DIAGNOSING, MANAGING, AND RESOLVING LAMENESS IN HORSES


ometer is a protractor with extending arms. The fulcrum of the goniometer should be aligned with the center of joint rotation to be measured, and the arms of the device should radiate out to the proximal and distal joint’s center of rotation. If using a go- niometer without extendable arms, the center line of the arms should be aligned along the center of the bony column. The center of rotation for each joint is found using previously described anatomical land- marks while taking the joint through the full range of motion.1 Goniometry has been proven to be a useful and


easy tool that allows veterinarians to measure prog- ress in joint mobility. Rehabilitation protocols that are designed around increasing passive joint range of motion include muscle stretching and passive joint mobilization. Each protocol is aimed at en- hancing soft tissue extensibility to restore normal joint mobility. Previously determined anatomical landmarks are


used to locate the center of joint rotation. Knowl- edge of the location of the center of joint rotation is critical for evaluating the accuracy of joint angula- tion measurements.2 Center or axis of joint rotation (COR):


● Scapulohumeral/Shoulder–COR: Distal and caudal to the caudal portion of the greater tubercle of the humerus. The proximal and distal arms of the goniometer are aligned with the spine of the scapula and the longitudinal axis of the humerus, respectively.3


● Humeroradial/Elbow–COR: Lateral collat- eral ligament where it attaches on the lateral epicondyle of the humerus.3


● Carpus–COR: Dorsal half of the accessory carpal bone in extreme flexion.3


● Metacarpophalangeal/Metatarsophalangeal– COR: Attachment of the lateral collateral lig- ament on metacarpal/tarsal III.3


● Coffin–COR: Attachment of the lateral col- lateral ligament on the middle phalanx.


● Coxofemoral–COR: Greater trochanter. The proximal and distal arms of the goniometer are aligned with the body of the ilium and longitudinal axis of the femur, respectively.


● Femorotibial/Stifle–COR: Caudal to the fem- oral attachment of the lateral collateral ligament.3


● Tarsus–COR: Attachment of the lateral col- lateral ligament of the tarsocrural joint on the talus3 (Fig. 1).


Pressure Algometry


Pain is characteristically the primary complaint in hu- man patients suffering from musculoskeletal injury. However, as the equine patient cannot verbally ex- press their level of discomfort, the assessment of pain is typically subjective based on clinical presentation and examination. Often, the localization of the pri- mary source of pain can be difficult due to increased


302 2019  Vol. 65  AAEP PROCEEDINGS


Fig. 1. Tarsal flexion measured with a goniometer.


nociceptive plasticity (i.e., behavioral and cellular modifications produced by activation of nociceptors) causing radiating and referred pain. Mechanical no- ciceptive threshold (MNT) assessment has been inves- tigated in numerous human clinical studies and more recently used to establish normal reference values in the horse, as well as assessing equine axial and appendicular musculoskeletal pain. The use of the pressure algometer to assess MNTs provides a repeat- able, objective quantification of pain, allowing changes in stimulus intensity to be compared. Importantly, human studies have demonstrated not only that MNTs are decreased over the injured region but also that lower thresholds are often found over sites remote to the primary source of pain. Similarly, experimen- tally induced osteoarthritis in the equine carpus re- sulted in lowerMNTvalues recorded from sites tested directly in the region of the carpus, as well as de- creased values in sites both distal and proximal to the osteoarthritic joint. MNT testing can be used to quantify the degree of pain associated with the pri- mary injury, to identify and localize referred musculo- skeletal pain, and may assess nociceptive changes related to rehabilitative therapies. Using a pressure algometer allows for objective, repeatable numbers to be tracked as to the pain coming from specific structures, including both soft tissue and bone.4 Applying localized pressure to specific areas causes the horse to withdraw from the focal pressure. The lower the MNT when a with- draw response is noted, the higher the pain level. If secondary muscle pain is also present, these spe- cific locations should be chosen for repeatable mea- surements. For example, coexisting muscle pain in a forelimb lameness could be tracked through the use of pressure algometry typically over the distal brachiocephalicus muscle. The pressure algometer may be used in axial skeletal pain to differentiate bone from muscle pain (measured directly over spi- nous processes [Fig. 2] and/or along the epaxial mus-


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