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Lumbar Spine Anatomy and Examination

  • The spine is a complex system composed of bony elements, articulations, ligaments, muscles, spinal cord, and peripheral nerves divided into anterior, middle, and posterior columns.
  • The vertebral body, lamina, and the spinous process protect the spinal cord.
  • The lumbar spine contains 5 vertebrae and 5 nerve roots.
    • Most lumbar spines have a lordotic secondary curvature acquired when an infant begins walking.
    • The defining characteristics of the lumbar spine include a substantially large, kidney-shaped vertebral body, long and slender transverse processes (with accessory processes on the posterior base), and short and sturdy spinous processes.
  • The thick intervertebral discs, large articular surfaces, and the lack of rib attachments give the lumbar spine a wide ROM.
    • This freedom of motion allows for lumbar flexion, extension, lateral bending, and trunk rotation.
    • The lumbar spine also functions to support the lumbosacral nerve roots (cauda equina), transmit weight to the pelvis and legs, and support the upper body.
Signs and Symptoms
Physical Exam
  • Gait: Look for:
    • Antalgic (painful) gait
    • Muscle wasting and weakness
    • Signs of hip or knee problems
    • Trendelenburg sign (abductor weakness with an ipsilateral pelvic tilt when the leg is lifted off the ground)
  • Inspection:
    • As the patient disrobes, pay attention to fluidity of motion and any associated pain.
    • Inspect the back for clues to underlying bone or neurologic pathology: Areas of redness, hair patches, birthmarks, or skin markings such as cafe-au-lait spots.
    • Analyze the patient’s posture and inspect the curvature of the lumbar spine.
    • A slight lordotic curve is normal, but normal lordosis can be absent in cases of paravertebral muscle spasm, and occasionally an extreme kyphosis (Gibbus deformity) is present.
      • A weak anterior abdominal wall generally leads to an exaggerated lordosis.
    • Structural scoliosis:
      • A patient’s tendency to favor 1 side while standing may indicate structural scoliosis, which is characterized by a fixed curve and no change with flexion or recumbency.
    • Sciatic scoliosis:
      • Characterized by a more diffuse curve that worsens with flexion and by limited flexion that disappears with recumbency
    • Spondylolisthesis:
      • A palpable step from 1 spinous process to another may indicate spondylolisthesis.
      • May also present with segmental tenderness or nerve root injury
    • NF:
      • May impinge on the spinal cord and roots
      • Often accompanied by cafe-au-lait spots
    • Spina bifida:
      • Absence of spinous processes, along with birthmarks, excessive port wine marks, or a tuft of hair, may indicate spina bifida.
    • AS:
      • Usually begins with pain and stiffness in the SI joints, spreads to the spine, and eventually leads to the ossification of spinal ligaments; eventually, the spine may fuse.
  • Palpation:
    • Bony (anterior):
      • Vertebral body and disc: L4, L5, S1 (abdominal palpation: below aortic bifurcation)
      • Sacral promontory: L5-S1 (abdominal palpation through the linea alba below the umbilicus)
    • Bony (posterior):
      • Spinous processes of the lumbar region
      • Spinous processes of the sacral region
      • Iliac crest: L4-L5
      • Posterior superior iliac spine: S2
    • Soft tissue
  • ROM evaluation:
    • Substantial motion in the lumbar spine
    • Motion between L5-S1 >motion between L1-L2
    • Flexion:
      • Anterior longitudinal ligament relaxes as the supraspinous and interspinous ligaments, ligamentum flavum, and posterior longitudinal ligament stretch.
    • Extension:
      • Posterior ligaments relax as the anterior longitudinal ligament stretches.
    • Lateral bending
    • Rotation
    • Resisted movement tests of flexion, lateral bending, and rotation
    • Passive movement tests:
      • Conduct when a patient does not have full ROM.
      • Do not test for passive flexion because of possible aggravation of a disc herniation.
    • Root irritation from disc herniation: Deviation to painful side with spine flexion
  • Waddell signs: 3 of the following 5 signs indicate a malingering patient:
    • Nonanatomic superficial tenderness
    • Simulation tests (pain with axial loading or rotation of the spine)
    • Nonanatomic weakness and sensory findings
    • Overreaction: Cogwheeling or jerky muscle relaxation
    • Inappropriate response to provocative maneuvers with distraction (i.e., supine versus seated straight-leg-raise test)
  • Rectal examination checks for:
    • Tone
    • Volition
    • Anal wink (stroke perianal skin, feel anal sphincter contraction around finger)
    • Bulbocavernosus maneuver: Signals end of spinal shock (Pull on Foley catheter in urethra or pull on glans penis; feel anal wink.)
    • Light touch and pin-prick perianal sensation: S2-S4 (If sensation is absent, a mass lesion such as a disc or tumor may be pressing on the nerve roots.)
  • Upper motor neuron disorders:
    • Hoffman sign:
      • Nip the nail of the patient’s middle finger.
      • A positive reaction produces flexion of the terminal phalanx of the thumb and of the 2nd and 3rd phalanx of another finger.
    • Babinski sign:
      • Stroke the plantar lateral foot.
      • A positive test (extended great toe while other toes plantarflex and splay) indicates an upper motor neuron lesion.
      • Use to rule out cervical or thoracic myelopathy.
    • Loss of any of the superficial reflexes, such as the abdominal, cremasteric, or anal reflex, suggests an upper motor neuron lesion.
    • Sustained clonus of the patellar or Achilles reflex or hyperreflexia indicates an upper motor neuron lesion.
  • Motor examination:
    • Systematically examines the nerve roots
    • Muscle wasting and weakness suggests nerve root compression.
  • Reflex tests:
    • Loss of the patellar or Achilles reflex suggests ipsilateral nerve root compression.
  • Sensation tests:
    • Pin-prick testing compares 2-point discriminatory sensibility on the lower extremities.
    • Vibration sensibility and temperature sense also are tested.
  • Nerve root tension tests:
    • Straight-leg-raise test:
      • Raise the leg of the supine patient slowly by supporting the foot slightly above the malleoli and keeping the knee extended.
      • Differentiating radiculopathy from tight hamstring pain is important.
      • This procedure reproduces the sciatic-type radicular leg pain that is relieved when the knee is bent and is exacerbated by foot dorsiflexion.
      • Cross-leg straight-leg-raise test is less sensitive than the straight-leg-raise test but a more specific physical examination finding for lumbar disc herniation.
      • A positive test (flexion of 1 leg with pain in the contralateral leg or buttocks) suggests disc herniation axillary or medial to the root.
    • Femoral nerve stretch test:
      • The patient is prone, and the hip is extended with the knee slightly flexed.
      • Pain radiating down the front of the thigh indicates L3-L4 nerve root irritation.
    • Patrick (FABER) test:
      • Test the SI joint by Flexing, ABducting, and Externally Rotating the hip to reproduce SI joint pain.
      • Pain usually is associated with pelvic trauma or infectious disease.
  • Muscle strength grading:
    • 5: Normal strength
    • 4: Weakness with resistance, full movement against gravity
    • 3: Full ROM against gravity but marked weakness against resistance
    • 2: Full ROM with gravity eliminated
    • 1: Flicker of tendon unit
    • 0: No movement
  • Imaging confirms or supports the diagnosis of disorders suspected from the history and physical examination.
  • Radiographs should show normal alignment of the vertebrae, the presence of bony landmarks, and maintenance of the disc spaces.
  • False-positive MRI scans occur in 35% of patients <40 years old and in 93% of patients >60 years old.
  • SPECT is more sensitive in detecting isthmic spondylolisthesis than technetium-99m methylene diphosphonate bone scintigraphy, and plain radiographs.
Q: Which reflex evaluates the L5 nerve root?
A: No reflex exists for L5. The patellar reflex evaluates the L4 nerve root, and the Achilles reflex evaluates the S1 nerve root.
Q: Which test is more specific for a lumbar disc herniation at the L4-L5 level: the straight-leg-raise test or the contralateral straight-leg-raise test?
A: The contralateral straight-leg-raise test.

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