Cervical defect repair in the mare

Introduction

The vast majority of cervical defects found in broodmares are the result of cervical tears or lacerations that occurred during foaling. By the time surgical repair is performed, the edges of the wound have healed over with mucosa. Thus, when repaired, it is more accurate to describe these as defects, rather than tears or lacerations. Most of the cervical injuries occur during an apparently normal foaling. However, mares encountering dystocia are at higher risk for cervical injury than those experiencing a normal foaling.

Most cervical injuries result in a full thickness defect in the cervical wall. The defect is of variable length and width and extends from the external os cranially. Partial thickness defects, where the mucosa remains intact, but there is a separation in the muscle layer, occur less frequently. These defects are also of variable length and width and usually extend from the external os cranially. Occasionally, a cervical defect will start as a full thickness defect and then continue as a partial thickness defect. Partial thickness defects infrequently occur in the middle of the cervix, with intact muscle cranial and caudal. Defects can create infertility by not allowing the cervix to tighten adequately enabling an ascending infection and loss of the pregnancy.

Occasionally, the cervical injury extends into the vaginal fornix. As this wound heals, a scar tissue band forms from the cervix across the vaginal fornix. This is often referred to as a type of cervical adhesion. These adhesions are often near an edge of a defect and may contribute to infertility by pulling on the cervical wall, not allowing the cervix to tighten adequately during pregnancy.

Diagnosis and Timing of Repair

Cervical injuries that result in defects are difficult to accurately assess in the immediate postpartum period. The cervix is best evaluated with digital palpation when tight. If a cervical defect that warrants surgical repair is diagnosed in the postpartum period, it is best to wait at least 3-4 weeks postpartum before attempting repair. This provides time for the tissues to heal. If the mare will not be bred that same season, waiting 2-3 months to repair the defect yields even better tissue to work with. Many defects are diagnosed much later, when fertility becomes a problem and the cervix is closely examined. It is imperative that the cervix is palpated to accurately diagnose a defect. The extent of most defects is not appreciated visually through a speculum. Surgical repair of cervical defects is best done when the cervix is tight.

Cervical Defect Characteristics

A review of the cervical defects repaired at our hospital over the past 10 years revealed that the mean age of the mare at surgery was 12 years. Over 75% of the cervical defects were located in the ventral half of the cervix. About 85% of the defects were longer than 33% and about 35% of the defects were longer than 66% of the length of the cervix.

Surgical Candidates

Not all cervical defects require repair for the mare to be fertile. Some reports suggest surgery is not needed for defects that are <50% of the length of the cervix. However, potential economic significance of infertility or abortion plays a role in these decisions. Most of the mares with cervical defects are sent to our hospital for repair by experienced reproduction clinicians. Many of the cervical defects repaired have been <50% of the length of the cervix and have contributed to infertility in the mare. Experience would suggest recommending repair of defects that extend more than one third of the length of the cervix, especially if the defect is ventral.

Approach to Surgical Repair of Cervical Defects (based on 500kg TB mare)

The mare is sedated with 200mg xylazine IV and placed in stocks. The rectum is evacuated, the perineal region is cleansed and the cervix palpated to confirm the findings of the RDVM. Detomidine (15mg) is administered IM, flunixin administered IV, and epidural anesthesia is induced. The epidural solution consists of xylazine (0.85mg), 2% lidocaine (1ml), and saline (4ml). The tail wrapped and tied straight up to a bar on the stocks. Modified Finochietto retractors with 9” blades (Aanes Retractor – Sontec) are placed in the vaginal vault and tied up to the tail. A head lamp is essential. The primary instruments used for this size mare measure 12” in length and include: tissue forceps (1x2 teeth), Metzenbaum scissors, Mayo-Hager needle holders, Allis tissue forceps, and scalpel blade handle (with #10 blade). Topical 2% lidocaine on the mucosa of the cervix and vagina may help decrease sensation for less than adequate epidural anesthesia. Two stay sutures are placed through the wall of the cervix on either side of the defect and positioned about 2 hours away from the caudal edges of the defect. This usually enables retraction of the cervix to the level of the vaginovestibular junction. Most of the cervical defects are ventral and more dorsal mucosa may hang down over the area that needs to be visualized. Suturing this mucosa dorsally enables better visualization of the defect. [...]