How to Use a Digital Extension Device in Lameness Examinations

Introduction: Many clinicians use dorsal digital extension tests, when doing a lameness examination of the front limbs. Traditionally, the limb under examination is placed on the extremity of a long board, while an assistant picks up the contra-lateral limb. The opposite end of the board is then slowly raised, extending the digital joints, tensing the deep digital flexor tendon (DDFT), its inferior check ligament and the collateral and impart ligaments of the distal sesamoid (D.S.), as the palmar angle of the DDFT around the navicular bursa and the D.S. increases. Apart from practical problems like bending or breaking boards, pinched fingers, and slipping of the subject’s foot, evaluation of positive or negative responses are only standardized, if at all, with a personal protocol, e.g. by using always the same board, careful placing of the foot at its extremity and deciding on a height to be reached at the opposite end (e.g. The examiner’s knee) [1] . Horses show they are getting close to maximum tolerated extension, first by the shivering of their cleidobrachial and extensor carpi muscles, followed by the shifting of their weight on to their hind quarters, inclining their cannon bone backwards. In rare cases the heels will start lifting of the board. Maximum tolerance is therefore determined by slowly raising the board, till the horse shows any of these signs, of which specially the weight shifting, is easily perceived by the clinician, indicating that the horse is about to jump off. […]