The Use of Negative Pressure Wound Therapy in Orthopaedic Trauma
Sven Putnis, Wasim S Khan, and James M-L. Wong
The authors have no disclosures relevant to this article.
The use of negative pressure wound therapy (NPWT), most commonly provided with the vacuum-assisted closure system (VAC; KCI, San Antonio, Texas) using a sealed open-pore sponge or gauze, is now common place within orthopaedic and trauma departments.
Since their introduction 18 years ago, modern NPWT systems have enjoyed an increasing popularity, despite a comparative paucity of reliable clinical evidence. More recently, randomized controlled trials and larger studies have been published studying the clinical benefits of NPWT in orthopaedic trauma setting.
Mechanism of Action
The advent of modern NPWT systems is attributed to Argentas and Morykwas [1,2], who developed several prototypes to facilitate wound healing by distributing suction across wounds to help draw the skin edges together. They developed a system in which an open-pore polyurethane foam sponge was placed within a wound, covered by a semi-occlusive dressing, and then connected to a device producing suction. NPWT facilitates wound healing through multiple mechanisms of action both at the macroscopic and microscopic level [3,4]. The primary mechanisms of action include:
- Macrodeformation of the wound when, depending on the deformability of the surrounding tissues, the wound edges are brought closer together by the suction distributed through the foam sponge. This reduces the space that needs to be healed by primary closure or secondary granulation (Figure 1).
- Microdeformation of the wound surface at the microscopic level. Finite element computer models have shown that NPWT produces 5-20% strain across the healing tissues, which promotes cell division and proliferation, growth factor production, and angiogenesis .
- Extraction of oedematous fluid and exudate from the extracellular space, removing inflammatory mediators and cytokines whose prolonged effect can hinder the ability of the microcirculation to support damaged tissue. This can lead to further tissue necrosis frequently seen at further debridement.
- A warm and moist environment that prevents desiccation of the wound and enhances formation of granulation tissue (Figure 1) .
Figure 1. NPWT dressings can bring wound edges closer together and promote the production of granulation tissue in large wounds.
Components of an NPWT System
A number of systems are now available on the market, and they all share a similar design:
- Base unit pump to provide negative pressure
- Canister to collect wound drainage
- Segment of tubing connecting this to the sealed wound
The NPWT device works by providing and distributing negative pressure evenly across the wound bed either through the application of an open cell foam or a gauze dressing . Foam and gauze have been shown to be equally effective at wound contraction and stimulation of blood flow at the wound edge .
Foam has been shown to provide rapid granulation , but this can be offset by in-growth with potential to disturb the epithelialization process and also be painful when the foam is changed [10–13]. An example of multiple large wounds being treated with foam NPWT dressings can be seen in Figure 2.
Figure 2. Multiple large wounds caused by a suicide bombing are being treated with NPWT dressings.
Base unit pumps can be set to various pressures and usually have 2 settings: continuous and intermittent. Wounds with high drainage require continuous suction, and lower pressure settings tend to be indicated when wound edges are fragile, have low perfusion, are painful, or where a skin graft is being used . A continuous pressure of -80 mmHg to -125 mmHg is therefore most commonly used in traumatic orthopaedic wounds.
As of January 2014, NPWT has been used in more than 800 peer-reviewed studies published in journals across all medical and surgical specialties, demonstrating its potential in acute and chronic wounds and postoperative recovery .
The evidence for its use in orthopaedic trauma departments initially focused on open fractures with soft tissue defects, but usage is frequently seen in contaminated wounds, and more recently, increasing evidence is emerging on its ability to aid closed incisions that have a high risk of wound breakdown. The evidence for its use on skin grafts is now well established.
Open Fractures with Soft Tissue Defects
Open fractures are at risk of developing complications; infection and non-union are often the most common and can cause the most significant morbidity . Published deep infection rates for open tibial fractures range from 8% to 12% [16–18]. NPWT dressings were first described in the medical literature for use with open fracture wounds .
The primary surgical treatment of an open fracture must always start with thorough debridement and stabilization of the fracture before addressing the soft tissue defects . Following the British Orthopaedic Association Standards for Trauma (BOAST) and British Association of Plastic & Aesthetic Surgeons (BAPRAS) guidelines ensures that a thorough exploration of the wound is performed to facilitate diagnosis of the extent of damage.
A subsequent careful debridement of non-viable tissue and contaminants followed by irrigation reduces the risk of infection. Careful hemostasis and coverage of all vital structures such as vessels or nerves prepares the wound for the application of NPWT.
Further debridement of tissue that is subsequently noted to be non-viable may be required prior to healing by secondary intention with granulation tissue, wound closure, or plastic surgical coverage .
It is these periods between operative interventions in which NPWT is most commonly used, showing advantages over the standard wet-to-dry (WTD) dressings. This is particularly relevant to open fractures with extensive soft-tissue injury, with reported infection rates as high as 66%, mainly caused by nosocomial bacteria [22,23]. By sealing the wound, NPWT offers protection from nosocomial contaminants as well as promoting local wound perfusion and drainage.
A number of studies have compared NPWT with WTD dressings. Stannard et al  studied 62 severe high-energy open fractures, all receiving an initial irrigation and debridement and returning to operating room every 48 to 72 hours until wound closure. Thirty-seven fractures were randomized to interval NPWT and 25 had standard fine mesh gauze dressing.
The NPWT group showed significantly less infections than the control (0 acute and 2 delayed versus 2 acute and 5 delayed, P=0.024). Of the entire study group of 58 patients, 21 had either a rotational, free flap, or skin graft, but the infection rate in this group was not separately analyzed .
A further study by Sinha et al  randomized 30 open musculoskeletal injuries to NPWT dressings changed every 3 to 4 days or standard dressings changed daily. Each time the dressings were changed, measurements were taken, and at day 4 and 8 post-initial debridement, tissue biopsies were taken for histopathologic analysis.
In the NPWT group, significantly reduced wound size (mean 13.24 mm versus 3.02 mm, P=0.0001) and bacterial growth (60% no growth versus 20%) were found over the 8 days, as was significantly increased angiogenesis, granulation tissue, and fibrosis (Wilcoxon signed-rank test P<0.05). All patients healed without infection, with 1 requiring a free flap.
As a demonstration of the ability of NPWT to encourage the formation of granulation tissue over longer periods, Lee et al  prospectively treated 16 patients with open wounds (exposed tendon or bone) in the foot and ankle region. After initial debridement, NPWT was applied and changed every 3 or 4 days for 11 or 29 days. All but 1 patient healed by secondary intention (production of granulation tissue); a free flap was required in the 1 case that did not heal. There were no reports of infection.
Blum et al  retrospectively reviewed 229 open tibial fractures, with 72% receiving NPWT and 28% receiving conventional dressings. They found a significantly reduced deep infection rate in the NPWT group (8.4% versus 20.6%, P=0.01).
Severity of the injury, using the Gustilo classification, was found to be a univariate predictor of deep infection, with NPWT reducing the risk of deep infection by almost 80%. This is an extremely high figure, even when taking into account the significantly higher rate of free flaps in the NPWT group (28% versus 14%, p=0.03) .
Over a similar retrospective period and in the same trauma center, Liu et al  found that following open lower limb trauma, soft tissue coverage within 3 days of injury and immediately following fracture fixation with exposed metalware minimized pre-flap wound infection and optimized surgical outcomes. NPWT provided effective temporary wound coverage, and did not delay definitive free-flap reconstruction.
The randomized clinical trial findings of Stannard et al , with NPWT patients a fifth less likely to develop infection, and Sinha et al , with a reduction in positive bacterial cultures after 8 days of NPWT, are encouraging.
There is some dispute, however, about whether NPWT actually reduces bacterial load. Although the sealed environment and infrequent dressing changes reduce the potential for nosocomial contamination, the effect on initial contamination is unclear.
An early NPWT animal model study by Morykwas et al  showed reduced bacterial loads of Staphylococcus aureus and Staphylococcus epidermis. Conversely, a retrospective review of 25 patients undergoing NPWT showed an increase in bacterial load throughout the duration of treatment, although beneficial effects on wound healing were noted in most cases .
Lalliss et al  used animal models to create complex open fractures contaminated with either Pseudomonas aeruginosa or Staphylococcus aureus. After a period of 6 days, with debridement every 48 hours, a significant reduction in Pseudomonas levels was seen when compared with the use of WTD dressings, but there was no reduction in Staphylococcus aureus in either group.
A further animal study has shown reduced bacterial loads of Pseudomonas and Staphylococcus when comparing silver-impregnated gauze with standard sponges after 6 days (43% versus 21% reduction in Pseudomonas contamination and 25% versus 11.5% in Staphylococcus aureus) .
NPWT therapy may reduce the effectiveness of antibiotic loaded polymethylmethacrylate (PMMA) bone cement beads. Stinner et al  used a live animal wound model to demonstrate a reduction in effectiveness of vancomycin-impregnated cement beads when used in conjunction with NPWT. The wounds not subjected to NPWT showed a 6-fold reduction in bacteria after 2 days of treatment.
Large, et al  also used a live animal model to compare the effect of NPWT on antibiotic-loaded PMMA beads, but chose to measure antibiotic concentration rather than bacterial count. Sponges were placed directly on the beads or over a closed fascia prior to application of NPWT and compared with a group who had primary wound closure over the beads. All wounds had a deep drain inserted to measure eluted antibiotics. Although wounds with open fascia and NWPT showed significantly less eluted antibiotic in the drains, implying that the action of NWPT reduced antibiotic release, periosteal samples taken at 72 hours from the corticotomy sites to determine tissue antibiotic concentration were similar in all groups.
Incisions at Risk of Breakdown
Emerging evidence supports the use of NPWT on closed surgical incisions and closed wounds that are deemed to be at high risk of wound complications such as breakdown or hematoma formation.
Meeker et al  used a porcine model to demonstrate that wounds appeared significantly healthier and were stronger after 3 days of NPWT, with a significantly higher tensile strength.
Stannard et al  looked at the action of NPWT to treat hematomas and surgical incisions following high-energy trauma. Forty-four patients with post-surgical hematomas with wound drainage for more than 5 days were randomized to be treated with NPWT or compression bandaging. The NPWT group settled quicker, with a lower infection rate (1.6 versus 3.1 days; 8% versus 16% infection).
Forty-four separate patients who had internal fixation of high-risk fractures (calcaneus, tibial plateau, tibial pilon) were also randomized . Although the NPWT group had better postoperative drainage (1.8 versus 4.8 days to achieve grade 3 status, defined as drainage <2 quarter American dollar coin size drops, P=0.02), there were similar rates of wound breakdown and infection.
Another paper from Stannard et al , with a larger cohort of 263 high-risk fractures, added to these findings. In this study, infection rates in the NPWT group were shown to be lower than a control group (14 versus 23, P=0.049), with the relative risk of developing an infection calculated to be 1.9 times higher in the control group than in patients treated with NPWT (95% confidence interval 1.03-3.55).
The use of NPWT for wounds at risk of breakdown has also been supported in a systematic review  by the International Negative Pressure Wound Therapy Expert Panel (NPWT-EP), which has met annually since 2009 to establish an international consensus that allows the formulation of clinical guidelines.
The application of NPWT to a new skin graft is common practice, with a number of studies showing an improvement in graft incorporation using a pressure range between -50 to -80 mmHg [1,36,37]. Loss of partial-thickness skin graft has been shown to be consistently lower when compared with standard bolstering [38–40].
Despite the increasing clinical support for the use of NPWT seen in this article, few studies have commented on the rate of complications in their series, or the impact therapy has had on the patient.
Failure of the vacuum pump has been shown to affect the efficacy of the therapy. In a series of 123 consecutive orthopaedic trauma patients treated with NPWT, the device unexpectedly powered off in 12 patients (10%), causing an initially unrecognized interruption of therapy. Despite 11 of those patients undergoing early (<6 hours) wound debridement and reapplication of NPWT, 7 patients experienced wound complications, with an overall significantly higher rate of infection and graft loss (P<0.05) .
Pain and skin trauma have been noted in a number of studies when reviewing all applications of NPWT across all specialties. A recent systematic review identified 30 papers in which pain and skin trauma were noted. The article went on to indicate that a gauze-based dressing, rather than foam, may reduce both issues .
A randomized study on the use of NPWT versus sterile gauze dressings on closed total knee arthroplasty incisions had to be abandoned early as 15 of the 24 patients in the NPWT group developed blistering .
In 2011, the US Food and Drug Administration (FDA) reviewed NPWT use over the previous 4 years in hospitals and in the community . In total, 12 deaths and 174 injury reports were attributable to NPWT. The most severe complications were seen in excessive bleeding from wounds near the groin, presternal region, and over vascular grafts.
The review also noted excessive bleeding could occur at the time of dressings changes in patients on anticoagulation or in patients with significant adhesions between sponge and wound bed.
In addition, the FDA review highlighted 27 reports that indicated worsening infection when treating infected wounds with NPWT, as well as infection resulting from pieces of dressing that remained in the wound. There were also 32 reports that noted injury from foam dressing pieces and foam sticking to tissues or clinging to the wound.
The FDA subsequently released guidelines for healthcare providers using NPWT devices . They recommend that users of NPWT undergo appropriate training on device use, including its indications and contraindications and recognition and management of potential complications. NPWT training for patients and their caregivers who will be using the device at home should include how to:
- Safely operate the device; provide a copy of printed instructions for patient use from the specific device manufacturer
- Respond to audio and visual alarms
- Perform dressing changes
- Recognize signs and symptoms of complications, such as redness, warmth, and pain associated with possible infection
- Contact appropriate healthcare providers, especially in emergency situations
- Respond to emergency situation – for example, if bright red blood is seen in the tubing or canister, immediately stop NPWT, apply direct manual pressure to the dressing, and activate emergency medical services
NPWT is an attractive alternative to standard dressings in a number of orthopaedic trauma-related wounds. Benefits include maintaining a seal against contamination and reducing the number of dressing changes.
There appears to be a reduction in the rate of infection, but whether this is due to a decrease in nosocomial infection or due to the environment created by the NWPT is unclear, and there may be a difference in effectiveness across types of bacteria. Routine NWPT practice should always include regular wound re-evaluation with debridement and irrigation as required.
With increasing adoption of NPWT and some good evidence for its efficacy, researchers may be unwilling to subject patients to standard dressings as control groups for trials. Further studies are, however, still required in a number of areas such as the duration of therapy, the effect on antibiotic concentration, and the effect on the type of dressing subjected to NWPT – for example silver-impregnated or gauze versus sponge.
As an emerging indication, there are some encouraging early results from the use of NPWT on post-traumatic surgical incisions. It will be fascinating to see if further research can demonstrate whether NPWT can improve wound healing or reduce the impact of a post-surgical wound complication.
Sven Putnis is from the Royal National Orthopaedic Hospital, Stanmore, Middlesex, United Kingdom. Wasim S. Khan is from the University College London Institute of Orthopaedics and Musculoskeletal Sciences, Royal National Orthopaedic Hospital, Stanmore, Middlesex, United Kingdom. James M-L. Wong is from the Department of Trauma and Orthopaedics, Queens Hospital, Barking Havering and Redbridge University Hospitals NHS Trust, Romford, Essex, United Kingdom.
Putnis S, Khan WS, JM-L. Negative Pressure Wound Therapy – A Review of its Uses in Orthopaedic Trauma. Open Orthop J. 2014; 8: 142–147. Published online 2014 Jun 27.
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