Stabilization Mechanisms of the Lumbar Spine

1
Stabilization Mechanisms of the Lumbar Spine

• Kevin Domboski
• Nick Richey

2

• The spine is inherently unstable, without the
  support of the surrounding musculature.

3
Posterior Ligamentous System

• Interspinous, Supraspinous, Facet Jt Capsule, and
  Thoracolumbar Fascia (TLF) provide PASSIVE
  SUPPORT
• Balance between 24 55 of imposed flexion
  stress

4
Posterior Ligamentous System (Cont.)

• ALL, PLL, and Ligamentum Flavum become aligned
  during flexion/extension
• Ligaments become stiffer when loaded rapidly
  (Visoelastic)
• Posterior Ligaments can sustain over 50 of the
  flexion stress on the spine

5
Posterior Ligamentous System (Cont.) 2 Passive
Systems at Work

• Erector Spinae Recoil
• In full flexion the muscle no longer contract
• Recoil Force Potential Contractile Force

• Recoil of Posterior Ligament System

6
Thoracolumbar Fascia (TLF)

• Consists of 3 layers that cover the back
  musculature
• Primary Importance of TLF is passive resistance
  to flexion
• TLF Mechanism- tends to approximate the vertebrae

7
TLF Hydraulic Amplifier

• Hydraulic Amplifier acts as even more of a
  stabilizing mechanism
• The erector spinae contract
• The TLF resists the muscle by increasing the
  tension in the fascia

8
Trunk Muscle Action

• Spinal Extensor Muscles
• Superficial Erector Spinae
• Deep Multifidi, Interspinales,
  Intertransversarii
• Abdominal Muscles
• Superficial Recutus Abdominus, External Oblique
• Deep Transversus Abdominus, Internal Oblique

9
Intersegemental (Deep) Muscles

• Location gives faster reaction time
• Smooth and more efficient stabilizing control
  system
• 7x the muscle spindles ? Proprioceptive Role

10
Multifidus

• Primary Function- Control lordosis at its level
  and counteract any imposed loading
• Most important for lumbar stabilization

11
Multifidus

• Act at a 90 angle to spinous process
• Produces posterior sagittal rotation (rocking)
• Neutralizes spinal flexion
• Active during whole range of flexion, rotation in
  either direction, and during extension movements
  of the hip

12
Multifidus

• Recovery does not occur automatically
• Can be retrained Must Be retrained
• Treatment ( Bed Rest, Analgesics, NSAIDS)
• 4 wks 17diff
• Treatment and Rehabilitation
• 4 wks .7 diff.

13
Superficial Muscles

• Consist of two muscles Iliocostalis
  Longissimus
• Lumbar Longissimus Act more on the posterior
  translation of the vertabrae than the posterior
  sagittal rotation.
• Lumbar Iliocostalis Cooperate with multifidus to
  neutralize flexion

14
Abdominal Muscles

• Superficial Abdominals
• Rectus Abdominus
• External Obliques
• Prime movers of trunk flexion

• Deep Abdominals
• Transversus Abdominus
• Internal Obliques
• Are the major stabilizers
• Tough to contract voluntarily
• Activated by Abdominal hollowing
• Activated at the initiation of overhead and lower
  extremity movement

15
Abdominal Performance

• The ratio of the muscle activity is more
  important than intensity.
• Abdominal Hollowing helps to train the deep
  abdominal muscles and differentiate from the
  superficial muscles.

• Transversus Abdominus always activates during any
  trunk movement
• Always precedes the contraction of other trunk
  muscles in normal subjects.

16
Intra-abdominal Pressure Mechanism

• Created by the synchronous contraction of the
  abdominal muscles, the diaphragm, and the muscles
  of pelvic floor.

• Helps reduce axial compression, shear loads and
  transmits loads over a wider area.

17
Local Muscle Dysfunction in Low Back Pain

• Dysfunction of Traversus Abdmonius
• Dysfunction of the Multifidus

18
Transversus Abdominus Dysfunction

• Changes in Motor Control
• Delayed Activation
• Direction Specific Contraction
• Phasic Contraction
• Loss of Independent Control
• Response Failure in Natural Speed Movements
• Mechanism, Relevance and Timing

19
Changes in Motor Control

• Transversus Abdominus contractions precede
  movement in extremities.
• T.A. function is found to be poor in patients
  with low back pain.
• EMG studies show that pts. With low back pain
  have no contraction of T.A. in pre-movement
  period.
• Lack of T.A. function fails to prepare spine for
  motion.

20
Changes in Motor Control cont.

• Studies in Upper and Lower extremity reveals
  identical results.
• In studies of Upper and Lower extremities, T.A.
  function actually occurs after Prime Mover
  Function.

21
Direction Specific and Phasic Contractions

• T.A. is normally not direction specific however,
  in patients with low back pain, it begins to
  respond in a directionally specific manner.(T.A.
  is unable to control direction specific forces)
• T.A. also begins to fire in phasic bursts in
  patients with low back pain.
• Test show one burst with shoulder flx and two
  bursts with ext. (Works with flexing abs)
• Indicates a change in control by CNS, loss of
  tonic or isometric function of T.A. in patients
  with low back pain

22
Loss of Independent Control

• Patients with low back pain have delayed T.A.
  function which suggests that the CNS is waiting
  to know what movement is being performed before
  firing the T.A.
• This change in CNS control suggests that control
  of the T.A. is no longer independent.

23
Natural Speed Movements

• Patients without low back pain had T.A. that
  responds at high and normal speeds but not slower
  speeds. This suggests the T.A. operates between
  thresholds.
• Threshold is increased in low back pain patients
  so that T.A. only responds at high speeds.

24
Mechanism, Relevance and Timing

• Why does low back pain happen?
• Changes in control of movement by CNS
• Reflex inhibitiondecreased motor pooldelayed
  muscle activity.
• Joint effusion, pain, ligament stretch, capsular
  compression are all causes.
• Fatigue and postural variation also have been
  linked to decreased excitability in the motor
  neuron pool.

25
Summary

• Transverse Abdominus problems arise because of
  issues with motor control.
• T.A. issues remain consistent with each other
  regardless of pathology

26
Dysfunction in the Multifidus

• Muscle Activation
• Fatiguability
• Composition
• Size and Consistency

27
Muscle Activation

• EMG results show decreased muscle activity at L4
  and L5 vertebral levels during lumbar extension
• EMG also shows less activity at unstable
  vertebral levels in patients with segmental
  instability.(28 of 87 patients having 4mm or more
  sliding.)

28
Fatiguability

• Potentially inadequate muscular support over
  extended periods of time.
• Evidence of fatigue in paraspinals in patients
  with low back pain.
• Isometric contraction can no longer be
  maintained at a certain level.
• Dynamic repetitive work can no longer be
  maintained at a certain output.

29
Fatiguability Cont.

• Patients with low back pain show considerably
  less muscular endurance.
• greater fatiguability
• No specific muscles have been identified within
  the extensor group
• Study by Biedermann et al identifies the
  Multifidus as demonstrating the most fatigue.
• Local weakness in multifidus is found in elite
  athletes on regular, rigorous training schedules.

30
Composition

• Muscle fiber size and muscle fiber internal
  structure have been examined.
• Atrophy is reported as causing some problems but
  its significance is not understood because some
  patients with atrophy never have any problems at
  all.

31
Composition Cont.

• Internal Structure changes seem to be much more
  of a problem.
• Fibers appear core-targetoid and moth-eaten
  these changes are considered abnormal.
• It seems that through surgical intervention and
  physical therapy, that these pathological changes
  can be reversed.

32
Size and Consistency

• Decreased muscle density can lead to problems in
  the low back.
• Paraspinals and multifidus have shown atrophy
  with disuse and deconditioning.
• Pain, caused by injury or trauma is shown to
  significantly decrease multifidus size.
• Studies show mixed reviews concerning muscle
  size some patients with decreased muscle size
  have back problems and some do not.

33
Size and Consistency Cont.

• Patients with back injuries lose less muscle size
  and are less likely to have a recurrence of the
  back pain episode when an active treatment
  approach is taken to localize the multifidus.
• Patients with a more generalized approach to
  treatment showed a lack on recovery of multifidus
  size and are more likely to have long term,
  recurring problems.

34
Summary

• Since the multifidus provides segmental stability
  in the lumbar spine in normal function,
  dysfunction of the muscle can adversely effect
  patients with low back pain.
• Rehabilitation that focuses on the multifidus,
  rather than generalizing the low back, is shown
  to be much more effective.