How to Perform Levator Labii Superioris Muscle Transposition to Treat Oromaxillary Sinus Fistulae in Horses

1. Introduction

Oromaxillary sinus fistula formation is a reported complication after loss or removal of the caudal four maxillary teeth in horses, occurring in 7 - 33% of cases [1-4]. Repulsion of sinus-associated cheek tooth in horses creates communication between the oral cavity and paranasal sinuses [5-8]. Typically, the oral aspect of vacant alveolus is temporarily protected until the alveolus fills with granulation tissue to prevent fistula formation [1-4,6,8-10]. Overfilling the alveolus so that the temporary alveolar plug extends into the sinus can result in fistula formation because the alveolus becomes epithelialized, preventing granulation tissue closure when the plug is removed or lost. This can occur more easily in older horses because of the relatively short length of their alveoli. Other causes of fistula formation are inadequate seal of the alveolus, early loss of the temporary alveolar plug, incomplete removal of dental tissue, development of osseous sequestra, or residual infection [9,10].

Conventional treatment of orosinus fistula is by removal of alveolar sequestrae or dental tissue remnants and debridement of the epithelium-lined fistula tract, sinus lavage, and insertion of a temporary alveolar plug to protect the oral aspect of the alveolus until granulation tissue fills the remainder of the debrided socket. If this approach fails to resolve the fistula, muscle transposition into the fistula can be considered [11-15]. In horses, two facial muscles, the temporal [11] and levator labii superioris [12], have been used for correction of sinocutaneous fistulae, and the levator nasolabialis muscle has been used for prevention of orosinus fistulae [13-14] and for reconstruction of a maxillary sinus defect [15]. Transposition of the levator nasolabialis muscle to obliterate an oromaxillary sinus fistula is complicated because the muscle is difficult to mobilize, and its flat configuration can result in a poor fit in the dorsal aspect of an oromaxillary sinus fistula.

This report describes a technique for transposition of the levator labii superioris muscle to treat oromaxillary sinus fistula and reports the outcome in three horses.

2. Materials and Methods

Surgical Technique

Horses are anesthetized and positioned in lateral recumbency with the affected side uppermost. After cleaning the mouth and sinus of debris with water from a hose, the facial region between the eye and nostril is aseptically prepared for surgery.

Figure 1. Drawing depicting the location of the levator labii superioris muscle and surgical incisions used to expose the tendon of insertion and muscle belly. The transected tendon end is identified with long suture ends to facilitate transposition. A straight Rochester-Pean forceps is inserted under the muscle belly to facilitate elevation and retraction of the muscle belly from its subcutaneous location.

The external opening of the fistula is exposed by an ≈8-cm longitudinal skin incision centered over either the scar of a trauma-induced wound (horse 1) or the healed trephine site (horses 2 and 3). The fistula is debrided by curettage, to remove lining epithelial tissue and leaving bleeding surfaces. The wound, fistula, and paranasal sinus cavity is lavaged with 3 l isotonic saline solution.

The palpable tendon of the levator labii superioris muscle is exposed through a 2-cm longitudinal skin incision directly over the tendon and transected 2 - 3 cm rostral to its musculotendinous junction (Fig. 1). A locking-loop, 1-polyglactin-910, suture with ≈10-cm tails is inserted in the tendon. The levator labii superioris muscle and its severed tendon are bluntly separated from the maxillary and nasal bones and subcutaneous tissue to the muscle’s origin beneath the orbit at the junction of the lacrimal, maxillary, and zygomatic bones by scissor dissection through the incision used to expose the tendon and the incision over the fistula (Fig. 1).

A 20-cm, straight Rochester-Pean forceps is inserted subcutaneously through the incision over the fistula and advanced rostrally beneath the levator nasolabialis muscle until it emerges at the rostral incision used to expose the tendon of the levator labii superioris muscle. The ends of the suture inserted in the tendon are grasped, and the forceps are withdrawn to retract and expose the muscle and its tendon (Fig. 2). A 2-cm, longitudinal, buccal incision that extended into the oral cavity is created adjacent to the oral end of the fistula (Fig. 2), and the jaws of a forceps are introduced into the oral cavity through this incision. The suture ends attached to the tendon are fed through the fistula into the oral cavity (Figs. 2 and 3) and, using hand assistance through the mouth, are grasped with the forceps. Using traction on the suture, the tendon and muscle belly of the levator labii superioris are advanced through the fistula and the buccal incision until the muscle fills the fistula (Fig. 3).

A 5-mm longitudinal skin incision is made ≈2 - 4 cm ventral to the buccotomy, and using a curved mosquito hemostat, a subcutaneous tunnel is created from this incision to the buccotomy (Fig. 4). The suture ends are grasped with the forceps and pulled subcutaneously until the tendon emerges through the ventral incision (Fig. 4). The tendon is securely fastened under slight tension to the skin and buccal musculature at the ventral buccal incision with several single interrupted sutures of 2-polypropylene (Fig. 4).

A 6-to 8-cm-long, 6-or 8-mm-diameter polyethylene tube is inserted into the space originally occupied by the levator labii superioris muscle (Fig. 5). One end of this tube exits a stab incision created ≈1 cm rostral to the incision used to expose the tendon of the levator labii superioris (Fig. 5). An 8-mm-diameter Penrose drain is placed subcutaneously at the maxillary incision; one end exits a stab incision created 1 - 2 cm ventral to the rostral end of the maxillary incision, and the other end exits a stab incision created 1 - 2 cm ventral to the caudal end of the maxillary incision (Fig. 5). Drain and tubing ends are secured with a simple interrupted skin suture of 1-polypropylene. Drains are inserted in anticipation of subcutaneous infection from the clean-contaminated surgical field. A 26-F Foley catheter is inserted into the caudal maxillary sinus through a 4-mm-diameter trephine portal, created ≈2 cm caudodorsal to the maxillary incision, for postoperative paranasal sinus lavage (Fig. 5).

Figure 2. The levator labii superioris muscle is transposed through the skin incision over maxillary sinus fistula opening and through the fistula into the oral cavity by hand traction on the suture ends through the muscle tendon.

The ventral buccal incision through which the muscle tendon protrudes is allowed to heal by second intention (Fig. 4). Subcutaneous tissues at the maxillary incision and the incision used to expose the tendon are closed with 0-polyglactin-910 in simple continuous patterns (Fig. 4). Skin incisions are closed with 0-polypropylene in an interrupted vertical mattress pattern (Figs. 4 and 5). A stent bandage, composed of sterile gauze sponges, is sutured over the maxillary incision with 1-polypropylene.

A non-eugenol zinc oxide-based, periodontal dressing [a] is inserted orally to fill the small ventrolingual portion of the fistula in horses 2 and 3 and to protect the exposed muscle from abrasion by food during mastication. Only a small part of the muscle exposed to the oral cavity is encompassed with periodontal dressing.

Clinical Cases

Horse 1

A 6-mo-old Standardbred trotter filly was admitted because of a malodorous, purulent discharge from the right nasal cavity. A 2-mo-old right facial crest wound communicated with the rostral maxillary sinus. The sinuses had been lavaged with isotonic saline solution twice through the wound, and the foal had been administered trimethoprim-sulfadiazine and flunixin meglumine for several weeks without resolution. On physical examination, an oromaxillary fistula was identified next to the buccal aspect of the right maxillary fourth premolar. On a dorsoventral radiographic projection of the skull, alveolar bone was observed to be missing from the buccal aspect of this alveolus.

Horse 2

A 5-yr-old Warmblood mare was admitted because of malodorous discharge from the left nasal cavity associated with an oromaxillary fistula that occurred after repulsion of a diseased maxillary second molar 8 wk earlier.

Horse 3

A 3-yr-old Standardbred trotter stallion was admitted because of purulent right nasal discharge and halitosis associated with an oromaxillary fistula that occurred after repulsion of a second molar 7 wk earlier.

Postoperative Care

Broad spectrum antibiotics were administered. Feed was withheld for 24 h after surgery to decrease jaw movement and minimize risk of disrupting the transposed muscle. Thereafter, horses were fed a slurry of alfalfa pellets, crushed wheat, and bran for 1 - 2 wk. The periodontal dressing plug was evaluated daily for 2 wk. The polypropylene tubing drain was removed on day 2 and the Penrose drain on day 3 or 4 when drainage ceased. The stent bandage was removed on day 3 and skin sutures on day 14. The affected sinuses were lavaged daily for 3 - 6 days with 1 l isotonic saline solution instilled through the sinus cannula, which was removed.

Figure 3. Cross-section of the maxillary sinus and oral cavity showing the path of the transposed levator labii superioris muscle and tendon through the maxillary sinus and fistula openings. A hemostat inserted through a buccotomy is used to grasp the suture ends in the tendon.

3. Results

Lavage fluid instilled into the sinuses exited solely through the ipsilateral nasal cavity. Antibiotics were administered for 11 - 25 days.

A small, subcutaneous abscess developed at the buccotomy in horses 2 and 3 at 4 or 5 days after surgery but resolved after suture removal; the wounds were opened to heal by second intention. The oral portion of the levator labii superioris muscle was observed, during oral examination, to have sloughed by day 5 (horse 3), day 6 (horse 2), or day 11 (horse 1) after surgery, but the fistula remained sealed with apparently vital muscle. In all three horses, the devitalized segment of muscle and tendon was easily removed through the oral cavity, after cutting the sutures anchoring the tendon to the ventral buccal incision.

The temporary alveolar plug of horse 3 became loose, was replaced standing at 6 days, and spontaneously dislodged at 31 days. The plug in horse 2 was in place when the horse was discharged at 23 days.

Figure 4. The tendon of the levator labii superioris muscle is tunneled subcutaneously ventral to the buccotomy, exited through the buccal skin, and secured with sutures. The skin incisions to expose the muscle, external aspect of the fistula, and buccotomy are sutured closed. The tunnel exit incision is left to heal by second intention. The tendon is secured in the tunnel with sutures placed through the skin.

Follow-up

Horse 1

At 10 yr, the surgical site had healed without blemish, but during mastication, slightly more prominent muscular activity was seen around the origin of the right levator labii superioris muscle (i.e., the transposed muscle) than at the origin of the left levator labii superioris muscle.

Horse 2

After a violent recovery from anesthesia, flaccidity of the left aspect of the lower lip (the surgical side) was observed. At 6 mo, the surgical wound and fistula had healed, and the nasal discharge had resolved. Flaccidity of the left side of the lower lip had improved but was still apparent; the horse had no difficulty eating. At 15 mo, the surgical site was only faintly visible with no facial deformity or nostril dysfunction, but mild flaccidity of the left side of the lower lip remained.

Figure 5. Final appearance of the surgical sites. Subcutaneous surgical drains are placed in the dead space previously occupied by the muscle belly and adjacent to the external fistula opening. A Foley catheter is inserted into the paranasal sinuses for postoperative lavage.

Horse 3

The fistula healed completely, and signs of paranasal sinusitis had disappeared by 8 wk. At ≈1.5 yr, purulent discharge occurred from the right nostril. On skull radiographs, several bone sequestra were identified within the treated alveolus, and fluid lines were present within the right paranasal sinuses. Sinusitis resolved after sequestra were removed through a lateral buccotomy. There was a barely visible scar at the tendon incision site, and there was no facial deformity or nostril dysfunction. The horse was still racing 6 yr after surgery.

4. Discussion

Development of orosinus fistula is a serious complication of repulsion or loss of one or more sinus associated molariform teeth. Despite techniques used to encourage alveolar healing [5,6,8], some sockets do not heal, and fistula formation occurs. Transposition of the levator nasolabialis muscle has been used to prevent fistula formation [13,14] but has not been evaluated for treatment of horses with established oromaxillary sinus fistula.

Unlike the levator nasolabialis muscle, which is flat, the levator labii superioris muscle is ellipsoid in its transverse plane, and in a 500-kg horse, has a diameter of ≈2.5 - 3 cm at its base decreasing rostrally, in a conical shape, toward a 4-to 6-mm-diameter tendon of insertion (personal observation). The levator labii superioris muscle originates beneath the orbit at the junction of the lacrimal, maxillary, and zygomatic bones and unites with the contralateral levator labii superioris tendon at the apex of the nose to form a tendinous plate that inserts on the upper lip [16]. The blood supply of the levator labii superioris muscle consists of the angularis oculi artery and vein and the dorsal nasal arteries and veins [17], and it is innervated by external nasal branches of the infraorbital nerve and by branches of the infratrochlear nerve [18]. The vessels and nerves enter and exit at the base of the muscle [17,18].

The anatomic location, neurovascular supply, shape, and size of the levator labii superioris muscle were ideal for transposing the muscle into the fistula of these three horses. Retention of upper lip elevation was expected by action of the contralateral intact levator labii superioris muscle through the common tendinous plate.

Transposition of the levator labii superioris muscle was associated with successful healing of oromaxillary sinus fistula of the third or fifth maxillary cheek teeth alveolar socket in these three horses. Muscle transposition did not seem to have adverse effects on labial and nasal function. Flaccidity of the left side of the lower lip in horse 2 may have been caused by damage to the ventral buccal branch of the facial nerve during buccotomy or occurred during recovery from anesthesia. Regardless of cause, subsequent function and cosmetic appearance of the lip were considered satisfactory. Care should be taken when performing lateral buccotomy to avoid damaging the dorsal buccal branch of the facial nerve and the parotid salivary duct [9,10]. Damage to the relatively wide buccal branch of the facial nerve can be avoided by perforating the buccal musculature and oral mucosa with a narrow, blunt instrument inserted through a small, horizontal skin incision.

Sequestra identified in the alveolus 16 mo after surgery in horse 2 were presumably present from the original dental surgery and may have contributed to fistula formation. Despite presence of the sequestra, muscle transposition resulted in fistula resolution.

Necrosis of the oral segment of the transposed muscle and tendon likely occurred because of insufficient blood supply, adverse microbial, and chemical conditions within the mouth, thermal damage from the periodontal dressing, and mechanical erosion caused by feed and jaw movement. The periodontal dressing selected was chosen in preference to conventional dental acrylic, because it produces less heat during polymerization, presumably minimizing thermal damage to the levator labii superioris muscle. It is likely that healing would have occurred without use of dental acrylic or periodontal dressing. No consequences were expected nor seen after the muscle stump necrosis, but if not removed, the subcutaneous segment of transposed tendon would likely have delayed buccotomy healing. Based on experience with these three horses, removal of exposed necrotic muscle and tendon is recommended at 1 - 2 wk.

Although antibiotic administration is likely only needed for a few days after surgery for the surgical incisions, prolonged administration was chosen to facilitate resolution of the chronic sinusitis.

A technique for transposition of the levator labii superioris is used to repair chronic orosinus fistula associated with molariform teeth loss in three horses. Use of this technique should be considered in preference to transposition of the levator nasolabialis muscle because the muscle shape is more suited to the profile of chronic orosinus fistula.

The author thanks Dr. Jim Schumacher for discussion and guidance in manuscript preparation and Barbara Degraves for the illustrations. The three horses in this report were treated at Bjerke Equine Hospital, Oslo, Norway; Department of Large Animal Surgery, Royal Veterinary University, Copenhagen, Denmark; and Helsingborg Equine Hospital, Helsingborg, Sweden. The involved hospital staffs are thanked for their help.

Footnote

[a] Coe-Pak periodontal dressing, Regular set, GC Europe N.V., B-3001 Leuven, Belgium.