ABSTRACT
Fetlock problems are a common cause of lameness in every type of discipline and use, especially in sport and race horses. The biomechanics of this region are usually considered in the sagittal plane, especially metacarpophalangeal extension during the stance phase. Functional events occurring during the swing phase and the consequences of asymmetric loads during turns or induced by conformational defects will be described and illustrated based on in vivo and in vitro biomechanical investigations. These data are essential for considering a rational corrective shoeing of fetlock conditions in sport and race horses, but also in horses with low athletic activity or at rest.
INTRODUCTION
Fetlock problems are a common cause of forelimb lameness in sport horses. This presentation is focused on the medial metacarpophalangeal overload, often associated with conformational abnormalities. The horse may be presented for recent lameness, but chronic, low-grade and intermittent manifestations are also common.
CLINICAL EXAMINATION
Medial metacarpophalangeal overload is often associated with various degrees of varus conformation in average-weighted or heavy horses. This defect can be unilateral or bilateral. A careful examination of the fetlock may reveal a dorsomedial enlargement. Passive flexion of the fetlock can be limited and painful in horses at work.
At gaits, the horse does not show specific abnormalities at the walk and may be sound on the circle when the affected limb is inside. A subtle defect of fetlock extension of the affected limb is usually seen, with a mild reduction of the cranial phase of the stride. There is a typical worsening of the lameness when the horse is at trot on the opposite circle, when the affected limb is outside with a mild reduction of the cranial phase of the stride (Fig. 1 and 2). There is a little improvement of these manifestations on soft surfaces.
The flexion test of the sounder limb may exacerbate the lameness of the affected limb (positive weight bearing test). The response to the flexion test of the affected limb depends on the horse’s physical level of activity when the horse is examined. During jumping in lunge, the horse has a tendency to land with the affected limb as the contact limb, continuing canter with the sound leading limb. Examination of the horse ridden does not provide any additional diagnostic data.
When these typical manifestations are observed, it is recommended to perform radiography and ultrasonography of both fetlocks and of the proximal suspensory attachment before doing any other investigation or diagnostic analgesia.
DIAGNOSTIC IMAGING
Conventional imaging of the equine fetlock using radiography and ultrasonography is the first step for approaching the diagnosis of this clinical picture. On the dorsopalmar radiographs, an increased bone density in the medial part of the metacarpal condyle is a consequence of chronic medial overload (Fig. 3).
Various degrees of lysis of the subchondral bone can be seen. Ultrasonographic examination of the distal aspect of the metacarpal condyle on the flexed fetlock provides essential information to assess the subchondral bone surface and articular cartilage (Fig. 4). Magnetic resonance imaging and CT scan confirm the bone alterations.
PROGNOSIS AND MANAGEMENT
The prognosis for complete soundness is fair, but some horses with this condition can continue to compete if adequately managed. The main aspect of the management is to reduce the load on the medial aspect of the limb using an adequate kinesitherapic (or corrective) shoe (Fig. 5).
This shoe can be placed on both forelimbs, as horses commonly present the same bilateral conformational defect predisposing to the same condition.
Then, an exercise program based on the clinical manifestations e.g. reducing the turns on the opposite side to the most affected limb must be designed. Intraarticular medication can complement these recommendations but, as most of the cases present cartilaginous failure, steroids should be avoided.
SELECTED REFERENCES
- Barone R, Simoens P: Anatomie comparée des Mammifères domestiques. Tome 2: Arthrologie et myologie. Paris, Vigot, 2010
- Denoix J-M: A look at lameness through the eyes of functional anatomy (and biomechanics). Proceedings 67th AAEP Convention, Nashville, 2021:106-133
- Denoix J-M: The equine distal limb – An atlas of clinical anatomy and comparative imaging: The equine fetlock. CRC Press, 2014; pages 243-373
About the Author
Jean-Marie Denoix, DVM, MS, DACVIM (LAIM)
Jean-Marie Denoix graduated from the Veterinary School of Lyon (France,1977). He became Agrégé in Veterinary Anatomy (1983) and defended a PhD thesis in Biomechanics (1987). In 1988 he moved to the Veterinary School of Alfort (Paris) and became professor of Anatomy, head of the equine clinical unit (until 2005) and head of a research unit devoted to Biomechanics and Pathology of the locomotor system in horses (until 2003). He became head of CIRALE (Center of Imaging and Research in Equine Locomotor Pathology in Horses) in 1999. Since 2006 he is President of the ISELP (International Society of Equine Locomotor Pathology), large animal imaging associate of the ECVDI since 2010, and President of the ALAPILE (South American Association) since 2012. In 2013 he became Diplomate of the American College of Veterinary Sport Medicine and Rehabilitation (ACVSMR) and is a founding Diplomate of the European College of Veterinary Sport Medicine and Rehabilitation (ECVSMR).