Surgical Treatment of an Elbow Hygroma Utilizing Microvascular Free Muscle Transfer in a Newfoundland

Introduction

A hygroma is defined as any chronic tissue swelling, which contains serous fluid that is often the result of repeated trauma to soft tissues overlying bony prominences.^1,3 Hygromas occur most frequently in large-and giant-breed dogs, with animals <2 years of age most commonly affected.^1–3 Often these animals are housed on hard surfaces with little to no opportunity to lie on a padded surface.^1–3 The pathophysiology of hygroma development is compromised vascular supply coupled with repetitive trauma, leading to localized ischemia and edema with poor healing and development of fibrous pockets of fluid.¹

Conservative treatment of hygromas with padded bandages may prove effective early in the course of disease; however, many hygromas are refractory to conservative management and require more aggressive therapy. ² Fluid aspiration and medical management of hygromas often fail because of recurrence. Additionally, iatrogenic introduction of bacteria into the hygroma during aspiration may cause infection.² Furthermore, corticosteroid infusion (once thought to promote the resolution of hygromas) is now contraindicated, because it contributes to delayed reparative processes associated with wound healing.^2,3 Surgical removal with primary closure is often the most effective means of treating hygromas, as the tissue responsible for the production of the transudate is removed, thereby minimizing the likelihood that further trauma will lead to recurrence. ¹ Surgical intervention may result in significant complications, including wound dehiscence caused by the motion of soft tissues around the joint, or ulceration as a consequence of the tension accompanying wound closure on an extremity lacking redundant tissue.² Ultimately, a combination of surgical and conservative management is often necessary to effectively treat and minimize the recurrence of complicated elbow hygromas in the dog. Despite the relatively common occurrence of elbow hygromas, there is a paucity of literature regarding their management, and a truly effective means of treatment has yet to be determined.

This report describes a novel surgical approach aimed at maximizing not only wound healing but also the cosmetic outcome of a dog following surgery for elbow hygromas. Rectus abdominis free muscle transfer is a proven technique in human patients with wounds requiring tissue grafts, and it is described experimentally as an effective means of repairing medial femorotibial skin defects in dogs.⁴ Arectus abdominis free muscle transfer, along with a mesh skin graft and transarticular external fixator, were used in the surgical treatment of an elbow hygroma.

Case Report

A 3-year-old, 54-kg, intact male Newfoundland was presented to the Virginia-Maryland Regional College of Veterinary Medicine for evaluation of an actively hemorrhaging hygroma over the left elbow. The hygroma had initially been treated with simple passive drainage by the referring veterinarian approximately 1 year earlier. The hygroma recurred 2 weeks prior to presentation and was treated conservatively with trimethoprim sulfadiazine^a (27 mg/kg per os [PO] q 12 hours) and carprofen^b (2.2 mg/kg PO q 12 hours) without response.

On physical examination, a 20 × 17-cm, fluctuant mass that was oozing marked amounts of serosanguineous fluid was observed over the left elbow. A grade IV/VI systolic heart murmur was auscultated that was attributed to a previously diagnosed subaortic stenosis. The mucous membranes were pale with a capillary refill time of >3 seconds.

A complete blood count (CBC) performed on the day of presentation revealed a markedly regenerative, severe anemia with moderate polychromasia and nucleated red blood cells (15.6%, reference range 39.5% to 62.1%), as well as a mild, mature neutrophilia (9.919 × 10³/UL, reference range 2.455 to 9.170 × 10³/UL) and lymphopenia (0.436 × 10³/UL, reference range 0.913 to 3.281 × 10³/UL). Platelets were found to be adequate in number (347.0 × 10³/UL, reference range 180.0 to 487.0 × 10³/UL). Serum biochemical results showed reduced total protein (4.8 g/dL, reference range 5.4 to 6.8 g/dL) and albumin (2.1 g/dL, reference range 2.8 to 3.7 g/dL). Because of the marked degree of anemia that was present, along with the presence of ongoing blood loss from the hygroma, a crossmatch for major and minor compatibility was performed in anticipation of a blood transfusion. Cytological examination of a fine-needle aspirate of the hygroma revealed cellular characteristics consistent with hemorrhage and inflammation.

A compression bandage was placed on the left forelimb, extending from the middle of the humerus to the distal phalanges to minimize further hemorrhage from the hygroma. Minimizing blood loss from the hygroma via bandaging proved mildly effective in increasing the packed cell volume (PCV), as the CBC performed 4 days later on the morning prior to surgery revealed a PCV of 18.9% that remained markedly regenerative and polychromatic. The mild, mature neutrophilia (10.044 × 10³/UL) was still present; however, the lymphopenia (1.364 × 10³/UL) had resolved.

An echocardiogram was performed prior to surgery to ensure the dog was an acceptable anesthetic risk, and it was judged that the presence of moderate subaortic stenosis would not preclude anesthesia and surgery. Preoperatively, 1 unit (132 mL) of packed red blood cells was administered over 2 hours because of the continued presence of a marked anemia and the anticipation of further blood loss during surgery. Morphine^c (0.25 mg/kg intravenously [IV]) was administered as a preanesthetic agent. Anesthesia was induced with propofol^d (5 mg/kg IV) and maintained with isoflurane^e in 100% oxygen with a mechanical ventilator. Cefazolin^f (22 mg/kg IV) was administered q 2 hours during surgery, while hydromorphone^g (0.04 mg/kg IV) was administered as needed to minimize the need for inhalant anesthetic. Hetastarch^h (0.5 L IV) was given at the onset of surgery over the first 2 hours, followed by crystalloid fluids. A second unit of packed red blood cells (132 mL) was administered intraoperatively.

The 405-minute surgery, involving three surgical sites, culminated in the surgical removal of the hygroma and subsequent wound repair and stabilization of the elbow. The hygroma was sharply excised in its entirety and submitted for histopathological evaluation, and a bacterial culture was obtained. No bacterial growth was noted after 3 days.

Following hygroma excision, the most caudal-pointed portion of the olecranon was removed in order to broaden the point of the elbow and minimize the pressure point postoperatively [Figure 1]. The brachial artery and vein were identified and isolated over the medial distal humerus, while the perivascular adventitial layer was removed from the area of the ensuing anastomosis.⁵ A ventral midline incision was made from the xiphoid to the pubis, and the rectus abdominis muscle to the left of midline was dissected away from the external rectus fascia and internal rectus fascia. The pudendal-epigastric trunk was ligated and removed along with a 12-cm portion of the caudal rectus abdominal muscle. The free muscle tissue was transferred to the defect on the elbow, and the adventitial layer from the recipient vasculature was removed prior to anastomosing the caudal epigastric artery and vein to the previously prepared brachial artery and vein. The arteries were anastomosed using 10-0 nylonⁱ in a simple interrupted pattern, while the veins were anastomosed using a 2.5-mm coupling device^j. The muscle flap was sutured to the surrounding subcutaneous tissues over the olecranon using 3-0 poliglecaprone 25^k in a horizontal mattress pattern [Figure 2].

A 12 × 10-cm area of thin skin was taken from the ventrolateral thorax and prepared as a mesh graft by removing the subcutaneous fat, stretching the graft, and creating fenestrations within it. The mesh graft was placed over the transfer muscle flap and attached to the surrounding skin using 3-0 poliglecaprone 25. The abdominal incision was closed by opposing the left external rectus sheath to the linea alba using 2-0 polydioxanone^l in a simple continuous pattern. The remaining abdominal wound was closed routinely, as was the sternal skin graft harvest site.

Prior to placement of the skin graft, the elbow was immobilized with a type 1A external fixator consisting of two positive-thread-profile pins placed laterally in the ulna and two positive-thread-profile pins placed laterally in the humerus that were connected with a transarticular connecting bar [Figure 3]. A bandage was applied from the middle of the humerus to the distal phalanges to provide added protection to the graft site.

Postoperatively, the dog was sedated with a combination of acepromazine^m (0.02 mg/kg IV as needed) and morphine (0.25 mg/kg subcutaneously [SC] q 4 to 6 hours) for 7 days. Cefazolin (22 mg/kg IV) and heparin (100 U/kg SC) were given immediately following surgery. The heparinⁿ was discontinued the day after surgery, and an antithrombotic dose of acetylsalicylic acid^o (1.5 mg/kg PO q 8 hours) was begun and continued for 6 days. Seventy-two hours after surgery, the bandage was removed and the graft was reevaluated and found to be viable [Figure 4]. Five days after surgery, the PCV had increased to 28%. The dog was hospitalized for 8 days following surgery, for a total stay of 14 days.

After leaving the hospital, the dog was treated at home with bandage changes every other day and thorough cleaning with the application of bacitracin-neomycin-polymyxin ointment^p to the areas immediately surrounding the external fixator pins. The dog received cephalexin^q (22 mg/kg PO q 12 hours) for 14 days.

Histopathological evaluation of the mass revealed it to be composed primarily of granulation tissue in varying stages of maturation. Most of the fibrous tissue was mature with abundant collagen, hypertrophic fibroblasts, and many thick-walled vessels. These findings were consistent with the diagnosis of hygroma.

Twenty-three days after surgery, the dog returned for reassessment of the graft and removal of the external fixator. At that time the dog was effectively using the limb, and the graft and free tissue transfer were viable [Figure 5]. Consultation with the owner 10 months postoperatively revealed that the dog had an excellent cosmetic result and was using the limb well.

Discussion

Surgical treatment of elbow hygromas is recommended for chronically painful, infected, or draining hygromas after all other conservative management options have been exhausted.¹ Surgical resection of persistent elbow hygromas refractory to conservative management can be very challenging; a potentially high complication rate is associated with primary closure, including dehiscence and ulceration.^2,3 Additionally, removal of the calloused skin overlying the hygroma removes the naturally occurring protective barrier, making the animal more susceptible to hygroma recurrence.² While primary drainage relies upon the lengthy process of fibrosis and granulation for healing, allowing more potential for infection, surgical excision with primary closure removes the problem tissue and allows for more rapid healing and less chance of recurrence.¹

Since resection of elbow hygromas was first described in 1961, little has changed in the surgical technique.⁶ Primary wound closure using the surrounding tissue is historically the most common technique employed after hygroma resection. Challenges are associated with this technique, because it generally involves managing a wound with the edges placed under tension. Stents have been used to alleviate some of the tension experienced along the incision; however, ulcerations caused by pressure can occur.³ The use of skin flaps has been rarely reported in instances where adequate amounts of tissue were not available to close the wound over the olecranon.¹ Regardless of the technique used to treat the hygroma, it is critical that the wound be protected and motion of the elbow be restricted to allow for tissue healing. This has historically been accomplished with Schroeder-Thomas splints or immobilizing bandages.³

Surgical excision of the hygroma reported here was chosen because the wound was hemorrhaging severely, thus limiting options of conservative or medical management. The large size of the hygroma also rendered primary closure or the utilization of an axial pattern flap unacceptable for addressing the large defect. Axial pattern flaps are effective for reconstructing some cutaneous defects; however, their use in the distal extremities is limited by the need to preserve an intact vascular supply to avoid partial flap necrosis. ⁷ However, microvascular free tissue transfer allows the movement of tissue from distant locations to repair defects without the constraints of maintaining a locally intact vascular pedicle. Furthermore, wound repair on distal extremities with microvascular free tissue transfer has proven effective in providing excellent cosmetic outcomes, shorter hospitalizations, and better function.⁴

Microvascular free muscle transfer using the rectus abdominis muscle was selected as the most viable treatment option after surgical excision of the hygroma. In general, muscle is highly vascular and offers increased oxygen delivery to healing tissues as well as more efficient delivery of antibiotics and immune system components to devascularized wounds.^4,8,9 Furthermore, muscle provides a physical barrier for the wound bed—in this case, the olecranon—and is an effective recipient medium for acute skin grafting, providing both nutrients and protection of the skin graft from the underlying bony prominence.^4,8,9

The rectus abdominis muscle meets the following criteria for use in tissue transfer. The muscle has an expendable function, is easily accessible, has a reliable vascular pedicle (vasculature a minimum of 10 mm in length and 0.5 mm in diameter), and a minimal donor site morbidity.^4,8,10 Additionally, the rectus abdominis muscle is enclosed within the rectus sheath, allowing muscle harvest without subcutaneous tissues; this makes for a less bulky transfer with a consistent thickness essential for a good cosmetic outcome. ⁴ Rectus abdominis muscle free tissue transfer has only been examined in one experimental study in veterinary medicine, and, to the authors’ knowledge, this is the first reported use of the transfer in a clinical setting.

Additional advantages of the free tissue transfer include its viability as a recipient for acute skin grafting, which allows the opportunity to harvest skin with similar hair growth patterns to the recipient site and thereby maximize the cosmetic outcome.⁴ This is in contrast to the use of skin flaps where hair growth is dependent upon the orientation of the vascular pedicle. Furthermore, a skin graft donor site can be selected that will heal with the least amount of visible scarring following surgery.⁴ In this case, the skin graft was harvested from the lateral thorax because of the ease of closure and the pattern of hair growth that would resemble the surrounding tissue on the forelimb.

Immobilization of the elbow joint after any surgical repair of a hygroma is important for optimal healing. It was imperative for this dog, because the free tissue transfer and skin graft needed to remain motionless to allow revascularization and healing. The authors were concerned that a splint and/or bandage would provide insufficient immobilization for the elbow of this young, active, 54-kg dog; therefore, a transarticular external fixator was applied. Transarticular external fixators provide better stabilization of the elbow joint, and they offer greater accessibility to soft-tissue wounds for monitoring and treatment than external coaptation.¹¹

While no major complications were encountered during the perioperative and postoperative periods for this dog, it is important to recognize potential complications during microvascular free tissue transfer and take precautions to avoid them when treating hygromas. Most intraoperative complications result from inappropriate preparation of the anastomosed vessels.¹² Adventitial tissues that are not properly dissected away from the site of the anastomosis may be entrapped in the anastomosis, causing vascular occlusion and thrombosis secondary to the high levels of thromboplastin present in these tissues.^12,13 Furthermore, it is imperative that the vessels be handled delicately, as endothelial disruption can lead to exposure of subendothelial collagen and potential clot formation within the vessel. ¹² Additionally, it is crucial to plan to leave enough vessel length to allow anastomosis and repair to occur without kinking, compression, or tension.¹² Thrombosis at the anastomosis site is also a potential complication that occurs secondary to poor technique and traumatic dissection.¹²

Careful surgical technique is essential when isolating and preparing the brachial artery and vein for anastomosis, to avoid damage to the median and musculocutaneous nerves.⁵ Other potential postoperative complications are infection, ulceration, and dehiscence of the elbow wound repair as well as the other two surgical donor sites.² Osteomyelitis associated with pin tract infections, fixation pin loosening, and soft-tissue irritation are potential complications of external fixator placement.¹⁴ Finally, failure of the skin graft to revascularize at the recipient site may lead to necrosis and possible infection. Ultimately, the success of this surgery depends upon proper planning and meticulous surgical technique.

Conclusion

While this is the first reported instance of microvascular free muscle transfer used in the repair of complicated elbow hygromas, the clinical outcome of this case validates the usefulness of this technique. The rectus abdominis muscle has proven itself to be effective for free muscle transfer with minimal donor site complications and functional and cosmetic outcomes at the recipient site. More microvascular free muscle transfer repairs of complicated elbow hygromas need to be performed in order to gain a true appreciation for the advantages and limitations surrounding the application of this technique; however, the outcome of this case is very encouraging.