study to be beneficial in reducing epibole.5
The practice of debriding wound edges at an approximately 45° angle allows the smooth migration of keratinocytes from the wound edge to the base of the wound, resulting in wound re-epithelialisation.6, 7 If epibole is present, keratinocytes migrate from the top layer down to the bottom layer of the skin and re-epithelialise the lower edges of the wound. This prevents merger of the wound edge with the wound base, thereby stalling wound healing. This is why wound edges need to be angulated to facilitate the process of merger and prevent epibole.
However, debridement of the wound edges at a 45° angle is not always practical, especially when the wound is deep. Based on the Pythagorean theorem, the area of the edge needing resection (the hypotenuse ‘c’) would be equal to the sum of the squares of the other two sides (depth of the wound ‘a’ and the projected width of the resected edge ‘b’, (c = √(a2 + b2)), and where ‘a’ would need to be equal to ‘b’ to create a 45° angle within the shortest possible distance). For example, if the vertical wall ‘a’ (i.e., wound depth) is 1cm and ‘a’ is equal to ‘b’, then ‘c’, the area of the edge needing to be debrided, would be 1.41cm (Fig 1a). The wound size would increase if vertical edges needing angulation are all around the wound periphery. In addition, the angle would also change and become >45° several days after debridement due to a physiological wound contraction.
Despite a well-known axiom that opening edges ‘makes the wound bigger to get it smaller’, this is sometimes not practicable or possible.
This article introduces a novel technique for complicated wounds with vertical edges when it is not possible or desirable to debride them at a 45° angle, or when the wound base and the wound edges do not merge. Often these two clinical scenarios coexist. ‘Edge trenching’ is a technique that can be used in such cases. A small curette (typically 2–3mm for shallower wounds and 4–5mm for deeper wounds) is used to excavate a trench at the point of merger of the wound base and the wound wall. The base of the wound and the edge are resected, at an approximate ratio of half and half, at each visit (Fig 1b). Results can be observed after 2–3 edge excavations, if the patient is seen every 1–2 weeks. This creates a new wound where the base of the wound connects to the edge. The newly created trench facilitates the healing process by stimulating the platelets to release growth factors that then move the wound into the inflammatory phase. Assuming all other impeding factors can be adequately managed (e.g., diabetes, perfusion, smoking cessation), the wound will then progress to proliferation where collagen crosslinking takes place. This allows tissues in the wound base to merge with the typically vertical edge and creates a favourable transitional angle (Fig 1c).
Case study
A 73-year-old male presented with an infected necrotic Charcot ulcer on his left foot which had been present for about a year. The patient had poorly controlled diabetes type 2 (his haemoglobin A1c was 8.3% at the time of the admission) and a history of chronic kidney disease, stage 3. A number of years before, the patient underwent below-the-knee amputation of the contralateral extremity due to infection. There was a known history of peripheral arterial disease and the patient underwent left iliac stenting and femoropopliteal bypass six months prior to his admission. Surgical debridement of the infected ulcer was performed in the operating room. The wound initially measured 3×6×1.5cm. Tunnelling was noted towards the 3 o'clock position, which was unroofed in the wound clinic (Fig 2a). Bone was palpable in the base but it was not exposed. The deep wound culture grew out meticillin-resistant Staphylococcus aureus (MRSA). A computed tomography (CT) scan of the extremity did not reveal osteomyelitis and the patient was given linezolid for treatment of his soft tissue infection. Negative pressure wound therapy was used initially; however, it was discontinued after a few weeks as the wound base tissue showed a hypergranulatory response and was not connected to the wound edges (Fig 2b). Debridement and cautery with silver nitrate was used to control tissue hypergranulation. Offloading of the left foot was an issue due to the previous right lower extremity amputation. A TCC-EZ (Integra LifeSciences, US) total contact cast system was applied to offload his left extremity during his weekly clinic visits. Debridement of the edges at a 45° degree angle was not an option due to wound depth and plantar tissue composition. Merger of the wound wall and edges was noted after the first month when excessive tissue hypergranulation in the wound base was brought under control by chemical cautery with silver nitrate and sharp debridement. By using the edge trenching technique, the base and the walls of the wound were merged, and healing progressed so that the wound closed within 13 months and remained closed after six years (Fig 2c–e). The patient is now using a Charcot restraint orthotic walker (CROW)-boot for ambulation. His foot X-rays have remained stable.
The patient provided written consent for the publication of these case details and photographs.
Discussion
Edge trenching facilitates connection of two walls that otherwise do not merge. After edge trenching is performed, the newly created wound starts undergoing typical healing stages. The trench involves two walls (the base and the edge) in equal proportion and two wounds become one. While they may not have been initially connected, the healing processes evolve simultaneously in both walls. During the process of proliferation, collagen fibres from the two walls crosslink and create one wound that becomes a connecting piece between the edges and the wound base. This process ‘glues’ the two walls. The newly created wound contracts and creates a smooth transitional wide angle that allows keratinocytes from the wound edge to migrate to the wound base. If wound edges are mobile, it is important to try to immobilise them to allow the crosslinking process to take place uninterrupted. The procedure is repeated during each visit until the connection between two walls is visible to the naked eye. The results are usually seen within the first 2–3 debridements.
Conclusion
In summary, the ‘edge trenching’ technique can be attempted when the tissue in the wound base is not merged with the walls or if vertical walls are present such that debridement of wound edges at a 45° angle is not possible. Further clinical research may shed light on the best curette size for edge trenching and histopathological changes in the excavated trench.