Musculus flexor digitorum superficialis
The superficial digital flexor muscle originates from the medial epicondyle of the humerus in the forelimb and from the supracondylar fossa of the distal femur in the hindlimb. The tendon runs down the palmar (forelimb) or plantar (hindlimb) aspect of the limb, superficial to the deep digital flexor tendon, and inserts primarily on the proximal and middle phalanges (P1 and P2). In the forelimb it receives an accessory ligament (superior check ligament) from the radius and forms a sleeve around the deep flexor tendon at the fetlock joint. Its actions are to flex the fetlock and pastern joints, provide primary fetlock support during stance, and act as part of the stay apparatus. In the hindlimb it is more tendinous, forms part of the common calcanean tendon, passes over the calcaneus, and functions as part of the reciprocal apparatus. It is innervated by the median and ulnar nerves in the forelimb and the tibial nerve in the hindlimb. Injuries are less common in the hindlimb than in the forelimb.
Origin: Medial epicondyle of the humerus
Insertion: Proximal and middle phalanges (P1 and P2) via the branches of insertion
Action: Flexes the fetlock and pastern joints; primary fetlock support during stance; part of the stay apparatus
Innervation: Median and ulnar nerves (C8-T2)
Superficial digital flexor tendon (SDFT) injuries are common in performance horses, especially in the mid-cannon region. Diagnosis uses clinical examination and ultrasound. Management is usually medical with rest and controlled rehabilitation. Injuries can alter limb biomechanics and indirectly affect loading of the foot. The accessory ligament can also be injured.
## Overview A bowed tendon is the visible swelling that results from injury to the superficial digital flexor tendon (SDFT), most often in the mid-cannon region of a forelimb. Tearing of tendon fiber
## Overview A core lesion of the superficial digital flexor tendon (SDFT) is central degeneration within the tendon that may not produce external swelling at first. The tendon can feel normal on palp
## Overview Chronic superficial digital flexor tendon degeneration (tendinopathy) is the long-term remodeling and weakening of the superficial digital flexor tendon after repeated microdamage or inco
## Overview Suspensory apparatus failure is catastrophic disruption of the structures that support the fetlock (suspensory ligament, sesamoid bones, and often the superficial digital flexor tendon).
Sudden swelling or heat along the back of the cannon bone after work should be evaluated. Early diagnosis and appropriate rest improve outcomes. Protective boots can help reduce risk in some disciplines.
## Overview A bowed tendon is the visible swelling that results from injury to the superficial digital flexor tendon (SDFT), most often in the mid-cannon region of a forelimb. Tearing of tendon fibers and hemorrhage produce the characteristic convex “bow” on the back of the leg. The SDFT is an energy-storing tendon that operates near its functional limit during high-speed work, making it the most commonly injured tendon in equine athletes. ## Causes Overstrain during fast exercise, fatigue, poor conditioning, unsuitable footing, and pre-existing low-grade tendon degeneration are the main causes. The lesion is typically a central core tear. ## Diagnosis Palpation reveals heat, pain, and thickening. Ultrasound is the gold standard; it shows fiber disruption, core lesions, or diffuse tendinitis and is used to monitor healing. Horses are not always markedly lame, so absence of severe lameness does not rule out significant damage. ## Treatment Immediate rest, cold therapy, anti-inflammatory medication, and supportive bandaging are essential in the acute phase. A controlled, progressive rehabilitation program lasting 8 to 12 months or longer, guided by serial ultrasound, gives the best chance of return to work. Adjunctive treatments (superior check ligament desmotomy, biologics) are sometimes used; evidence for many is still evolving. ## Recovery and Prognosis Tendon heals with scar tissue that is weaker and less elastic than original tendon, so re-injury rates are high (reported between roughly 23 and 67 percent within two years with conventional management). Careful rehabilitation improves outcomes, but many horses do not return to their previous level of performance. ## Prevention Gradual conditioning, attention to footing, and early detection of heat or thickening allow intervention before catastrophic tearing occurs. Signs include: visible bow-shaped swelling on the back of the cannon; heat and pain on palpation; variable lameness; thickening of the superficial digital flexor tendon
## Overview A core lesion of the superficial digital flexor tendon (SDFT) is central degeneration within the tendon that may not produce external swelling at first. The tendon can feel normal on palpation while ultrasound shows a hypoechoic core. Lameness is often subtle initially but worsens if work continues. Core lesions can progress to full rupture. ## Causes Cumulative microdamage from repetitive loading. ## Diagnosis Ultrasound. The lesion is central and anechoic or hypoechoic. ## Treatment Prolonged rest and controlled rehabilitation. Regenerative therapies are sometimes used. Premature return to work risks progression. ## Recovery and Prognosis Fair to good with adequate time. Re-injury risk remains. ## Prevention Appropriate conditioning and early imaging of subtle tendon soreness. Signs include: subtle or intermittent lameness; tendon feels normal initially; hypoechoic core on ultrasound; worsens with continued work
## Overview Chronic superficial digital flexor tendon degeneration (tendinopathy) is the long-term remodeling and weakening of the superficial digital flexor tendon after repeated microdamage or incomplete healing of prior injury. The tendon may appear thickened, with altered fiber pattern on ultrasound, and remains prone to re-injury even when the horse is clinically sound. ## Causes Cumulative overload in athletic horses, especially racehorses and eventers, plus inadequate healing of earlier core lesions. ## Diagnosis History of prior bowed tendon, persistent thickening, and ultrasound showing fiber disruption, core lesions, or diffuse tendinopathy. Clinical lameness may be mild or absent. ## Treatment Controlled, ultrasound-guided rehabilitation lasting many months. Adjunctive therapies (biologics, shock wave) are sometimes used; evidence varies. Prevention of re-injury is the primary goal. ## Recovery and Prognosis Re-injury rates are high. Many horses return to a lower level of work; fewer regain previous elite performance. ## Prevention Careful conditioning, monitoring for early heat or thickening, and extended rehabilitation after any acute injury. Signs include: persistent tendon thickening; variable or absent lameness; ultrasound evidence of fiber disorganization or core lesions; history of previous bow
## Overview Suspensory apparatus failure is catastrophic disruption of the structures that support the fetlock (suspensory ligament, sesamoid bones, and often the superficial digital flexor tendon). The fetlock drops toward or onto the ground. It is a career-ending and often life-threatening emergency in racehorses. ## Causes Extreme hyperextension, usually at high speed, often after sesamoid fracture. ## Diagnosis Obvious dropped fetlock and severe lameness. ## Treatment Emergency stabilization. Surgical repair is rarely successful in complete breakdowns. Euthanasia is common. ## Recovery and Prognosis Grave for complete failure. ## Prevention Monitoring for early suspensory or sesamoid injury in racehorses. Signs include: fetlock drops toward or contacts the ground; severe lameness; career-ending or life-threatening in racehorses
Superficial digital flexor tendon (SDFT) injuries are common in performance horses, especially in the mid-cannon region. Diagnosis uses clinical examination and ultrasound. Management is usually medical with rest and controlled rehabilitation. Injuries can alter limb biomechanics and indirectly affect loading of the foot. The accessory ligament can also be injured.
Sudden swelling or heat along the back of the cannon bone after work should be evaluated. Early diagnosis and appropriate rest improve outcomes. Protective boots can help reduce risk in some disciplines.
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