Advances in minimally invasive surgery for equines

Minimally invasive surgery in the horse is a well-accepted technique. Minimally invasive surgery generally involves the use of smaller incisions, some type of optic that is introduced into a body cavity and a camera. Reports have been published using minimally invasive surgery to perform cryptorchidectomy, ovariectomy, abdominal exploration, bladder surgery, nephrectomy, nephrosplenic space ablation and thora-coscopy. The major benefits of minimally invasive surgery include: smaller incisions, tension-free dissections, better visualization, and in many cases, more rapid return to function. The challenges of minimally invasive surgery include: expensive equipment, increased level of necessary skills, and in some cases, instrument limitations. The purpose of this report is to describe some of the recent advances in equine laparoscopy.

Standing laparoscopic... ovariectomy using ... a radio-frequency device

Standing laparoscopic ovariectomy is used to remove ovaries bilaterally in mares with behavioral problems and unilaterally in mares with granulosa-thecal cell tumors (Dechant et al). The main challenge with this technique has been finding the best way to ligate the ovarian pedicle and provide hemostasis. Successful techniques include chain ecraseurs, lasers, staples, loop ligatures, ultrasonic devices - and more recently, radio-frequency devices. Most of the current literature has reported on the use of loop ligatures, ultrasonic devices and the radio-frequency devices. Loop ligatures obviously are the most cost effective of the latter options. The loop ligatures are available commercially as Endo-Loops (Ethicon) in many different suture materials in sizes two to zero. The major drawback of the commercially available loops is that the loop diameter is fixed and often too small for active ovaries, and the knot pusher is too short for use in 20-cm cannulas. In human laparoscopy, a variety of knots have been used. In a study by Shettko, the best knot type, suture type and suture-size combination for knot security was found using size No. 1 Maxon (Kendall/Tyco Healthcare) and a 4-S modified Roeder knot. The main benefit of hand-tied knots is the ability to make a large loop and use a long knot pusher (Figure 1). However, in some cases of granulosa-thecal cell tumors, the ovary is too large to get a ligating loop around. Fortunately, other devices are available for dissection and coagulation. The ultrasonic cutting coagulating devices, such as the Autosonix (Kendall/Tyco Healthcare) have been designed to cut tissue and coagulate vessels up to 3 mm in diameter effectively. While there have been successful reports of using ultrasonic devices for equine ovariectomy, the ovarian vessels are very close to the maximum vessel diameter suggested and would not be effective in horses with large granulosa-thecal cell tumors. (Alldredge) Radio-frequency devices, such as the Ligasure (Valley Lab/Tyco Healthcare), have been designed to cauterize vessels up to 7 mm in diameter. The Atlas wand is a 10-mm-diameter, 35-cm-long instrument that is used to coagulate tissue, including vessels (Figure 2). It has a built-in knife blade that is used to cut the tissue after the coagulation is complete. This device is very effective in cutting and coagulating the ovarian pedicle even in cases of large granulosa-thecal cell tumors (Figure 3). The author has successfully removed a 20 cm x 15 cm x 15 cm ovary using a standing flank laparoscopic approach. The main drawback of the Ligasure device is the equipment cost.

The least expensive alternative for ovarian ligation is a hand-tied ligating loop. However, if a granulosa-thecal cell tumor is present, a radio-frequency device, such as the Ligasure, might provide better hemostasis and require less manual dexterity. Regardless, the tension-free dissection causes much less post-operative morbidity than do the other techniques that have been described.

Adhesiolysis

Adhesions are a possible sequela to any abdominal procedure. Recently the author has performed surgeries on two cryptorchid stallions that were presented after two unsuccessful attempts each at removing the abdominal testis. In each case there were multiple adhesions present in the abdomen from the previous surgical attempts (Figure 4). Adhesiolysis can be performed using blunt dissection, sharp dissection, bipolar cauterization, ultrasonic shears or radio-frequency devices. In each of the cases previously described, the Ligasure device was used to break down the adhesions (Figure 5). The main benefit of the Ligasure device is a relatively, if not completely, blood-free dissection. While it is always possible that the adhesions will recur, the blood-free technique likely will reduce the chances.

Suggested reading

Nephrosplenic Space Ablation

Nephrosplenic or renosplenic entrapments are a relatively common cause of equine colic. It is generally considered that once a horse has had a nephrosplenic entrapment, it is more likely to recur. There have been at least four various surgical techniques described to reduce the probability of recurrence of the entrapment, including colopexy, colonic resection, left flank nephrosplenic space ablation through a rib resection, and left flank standing laparoscopic nephrosplenic space ablation. Colopexies generally are reserved for non-athletic horses due to possible complications of colonic rupture. Colonic resection can be very expensive and can lead to absorption problems. Left flank nephrosplenic space ablation via rib resection is a difficult procedure that often creates significant patient morbidity postoperatively and provides very poor access to the nephrosplenic space. The laparoscopic approach provides excellent access to the nephrosplenic space and the ability to do a more complete abdominal exploration. In most cases, the horses have minimal discomfort post-operatively. The approach was described first by Marien (see Suggested Reading) using a three-portal technique with a specially designed large-diameter cannula. The author has modified the approach by switching the large diameter cannula to the caudal-most ventral location. In general, the approach involves a 10-11-mm-diameter, 20-cm-long cannula in the 17th intercostal space at the ventral aspect of the epaxial muscles, a similar cannula just caudal to the last rib at the same level, and a specially designed 33-mm-diameter, 15-cm-long cannula (Figure 6) just ventral to the 2nd cannula in the left flank. Two needle holders are used for the procedure along with a strand of 0 Maxon 120-cm looped suture (Kendall/Tyco Healthcare) with a 48-mm ½ circle taper needle.

One arm of the suture material is cut at the needle effectively making a 120-cm strand of suture material. A loop is tied at the end of the suture material, and the needle introduced into the large diameter cannula. The needle is advanced to the rostral-most portion of the spleen possible. This rostral-most extent is generally limited by the length of the needle holders. The needle is first placed through the peritoneum surrounding the kidney and the capsule of the spleen, then through the loop that was previously tied (Figure 7). The suture then is pulled tight to begin the closure. As many suture bites as needed are used to close the entire nephrosplenic space (Figure 8). An extracorporeal knot is used to finish the suture line. In our experience with 10 horses, none of the horses have had a re-displacement in the nephrosplenic space, although two animals have re-presented with right dorsal displacement of the large colon.

In summary, this is a very effective technique in reducing the likelihood of recurrence of nephrosplenic entrapment. It is technically challenging to perform but feasible for surgeons with laparoscopic surgery experience.

Equine minimally invasive surgery offers many solutions to difficult surgical procedures. The horses generally are more comfortable post-operatively, go home more quickly and are able to go back to work sooner.

Dr. Dean A. Hendrickson joined the equine surgery faculty at Colorado State University in 1994. He earned his DVM from Colorado State University in 1988 and then completed an equine medicine and surgery internship at The University of Sydney, Australia, in 1989. Following the internship, he completed a combined residency/master's program in large animal surgery in 1992 at Cornell University. His current research focuses on minimally invasive surgery and wound care. Dr. Hendrickson is currently an associate professor of surgery and the equine section chief. He is a diplomate of the American College of Veterinary Surgeons.