Anatomy of Back Muscles

Back Muscles

• The back muscles can be categorized into three layers: superficial, intermediate, and deep.

Superficial Muscles

• The superficial muscles are also known as the spinotransversales.
• There are two muscles in this group: splenius capitis and splenius cervicis.
• They are associated with movements of the head and neck.
• Located on the posterolateral aspect of the neck, covering the deeper neck muscles.

Splenius Capitis

• Originates from the lower aspect of the ligamentum nuchae and the spinous processes of C7-T3/4 vertebrae.
• Fibers ascend, attaching to the mastoid process and the occipital bone of the skull.
• Innervated by posterior rami of spinal nerves C3 and C4.
• Actions: Rotate head to the same side.

Splenius Cervicis

• Originates from the spinous processes of T3-T6 vertebrae.
• Fibers ascend, attaching to the transverse processes of C1-3/4.

Intermediate Muscles

• There are three intermediate intrinsic back muscles: iliocostalis, longissimus, and spinalis.
• Together, these muscles form a column known as the erector spinae.
• The erector spinae is situated posterolaterally to the spinal column, between the vertebral spinous processes and the costal angle of the ribs.

Iliocostalis

• Located laterally within the erector spinae.
• Associated with the ribs.
• Can be divided into three parts: lumborum, thoracis, and cervicis.

Longissimus

• Situated between the iliocostalis and spinalis.
• Largest of the three columns.
• Can be divided into three parts: thoracic, cervicis, and capitis.
• Attachments: Arises from the common tendinous origin and attaches to the lower ribs, the transverse processes of C2-T12, and the mastoid process of the skull.
• Innervation: Posterior rami of the spinal nerves.
• Actions: Acts unilaterally to laterally flex the vertebral column, and acts bilaterally to extend the vertebral column and head.

Spinalis

• Located medially within the erector spinae.
• Smallest of the three muscle columns.
• Can be divided into the thoracic, cervicis, and capitis.
• Attachments: Arises from the common tendinous origin, and attaches to the spinous processes of C2, T1-T8, and the occipital bone of the skull.
• Innervation: Posterior rami of the spinal nerves.
• Actions: Acts unilaterally to laterally flex the vertebral column, and acts bilaterally to extend the vertebral column and head.

Deep Intrinsic Muscles

• Located underneath the erector spinae.
• Known collectively as the transversospinales.
• Three major muscles in this group: semispinalis, multifidus, and rotatores.

Semispinalis

• Most superficial of the deep intrinsic muscles.
• Can be divided by its superior attachments into thoracic, cervicis, and capitis.
• Attachments: Originates from the transverse processes of C4-T10.
• Fibers ascend 4-6 vertebral segments, attaching to the spinous processes of C2-T4 and the occipital bone of the skull.
• Innervation: Posterior rami of the spinal nerves.
• Actions: Extends and contralaterally rotates the head and vertebral column.

Multifidus

• Located underneath the semispinalis muscle.
• Best developed in the lumbar area.
• Attachments: Has a broad origin – arises from the sacrum, posterior iliac spine, common tendinous origin of the erector spinae, mamillary processes of lumbar vertebrae, transverse processes of T1-T3, and articular processes of C4-C7.
• Fibers ascend 2-4 vertebral segments, attaching to the spinous processes of the vertebrae.
• Innervation: Posterior rami of the spinal nerves.
• Actions: Stabilizes the vertebral column.

Rotatores

• Most prominent in the thoracic region.
• Attachments: Originates from the vertebral transverse processes.
• Fibers ascend, and attach to the lamina and spinous processes of the immediately superior vertebrae.
• Innervation: Posterior rami of the spinal nerves.
• Actions: Stabilizes the vertebral column and has a proprioceptive function.

Minor Deep Intrinsic Muscles

• Interspinales: Spans between adjacent spinous processes, and acts to stabilize the vertebral column.
• Intertranversari: Spans between adjacent transverse processes, and acts to stabilize the vertebral column.
• Levatores costarum: Originates from the transverse processes of C7-T11, and attaches to the rib immediately below, and acts to elevate the ribs.

Tracheobronchial Tree Injuries

• Can be conservative or surgical, depending on the severity of the injury
• Surgical approach is based on the location and extension of the injury
  • Cervical collar incision for proximal trachea
  • Right postero-lateral thoracotomy for lower trachea, carina, and proximal right main bronchus
  • Left postero-lateral thoracotomy for distal left main bronchus

Foreign Body in the Airway

• Management depends on the severity of the injury
  • Acute: Urgent bronchoscopy with or without bronchotomy
  • Chronic: Bronchoscopy with precaution, with or without lung resection

Esophagus Injuries

• Rare, but can occur due to blunt or penetrating trauma
• Cervical esophageal injuries are the most common
• Symptoms include:
  • Pneumothorax (left)
  • Hemorrhage without rib fractures
  • Lower sternum or epigastric pain (severe blunt trauma)
  • Particulate matter in the ICD
  • Penetrating injury that has crossed the mediastinum
  • Odynophagia
  • Dysphagia
  • Surgical emphysema
  • Mediastinitis
• Investigations:
  • Combination of clinical suspicion, CXR, water-soluble contrast swallow, and oesophagoscopy
• Management:
  • Timing: 24 hours, debride and drainage, surgical repair or resection with delayed reconstruction
  • Approach: Right postero-lateral thoracotomy (RPLT) for upper esophagus, left postero-lateral thoracotomy (LPLT) for lower esophagus

Complications of Esophagus Injuries

• Mediastinal contamination
• Abscess formation
• Empyema thoracis

Foreign Body in the Esophagus

• Types: bone, meat, battery, coin
• Clinical presentation:
  • Acute: dysphagia, choking, hematemesis
  • Chronic: hemoptysis, coughing when feeding
• Management:
  • Oesophagoscopy with or without mediastinal drainage and repair

Diaphragmatic Injuries

• Often occult, easily missed, especially on the left side
• Marker of severe thoracoabdominal trauma
• Causes:
  • Blunt trauma
  • Penetrating trauma (stab or iatrogenic)
• Clinical features:
  • With or without signs of bowel obstruction, drainage of peritoneal content via chest drain
  • NGT in the chest (CXR)
  • Herniation of GIT
  • Acute, delayed, common left
• Investigations:
  • CXR: elevated hemidiaphragm, hemo-pneumothorax
  • Swallow and follow through
  • Contrast-enhanced CT scan
• Management:
  • Surgical repair: thoracotomy, thoraco-abdominal incision, or laparotomy, laparoscopy

Cardiac Injuries

• Penetrating:
  • Myocardial contusion, transient arrhythmias
  • Valve injuries
  • IVS rupture
• Blunt:
  • Myocardial contusion, patchy areas of muscle necrosis, hemorrhagic infiltrate, rupture of small vessels
  • Hemorrhage into the interstitium and around the muscle fibers
• Investigations:
  • Admit to HCU/ICU for monitoring
  • ECG, cardiac enzymes
  • Treat dysarrhythmias and heart failure
  • Formal ECHO/TEE
• Management:
  • Elective or urgent surgery
  • Myocardial rupture: simple cardiorrhaphy, pledgetted suture
  • Mitral valve: repair or replacement
  • Tricuspid valve: repair
  • IVS: traumatic VSD, closure for larger ones, bypass or not

Surgery

• Elective or urgent
• Myocardial rupture: simple cardiorrhaphy, pledgetted suture
• Mitral valve: repair or replacement
• Tricuspid valve: repair
• IVS: traumatic VSD, closure for larger ones, bypass or not

Great Vessel Injuries

• Aorta is the most commonly injured in severe blunt or penetrating trauma
• 85-95% mortality
• Typically, patients survive the initial injury insult
• Mortality rates:
  • 30% within 6 hours
  • 50% within 24 hours
  • 70% within 1 week

Blunt Aortic Injuries

• Mechanisms:
  • Acceleration-deceleration
  • Production of shearing forces
  • Direct luminal compression - fixation points
• Site: isthmus, near ligamentum arteriosum
• Clinical features:
  • Death on the scene - rapid exsanguination
  • Expanding thoracic inlet hematoma, bruit, hypotension, pulse deficit

Aortic Disruption

• Radiographic features associated with thoracic aortic injury:
  • Loss of aortic knuckle contour
  • Widened mediastinum
  • Obliteration of aorto-pulmonary window
  • 1st/2nd rib fracture
  • Depression of the right main bronchus
  • Deviated NGT and tracheal displacement to the right
  • Widened paratracheal stripe
  • Left massive hemithorax
  • Left pleural cap

Management

• Medical: endovascular stents
• Surgical: open surgical procedures

Thoracic Trauma

• Accounts for 20-25% of thoracic deaths worldwide
• Male vs female
• Age
• Blunt, penetrating, transfixing

Mechanism of Injury

• 1. Penetrating:
  • High velocity - gunshots
  • Low velocity - stab wounds
• 2. Blunt:
  • Direct:
    • Assault and blast
  • Indirect:
    • Falls, MVA (acceleration-deceleration injuries, crush injuries, and shearing forces)
• 3. Transfixing

Special Factors

• Pediatric thorax: more cartilage, absorbs forces
• Geriatric thorax: calcification and osteoporosis, more fractures

Initial Evaluation

• Goal: prompt identification of life-threatening injuries
• Pathology:
  • Airway obstruction
  • Loss of oxygenation or ventilation
  • Hypovolaemia
  • Obstructive shock
  • Ventilation-perfusion mismatch
• Physiological causes of death:
  • Tissue hypoxia
  • Hypercarbia
  • Metabolic acidosis

Traumatic Rib Fractures

• Other bony fractures of the chest wall
  • Sternal fractures:
    • Up to 4%
    • Transverse, in the upper or midportions
    • Associated injuries: myocardium
    • Cf: point of tenderness, swelling, and deformity

This quiz covers the origin, innervation, and actions of the muscles of the back, including the longissimus muscle.