JSUR Journal

Introduction

Several treatment options are known for skin defects on the hand or forearm depending on exposed structures and area. Therefore, the use of split- or full thickness skin grafts, pedicled (rotation or transposition flaps with or without skin) or free flaps are sufficiently described. Also, the use of artificial dermal templates plays a role in wound closure after injury. However, defects after severe trauma, infections, burns or excisional biopsies of a tumor may be challenging, especially in multimorbid patients, with exposed bone, tendons and nerves. NovoSorb^®, Biodegradable Temporizing Matrix (BTM, NovoSorb^®, Polymedics, Woodstock, United States), is a synthetic device with a polyurethane bilayer matrix. According to the manufacturer, BTM is robust in the presence of infection, minimize scarring and contracture, is easy to apply and serves as a cost-effective alternative to biologics [1]. Several studies have determined the safety and ability to provide permanent wound closure when combined with a split thickness skin graft in a two-stage procedure in pigs, mice and humans [26]. This study was designed to assess wound closure especially in finger, hand and forearm injuries with exposed structures that otherwise require a flap. The aim was also to analyze the range of motion and therefore the gliding behavior of the tendons, which is essential in hand function. In addition, we analyzed the various indications and suitability for covering defects with BTM.

Material and Methods

 BTM is described as a bilayer matrix with a sealing membrane and the NovoSorb^® matrix. The non-biodegradable sealing membrane limits the loss of moisture while providing a barrier against bacteria. The bioabsorbable matrix allows a cellular infiltration whereby the dermis regenerated within the matrix [1]. Integration of BTM proceeds in phases and after removal of the sealing membrane the surgeon has the choice between a closure by secondary intention or a split-thickness skin graft. In this study, the following procedure was used: after initial debridement, BTM was applied to the wound. A cellular migration into the matrix leads to new blood vessel formation and production of collagen. After the granulation tissue has formed and fully visibly integrated into the BTM layer, the sealing membrane is removed and a new, vascularized dermal layer emerges. An unmeshed split-thickness skin graft was then harvested from the thigh or inner side of the upper arm and added to the vascularized layer followed by a vacuum-therapy or a tie-over dressing for five days. During that period, the hand was immobilized in a splint to protect wound healing.

Results

Between December 2021 and December 2022, 27 patients were treated with BTM. 16 patients were male with a median age of 55 years (range 12-77 years), while 11 patients were female with a median age of 45 years (range 18-77 years). In 20 cases, the soft tissue defect was caused by a severe trauma. In four patients, there was a skin defect because of an infection. In one case each, an epitheloid sarcoma, Dupuytren’s disease or a MDA5 Dermatomyositis caused a skin defect. The dorsum of a finger was affected in 13 cases and the dorsum of the hand in five cases. Four patients suffered from an amputation of one finger (Level of amputation: Zone I and II according to Tamai [7]). One patient each demonstrated a substantial defect at the forearm, at the thenar respectively at the palm. The size of the skin defect ranged from 1 cm² to 200 cm². In four cases the final wound closure was initiated by secondary intention and in one case, the BTM was used in a double layer of the matrix height to rebuild the finger pulp. The BTM was applied in nine cases on exposed extensor tendons (see Figure 1 and Figure 2). Furthermore, it was used in nine cases to cover muscle or soft tissue, in five cases to cover bone, in two cases to cover the neurovascular bundle and on one patient each to cover a flexor tendon and nerve transfer (see Figure 3). On average, the duration between covering the soft tissue defect with BTM and the application of a split-thickness skin graft was 36 days (range 21111). The take rate for the split-thickness grafts was 96% (Table 1).

Figure 1: Example for BTM covering extensor tendon reconstruction.

a)  65 years old patient with skin defect (6x2cm), extensor tendon defect und nail bed defect caused by milling machine injury.

b)  Reconstruction of the extensor tendon with palmaris longus tendon graft.

c)  Application of BTM (6x2cm) over the tendon graft.

d)  Granulation tissue after removal of the sealing membrane.

e)  Unmeshed split thickness graft with drainage holes.

f)   Situation four weeks after split thickness skin-grafting.

Figure 2: Example for BTM covering branches of the superficial radial nerve and tendons of first extensor compartment.

a) 78 years old patient with exposed branches of the superficial radial nerve and first extensor compartment including a 25x7cm soft tissue defect caused by a fall.

b)  Application of 25x5 cm BTM.

c)  30 days after BTM application.

d)  5 days after split thickness skin-grafting.

Figure 3: Example for BTM covering nerve transfer at the left thumb.

a)  45 years old patient with defect of the radio-palmar nerve of the left thumb caused by dog bite.

b) Sensitive end-to-end nerve transfer of the radio-dorsal to the radio-palmar digital nerve of the thumb.c) After BTM Application (size 7x5 cm).

d)  24 days after BTM.

e)  44 days after split thickness skin-grafting.

In one case an intermetacarpal island flap was required to reach soft tissue reconstruction (Figure 5) after an enterobacter cloacae infection and already performed BTM application. All other defects healed with BTM and split thickness skin graft (25x) or secondary intention (1x). There were four soft tissue defects that could be successfully covered with BTM despite a known wound infection with pan-sensitive and penicillin-resistant staphylococcus aureus, group B beta hemolytic streptococcus and multiresistent enterobacter cloacae bacteria (Table 1). The average active Range Of Motion (ROM) at least three months after the application of the split thickness graft was analyzed for the fingers and separate for the thumb, (see Tables 2,3). The gliding capacity depended not only on the coverage with BTM, but also on the accompanying injuries.

Table 1: Study population and statistics.

Table 2: ROM for fingers at least three months after surgery.

Table 3: ROM for thumbs at least three months after surgery.

Histological Assessment: The histological assessment of one reference case showed a pronounced scarring fibrosis and a foreign body giant cell reaction. 72 days after the split thickness skin graft was applied, the actual polymer could not be detected but still focal optically empty cavities were identified, perhaps indicating residual portions of the polymer.

Complications: The soft tissue cover over the bony stump after a finger amputation (Tamai Level II) was found to be insufficient at 8 weeks in one patient after split thickness skin-graft. The vulnerability lasted up to five months and then completely regressed. After the fifth month, the patient was able to perform heavy labor without coverage of the stump with a dressing anymore (Figure 4).

Figure 4: Vulnerable bony stump palmar after an IV. Finger amputation (Tamai level II) 8 weeks after skin-grafting. View from palmar (a), lateral (b) and dorsal (c).

One patient suffered from a milling machine injury of the dorsal index finger with a defect of the extensor tendon. A reconstruction with a palmaris longus tendon graft and debriding was performed. The skin defect was covered with a 6x2cm BTM and an empirical oral antibiotic therapy was started (Amoxicillin and clavulanic acid). Penicillin resistant enterobacter cloacae bacteria could be detected from the initial injury and the empirical oral antibiotic therapy was switched to targeted therapy. 47 days after surgery and BTM application the finger was red, swollen and overheated with pus oozing out, see Figure 5. Another debridement was carried out with renewed evidence of enterobacter cloacae bacteria. The definitive soft tissue covering was carried out with a pedicled intermetacarpal flap.

Figure 5: Exemplary infection after BTM application.

a) Initial trauma with reconstruction of the extensor tendon with palmaris longus tendon graft and coverage with BTM. b) BTM coverage 15 days post surgery

c) Enterobacter cloacae infection 47 days after BTM application d) Final result after covery with a intermetacarpal flap.