Musculus biceps femoris
The biceps femoris is a large, multi-headed hindquarter muscle. It has a vertebral head arising from the sacral vertebrae, sacrosciatic ligament, and caudal fascia, and a pelvic head from the ischial tuber. Insertions include the patella and patellar ligaments, cranial tibia, crural fascia, and a tarsal tendon that contributes to the calcaneal (Achilles) tendon. It extends the hip and hock, abducts the limb, and can flex the stifle depending on the portion acting. It is a major propulsive muscle of the hind limb. The sciatic nerve runs deep to it. Clinically, fibrotic myopathy (scar tissue within or between the hamstring muscles) produces a characteristic mechanical "slapping" gait at the walk. The biceps femoris can be involved, though the semitendinosus is most common. Intramuscular injections in this region risk sciatic nerve damage.
Origin: Sacrotuberous ligament, ischial tuberosity, and sacral/caudal vertebrae
Insertion: Patella, tibial crest, and calcaneal tuber (point of hock)
Action: Extends the hip and hock; abducts the hindlimb; flexes the stifle
Innervation: Caudal gluteal nerve and sciatic nerve (L6-S2)
Diagnosis of fibrotic myopathy is clinical (gait) ± ultrasound. Surgical options include myotomy or tenotomy; recurrence is possible. Sciatic nerve proximity is important for injection technique.
## Overview Fibrotic myopathy is scarring and contracture within a muscle, most often the hamstring group (semitendinosus). It produces a characteristic mechanical gait in which the foot slaps down a
## Overview Biceps femoris strain is an injury to one of the major hamstring muscles of the hind limb. The biceps femoris helps extend the hip and flex the stifle and is heavily loaded during explosi
## Overview Sciatic nerve injury affects the major nerve supplying the muscles below the stifle. Damage from injections, fractures, or compression causes loss of hock flexion and digit extension, knu
A hind limb that suddenly stops mid-swing and slaps the ground (especially at the walk, often non-painful) should be evaluated; do not assume it is a stifle or hock problem. Avoid repeated IM injections in the caudal thigh.
## Overview Fibrotic myopathy is scarring and contracture within a muscle, most often the hamstring group (semitendinosus). It produces a characteristic mechanical gait in which the foot slaps down abruptly before completing the forward swing. The condition is usually non-painful and often follows trauma or an intramuscular injection. ## Causes Trauma, tearing, or injection-site fibrosis leading to muscle contracture. ## Diagnosis Classic gait at the walk plus palpation of a firm fibrous band. Ultrasound confirms the scar. ## Treatment Many horses need no treatment. Severe cases may undergo surgical transection of the fibrotic band. Conservative therapy (stretching, controlled exercise) helps some. ## Recovery and Prognosis The gait abnormality is often permanent but non-progressive. Surgery improves some horses. ## Prevention Careful injection technique in the hamstring region. Signs include: foot slaps down early in the swing phase; mechanical non-painful gait; shortened forward stride; firm band in the muscle; usually unilateral
## Overview Biceps femoris strain is an injury to one of the major hamstring muscles of the hind limb. The biceps femoris helps extend the hip and flex the stifle and is heavily loaded during explosive acceleration, hill work, and sudden stops. Strain ranges from mild fiber disruption to partial or complete tear and produces hind-limb lameness of variable severity. ## Causes Explosive work, racing, steep hill climbing, slipping, or unaccustomed exercise commonly overload the muscle. Fatigue, inadequate warm-up, and previous injury increase risk. Direct trauma is less common but can also produce tearing. ## Diagnosis Acute or subacute hind-limb lameness, heat and swelling over the lateral thigh, and pain on palpation of the muscle belly are typical. Ultrasound readily identifies fiber disruption, hematoma, or later fibrosis. Nuclear scintigraphy can help when the lesion is deep. ## Treatment Rest, cold therapy in the acute phase, and short-term non-steroidal anti-inflammatory drugs form the basis of care. Controlled walking is introduced once pain subsides, followed by progressive strengthening. Premature return to hard work frequently causes reinjury. ## Recovery and Prognosis Mild strains often resolve in a few weeks. Moderate to severe tears may require two to four months or longer. Prognosis is generally good with adequate rest, although some horses retain mild gait asymmetry or are prone to recurrence. ## Prevention Progressive conditioning, proper warm-up, and avoidance of sudden increases in speed or hill work reduce risk. Signs include: hindlimb lameness; swelling and heat over the lateral thigh; pain on palpation behind the stifle; shortened stride; reluctance to extend the hip
## Overview Sciatic nerve injury affects the major nerve supplying the muscles below the stifle. Damage from injections, fractures, or compression causes loss of hock flexion and digit extension, knuckling, dragging of the limb, and eventual atrophy of the entire gaskin. The nerve runs beneath the biceps femoris. ## Causes Injection trauma, pelvic or femoral fracture, or compression. ## Diagnosis Neurologic examination showing characteristic deficits. ## Treatment Supportive care and protection of the limb. Recovery depends on the severity of nerve damage. ## Recovery and Prognosis Variable. Partial injuries may improve. Complete severance has a poor outlook. ## Prevention Careful injection technique in the hindquarter. Signs include: loss of function below the stifle; inability to flex the hock or extend the digit; knuckling; dragging the hind limb; gaskin muscle atrophy
Diagnosis of fibrotic myopathy is clinical (gait) ± ultrasound. Surgical options include myotomy or tenotomy; recurrence is possible. Sciatic nerve proximity is important for injection technique.
A hind limb that suddenly stops mid-swing and slaps the ground (especially at the walk, often non-painful) should be evaluated; do not assume it is a stifle or hock problem. Avoid repeated IM injections in the caudal thigh.
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