How to Use the Henderson Castrating Instrument and Minimize Castration Complications

Various techniques of castrating the equine patient have been described. Open or closed techniques, with first or second intention healing, are all commonly used. Complications associated with equine castrations are among the most common cause of malpractice claims. Such complications also result in patient discomfort. This paper describes a closed castration technique with primary closure in a recumbent horse as an easy, effective, and safe method of castration, which also minimizes complications.

1. Introduction

Equine castration is one of the most commonly performed surgical procedures in horses [1]. Additionally, castration complications are the most common cause of malpractice claims against equine practitioners [2]. Complications include hemorrhage, edema, pain, evisceration, septic funiculitis (infection of the spermatic cord), hydrocele (accumulation of fluid within the vaginal tunic), peritonitis, and penile damage [1,3].

The following is a review of the pertinent anatomical structures. The testicular tissue is encased in the tunica albuginea. The testes lie within an outpocket of the abdominal peritoneum called the tunica vaginalis. The tunica vaginalis is separated into the visceral layer, which is tightly adhered to the testicles, ductus, and vessels, and the parietal layer, which is continuous with the parietal peritoneum. The parietal peritoneum is intimately adhered to the scrotal skin through the fascia and tunica dartos muscle. The tunica dartos muscle functions to constrict the scrotum. The cremaster muscle is a caudolateral extension of the internal abdominal oblique muscle and is continuous with the parietal layer of the tunica vaginalis inserting at the pole of the testicle. The cremaster muscle functions to retract the testicle toward or into the inguinal canal. The spermatic cord courses from the abdomen to the scrotum through the inguinal canal that is bounded by deep and superficial inguinal rings. The deep inguinal ring is an opening between the abdominal musculature, and the superficial inguinal ring is formed by a small opening within the external oblique muscle [4,5].

Castration can be performed in the standing, sedated horse or in the anesthetized patient in dorsal or lateral recumbency. For safety reasons, standing castration should only be performed in docile stallions with well-developed testes [1,4,5]. Attempting to castrate small ponies or donkeys can be mechanically difficult in the standing patient [1]. There are two commonly used techniques of castration:open and closed. In the closed method, the testes and parietal tunic are removed after a skin incision and superficial fascia stripping. This method leaves the cavity of the vaginal tunic (the peritoneal cavity) closed to the outside [4]. In an open technique, the testes are exposed through incisions in the parietal tunic, which allows communication with the peritoneal cavity. In the latter method, a portion of the parietal tunic, and many times the cremaster muscle, remain with the horse [4,5].

A closed technique using either emasculators or a rotating castration instrument a] provides a safe, effective means of equine castration (Fig. 1).

Figure 1. Henderson castrating instrument inserted into cordless 0.375-in drill.

It is the authors' opinion that the use of this instrument provides advantages over emasculators by minimizing complications, particularly hemorrhage, and it is easy to incorporate into any practice. The Henderson equine castrating instrument may be used in the field or in the surgical suite.

2. Materials and Methods

Before performing a castration in the equine patient, a pre-operative examination is imperative. The scrotum must be palpated (under sedation, if necessary) to confirm the presence of one or both testes as well as to detect any indication of inguinal herniation [1,4,5]. The presence or history of inguinal herniation is vital to help avoid evisceration post-operatively. Evidence of inguinal herniation or the absence of one or both testes requires referral to an operative center for potential abdominal invasion [4-6]. Other pre-operative considerations include tetanus prophylaxis, antimicrobial administration, and pre-operative administration of non-steroidal anti-inflammatory drugs (NSAIDs; phenylbutazone [b] [2.2 - 4.4 mg/kg], flunixin meglumine [c] [1 mg/kg], or ketoprofen [d] [0.5 mg/kg]) [5].

The authors prefer to use general anesthesia when using the Hendersen castrating instrument, because surgical exposure is improved. Additionally, it carries less risk for the surgeon and patient [4,5]. Various drugs and combinations of drugs can be used. Drug combination familiarity is essential for proper patient monitoring and safety. Pre-operative sedation with xylazine [e] (0.5 - 1.0 mg/kg, IV) and butorphanol [f] (0.01 - 0.02 mg/kg, IV) followed by induction with ketamine hydrochloride [g] (2.2 mg/kg, IV) combined with diazepam [h] (0.03 - 0.06 mg/kg, IV) is commonly used by the authors. After induction, the patient is positioned in lateral recumbency. The upper hindlimb is pulled forward after passing a slip knot of rope around his pastern (Fig. 2). An assistant secures the position of the upper hindlimb, staying at the head and behind the horse.

Figure 2. Patient in lateral recumbency with upper limb pulled forward.

Before recumbency, a betadine [i] scrub is performed on the scrotum and surrounding area (on cooperative patients). When recumbent, a local injection of 5 - 10 ml of lidocaine hydrochloride [j] is injected into each spermatic cord, the testicular parenchyma, or both. This decreases the likelihood of additional doses of anesthetics as well as helps to prevent retraction of the cord by the cremaster muscle. This anesthesia protocol generally allows 15 - 20 min of surgical time. At this point, prepping of the surgical site is performed. Three scrubs, 30 s each, using betadine or chlorhexidine [k] scrub are performed at the scrotum and surrounding area.

Standing over the dorsum of the patient, the surgeon has good access to the surgical site [4]. The midline of the scrotum is cross-clamped with two hemostats or carmalt clamps, and a 2- to 3-cm strip of skin is excised with Metzenbaum scissors. Minimal skin bleeders result. The scrotal fascia is stripped from one exteriorized testicle using a dry piece of gauze.

The fascia is stripped from the spermatic cord as far proximal as possible. The surgeon then moves to the ventral aspect of the patient. The sterile castrating tool is inserted in a standard 14.4-V variable-speed cordless hand drill with a reverse switch and a 0.375-in chuck. It is essential that the castrating instrument be tight and secure in the drill chuck. The drill is placed in a sterile shroud; otherwise, a change of gloves is necessary after removal of the first testicle. With one hand holding the Henderson instrument and the other hand holding the testicle, the pliers of the Henderson instrument is clamped onto the entire stripped spermatic cord just proximal to the testicle. The tip of the tool is placed inside the scrotal skin incision in a distal to proximal orientation that is in a straight line with the cord (Fig. 3).

Figure 3. Proper orientation of drill and Henderson castrating instrument.

The drill is powered to rotate the clamp at a slow to moderate speed in a clockwise direction. It is important that the surgeon does not place any tension on the cord. The spermatic cord will retract into the scrotum as it initially shortens when it begins to twist. The cord will then elongate as it nears complete severance. The cord will continue to twist until it fatigues and separates with only minimal tension by the operator, typically 15 - 25 turns. The testicle is removed from the castrating instrument, leaving behind a tightly coiled and sealed segment of the closed spermatic cord (Fig. 4).

Figure 4. Coiled, sealed segment of spermatic cord attached to testicle.

The second testicle is removed in the same fashion. The left and right scrotal sacs are closed by passing absorbable monofilament suture [l] (0 or 1 PDS) from the SC scrotal fascia of one pouch through the sagittal septum and then through the SC tissue of the other pouch in a simple continuous pattern. The skin edges can be closed using absorbable monofilament suture (0 or 1 PDS) in a continuous subcuticular pattern. The horse is then recovered.

3. Discussion

Horses castrated by primary closure develop fewer complications [1,7]. The authors have successfully removed over 150 testicles from anesthetized patients in the last 2 yr using the described technique without any complications. The Henderson castrating instrument has been used in many breeds and sizes of horses, donkeys, mules, and ponies. The instrument cannot be used on a spermatic cord that is not completely clamped and immobilized by the pliers when placed in position (i.e. , very young horses or small breeds). The instrument is also not recommended for use in removing a retained testicle.

In addition to the safety of the patient and surgeon, the primary advantage of the described technique is the significant reduction of intra-operative and post-operative complications. There is minimal, if any, bleeding. Hemorrhage generally occurs from the testicular artery of the spermatic cord or branches of the external pudendal vein of the scrotum and scrotal septum [8]. The Henderson castrating instrument coils and seals the testicular artery. Cross-clamping the scrotal skin eliminates most scrotal and skin bleeders.

Post-operative swelling is the most common complication of equine castration. Primary closure of castration sites results in reduction of post-operative swelling [7,8]. By making one incision, maintaining sterility, and avoiding excessive tissue trauma, the swelling is minimal. The Henderson tool does not create appreciable tissue trauma. The minimal expected post-operative swelling is effectively controlled with the administration of the pre-operative NSAIDs and using post-operative NSAIDs as needed.

Protrusion of the small intestine from the castration site is the most serious complication of equine castration [1,9,10]. It is life threatening, usually occurring within the first 24 h of surgery [ 1,9,10]. Using the described closed technique results in virtual sealing of the vaginal tunic. Therefore, any communication with the abdomen is eliminated, and the incidence of eventration is minimized. Closing the incision site further reduces the possibility of eventration of the small intestine through the surgical site [1,11]. Hydrocele formation after castration is prevented by complete removal of the parietal tunic [3]. The rotation of the cord results in removal of the parietal tunic as far proximally as possible. Adherence to sterile techniques using a closed technique and primary closure will reduce/eliminate the likelihood of infection of the cord or ascending infectious peritonitis. Iatrogenic penile trauma is unlikely using the castrating tool, because the spermatic cord must be identified before application and placement of the clamp.

Surgical time is extended for primary closure, but the castrating tool eliminates 8 - 30 min [7,11,12] of surgical time. The authors have allowed second-intention healing of the surgical site with no complications and no appreciable difference in healing.

Potential complications of this castrating technique include infection, tearing of the spermatic cord (if excessive tension is placed on the cord before it fatigues itself by the twisting action), and bleeding (if the cord is torn or if large scrotal vessels are severed at incision).

In a typical castration as described here, the patient remains recumbent for 5 - 15 min post-operatively. Recoveries have been routine and uneventful both in the surgical/recovery suite and in the field. In summary, a closed castration in a recumbent patient using the Henderson castrating instrument is a safe, technically easy, and quick surgical procedure. The procedure can be performed in a field or hospital situation, and common complications are minimized.

Footnotes

1. Henderson equine castrating instrument, Stone Manufacturing & Supply Co. , Kansas City, MO 64127.
2. Phenylbutazone, The Butler Company, Columbus, OH 43228.
3. Flunixin Meglumine, Phoenix Scientific, Inc., St. Joseph, MO 64503.
4. Ketofen ®, Fort Dodge Animal Health, Fort Dodge, IA 50501.
5. Xylazine, The Butler Company, Dublin, OH 43017.
6. Torbugesic, Fort Dodge Animal Health, Fort Dodge, IA 50501.
7. Ketaset, Fort Dodge Animal Health, Fort Dodge, IA 50501.
8. Diazepam, Abbott Laboratories, North Chicago, IL 60064.
9. Betadine, The Butler Company, Columbus, OH 43228.
10. Lidocaine 2% Injectable, The Butler Company, Columbus, OH 43228.
11. Chlorhexidine, Vet Solutions Inc., Fort Worth, TX 76118.
12. PDS, Ethicon Inc., Somerville, NJ 08876.