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Intermittent Upward Fixation of the Patella and Delayed Patella Release in Horses

By

Jane C. Boswell

, MA, VetMB, CertVA, CertES (Orth), DECVS, MRCVS, The Liphook Equine Hospital

Last full review/revision Sep 2015 | Content last modified Oct 2015

Intermittent upward fixation of the patella occurs when the medial patellar ligament remains hooked over the medial trochlear ridge of the femur and locks the reciprocal apparatus with the limb in extension. A horse with upward fixation of the patella stands with the hindlimb fixed in extension with the fetlock flexed. The leg will usually release with a sudden snap or jerking movement.

Some horses demonstrate a milder form of this condition. In these horses, there is delayed release of the patella during limb protraction, most commonly evident as the horse moves off or in downward transitions. This appears as a jerky movement of the patella. Horses with recurrent upward fixation or delayed release of the patella may develop chronic, low-grade lameness due to stifle soreness and may be reluctant to work on soft, deep surfaces or up or down hills.

Upward fixation or delayed release of the patella is most commonly seen in young horses and ponies, particularly if they are in poor body condition and poorly muscled. Straight hindlimb conformation may predispose to this condition. It may also be seen in older horses that have had trauma to the stifle region, particularly if the horses are stabled or have been inactive.

Diagnosis is based on recognition of typical clinical signs. In some horses, upward fixation of the patella may be induced by pushing the horse backward or manually pushing the patella proximally. Radiographs of the stifle should be taken in horses with femoropatellar joint effusion and lameness to establish concurrent or secondary pathology.

To release an upward fixated patella, the horse should be pushed backward while simultaneously pushing the patella medially and distally. Alternatively, pulling the limb forward with a rope around the pastern may unlock the patella. If upward fixation of the patella is intermittent and not causing lameness, a conditioning program should be instituted. This involves daily lungeing or riding of the horse, appropriate to its age and type, as well as ensuring an adequate plane of nutrition, good dentistry, and anthelmintic administration. Stable rest is contraindicated, and the horse should be turned out to pasture as much as possible. Remedial foot trimming to ensure the foot is well balanced and shoeing with a bevel-edged shoe with or without a lateral heel wedge may be beneficial. A significant proportion of horses will improve with maturity and conservative treatment, although signs may recur if the horse undergoes prolonged stall rest.

Medial patellar ligament desmotomy is indicated in horses that do not respond to conservative treatment or in horses with lameness caused by upward fixation of the patella. Medial patellar ligament desmotomy is most often performed in the sedated horse under local anesthesia, although some surgeons prefer general anesthesia. After surgery, the horse should be restricted to stable or small stall rest for 2 mo to reduce the risk of complications. Fragmentation of the apex of the patella is the most common complication after surgery (see below); if it results in lameness, it may be treated arthroscopically with good results. Other complications include lameness, local swelling, or even patella fracture. The prognosis after medial patellar ligament desmotomy is generally considered to be good, with recurrence of the condition rare. Medial patella ligament splitting, which involves making numerous small incisions in the ligament, has also been used successfully to manage these horses.

OTHER TOPICS IN THIS CHAPTER

Lameness in Horses
Overview of Lameness in Horses
The Lameness Examination in Horses
Imaging Techniques in Equine Lameness
Arthroscopy in Equine Lameness
Regional Anesthesia in Equine Lameness
Disorders of the Foot in Horses
Osseous Cyst-like Lesions in the Distal Phalanx in Horses
Bruised Sole and Corns in Horses
Canker in Horses
Fracture of Navicular Bone in Horses
Fracture of Distal Phalanx in Horses
Keratoma in Horses
Laminitis in Horses
Navicular Disease in Horses
Pedal Osteitis in Horses
Puncture Wounds of the Foot in Horses
Pyramidal Disease in Horses
Quittor in Horses
Quarter Crack in Horses
Scratches in Horses
White Line Disease in Horses
Sheared Heels in Horses
Sidebone in Horses
Thrush in Horses
Disorders of the Pastern and Fetlock
Fractures of the First and Second Phalanx in Horses
Fractures of the Proximal Sesamoid Bones in Horses
Osteoarthritis of the Proximal Interphalangeal Joint in Horses
Palmar/Plantar Metacarpal/Metatarsal Nonadaptive Bone Remodeling in Horses
Sesamoiditis in Horses
Chronic Proliferative Synovitis in Horses
Digital Sheath Tenosynovitis in Horses
Disorders of the Metacarpus in Horses
Tendinitis in Horses
Suspensory Desmitis in Horses
Inferior Check Desmitis in Horses
Bucked Shins in Horses
Exostoses of the Second and Fourth Metacarpal Bones in Horses
Fractures of the Small Metacarpal (Splint) Bones in Horses
Fracture of the Third Metacarpal (Cannon) Bone in Horses
Disorders of the Carpus in Horses
Fracture of the Carpal Bones in Horses
Subchondral Bone Disease of the Third Carpal Bone in Horses
Tearing of the Medial Palmar Intercarpal Ligament in Horses
Osteoarthritis of the Carpus in Horses
Distal Radial Exostosis and Osteochondroma of the Distal Radius in Horses
Carpal Hygroma in Horses
Rupture of the Common Digital Extensor Tendon in Horses
Disorders of the Shoulder in Horses
Developmental Diseases of the Shoulder in Horses
Fractures of the Shoulder in Horses
Bicipital Bursitis in Horses
Infection of the Shoulder in Horses
Suprascapular Neuropathy in Horses
Osteoarthritis of the Shoulder in Horses
Disorders of the Elbow in Horses
Developmental Orthopedic Disease in the Elbow of Horses
Fractures of the Elbow in Horses
Osteoarthritis of the Elbow in Horses
Collateral Ligament Injury in the Elbow of Horses
Disorders of the Metatarsus in Horses
Bucked Shins/Dorsal Cortical Fractures of the Third Metatarsal Bone in Horses
Exostoses of the Metatarsal Bones in Horses
Diaphyseal Fracture of the Third Metatarsal Bone in Horses
Incomplete Longitudinal Fractures of the Plantar Aspect of the Third Metatarsal Bone in Horses
Focal Bone Reaction and Avulsion Fractures of the Third Metatarsal Bone in Horses
Fractures of the Second and Fourth Metatarsal Bones in Horses
Enostosis-like Lesions of the Third Metatarsal Bone in Horses
Disorders of the Tarsus in Horses
Failure of Ossification of the Distal Tarsal Bones in Horses
Osteoarthritis of the Distal Tarsal Joints in Horses
Osteoarthritis of the Talocalcaneal Joint in Horses
Osteoarthritis of the Tarsocrural Joint in Horses
Synovitis/Capsulitis of the Tarsocrural Joint in Horses
Osteochondrosis of the Tarsocrural Joint in Horses
Osteitis of the Calcaneus in Horses
Fractures of the Distal Tarsal Bones in Horses
Fracture of the Talus in Horses
Fracture of the Fibular Tarsal Bone (Calcaneus) in Horses
Fracture of the Lateral Malleolus of the Tibia in Horses
Tarsal Joint Luxation in Horses
Desmitis of the Collateral Ligaments of the Tarsus in Horses
Rupture of the Fibularis (Peroneus) Tertius in Horses
Stringhalt
Curb in Horses
Disorders of the Tarsal Sheath in Horses
False Thoroughpin in Horses
Luxation of the Superficial Digital Flexor Tendon from the Tuber Calcanei in Horses
Gastrocnemius Tendinitis in Horses
Calcaneal Bursitis in Horses
Capped Hock
Disorders of the Stifle in Horses
Osteochondrosis of the Stifle in Horses
Subchondral Cystic Lesions in Horses
Meniscus and Meniscal Ligament Injuries in Horses
Cranial and Caudal Cruciate Ligament Injuries in Horses
Collateral Ligament Injuries in Horses
Intermittent Upward Fixation of the Patella and Delayed Patella Release in Horses
Fragmentation of the Patella in Horses
Patellar Luxation in Horses
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