Musculus gastrocnemius
The gastrocnemius has medial and lateral heads that originate from the corresponding supracondylar tuberosities of the distal femur. The two heads converge into a strong tendon that joins the common calcanean (Achilles) tendon and inserts on the calcaneal tuber (point of the hock). It is innervated by the tibial nerve (roughly L5–S2). Its primary actions are to extend the hock and flex the stifle. Because the gastrocnemius and the superficial digital flexor are mechanically linked to the stifle, the muscle is a major component of the caudal part of the reciprocal apparatus. When the stifle is extended, the hock is forced to extend; when the stifle flexes, the hock must flex. This linkage allows the horse to stand and move efficiently with less muscular effort. Rupture or severe strain of the gastrocnemius (or the common calcanean tendon) disrupts the reciprocal apparatus. The characteristic sign is a dropped hock with simultaneous extension of the stifle: the horse cannot support weight normally on the affected limb.
Origin: Supracondylar tuberosities of the distal femur (lateral and medial heads)
Insertion: Calcaneal tuber (point of hock) via the common calcanean tendon
Action: Extends the hock; flexes the stifle; weight bearing during stance
Innervation: Tibial nerve (L5-S2)
Complete or partial rupture of the gastrocnemius tendon or common calcanean tendon is a serious injury, often caused by a fall with the limb extended under the body or by extreme loading. The hock drops and the reciprocal mechanism fails. Diagnosis is clinical (characteristic posture) plus ultrasound or radiography to rule out avulsion fractures. Prognosis for return to athletic use is guarded to poor; many horses can be salvaged for breeding or light use with prolonged rest and support.
## Overview Complete rupture of the gastrocnemius (and often the superficial digital flexor) disrupts the reciprocal apparatus. The hock drops dramatically when the horse bears weight, and the limb c
## Overview Strain of the gastrocnemius or injury to the calcanean (Achilles) tendon produces hind-limb lameness that is worse when the hock is loaded. Mild dropping of the hock and swelling over the
## Overview Curb is soft-tissue swelling on the plantar distal aspect of the hock. Historically it referred to enlargement of the long plantar ligament, but similar swelling can arise from superficia
Sudden severe hind-limb lameness with a dropped hock (the point of the hock sinks while the stifle stays straight) is an emergency. Keep the horse quiet, support the limb if possible, and call the veterinarian immediately. Do not force the horse to walk.
## Overview Complete rupture of the gastrocnemius (and often the superficial digital flexor) disrupts the reciprocal apparatus. The hock drops dramatically when the horse bears weight, and the limb cannot support the body. It is usually caused by a fall with the limb extended under the body. ## Causes Forced extension of a contracting muscle during a fall or slip. ## Diagnosis Characteristic dropped hock, inability to bear weight, and a palpable defect or swelling in the Achilles region. Ultrasound confirms the tear. ## Treatment Supportive care with slings or prolonged external support in selected incomplete cases. Complete rupture of both heads plus the superficial digital flexor carries a grave prognosis. Most complete cases are euthanized. ## Recovery and Prognosis Poor to grave for complete rupture. Incomplete injuries have a better chance with intensive nursing. ## Prevention None specific. Signs include: hock drops dramatically when weight-bearing; severe lameness; cannot support weight; swelling or defect in the Achilles area
## Overview Strain of the gastrocnemius or injury to the calcanean (Achilles) tendon produces hind-limb lameness that is worse when the hock is loaded. Mild dropping of the hock and swelling over the tendon region are typical. It is less severe than complete rupture. ## Causes Overload, slip, or partial tear. ## Diagnosis Palpation of pain and swelling, ultrasound of the tendon and muscle, and observation of hock posture under load. ## Treatment Prolonged rest, anti-inflammatories, and controlled rehabilitation. External support may be used in more significant partial tears. ## Recovery and Prognosis Fair to good for strains. Partial tears require months of recovery. ## Prevention Conditioning and avoidance of slippery surfaces. Signs include: hind-limb lameness worse when the hock is loaded; swelling over the calcanean tendon; pain on palpation; slight dropping of the hock
## Overview Curb is soft-tissue swelling on the plantar distal aspect of the hock. Historically it referred to enlargement of the long plantar ligament, but similar swelling can arise from superficial or deep digital flexor tendinitis, periligamentous inflammation, or a combination. It is seen most often in racehorses, particularly Standardbreds, and may or may not cause lameness. ## Causes Conformational faults (sickle or curby hocks), trauma, or overload during training. ## Diagnosis Visible and palpable thickening distal to the point of the hock. Ultrasound identifies the specific structures involved. ## Treatment Rest, anti-inflammatory medication, and controlled exercise. Corrective shoeing addresses conformational contributors. Most cases resolve without long-term effects. ## Recovery and Prognosis Good. Recovery typically takes weeks to a few months. ## Prevention Attention to conformation and gradual conditioning. Signs include: firm swelling on the back of the distal hock; variable heat and lameness; thickening of plantar soft tissues
Complete or partial rupture of the gastrocnemius tendon or common calcanean tendon is a serious injury, often caused by a fall with the limb extended under the body or by extreme loading. The hock drops and the reciprocal mechanism fails. Diagnosis is clinical (characteristic posture) plus ultrasound or radiography to rule out avulsion fractures. Prognosis for return to athletic use is guarded to poor; many horses can be salvaged for breeding or light use with prolonged rest and support.
Sudden severe hind-limb lameness with a dropped hock (the point of the hock sinks while the stifle stays straight) is an emergency. Keep the horse quiet, support the limb if possible, and call the veterinarian immediately. Do not force the horse to walk.
See the Gastrocnemius on our interactive 3D horse model. Open 3D Model