Injuries to the carpus and tarsus are common in agility and sporting dogs. The carpal and tarsal joints act as sock absorbers
for the limb during weight bearing. They are prone to injury due to their complexity and lack of muscular support. The complexity
of these joints creates a diagnostic problem for many veterinarians. Many carpal and tarsal injuries, particularly those that
go undiagnosed or untreated, can result in an increased risk of osteoarthritis and potential long-term lameness.
Anatomy
The carpus and tarsus are multilevel joints with several supportive ligaments and joint capsule. The carpus is composed of
three articulations; the antebrachiocarpal joint, the middle carpal joint, and the carpometacarpal joint. The majority of
carpal range of motion (70%) is at the antebrachiocarpal joint with relative minimal motion of the middle carpal and carpometacarpal
joints. There is a thick fibrocartilage pad on the underside (palmar aspect) of the joint that attaches to the individual
carpal and metacarpal bones. The main supportive ligaments of the carpus include the medial (radial) and lateral (ulnar) collateral
ligaments which support each side of the joint and numerous dorsal (upperside) and palmar (underside) ligaments resulting
in a supportive web. Similarly, the tarsal joint is complex, comprised of four articulations; the tibiotarsal joint, proximal
(top) intertarsal joint, distal (bottom) intertarsal joint, and tarsometatarsal joint. The majority of tarsal range of motion
(80%) occurs at the tibiotarsal joint. The joint is supportive by numerous ligaments including the medial and lateral collateral
ligaments, dorsal (upperside) and plantar (underside) ligaments.
Cause of injury
Carpal and tarsal injuries can result from either acute traumatic events or activities resulting in repetitive sprains to
the supportive structures of the joint. Possible modes of injury include; hyperextension (disruption of the underside ligaments
+/- joint capsule which is the most common type seen in agility dogs), hyperflexion with rotation (upperside ligaments and
collateral ligaments +/- joint capsule), varus (inside of the limb) or valgus (outside) injuries or degeneration of any
ligaments in some breeds ( Collies and Shelties) and certain immune mediated diseases (eg. Rheumatoid arthritis).
Diagnosis
The diagnosis of carpal and tarsal injuries, especially mild in severity, can be difficult. Diagnosis is based on a combination
of physical examination and imaging techniques. Dogs with carpal or tarsal injuries can present with either an acute (sudden)
or chronic (slowly progressive) lameness of varying degrees depending on the severity of the injury. Palpation of the affected
joint may reveal soft tissue swelling, discomfort, crepitus (crunching on manipulation), decreased range of motion, or instability
when stressed (either in extension, flexion, varus or valgus, internal or external rotation). Palpation of the nonaffected
joint on the other side can be helpful in determining normal from abnormal motion. Radiographs can be taken to evaluate the
type and severity of injury. Ligamentous structures cannot be seen on radiographs, but fractures, luxations, or abnormal opening
of a joint when stressed (extension, flexion, varus or valgus) can be used to determine ligament integrity. Chronic, or long
standing/ repetitive injuries may have bone spurs present at the site of ligamentous attachment to the bone. Fluoroscopy which
is performed "real time" can take radiographic images/ video when placing the joint through range of motion. Excessive opening
of the joint spaces or abnormal gliding (subluxation) may be noted fluoroscopically for carpal and tarsal injuries (Figure
3). When available, this is ideal over "stress" radiographs to evaluate specific joint motion during manipulation of the
carpal or tarsal joint for diagnosis of the injury incurred. In the presence of carpal or tarsal pain without radiographic
or abnormalities, magnetic resonance imaging (MRI) can be useful to assist in the diagnosis of minor ligament sprains.
