What is spinal cord injury?

Spinal cord injury (SCI) is an injury to the spinal cord that can results in motor and/ or sensory defects and paralysis.

As well as mobility and sensory deficits, SCI patients (animals and humans) can experience nociceptive and / or neuropathic pain. Pain is caused by dysfunction of the nervous system and / or damage to musculoskeletal tissue (muscle, joints, bones) from trauma, mechanical instability or muscle spasm. The pain associated with spinal cord injury may be localised around the site of injury and occur immediately or become chronic, thereby affecting the patient’s quality of life.

How to treat dogs with spinal cord injury?

Traditionally, treatment for spinal cord injury in patients, both human and animals, has comprised physical and manual therapies. The objectives of these therapies were to:

• Prevent further sensorimotor impairment

• For acute cases, promote functional recovery

• For chronic cases maintain joint mobility by preventing loss of muscle extensibility to maintain function and allow optional neuroplasticity

• Improve quality of life by managing muscle contractures

To achieve these objectives, animal studies have shown the beneficial effect of stretching on the following:

• Muscle remodelling and extensibility

• Sarcomere length

• Collagen arrangement in muscle fibres

• Increases in force production

In human and animal studies, the effects of stretching on muscle healing, extensibility and force production is short term and not likely to be sustained. For patients with SCI, managing muscle contracture long term is required.

How does stretching affect recovery from spinal cord injury in animals?

Based on previous studies into the effect of stretching on muscle healing, an animal study was undertaken to assess the effect of stretching on the recovery of coordinated stepping in animals with moderate thoracic contusive injury.

The study hypothesized that hindlimb stretching therapy applied acutely after injury will disrupt healing and delay functional recovery in rats with lower thoracic moderate contusion SCI.

Study design

19 rats were randomly assigned to two groups as follows:

• 7 rats (Stretch group)

• 12 rats (Control group).

All animals were anaesthetised and received a moderate contusion injury at T10 (thoracic vertebrae 10). On day 4, post-surgery injury, the stretch protocol commenced with the stretch group. The stretch protocol continued for 8 weeks (Monday to Friday). The protocol comprised 1 minute static stretch and hold for the following muscle groups on both right and left hind legs:

• Ankle flexor

• Ankle extensor

• Knee flexor

• Knee extensor

• Hip adductors

• Hip abductors

At 10 weeks post-surgery, a subset of the control group were chosen to undergo the stretching protocol for 6 days.

The force of the stretch was monitored by observing joint angles and based on end feel. For all muscle groups except the ankle extensor, the therapist held the stretch based on a soft end feel. For the ankle extensor, a capsular end feel indicated the force of the stretch.

Measurements and assessments

The study performed the following assessments on all groups for comparison purposes.

Overground stepping

This activity was commenced 4 days post-surgery and measurements were taken:

• Before stretching

• 3 hours post stretching

• After five days consecutive stretching

The following two measures were taken from the stepping exercise:

• CPI – Central Pattern Index – number of correctly patterned step cycles / total cycles. Indication of interlimb co-ordination.

• PSI – Plantar stepping index – number of hindlimb plantar (bottom of foot) steps. Indication of how consistently the animal is able to achieve hindlimb plantar stepping.

Swimming

Swimming commenced two weeks after surgery and continued every other week through the 8 week trial period. Swimming was used as a way of assessing the animal’s locomotion as it doesn’t require the animal to support their body weight.

Swimming scores were assigned based on the amount of hindlimb and forelimb movement for forward propulsion and the level of trunk stability.

Passive range of motion

An assessment of the range of motion of the hip, knee, and ankle were taken prior to surgery and every other week post-surgery. Joint movement is a measure of functional recovery.

MER – Magnetically evoked muscle response

The magnetically evoked muscle response was assessed at weeks 3.5, 6.5 and 9.5. The purpose of this measure was to stimulate afferent nerves to determine the motor output in hindlimb muscles.

Does stretching speed up or delay recovery from spinal cord injury?

Stepping

In week 2, a loss of locomotor function was observed in the stretch group. Function, however improved from Friday PM to Monday AM when no stretching occurred. Scores improved from Week 5 – 9 with drops in function following Monday stretching.

In the sub-set of the control group that commenced stretching in week 10, after two days of stretching the animals were not weight bearing indicating a decline in function.

By Week 3, the stretch group were not capable of stepping, demonstrated minimal movement of the hindlimb and were not supporting their weight. By Week 13, the stretch groups’ gait analysis scores were not different to the control group and they were demonstrating correct placement of hindlimbs.

Swimming

Stretching negatively affected the stretch group’s hindlimb movement when swimming. In weeks 1 – 4, this group relied on the forelimbs for forward movement with limited hindlimb movement and severe trunk instability.

The swimming scores of the stretch group improved weeks 4 – 8 and plateaued weeks 10 – 12.

The animals that did not receive the stretch protocol were better swimmers throughout the entire study.

MER

Magnetic stimulation at the base of the tail evokes muscle response and indicates the level of excitability of the motor neurons. In week 6.5, the muscle response in the stretch group, was lower than the control group however muscle excitability recovered by the end of the study.

Finally, an assessment of the muscle fibres in the stretch group found the ankle extensors and flexor muscle groups were lighter (less mass) than those in the control group.

Is stretching effective in rehabilitating an animal after spinal cord injury?

This study concluded there was a loss of locomotor function due to hindlimb stretching in animals with spinal cord injury. Repeating stretching resulted in the following:

• Delayed and limited functional recovery from week 1 – 4

• Substantial recovery after 6 weeks of stretching. In weeks 5 – 8 function returned to sub-optimal levels.

In the sub-set of the control group that received stretching in week 10 post-surgery, a transient decline in locomotion was observed.

The mechanisms by which the stretching protocol is thought to delay functional recovery from spinal cord injury are (1) by inducing inflammation and (2) activating nociceptors.

Previous studies have shown that similar treatments have increased the secretion of pro-inflammatory cytokine TNF-a. TNF-a is implicated in spinal cord dysfunction and inhibits long term learning. While pro-inflammatory substances were not measured in this study, the excitability of motor neurons was assessed. Stretching is correlated with a decline in motor function and likely influenced spinal cord circuitry inducing decrease in motor neuron excitability.

Other studies also found that stretching sensitised the spinal cord. Sensitising the spinal cord resulted in noxious afferent input that is dependent on NMDA (N-methyl-D-aspartate) receptors found in nerve cells and Substance P. It is known that excessive substance P diminishes neuroplasticity and overactivation of NMDA can damage neurons.

What is the best rehabilitation approach for spinal cord injury?

When designing a rehabilitation plan for animals with spinal cord injury it should be considered that all daily afferent input either contributes to or detracts from spinal cord function. The interaction of afferent and descending input results in adaptive and / or maladaptive function changes. The focus of therapies for optimal recovery should therefore be to:

• Maintain the potential for adaptive plasticity

• Retain components of recovery not intrinsic to locomotor circuitry

• Minimise exposure to afferent input that does not contribute to functional recovery

In this study, task specific gain of function (i.e. stepping) coupled with loss of function of untrained behaviour (day to day in cage movement) implies certain activities need to be avoided to improve a given function. The range of behaviours that can be re-trained depends on the amount and location of spared tissue.

This study concluded that stretch therapy does not aid recovery of locomotor function in animals with induced spinal cord injury. In the next article, rehabilitation approaches that help restore limb function and address the pain associated with spinal cord injury will be discussed.

Full Stride offers canine massage treatments to maintain mobility and proper locomotion in all dogs. Treatments are offered in my treatment room based on Brisbane’s northside. Home visits are also available within a service area.

Until next time, enjoy your dogs.

Sources:

Caudle, K. L., Atkinson, D. A., Brown, E. H., Donaldson, K., Seibt, E., Chea, T., … & Magnuson, D. S. (2015). Hindlimb stretching alters locomotor function after spinal cord injury in the adult rat. Neurorehabilitation and neural repair, 29(3), 268-277.

Hagen, E. M., & Rekand, T. (2015). Management of neuropathic pain associated with spinal cord injury. Pain and therapy, 4(1), 51-65.