Patellar fragmentation keeps desmotomy in check for horses
Bottom line
Medial patellar ligament desmotomy is still an effective salvage procedure for confirmed upward fixation of the patella in horses, but the dvm360 review underscores why many equine surgeons now approach it cautiously: patellar fragmentation remains a documented postoperative complication, alongside femoropatellar instability and later osteoarthritic change. Conservative management, corrective farriery, and less invasive surgical alternatives such as medial patellar ligament splitting or desmoplasty are now more commonly emphasized before a complete desmotomy is considered. (msdvetmanual.com)
Why it matters: For veterinary professionals, this is a reminder that case selection and client communication do most of the heavy lifting. Upward fixation of the patella often improves with conditioning, nutrition, and hoof balance, especially in young or poorly muscled horses, while complete desmotomy has been linked in both experimental and clinical literature to distal patellar fragmentation, cartilage injury, and persistent lameness in a subset of cases. That makes preoperative confirmation of the diagnosis, discussion of alternatives, and postoperative monitoring with radiography or arthroscopy especially important when horses remain lame after surgery. (msdvetmanual.com)
What to watch: Expect continued interest in ligament-sparing approaches and in better defining which horses truly benefit from desmotomy versus splitting or conservative care. (msdvetmanual.com)
Key facts
- Condition
- Upward fixation of the patella, or delayed patellar release, in horses
- Procedure
- Medial patellar ligament desmotomy
- Use
- Salvage procedure for confirmed cases
- Common alternatives
- Conditioning, corrective farriery, medial patellar ligament splitting, and desmoplasty
- Key complication
- Patellar fragmentation
- Other reported complications
- Femoropatellar instability, osteoarthritis, synovitis, and ligament fibrosis or enthesiopathy
- Experimental study
- 1989 Veterinary Surgery study, 12 horses
- Experimental finding
- All 12 horses became lame within three months; 11 had distal patellar fragments
- Clinical report
- AAEP retrospective report, 49 horses
A dvm360 review is putting fresh attention on an old equine surgery question: where, if anywhere, does medial patellar ligament desmotomy still fit in the management of upward fixation of the patella. The procedure can resolve locking stifle in selected horses, but the tradeoff is well established in the literature, with patellar fragmentation cited as one of the most important postoperative complications. (msdvetmanual.com)
Upward fixation of the patella, or delayed patellar release, is most often seen in young horses and ponies, especially those with poor muscling or straighter hindlimb conformation. Standard first-line management has long centered on conditioning, turnout, nutrition, and corrective trimming or shoeing, with counterirritation or other intermediate measures used in some cases that don't improve. According to the MSD Veterinary Manual, complete medial patellar desmotomy has been largely abandoned historically because fragmentation of the apex of the patella can follow the procedure, while desmoplasty or ligament splitting is more commonly discussed as a surgical alternative. (msdvetmanual.com)
The complication concern isn't theoretical. In a frequently cited experimental study published in Veterinary Surgery in 1989, all 12 normal horses that underwent unilateral medial patellar desmotomy developed lameness in the treated limb within three months, and radiographic changes included fragment formation at the distal patella in 11 horses. Arthroscopy also identified cartilage fibrillation or detachment in all treated limbs. The authors concluded the procedure should be reserved for persistent, confirmed cases of upward fixation. (pubmed.ncbi.nlm.nih.gov)
At the same time, clinical outcome data are more nuanced than the experimental work alone suggests. In a retrospective AAEP report covering 49 horses treated after failed conservative management, 46 returned to their intended athletic use, and 40 had no postoperative complications reported. Still, three horses did not return to full function, including one with patellar fragmentation and another with distal patellar new bone formation, reinforcing that the risk is real even if it may not affect every clinical case. The authors argued that desmotomy can work in correctly diagnosed horses, but should remain a last-resort option rather than a routine fix. (ivis.org)
That tension has helped push the field toward ligament-sparing techniques. A retrospective study of medial patellar ligament desmoplasty in 24 horses reported good long-term outcomes and noted that desmotomy had fallen out of favor because of long-term complications including femoropatellar instability, osteoarthritis, osteochondral fragmentation, synovitis, and ligament fibrosis or enthesiopathy. Separate long-term follow-up work on medial patellar ligament splitting also described it as effective and minimally invasive for intermittent upward fixation. More recently, a 2025 Equine Veterinary Education case report highlighted patellar fragmentation even after a variation of ligament splitting, suggesting that complication surveillance still matters even with modified techniques. (pmc.ncbi.nlm.nih.gov)
For equine practitioners, the practical message is less about whether desmotomy "works" and more about when it's justified. Horses with intermittent signs and minimal lameness may improve with exercise, quadriceps strengthening, nutritional support, and farriery changes. When surgery is on the table, the literature supports a more conservative decision tree: confirm the diagnosis, rule out concurrent stifle pathology, discuss the possibility of persistent lameness and patellar fragmentation with the pet parent, and set expectations for follow-up imaging if recovery stalls. (msdvetmanual.com)
The dvm360 review also lands at a time when the profession is paying closer attention to function after stifle procedures, not just immediate release of the locked patella. A 2024 study in Veterinary Research Communications examined electromyographic and behavioral changes after medial patellar desmotomy, reflecting continued interest in how altering the passive stay apparatus affects movement beyond the short term. That doesn't overturn the older complication literature, but it does suggest the conversation is broadening from technical success to biomechanical consequence. (pubmed.ncbi.nlm.nih.gov)
What to watch: Expect more emphasis on comparative outcomes between desmotomy, desmoplasty, and splitting, along with closer scrutiny of postoperative imaging findings and longer-term athletic soundness in horses treated for upward fixation of the patella. (pmc.ncbi.nlm.nih.gov)