1. Smudging the motor brain in recurrent low back pain
Henry Tsao1, Lieven Danneels2, Paul Hodges1
1. The University of Queensland, Australia
2. Ghent University, Belgium

2. Back muscle changes are common in low back pain
Common observation
Atrophy Knutsson B Acta Orthop Scand Suppl 49: 1-135; Hides J et al Spine 19: Danneels L et al Eur Spine J 9:
Denervation Yoshihara K et al Spine 26:
Fatty infiltration Kjaer P et al BMC Med 5: 2
Motor control changes MacDonald D 2009 Pain 142:
Muscle fascicles are often differentially affected

3. Complex multifasicular anatomy of back muscles
Discrete functions based on biomechanical differences

4. Discrete control of muscle activity in sitting
Lumbar multifidus
(deep fibres)
Longissimus thoracis
100 80 60
% peak sitting activity 40 20
Slump
Flat
Thoraco-lumbar
extension
Lumbar
lordosis
Claus et al 2009 Spine 34: E

5. Discrete control of muscle activity in sitting
Lumbar multifidus
(deep fibres)
Longissimus thoracis
100 80 60
% peak sitting activity 40 20
Slump
Flat
Thoraco-lumbar
extension
Lumbar
lordosis
Claus et al 2009 Spine 34: E

6. Discrete control of muscle activity in sitting
Lumbar multifidus
(deep fibres)
Longissimus thoracis
100 80 60
% peak sitting activity 40 20
Slump
Flat
Thoraco-lumbar
extension
Lumbar
lordosis
Claus et al 2009 Spine 34: E

7. EMG onset relative to deltoid (ms)
Discrete control of muscle activity in arm movements
Flexion
No pain
Short MF *
Long MF
-20 20 40 60 80
100
120
EMG onset relative to deltoid (ms)
MacDonald et al 2009 Pain 142:

8. EMG onset relative to deltoid (ms)
Loss of discrete control of muscle activity in back pain
Flexion
No pain
Short MF *
Long MF
Pain
Short MF
Long MF
-20 20 40 60 80
100
120
EMG onset relative to deltoid (ms)
MacDonald et al 2009 Pain 142:

9. Cortical mechanisms for discrete control of back muscles?

10. Similar complexity of spine & hand

11. Discrete organisation allow for differential function of hand
Separate motor cortex representation for functionally related muscles Loss of discrete organisation during chronic pain conditions (Byl et al 1996)
HC Kwan et al J Neurophysiol 41:1120

12. Hypotheses
Discrete control of paraspinal muscles may be reflected in discrete representations at the motor cortex
Discrete organisation may be compromised in low back pain

13. Methods Participants 8 pain-free controls
11 low back pain patients - recurring episodes, no pain at time of testing

14. Transcranial magnetic stimulation

15. A. Transcranial magnetic stimulation over scalp grid
Vertex (Cz)
Corticospinal tract
B. Paraspinal muscle EMG recordings
LES DM
Motor cortex (M1)
Medulla
Spinal cord
E. Motor cortical map
Vertex (Cz)
D. MEPs superimposed over scalp sites
C. MEP recorded at each site

16. Fine-wire electrodes bilaterally: Deep fibres of multifidus (DM)
Longissimus erector spinae at L4 (LES4) and L1 (LES1)
LES4 DM DM
LES4
LES1
LES DM

17. LES DM
LES4
LES1 DM
Prop. Peak
1.0
0.8
0.6
2 cm
0.4
0.2
2 cm

18. Group data Individual data LES (L1) LES (L4) DM 5 5 4 4 3 3
Vertex (Cz)
Group data
Individual data 5 5 4 4 3 3
Anterior to vertex (cm)
Anterior to vertex (cm) 2 2 1 1 1 2 3 4 5 1 2 3 4 5
Lateral to vertex (cm)
Lateral to vertex (cm)

19. Hypotheses
Discrete control of paraspinal muscles may be reflected in discrete representations at the motor cortex
Discrete organisation may be compromised in low back pain

20. DM – fine wire
LES – fine wire
2 cm
Healthy
0.2
0.4
0.6
0.8
1.0
Prop. Peak
Back pain

21. * DM (Healthy) LES (Healthy) 5 DM (LBP) LES (LBP) 4 3
Vertex (Cz)
DM (Healthy)
LES (Healthy) 5
DM (LBP)
LES (LBP) 4 3
Anterior to Cz (cm) * 2
LES DM 1 Cz 1 2 3 4 5
Lateral to Cz (cm)

22. Hypotheses
Discrete control of paraspinal muscles may be reflected in discrete representations at the motor cortex
Discrete organisation may be compromised in low back pain

23. “Smudging” of the motor cortex in low back pain
Loss of discrete organisation at motor cortical representation for back muscles
Associated with loss of differential control of multifidus and erector spinae

24. Implication
Loss of discrete function in back pain may help protect injury in acute stage Adaptive changes may contribute to further injury and recurrence of pain Rehabilitation must include strategies to restore discrete control of back muscles

25. Prof Paul Hodges Prof Lieven Danneels