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MEDIAL PATELLAR DESMOTOMY (MPD)

This article highlights a surgical procedure intended to treat cases of proximal patellar hesitation (also known as delayed patellar release) and intermittent upward patellar fixation (IUPF) that are particularly stubborn and/or that involve elderly, retired horses.

The medial patellar ligament is one of the key structures (along with the patella and middle patellar ligament) that is required to lock the patella (kneecap) on the end the femur. Proximal patellar hesitation (PPH) and intermittent upward patellar fixation (IUPF) are biomechanical issues that constitute the horse’s inability to timely disengage the patella from the medial femoral trochlea.

Hind Stay-Apparatus

In cases of proximal patellar hesitation (PPH) and intermittent upward patellar fixation (IUPF), surgical resection of the medial patellar ligament can generate complete resolution of the problem. Once the medial patellar ligament is resected, patellar hesitation/ fixation is no longer possible and the clinical signs associated with these conditions disappear. Accordingly, this strategy has been considered to be a cure by some professionals and is often recommended as a first-line means to treat extracapsular stifle interference in the horse.

It is extremely important to note, however, that the medial patellar ligament also performs another function for the horse: to help stabilize the patella within the trochlear groove of the femur. Without tension from the medial patellar ligament, the patella becomes unstable within the femoropatellar joint; femoropatellar synovitis and oftentimes osteoarthritis result. Osseous fragmentation along the distal margin of the patella (at the origin of the middle patellar ligament) is another common sequelae to medial patellar desmotomy (MPD).

Since the stifle is a high-motion structure, chronic inflammation within any of its joint pouches may pose significant concern with respect to the horse's future soundness and performance. Persistent femoropatellar joint inflammation usually needs to be addressed on a continual basis and often requires considerable maintenance.

You can review current therapies for degenerative joint disease HERE.

The inevitable development of degenerative joint disease (arthritis) is the primary reason that The Atlanta Equine Clinic views this form of treatment inappropriate barring the following circumstances:

• Severe cases of PPH or IUPF that have proven refractory to all other forms of therapy, and

• Cases involving older horses that are severely affected and are not able to undergo fitness training as part of their treatment regimen.

Medial Patellar Desmotomy: PROS and CONS

PROS:

• This procedure effectively eliminates biomechanical interference associated with the stifle.

• Arthritis will result from the surgery, but probably won't catch up to horses that are over 20 years of age.

• Arthritis will result from the surgery, but many not significantly worsen horses already exhibiting clinical evidence of stifle arthritis.

CONS:

• Cutting the ligament will destabilize the stifle joint (most notably the femoropatellar pouch) as described above. This will result in arthritis and pain within the joint. More aggressive arthrotherapy (both systemic and local) may be necessary to maintain comfort and soundness.

• Arthritis will result from the surgery, but probably won't catch up to horses that are over 20 years of age.

• There is no guarantee that the procedure will resolve the horse's lameness. In many cases, stifle interference is only one part of the overall problem.

• Post-operatively, the horse will require 45-60 days OFF (i.e. out of work) in order to adapt to the new stifle function. Training or showing is prohibited during this period.

• Fragmentation of the distal (bottom) aspect of the patella (kneecap) is a common consequence of performing this procedure. This would be visible radiographically in the event that the horse is resold in the future.

• The procedure costs about $750 to perform on both stifles.

Medial Patellar Desmotomy: SURGICAL TECHNIQUE

Medial patellar desmotomy is performed in the standing, sedated and locally-anesthetized horse.

Medial Patellar Desmotomy

The medial patellar ligament is identified along the front and inside aspect of the stifle. The ligament is easily palpable in the standing horse.

Medial Patellar Desmotomy

The tissue adjacent to and beneath the medial patellar ligament is aseptically prepared (scrubbed) and locally anesthetized (blocked).

Medial Patellar Desmotomy

An incision is made along the medial aspect (inside) of the medial patellar ligament. The incision is adjacent and parallel to the ligament.

Medial Patellar Desmotomy

The medial patellar ligament is isolated using a pair of hemostats and partially exteriorized from the incision. Once capture of all ligament fibers is confirmed, the ligament is transected (in a horizontal plane).

Medial Patellar Desmotomy

Following complete ligament transection, the incision is closed with 3-4 interrupted sutures.

Medial Patellar Desmotomy

Minimal care of the incision is necessary following the procedure.

Perioperative antiinflammatory and antimicrobial therapy is recommended. Suture removal is typically performed at 2 weeks postoperatively.

Stall rest is recommended for 2 weeks postoperatively, followed by 2-4 weeks of turnout in a small paddock. Regular pasture turnout may resume after 30-45 postoperative days. Depending on the comfort of the horse, training can also recommence after 30-45 days of recovery.