A tendon is a band or cord of dense fibrous connective tissue that anchors muscle to bone, transmitting the contractile force of the muscle across a joint to produce movement. Tendons are composed primarily of parallel bundles of type I collagen, which gives them high tensile strength but limited elasticity. In the horse, the tendons of the lower limb — particularly those running from the carpus or tarsus down to the joint loaded by flexor tendon tension and pastern — are among the most critically loaded structures in the body.
The two major structures prone to injury in the equine forelimb are the superficial digital flexor tendon (SDFT) and the deep digital flexor tendon (DDFT). The SDFT runs along the back of the mid-cannon region of the SDFT and is the most commonly injured tendon in sport horses, presenting as heat, swelling, and pain over the mid-cannon region. Ultrasonography has largely replaced palpation alone as the gold-standard diagnostic tool for characterizing tendon lesions — identifying the size and location of core lesions that are invisible externally.
Tendon healing is slow and often incomplete; unlike bone, tendon repairs itself with a mixture of fibrous scar tissue and disorganized collagen that is biomechanically inferior to the original structure. Controlled rehabilitation over months to years, often guided by serial ultrasound exams, is necessary to reduce the probability of re-injury.
The suspensory ligament, often discussed alongside tendons, is a modified interosseous muscle that provides additional support to the joint loaded by flexor tendon tension. Though technically a ligament, it behaves functionally similarly to a tendon and is subject to the same injury patterns in performance horses.