Transcript Smudging the motor brain in recurrent low back

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
Back muscle changes are
common in low back pain
• Common observation
– Atrophy Knutsson B 1961. Acta Orthop Scand Suppl 49: 1135; Hides J et al. 1994 Spine 19: 165-177. Danneels L et al. 2000. Eur
Spine J 9: 266-272
– Denervation Yoshihara K et al. 2001 Spine 26: 622-626.
– Fatty infiltration Kjaer P et al. 2007. BMC Med 5: 2
– Motor control changes MacDonald D
2009 Pain 142: 183-188
• Muscle fascicles are often
differentially affected
Complex multifasicular anatomy
of back muscles
Discrete functions based
on biomechanical
differences
Discrete control of muscle
activity in sitting
% peak sitting activity
Longissimus thoracis
100
Lumbar multifidus
(deep fibres)
80
60
40
20
0
Slump
Flat
Thoracolumbar
extension
Lumbar
lordosis
Claus et al 2009 Spine 34: E208-214
Discrete control of muscle
activity in sitting
% peak sitting activity
Longissimus thoracis
100
Lumbar multifidus
(deep fibres)
80
60
40
20
0
Slump
Flat
Thoracolumbar
extension
Lumbar
lordosis
Claus et al 2009 Spine 34: E208-214
Discrete control of muscle
activity in sitting
% peak sitting activity
Longissimus thoracis
100
Lumbar multifidus
(deep fibres)
80
60
40
20
0
Slump
Flat
Thoracolumbar
extension
Lumbar
lordosis
Claus et al 2009 Spine 34: E208-214
Discrete control of muscle
activity in arm movements
Flexion
No pain
Short MF
*
Long MF
-20
0
20
40
60
80
100
120
EMG onset relative to deltoid (ms)
MacDonald et al 2009 Pain 142: 183-188
Loss of discrete control of
muscle activity in back pain
Flexion
No pain
Short MF
*
Long MF
Pain
Short MF
Long MF
-20
0
20
40
60
80
100
120
EMG onset relative to deltoid (ms)
MacDonald et al 2009 Pain 142: 183-188
Cortical mechanisms for discrete
control of back muscles?
Similar complexity of spine & hand
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. 1978 J Neurophysiol 41:1120
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
Methods
• Participants
– 8 pain-free controls
– 11 low back pain patients - recurring
episodes, no pain at time of testing
Transcranial magnetic
stimulation
A. Transcranial magnetic stimulation
over scalp grid
B. Paraspinal muscle EMG recordings
Motor
cortex (M1)
Medulla
Corticospinal
tract
Vertex
(Cz)
Spinal
cord
LES
DM
Vertex
(Cz)
E. Motor cortical map
D. MEPs superimposed
over scalp sites
C. MEP recorded at each site
Fine-wire electrodes bilaterally:
- Deep fibres of multifidus (DM)
- Longissimus erector spinae at
L4 (LES4) and L1 (LES1)
LES
4
DM
LES1
LES4
LES
DM
DM
LES
LES4
DM
DM
LES1
2 cm
Prop. Peak
2 cm
1.0
0.8
0.6
0.4
0.2
0
LES (L1)
LES (L4)
DM
Vertex (Cz)
Group data
Individual data
5
Anterior to vertex (cm)
Anterior to vertex (cm)
5
4
3
2
1
0
4
3
2
1
0
0
1
2
3
4
Lateral to vertex (cm)
5
0
1
2
3
4
Lateral to vertex (cm)
5
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
DM – fine wire
LES – fine wire
2 cm
Healthy
2 cm
Prop. Peak
Back pain
1.0
0.8
0.6
0.4
0.2
0
DM (Healthy)
LES (Healthy)
5
Anterior to Cz (cm)
Vertex (Cz)
DM (LBP)
LES (LBP)
4
3
*
2
LES
DM
1
Cz
1
2
3
4
Lateral to Cz (cm)
5
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
“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
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
Prof Paul Hodges
Prof Lieven Danneels