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5.4. Farriery diagnostics - Examination with digital extension device by Dr. Castelijns, Author: Ing. Jindřich Vinčálek

Examination with Digital extension device by Dr. Hans Castelijns

From a farrier's point of view, a very important examination is a Digital extension device test. The author of this device and method of examination is Dr. Hans Castelijns, who was inspired by the so-called board test. It is a method that can provide farriers and veterinarians with much information on the condition of joints and soft tissues of the distal limb. The device consists of a circular swivel plate with a bevelled side edge allowing the plate to be tilted to the sides. A lever with the protractor and the spirit level is connected to the rotating ring of the plate. With this device, we mainly examine the forelimbs and, to a limited extent, the hind limbs. Thanks to the turntable we can measure the extension levels in all directions.

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Fig.1: Digital extension device by Dr. Hanse Castelijns

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Fig. 2: Detail of circular swivel plate

Fig. 3: Lever end with contractor and spirit level

The basic examination is dorsal (cranial) extension. Place the examined leg of the horse on the turntable and hold the other freely raised. Turn the lever with the protractor to the dorsal side of the limb and slowly raise it.  The level of dorsal extension in a healthy horse is 30 ° - 45 ° without painful reaction. We measure the level of extension when the hoof heels or shoe branches are lifted from the turntable or the first painful horse reaction.  In horses without painful reactions, it is unnecessary to extend over 40°. The dorsal extension examines the health condition of the coffin joint, navicular bone, DDFT and partially also collateral ligaments of the navicular bone.

Another possibility of examination with a digital balance device is the palmar (caudal) extension. With the limb standing on the balancing plate, turn the extension lever backwards and by lifting it we can verify the health condition of the suspension apparatus of the fetlock, especially the suspensory ligament  and its branches, palmar sesame ligaments of the fetlock and superficial flexor tendon. When measuring palmar extension, we observe primarily the size of the angle, which should reach at a healthy limb 15 ° - 25 ° without painful reaction. Any pain at a smaller angle is indicative of the extent of damage to the fetlock suspension apparatus.


With the help of the swivel plate, we can investigate damage to the collateral ligaments of the digital joints, especially the coffin joint, by lifting the lever in the lateromedial (transverse) direction. A painful reaction can also occur when the opposite branch of the suspensory ligament or collateral ligament of the navicular bone is damaged.

The extension lever is first turned to the lateral (outer) direction of the examined limb and by its elevation we stretch the soft structures on the medial (inner) side of the limb. Raise the lever until the inner bearing edge of the hoof or horseshoe begins to lift away from the surface of the turntable. At this point, align the protractor arm and read off the measured angle. Repeat the same procedure with the lever in the medial (inner) side of the limb. If the horse exhibits a painful reaction at elevations, we measure the magnitude of the angle at the first sign of pain. The optimal extension angle without painful reactions is 18 ° - 19 ° on the medial side and 19 ° - 20 ° on the lateral side. Measured angles less than 18 ° and a difference in angles between both sides greater than 5 ° indicate poor lateromedial balance of the limb and the possibility of damage to the joint or ligament structures.

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