Chronic axillary wounds in cats: what do we know and how should we manage them?

Abstract

Practical relevance:

Axillary wounds most often occur in outdoor cats that wear a collar, typically after having been missing. These wounds are commonly chronic and indolent in nature, and although there is so far no consensus on an explanation for this, it is likely that there are several factors involved.

Clinical challenges:

Axillary wounds are often difficult to manage due to the frequent presence of infection, their histopathological characteristics and their location, where there is excessive tension and movement of the axillary tissues. Initial surgical treatment has a high reported incidence of failure and complications in the literature, with wound breakdown reported most commonly. Giving due consideration to the difficulties of managing these wounds, however, will help practitioners to decrease the occurrence of complications and the need for multiple procedures, and therefore improve the outcome.

Equipment:

Initial approach and surgical management can be achieved using standard medical equipment and surgical kit available to general practitioners.

Evidence base:

This review discusses the surgical techniques reported in the literature to have successfully treated chronic axillary wounds and recommendations are also provided based on the authors’ clinical experience.

Pathophysiology

Axillary collar injuries are described mostly in cats and are usually the consequence of entrapment of one of the thoracic limbs in the neck collar (see box). Typically these wounds are seen in outdoor cats after they have returned from being missing for a long period. Feline chronic non-healing axillary wounds are uncommon in small animal practice, with 26 cases out of 15,000 cats seen over a 4-year period being reported in one case series. ³

Axillary wounds are usually chronic at presentation. There is no clear explanation as to why chronic non-healing axillary wounds form, but several theories have been discussed, and it is likely that the cause of this condition is multifactorial. It has been proposed that the presence of foreign material, such as hair follicles, may impair the healing process;^3,4 another suggestion is that poor local blood supply in the area leads to the formation of poorly vascularised fibrous granulation tissue (Figure 2). ³ The high mobility of the shoulder and elbow joints, as well as movement across the wound, are also suspected to play a role in creating a non-healing environment, and tension and pressure points have additionally been implicated as potential causes.^3-7

Figure 2.

Chronic axillary wound in a cat. The wound bed is pale pink in colour, indicating the presence of fibrous tissue instead of healthy granulation tissue, which would be a brighter red

No concurrent diseases linked with the presentation of chronic axillary wounds have been reported in cats. Feline leukaemia virus and feline immunodeficiency virus (FIV) have been screened for in at least two reports; however, most of the patients were negative for the presence of viral diseases, failing to prove a link between viral infection and this type of chronic wound in cats.^5,6 Culture and sensitivity results have described the presence of a range of organisms, including Pasteurella species, Staphylococcus species, Streptococcus species and Proteus species.^4,5,6

In the authors’ opinion, it is likely that biofilm formation (see box) plays a role in chronic non-healing axillary wounds, but, to their knowledge, this has not, to date, been investigated.

Cats that are found with their collar missing tend to have wounds that appear clean, whereas those that still have the collar in place (Figure 1) typically present with exudative and grossly contaminated malodorous wounds, often with visible embedded hair. ³ Samples examined using microscopy histologically present as chronic inflammatory tissue and, in some cases, chronic active pyogranulomatous dermatitis, with the inclusion of hair follicles.^4,5,7

Figure 1.

Cat with a chronic axillary wound, which presented with its non-quick-release collar still in place. In this instance, the granulation tissue had started to grow around the collar, embedding it into the wound. Courtesy of Anna Smith

Initial triage and management

At the time of presentation, cats with axillary wounds require initial assessment and stabilisation before any definitive wound management can be considered. While the majority of case reports have described cats with axillary wounds as being in good physical condition on presentation,^3,5 these reports are mostly from referral practices where the patients had already undergone an initial assessment at a first-opinion veterinary practice. As most cats with axillary wounds have been missing for several weeks, they are likely to be dehydrated and possibly emaciated. Fluid resuscitation is often necessary and pain relief is also typically warranted.

Performing initial bloodwork is recommended in order to screen for underlying diseases that may affect the management of the cat and the healing of the wound. Biochemistry results can support a diagnosis of hypovolemic shock ¹³ initially made upon physical examination. Complete blood count is also important to identify lymphopenia and neutropenia, which can indicate an immunosuppressed or immune-compromised patient that would have impaired healing capacity. ¹⁴ Although a link has not been detected between FIV and chronic axillary wounds, other immunosuppressive diseases can lead to the chronic nature of these wounds.

In the authors’ experience, radiography of the thoracic limb may also be useful. Not all wounds in the axillary region are caused by thoracic limb entrapment in neck collars and acute wounds in this area can be the result of trauma; radiography of the thoracic limb and thorax is therefore necessary in some cases, ¹⁵ for instance if abnormal thoracic auscultation or abnormal limb movement/alignment or crepitus on palpation are identified.

For further information on triage and emergency medicine, the authors refer readers to Donnelly and Lewis. ¹⁶

Immediate wound care

The first step in managing the wound is irrigation, in order to remove debris and decrease the microbial burden. The volume of the cleaning solution is more important than its antimicrobial or sterility proprieties.^17,18 Sterile water and tap water appear to have similar results when used to flush wounds,^18,19 although in one in vitro study normal saline solution (not buffered) and tap water were shown to cause injury to canine fibroblasts, whereas other isotonic solutions (buffered) did not. ²⁰ The authors use a 1 l bag of isotonic fluid attached to a giving set and a 19 G needle with a pressure bag at around 300-400 mmHg to flush wounds (Figure 3). ²¹ This should provide enough end pressure to remove both debris and bacteria from the wound without causing further trauma to the wound bed. ²²

Figure 3.

Wound irrigation system. From left to right: 1 l of saline, a fluid therapy giving set above an 18 G needle (left) and a three-way tap (right), sterile gloves and a pressure bag

Antimicrobial treatment

For long-term resolution of an axillary wound, antimicrobial therapy is important, and particularly when reconstruction with a skin flap is planned, as infection is one of the most common complications observed. ²³

As mentioned earlier, the reported microorganisms populating chronic axillary wounds are varied. While there are no specific guidelines regarding antimicrobial treatment of wounds in veterinary medicine, the following antimicrobial stewardship guidelines should be followed:

• ✜ taking measures to prevent common diseases;

• ✜ using evidence-based approaches when making decisions about antimicrobial drugs;

• ✜ using antimicrobial drugs wisely and carefully.^24,25

In order to follow these guidelines, a sample of tissue (or a swab; see box) should be taken for microbial culture and sensitivity testing to assess which antimicrobial drugs are appropriate. Until the results, which can take a few days to return from the laboratory, are known, the authors recommend that empirical first-line broad antimicrobial therapy is administered if the wound is considered to be infected, indicated either by obvious malodour and purulent discharge or in-house cytology demonstrating the presence of bacteria in the wound bed. ²⁹ Following antimicrobial usage guidelines from the Danish Small Animal Veterinary Association, ³⁰ the authors’ first choice of antimicrobial is amoxicillin/ clavulanate at a dosage between 12.5 mg/kg and 20 mg/kg q8-12h PO or IV. ³¹

Although broad-spectrum antimicrobial therapy may have already been started, the culture and antibiotic sensitivity results are important to assess the appropriateness of the antimicrobial initially provided, in order to follow evidence-based treatment as per the stewardship guidelines. A recent study did not show any significant value of performing culture on acute traumatic wounds in dogs; ³² however, the same has not been demonstrated in cats with chronic wounds, such as axillary wounds in patients that have been missing for a long period of time. As an example of the importance of culturing this type of wound, the multi-resistant bacteria methicillin-resistant Staphylococcus aureus (MRSA) has been reported in one cat. ³³

Initial wound protection and dressing

To protect the wound from further exterior contamination and possible injury, protection with a dressing may be required at initial presentation. The type of dressing should be chosen based on the type and healing phase of the wound. Dressings may not be appropriate, however, depending on the stage of wound healing and whether there is or is not the presence of active infection or exudative characteristics. Effective bandaging may also not be possible depending on the location of the wound.

Highly contaminated or necrot-ic wounds should be dressed using a wet-to-dry bandage to protect the wound while removing the unwanted bacteria and unhealthy tissue that will delay the healing process. A tie-over bandage may be a good option to dress an axillary wound (Figure 4).

Figure 4.

Example of a tie-over bandage used to dress an axillary wound. Courtesy of Nathalie Dowgray

Further information about wound management and dressings can be found in Bella and Williams. ³⁴

Surgical debridement to remove dead tissue from the wound should be considered and can be carried out prior to primary closure of the wound under the same general anaesthesic.

Definitive wound care - treatment approaches

Simple suturing of the wound edges

An initial approach to this type of wound can be as simple as suturing the wound edges together after minimal debridement. However, complications after initial wound closure leading to suboptimal outcomes and further treatment have frequently been reported in the literature.^3,4,6,7 The reasons described earlier for why a wound might become chronic and non-healing may also explain why the complications with this surgical approach are likely to occur. Due to the high incidence of dehiscence reported, several other techniques, which are described below, have been proposed in the literature to improve healing and, ultimately, the outcome.

Omentalisation of the wound

Omentalisation of the wound prior to primary wound closure has been suggested to enhance wound healing. The approach described by Lascelles and colleagues, which can be found in the box, achieved positive results in 70% of the wounds presented, and the average healing time was 24 days. ⁷

The aims of the omental pedicle graft are to reduce dead space and promote adequate blood supply and lymphatic tissue, as this assists with controlling infection by providing the wound with inflammatory factors and cells, which lead to adhesion formation and neovascularisation.^5,17

Figure 5.

Single paracostal approach for omentalisation. (a) Following a paracostal skin incision and laparotomy, the omental attachments are released and the omentum is exteriorised and tractioned cranially. (b) Subcutaneous tunneling is performed bluntly using a pair of artery forceps from an incision paracostal to the axillary wound and the released omentum is then tracked cranially through the tunnel, exiting at the caudal edge of the wound so it is (c) ready to be sutured to the wound bed

Figure 6.

Vascular anatomy of the axillary skin. TDA = thoracodorsal artery; ETA = external thoracic artery; AA = axillary artery; LTA = lateral thoracic artery

Skin flaps

Flank and elbow skin folds are very mobile and can be moved and used to close large defects in the thoracic limb or cranial thoracic regions. These skin folds are formed of two layers of elastic skin of triangular shape, one lateral (outer) and one medial (inner), which are kept together by loose connective tissue. A good understanding of the vascular anatomy of skin flaps (see box above) is important in order to ensure the vascular supply is not compromised while preparing a flap.

Axial pattern flaps, such as the thoracodorsal and lateral thoracic artery axial pattern flaps and the omocervical flap, have been described to provide full-thickness skin coverage, resistance to infection and early immobilisation and neovascularisation, which are major advantages that improve the outcome of the wound coverage. ⁵

An elbow skin fold flap, which, as mentioned in the box above, can function as an axial pattern flap, is created by detaching the skin from the trunk to allow cranial advancement (see the box below). In the authors’ opinion, an elbow skin fold flap can be used as the first approach for closing chronic axillary wounds, as this technique is less technically demanding than others described in the literature. Brinkley, ³ in a case series of five cats, also described the use of elbow skin fold flaps to be less technically demanding, quicker and cheaper, and to lead to less complicated recoveries than previously reported techniques. None of the five cats, which also had a Penrose drain placed in the surgical site, required further surgical intervention and the wounds had fully healed 10 days postoperatively. It is only possible to perform the elbow skin fold flap technique when there is enough axillary skin available; in most reported cases in a referral setting, however, chronic axillary wounds had been presented after several surgical attempts to close the skin defect and so there was not always enough elbow skin fold for this procedure.

One of the most common complications associated with skin flaps is seroma formation, which may lead to infection. ²³ For this reason, active suction drains are frequently placed in these patients. ³⁷ While passive drains could, alternatively, be considered, these have a higher incidence of infection since this drain system is open, allowing bacteria to enter the wound, potentially leading to ascending infection; in addition, the active drains are more effective as they do not rely on gravity.^38,39 The authors of this review therefore recommend active drains in preference to passive drains.

Figure 7.

The arrows indicate on the chronic axillary wound shown in Figure 2 the areas of skin to be released from the thoracic wall, once the skin edges and granulation tissue have been excised, in order to create an elbow skin fold flap

Omentalisation and skin flap combination

Combining omentalisation with a skin flap has also been reported as an alternative to omentalisation alone, and has led to a reduced number of cases requiring revision surgery to repair wound dehiscence. In one study combining omentalisation and a thoracodorsal axial pattern flap, 100% of the wounds had healed within 14 days and only 20% required minor revision surgery in the postoperative period. ⁴ In a case report, minor surgery involving wound debridement was required in a cat that had undergone omentalisation and an omocervical skin flap, but there was complete healing of the wound after 6 weeks. ⁵

The omentalisation-skin flap combination is believed to often achieve a good outcome because there is both the advantages provided by the omentalisation and the recruitment of extra skin, minimising the movement and tension in the area. Lascelles and White ⁴ also suggest that the ability to position the suture lines outside of the axilla, by performing an axial pattern flap, leads to reduced friction between suture and skin. The authors recommend omentalisation and a thoracodorsal axial pattern flap if an elbow skin fold flap is not possible.

Postoperative care and monitoring

Full healing (Figure 8) can take up to 2 months in some cases. ⁷ During this period, postoperative care should include strict cage rest to limit possible flap movement and friction. Cage rest also helps the owner to monitor the wound and report any complication as early as possible; as these cases are usually indoor–outdoor cats, cage rest is particularly helpful with this.

Figure 8.

(a,b) Fully healed axillary wound post-reconstruction using the elbow skin fold flap technique. Courtesy of Laura Owen

Dressing the wound should be avoided as it can impair vascular supply and has been associated with suboptimal outcomes in one study. ⁷ The authors of this review recommend the use of a soft buster collar to avoid wound interference from the patient.

Key Points

• ✜ A patient with chronic axillary wounds should first be stabilised. Fluid resuscitation is often necessary in conjunction with pain relief. Concomitant thoracic and forelimb injuries should be ruled out before wound treatment.

• ✜ The wound should be sampled for histopathological analysis and culture and antibiotic sensitivity testing.

• ✜ Antimicrobial therapy should be considered in cases where infection is determined to be present, either by the wound being visibly purulent, with discharge and/or abnormal odour, or there being direct visualisation of bacteria from a superficial swab or smear.

• ✜ Surgically, primary wound closure using an elbow skin fold flap can be used as the first approach; in the authors’ opinion, this is less technically demanding than other techniques described in the literature. When this is not possible, a combination of omentalisation and a thoracodorsal axial pattern flap can alternatively be used. An active suction drain, rather than a passive drain, is recommended.