Use of a synthetic biodegradable temporising matrix after necrotising fasciitis infection of the thigh

Background

Biodegradable temporising matrix (BTM NovoSorb; PolyNovo, Melbourne, Australia) is a novel completely synthetic dermal substitute.1 It is designed using NovoSorb biodegradable polyurethane foam.1 Licensed in Europe in 2020, this matrix was primarily developed for reconstruction of traumatic and infected wounds.1 Similar to Integra (Integra LifeSciences, Plainsboro, New Jersey, USA), BTM is considered an active temporiser that contributes to wound bed tissue ingrowth and a ‘neodermis’ that will sustain subsequent wound closure.2 However, the use of Integra has been limited as its biological composition makes it prone to infection and loss.2

BTM is composed of NovoSorb matrix sheet, a 2 mm thick bioabsorbable open cell matrix that allows cellular seeding (fibroblasts initially, followed by keratinocytes) to aid in reconstruction of the dermal layer.1–3 This matrix is bonded to a non-biodegradable sealing membrane that limits moisture loss and acts as a barrier to infection.1–3 The procedure is a two-stage reconstruction that involves inset of the material into the defect to allow for host integration and neodermis generation, followed by delamination of the superficial membrane and application of a split thickness skin graft (STSG) approximately 5 weeks later.3

Initially used in human trials to reconstruct free flap donor sites and in pressure sore management, several case reports have shown that it aids in the closure of complex defects such as bare tendon, acute burn injury and large complex wounds following necrotising fasciitis.2–10 BTM was offered as a potential solution to reconstruct the thigh of this relatively healthy man in his 60s with a large circumferential defect that he sustained postdebridement for necrotising fasciitis. A STSG alone has a high risk of failure because of the infected wound bed and absence of a vascularised dermal layer.

Case presentation

A relatively healthy man in his 60s was transferred to a tertiary trauma hospital postdebridement of necrotising fasciitis of his left thigh. Initially, he presented to the general practitioner with multiple purulent discharging sinuses on his left anterior, medial and posterior thigh. His medical history was significant for liposarcoma of the adductor compartment of the left thigh 16 years earlier that was treated by radical surgery. This involved an incision that extended from the groin to the knee. He later developed a number of recurrences that were managed by surgery and adjuvant radiotherapy. As a result, the quality of skin on his thigh was grossly abnormal.

The thigh was debrided circumferentially down to fascia exposing the quadriceps anteriorly and the hamstrings posteriorly into the popliteal fossa without exposing the neurovascular bundle. Despite a preoperative CT scan showing air and swelling within muscle, the muscle was essentially healthy and therefore preserved. A vacuum-assisted closure (VAC) dressing was applied to help regenerate the wound bed.

On physical examination, the patient had left foot drop and left lower limb lymphoedema dating back to his original treatment, and he used compression stockings and a foot brace. Otherwise, he had normal lower limb function and mobilised without walking aids at baseline.

Investigations

Preoperative urine and bloods tests were normal. The wound appeared to be colonised with Pseudomonas aeruginosa when the VAC dressing was removed and confirmed on wound culture.

Treatment

His wound was further debrided under general anaesthesia, and BTM was applied to close the defect (figure 1). The BTM was secured with staples and dressed with Acticoat Flex 7 silver-coated antimicrobial barrier dressing (Smith & Nephew, London, UK) (figure 2). The Acticoat Flex 7 fulfilled the recommended guidelines for outer dressings as it has both non-adherent and antimicrobial properties.1 Once he was able to weight bear, he was discharged. On postoperatively day 4, he developed left lower limb cellulitis despite being on oral antibiotics as his compression dressing was not tightly applied prior to discharge. The left thigh was free of infection, and he was admitted for 3 days intravenous antibiotics. Subsequently, he continued to attend the outpatient clinic on a weekly basis for dressing change and to monitor integration of the BTM (figure 3).

For the first 2 weeks, we expect the BTM to be visible through the clear sealing membrane, gradually forming a dark red colour due to ingress of blood from the wound.1 By the end of week 2, the colour of the BTM changes from a dark red to a light red.1 From weeks 3 to 6, the pattern and microstructure of the BTM will no longer be visible, which is a sign of further integration, and capillary refill is expected when applying digital pressure to the sealing membrane.1 Around the sixth week, the colour starts to become a uniform pink colour that blanches on digital pressure, making it ready for delamination.1

Potential complications to look out for during the weekly dressing changes are infection that should be treated with antibiotics and excess turbid fluid or haematoma beneath the sealing membrane that might interfere with the integration process and adherence of the BTM to the wound.1 If a collection of fluid cannot be expressed through the existing fenestrations in the BTM membrane, then new fenestrations can be made with a scalpel.1 7 Following that, it is advised to wash the BTM seal with either saline or an antimicrobial brush but to avoid soaking it as too much liquid can wash away cells that are integrating.1 7

On day 42, he returned to the operating theatre for delamination of the BTM (figure 4) and definitive closure of the wound with fenestrated STSGs (figure 5). A small region in the posterior superior area of the thigh and the popliteal fossa were not grafted and left to heal by secondary intention. He was on strict bed rest and was given 7 days of dual antibiotics (augmentin and ciprofloxacin). Seven days later, graft review showed more than 80% take of the STSGs (figure 6). The donor site (right thigh) was slow to heal but improved with a protein-rich diet and supplements (figure 7).

Outcome and follow-up

At 5 months, he had a soft, mature pliable scar on the left thigh with return to baseline mobilisation. His donor site wound has fully healed (figure 7). The two regions that were left to heal by secondary intention continue to be dressed with Inadine two times per week with good progression.