Snell - Anatomy Chapter 2: Back Muscles

Back Anatomy and Function

• Muscle attachments vary in importance based on professional field; details are frequently omitted.
• Superficial and intermediate back muscles primarily receive innervation from anterior rami of spinal nerves, except the trapezius, which is innervated by the spinal accessory nerve (cranial nerve XI).
• Deep back muscles receive innervation from posterior rami of spinal nerves.

Muscular Triangles

• Auscultatory Triangle: Important for auscultation of breath sounds; bordered by the latissimus dorsi, trapezius, and rhomboid major.
• Lumbar Triangle: Potential site for lumbar hernia or infection; bordered by the latissimus dorsi, external oblique muscle, and iliac crest.
• Suboccipital Triangle: Houses the suboccipital nerve and vertebral artery; bordered by the rectus capitis posterior major, obliquus capitis inferior, and obliquus capitis superior.

Thoracolumbar Fascia

• Located between the iliac crest and 12th rib; serves as a strong aponeurosis for the erector spinae muscles.
• Composed of three lamellae:
  • Posterior Lamella: Covers deep back muscles; attached to lumbar spines.
  • Middle Lamella: Attaches to transverse processes of lumbar vertebrae; lies anterior to deep muscles.
  • Anterior Lamella: Attaches to the anterior surface of transverse processes; lies anterior to quadratus lumborum.

Blood Supply

• Extensive vascular supply to the back, with branches connecting to the vertebral column from cervical and sacral regions.
• Cervical supply originates from occipital vessels; sacral supply comes from iliolumbar and lateral sacral arteries.

Lower Limb Conditions

• Metatarsus Varus: Adduction of the forefoot; corrected through manipulation and splinting.
• Overriding Toes: Typically affects fourth/fifth toes; may require splinting.
• Curly Toes: Affects toes that flex under neighbor; treated surgically in severe cases.

Radiographic Anatomy

• Focus on bony structures of the lower limb; important landmarks include anterior inferior iliac spine, acetabulum, neck of the femur, and sacroiliac joint.

Foot Conditions

• Ectromelia: Partial absence of a lower limb; similar condition described for upper limb.
• Congenital Hip Dislocation: 10 times more common in females; suspicion arises in breech births or in families with shallow acetabula; treatment involves splinting.
• Genu Recurvatum: Knee hyperextension in breech infants; typically resolves without treatment.

Clinical Notes on Foot Arches

• Medial longitudinal arch is critical for balance and weight distribution; directly affected by muscle tone, ligaments, and bone shape.
• Pes Planus (Flatfoot): Collapse of the medial longitudinal arch; leads to lateral displacement of the forefoot.
• Pes Cavus (Claw Foot): High medial longitudinal arch; often related to muscle imbalances from conditions like poliomyelitis.

Bursitis in the Lower Limb

• Inflammation of bursae due to various factors; may affect bursa around pelvic, knee, and ankle regions.
• Key bursae prone to inflammation include those over the ischial tuberosity, greater trochanter, and near the knee.

Development of Lower Limb

• Limb buds emerge in the 6th week; leg buds develop from lumbar and sacral segments.
• Development involves localized mesenchymal proliferation leading to flattened paddles of limbs.

Walking and Running Mechanics

• Walking involves a sequence of weight transfer through the foot, and muscular efforts to maintain stability and propel forward.
• Running shifts weight onto the forefoot, eliminating heel contact; similar mechanisms of motion are utilized for propulsion.

Arch Support Mechanisms

• Three arches in the foot supported by a combination of bone shape, muscle tone, and ligament strength; critical for function and stability during standing and movement.### Arch Support Mechanisms
• Wedge-shaped stones support arches effectively; the keystone is crucial for stability.
• Interlocking stones or binding them with metal staples prevents separation under weight.
• Large bridges utilize tie beams to connect pillars, preventing sagging.
• Suspension bridges rely on cables to support arches from above.

Medial Longitudinal Arch Maintenance

• The sustentaculum tali holds the talus; the navicular bone accommodates talus' rounded head.
• Plantar ligaments, particularly the plantar calcaneonavicular ligament, connect inferior edges of bones.
• Tying ends of the arch involves multiple muscles and ligaments, including the plantar aponeurosis.
• Tibialis anterior, tibialis posterior, and medial ligament of the ankle joint suspend the arch from above.

Lateral Longitudinal Arch Maintenance

• Structure and function are similar to the medial longitudinal arch but focus on the lateral aspect.

Talocalcaneonavicular Joint

• Anterior joint between talus, calcaneum, and navicular facilitates foot movement.
• Articular surfaces of the joint consist of hyaline cartilage; classified as a plane joint.
• The plantar calcaneonavicular ligament supports the talus' head and is reinforced with fibrocartilage.
• Allows gliding and rotational movements.

Calcaneocuboid Joint

• Articulates the calcaneum with the cuboid, also a plane joint.
• Joint is secured by the bifurcated, long plantar, and short plantar ligaments.
• The synovial membrane is present, enriching joint lubrication.

Movements in Subtalar, Talocalcaneonavicular, and Calcaneocuboid Joints

• These joints are instrumental in foot inversion and eversion.
• Inversion: sole of foot faces medially; eversion: sole faces laterally.
• Inversion movements are generally more extensive than eversion.
• Key muscles for inversion include tibialis anterior and posterior; for eversion, fibularis muscles are involved.

Cuneonavicular Joint

• Connects the navicular to three cuneiform bones, categorized as a gliding-type joint.
• Strengthened by dorsal and plantar ligaments; continuous joint cavity with other tarsal joints.

Clinical Notes

• Hallux valgus is a common condition in women characterized by lateral deviation of the big toe.
• Associated with poorly fitting shoes, leading to osteoarthritic changes in the first metatarsophalangeal joint.

Metatarsophalangeal and Interphalangeal Joints

• Similar to hand joints; deep transverse ligaments connect toe joints.
• Minimal abduction and adduction occur, centered around the second digit.

Foot as Functional Unit

• The foot supports body weight and acts as a lever for movement.
• Structure allows it to adapt to uneven surfaces despite being a weight-bearing lever.
• Flexor muscles contribute significantly to propulsion alongside larger leg muscles.

Arches

• The foot features three arches: medial longitudinal, lateral longitudinal, and transverse.
• A child's foot appears flat due to subcutaneous fat; arches become more pronounced with weight-bearing.
• Contact points on a wet foot imprint indicate how pressure is distributed across the foot.
• The transverse arch's unique structure relies on the arrangement of metatarsals and tarsal bones, resembling a half-dome.