Musculus obliquus internus abdominis
The internal abdominal oblique is the middle of the three lateral abdominal wall muscles. Its fibers run cranioventrally. It originates from the tuber coxae, inguinal ligament, and thoracolumbar fascia, and inserts on the linea alba and the last several ribs. Actions include compression of the abdomen, lateral flexion of the trunk, and assistance with respiration. In stallions it contributes to the walls of the inguinal canal (the passageway for the spermatic cord). It is innervated by the ventral branches of the thoracic and lumbar spinal nerves.
Origin: Tuber coxae, inguinal ligament, and thoracolumbar fascia
Insertion: Linea alba and last several ribs
Action: Compresses abdomen; lateral flexion of trunk; assists respiration
Innervation: Ventral branches of thoracic and lumbar spinal nerves
Isolated injury is uncommon. The muscle can be involved in body-wall trauma, hernias, or after abdominal surgery. It is relevant anatomically for the inguinal canal and potential sites of inguinal hernia in stallions.
## Overview Inguinal hernia occurs when intestine passes through the inguinal canal into the scrotum, most often in stallions. A reducible hernia may be present from birth or acquired. If the intesti
## Overview Abdominal strain from jumping refers to injury of the abdominal wall muscles or associated structures that occurs during the high-force loading of takeoff, flight, or landing in jumping s
Sudden swelling or asymmetry in the flank or groin after trauma or heavy work should be examined. In stallions, any inguinal swelling needs prompt veterinary attention to rule out hernia.
## Overview Inguinal hernia occurs when intestine passes through the inguinal canal into the scrotum, most often in stallions. A reducible hernia may be present from birth or acquired. If the intestine becomes trapped and strangulated, it is a surgical emergency with colic and a firm, painful, non-reducible swelling. ## Causes Congenital enlarged inguinal ring or acquired herniation, often after breeding or trauma. ## Diagnosis Palpation of scrotal swelling, ultrasound, and signs of colic if strangulated. ## Treatment Manual reduction under sedation for uncomplicated cases. Emergency surgery for strangulated hernias. Castration is often performed at the same time in stallions. ## Recovery and Prognosis Good if reduced before bowel compromise. Strangulated cases have a more guarded outlook. ## Prevention None for congenital predisposition. Prompt attention to scrotal swelling. Signs include: swelling in the groin or scrotum; colic if intestine is trapped; warm painful non-reducible swelling when strangulated; more common in stallions
## Overview Abdominal strain from jumping refers to injury of the abdominal wall muscles or associated structures that occurs during the high-force loading of takeoff, flight, or landing in jumping sports. The rectus abdominis, external and internal oblique muscles, and supporting fascia can be overstretched or torn when a horse engages its core to lift the forehand, round the back, or absorb landing forces. Mild strains may present as subtle performance changes, while more severe injuries can cause acute pain, reluctance to jump, or secondary issues such as mesenteric rents if internal tissues are involved. ## Causes The primary cause is repetitive or sudden overload during jumping. Poor footing, fatigue, inadequate core conditioning, conformational issues, or a sudden increase in jump height or volume raise risk. Trauma from a fall or awkward landing can also produce strain. In broodmares, abdominal strain during late pregnancy or foaling is a related risk factor that can predispose to mesenteric tears, but jumping-related strain is distinct and more common in sport horses. ## Diagnosis Diagnosis is largely clinical. History of recent jumping combined with reluctance to jump, shortened stride, or pain on palpation of the abdominal wall supports the diagnosis. Ultrasound can identify muscle tears, hematomas, or fascial disruption. Rectal examination and abdominal ultrasound help rule out more serious internal injuries such as mesenteric rents or intestinal entrapment. Differential diagnoses include back pain, sacroiliac dysfunction, and mild colic. ## Treatment Initial management focuses on rest, controlled exercise, and anti-inflammatory medication. Cold therapy and supportive bandaging may help in the acute phase. Gradual return to work under veterinary guidance is essential; premature jumping often leads to reinjury. Severe tears or associated internal injury may require surgical exploration. ## Recovery and Prognosis Most uncomplicated muscle strains heal with 4 to 12 weeks of rest and progressive rehabilitation. Prognosis is good for return to previous level of work if the injury is managed conservatively and the horse is not returned to jumping too soon. Cases involving mesenteric rents or intestinal compromise carry a more guarded prognosis and often require emergency surgery. ## Prevention Progressive conditioning of the core and hindquarters, appropriate footing, and avoidance of sudden increases in jumping demand reduce risk. Regular veterinary and farrier care to address underlying biomechanical issues is also helpful. Signs include: reluctance to jump or engage the core; shortened stride; pain on palpation of the abdominal wall; stiffness after work; occasional mild colic-like signs
Isolated injury is uncommon. The muscle can be involved in body-wall trauma, hernias, or after abdominal surgery. It is relevant anatomically for the inguinal canal and potential sites of inguinal hernia in stallions.
Sudden swelling or asymmetry in the flank or groin after trauma or heavy work should be examined. In stallions, any inguinal swelling needs prompt veterinary attention to rule out hernia.
See the Internal Abdominal Oblique on our interactive 3D horse model. Open 3D Model