Upward fixation of the patella

Veterinary advice should be sought before applying any treatment or vaccine.

Upward Fixation Of The Patella

Upward Patellar Fixation, Locking Stifle

Horses and ponies with upward fixation of the patella (UFP) are periodically unable to flex the stifle or the hock in the hind limb, causing them to drag the extended limb behind them on the toe of the hoof. Some horses may also develop an intermittent form of patellar fixation, which is referred to as delayed release of the patella, in which the patella appears to catch briefly, sometimes followed by exaggerated flexion of the stifle and hock. Low-grade intermittent upward fixation or delayed release of the patella occurs somewhat commonly in horses.
Image of Upward patella fixation in a horse
The condition is most noticeable during traditions from trot to the walk, cantering in a circle at a certain lead, and when worked in deep footing, especially involving turns. Upon transitioning from the trot to the walk horses may show a slight jerky movement of the patella. Horses with UPF may be reluctant to canter in a circle in a particular direction. When asked, these horses may stop cantering and refuse to canter, rear, buck, toss their head, or continue trotting fast instead of breaking into a canter. Affected horses show a preference to trot instead of cantering, which is a more difficult gait as opposed to the canter, for horses. When horses do canter, they will often do so on the wrong lead and/or has a very bouncy or rough canter stride which is difficult to sit through.

Both UFP and the intermittent form of PF may occur in one (unilaterally) or both (bilaterally) hind limbs. However, most horses with UFP are affected unilaterally.

Symptoms

Shortened strides
Abnormal gait
Hindlimb lameness
Difficulty flexing stifle or hock
Pelvic limb asymmetry
Resistance to cantering in a particular direction in a circle
Rough canter gait
Picks up the wrong canter lead or changes leads constantly
Prefers the trot over the canter gait
Drags the toe (wearing of the toe of the hoof or shoe may be evident)
Performs akward transitions
Unwilling to transition to canter from trot
Lameness improves with exercise
An audible popping sound during exercise
Stumbling in the hind end

Diagnosis

  • History
  • Clinical signs
  • Physical exam - Watching the horse in motion (backing up, turning in tight circles, walking down hills), listening for audible clicks or feeling for a catching sensation as the patella locks.
  • Radiographs
  • Ultrasound
  • Scintigraphy
  • Arthroscopy

Treatment


TreatmentDetails
Conditioning exerciseWork on hills, particularly uphill may result in complete resolution of UFP in affected horses.
Corrective trimming and shoeingShortening the toe to facilitate breakover, and correction of any mediolateral imbalance. Some horses may show benefit from rounding the medial aspect of the foot to promote medial breakover, in addition to elevation of the lateral heel using a wedge-heel shoe.
Estrogen compoundsAdministration of 1 mg of estradiol cypionate via intramuscular injection (IM) per 45 kg of body weight (11 mg/500 kg) once weekly for 3 to 5 weeks. Has been shown to be beneficial for some horses, however the exact reasoning is unclear.
Iodine-containing counterirritants2% solution of iodine in almond oil or ethanolamine oleate, injected into and around the medial and middle patellar ligaments has shown to be of benefit for help in thickening and strengthening the medial ligament.
Vitamin B12Most effective when used in younger horses with milder UFP signs.
Acupuncture/AquapressureIs most beneficial and effective for horses with mild UFP.
Medial patella ligament splitting (MPLS)A type of surgical treatment that may be necessary in some cases, and has been found to be highly effective, with 97.6% of the 85 horses which received treatment having a complete recovery of UFP immediately after the surgery or within the 2-week rehabilitation period. There was no reported recurrence of UFP signs or long-term complications associated with the surgery in horses that received the surgery.

Prevention

  • Ensuring that horses just coming off extended long term stall rest transition back to full athletic use gradually and in accordance with your veterinarian's recommendations.

Scientific Research References

Good Overviews

Risk Factors

  • Poor conformation- Horses with upright conformation and overly straight hindlimbs.
  • Unfit horses - Horses with poor quadriceps muscle tone, due to a disuse atrophy from injury, neurological disease or from inactivity, such as prolonged stall rest.
  • History of decline or cessation of training level
  • Genetics - Warmbloods, Thoroughbreds, Standardbreds, and some pony breeds such as Shetland ponies and Miniature ponies.
  • Poor or misshaped foot conformation - Long toes and/or a higher inside wall of the hind foot