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: 1-135; 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 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: E208-214

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: E208-214

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: E208-214

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: 183-188

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: 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 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

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

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

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)

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 0.2 0.4 0.6 0.8 1.0 Prop. Peak Back pain

* 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)

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