How to Perform a Standing Medial Patellar Ligament Splitting

1. Introduction

Upward fixation of the patella (UFP) affects horses of many breeds. Pre-disposing factors include increased femorotibial angle, loss of quadriceps muscle tone, and traumatic hyperextension of the hindlimbs [1]. Horses that have been in exercise and then stall confinement or horses that have been rested and then subjected to hard work are frequently affected. The traditional method of treatment for mildly affected horses has been conservative therapy with analgesics/anti-inflammatories and exercise for building the quadriceps muscle [1]. Internal blisters (counterirritants) have also been injected into the medial and middle patellar ligaments.

Surgical treatments of UFP include medial patellar desmotomy or medial patellar ligament splitting. Medial patellar ligament splitting has been shown to be an effective treatment for UFP [2]. This paper shows how to split the medial patellar ligament in a standing horse.

2. Materials and Methods

The affected stifle should be radiographed and evaluated for osteochondrosis lesions, fragmentation of the distal patella, or dysplasia of the trochlear ridges. The area overlying the medial patellar ligament is clipped, scrubbed for 5 min with chlorhexidine scrub [a], and rinsed with alcohol.

The horse is sedated with detomidine [b] (20 μg/kg body weight, IV). Local anesthetic (mepivicaine) [c] is infused subcutaneously over the length of the medial patellar ligament (Fig. 1). A 14-gauge, 1.5-in needle [d] (in miniatures, an 18-gauge, 1.5-in needle is used) is punctured pericutaneously into the medial patellar ligament from the distal portion and progressing proximad. A dorsolateral to plantaromedial approach is used to reduce the chance of puncturing the joint capsule (Fig. 2 and Fig. 3).

Figure 1. Deposit local anesthetic in three places subcutaneously over the medial patellar ligament.Then, surgically prepare the area again.

Figure 2. Location of the needle insertion.Two fingers are placed on the dorsal and plantar sides of the medial patellar ligament. The needle is inserted from the dorsal to plantar side through the skin and three-quarters of the way through the medial patellar ligament.

Figure 3. The two black lines outline the medial patellar ligament where the surgery is performed. The needle shows the angle of insertion for the procedure.

When the needle is punctured into the ligament, check for fluid or blood in the hub. Then, apply a slight upward pull with the hub of the needle; the needle is then removed from the ligament (but not from the skin) and reinserted slightly proximad (Fig. 4). Usually four to nine ligament punctures and only two to three skin punctures are necessary to split the medial patellar ligament from a point ~2 cm proximal to its tibial insertion to the point where the ligament begins to loop over the medial trochlear ridge of the femur (Fig. 5). The femoropatellar joint is then injected with hyaluronic acid [e], triamcinolone [f] (5.0 mg), and amikacin sulfate [g] (250 mg). Stall rest is recommended for 3 days followed by walking under saddle for 3 days. If the horse is moving comfortably and without signs of UFP at that time, light work under saddle is resumed. Exercise usually consists of hindlimb strengthening exercises and endurance.

Figure 4. The medial view of the patella.

Figure 5. The front view of the patella.

Phenylbutazone [h] (4.4 mg/kg, q 24 h, PO) is administered for the first 3 days after surgery.

3. Results

One miniature horse, two ponies, and three Warmbloods with bilateral UFP and one Tennessee Walking Horse with unilateral UFP were treated with standing medial patellar ligament splitting. A total of 13 joints underwent the procedure. UFP resolved in 12 of 13 joints (92%) after the first procedure. A second splitting procedure was recommended for one stifle of the miniature horse but was declined by the owner. UFP resolved within hours to 3 days after surgery, and no recurrence was observed for 4 or more mo after surgery (range = 4 - 14 mo).

4. Discussion

The results of this method of medial patellar ligament splitting make it an alternative method of treating upward fixation of the patella. Because the risks and additional expense associated with general anesthesia are eliminated, the procedure may be especially useful in large, heavily muscled horses and others that may be at higher risk of anesthetic complications.

The rationale for ligament splitting is that it causes a localized desmitis; this results in a thickening of the medial patellar ligament that limits the ability of the ligament to become caught on the medial femoral trochlea [2]. Early in the condition, there is a thickening of the ligament between fibers as seen on ultrasound (ultrasound was not performed on all ligaments, so results are not given). This swelling is probably the reason for the early resolution to the UFP.

After surgery, we administered anti-inflammatories/analgesics. The rationale for administering these drugs was to make the horse more comfortable so that they would work. The mechanical action of tearing/cutting fibers in the ligament will cause a severe desmitis with or without the administration of anti-inflammatories. Care should be taken not to tear or cut the synovial membrane of the femoropatellar joint or to split the ligament too far proximad. With the dorsolateral-medial plantar approach and the use of a 14-gauge needle, these problems are easily avoided in a large horse. The area is aseptically prepared in case the joint is invaded. There have been no complications thus far, except one stifle did not permanently resolve UFP. This stifle was in a miniature horse, and owner compliance to the exercise program may have been a problem. The joint is injected in all cases. Some of the stifles had previously been injected with no resolution to UFP. It is not determined whether the injection is necessary, but it is felt that it may make the horse more comfortable by decreasing synovitis and thus, letting the horse work more comfortably.

Based on the results of early resolution of UFP and early return to work, standing medial patellar ligament splitting is an acceptable method of treatment.

Footnotes

1. ChlorHex-Q Scrub, Vedco, Inc., St. Joseph, MO 64507.
2. Dormosedan, Pfizer, Orion Corp., Divison of Pfizer, Inc., New York, NY 10017.
3. Carbocaine-V (2% mepivicaine HCL, USP), Pharmacia & Upjohn Co., Kalamazoo, MI 49001.
4. Monoject Veterinary Aluminum Hub Hypodermic Needle, Kendall, Tyco Healthcare Group LP, Mansfield, MA 02048.
5. Hyvisc, Boehringer Ingleheim Vetmedica Inc., Anika Therapeutics, Inc., Woburn, MA 01801.
6. Kenalog-10, Bristol-Myers Squibb Company, Princeton, NJ 08543.
7. Equi-Phar EquiGlide, Vedco, Phoenix Scientific Inc., St. Joseph, MO 64503.
8. Equi-Phar ButePaste, Schering-Plough Animal Health Corp., Union, NJ 07083.