What is trunk stability?

The terms trunk/central and spinal stability are synonymous and are used interchangeably in clinical practice. Core stability is the equivalent lay term. In essence, trunk stability is a reflection of an individual’s postural control, the ability to orientate and stabilize the body using appropriate balance strategies and responses (Raine et al. 2009). As such, trunk stability is an essential core component of balance, the ability to maintain the centre of mass (COM) within the base of support (BOS) (S3.32) and functional activities, by which it provides proximal stability to allow for the coordinated free movement of the limbs and head (Brown 2006; Massion et al. 2004). Trunk stability is also important in controlling and supporting the spinal segments, so reducing the stresses upon soft tissue structures and helping to avoid injury and pain.

Trunk stability mainly incorporates muscle activation related to the trunk, head/neck and proximal limb girdles. However, it is also described as a muscular ‘box’ that is made up of the diaphragm superiorly, the pelvic floor and gluteal muscles inferiorly, the abdominals anteriorly and the back extensors posteriorly. The therapist should remain aware of the ‘box’ as a whole in terms of strategies they may use to facilitate treatment (through contraction of the pelvic floor) and tricks that the patient may use to achieve false stability (breath holding).

This section will focus upon the core trunk muscles which are commonly divided into two groups according to their functional anatomy (Bergmark 1989):

Why do I need to assess trunk stability?

Trunk instability results in less efficient movement, a limited ability to explore the environment (Cristea et al. 2003) and demands compensatory muscle activity to maintain an upright position. The latter may present as abnormal fixation of the trunk or, in extreme cases, excessive use of the upper limbs, and leads to effortful movement for the individual. Poor trunk stability resulting in deviations in posture may also cause abnormal stresses and potential damage to soft tissue structures leading to pain and further functional loss. Often rehabilitation focuses on improving general trunk stability without specific attention to the interaction between the local and global stabilizers. More focus on segmental stability initially may have the potential to improve the movement sequences and the functional outcome for the individual.

In a neurologically impaired patient, poor trunk stability has been linked with a poor functional outcome in multiple sclerosis (Lanzetta et al. 2004), cerebrovascular accident (CVA) (Hsieh et al. 2002) and Parkinson’s disease (PD) (Dibble and Lange 2006; Nardone and Schieppati 2006).

In CVA, trunk instability has also been linked with poor postural control in standing (Palmer et al. 1996; Slijper et al. 2002) and in sitting (Dickstein et al. 2004) and is viewed as a negative prognostic indicator for recovery. Proprioception (position sense) (Mergner et al. 2003; Peterka 2002) and reduced strength (Karatas et al. 2004) in the trunk have been found to be causal in CVA (Ryerson et al. 2008) and in PD (Vaugoyeau et al. 2007).

How do I assess trunk stability?

Assessment of the local muscle stabilizers

Patient

Initially in terms of patient safety, it is wise to begin assessing the patient in a sitting position. However, for higher level patients, a further assessment when standing may also be pertinent.

Therapist: observe and palpate

1 Initially the patient’s position should reflect their posture of choice, in order for the therapist to assess the trunk stabilizers under normal circumstances.

2 Ask the patient to perform a limb movement in order to challenge the trunk stabilizers. This could include one arm being lifted (shoulder flexion or abduction), two arms being raised or one leg being lifted (hip flexion or abduction). The amount the limb is moved will depend on the ability of the individual. In some cases the ability to raise a hand 2 inches may be very challenging.

3 Observe and then palpate the local stabilizers to evaluate the state of contraction.

a Multifidus (MT): Palpate for MT just medial to the posterior superior iliac spine (PSIS) (Fig. 25.1).

b Transversus abdominus (TAb): Palpate 1 inch medially and 1 inch inferiorly from the anterior superior iliac spine (ASIS) (Fig. 25.2).

Figure 25.1 Palpation for multifidus.

Figure 25.2 Palpation for transversus abdominus.

  Clinical hints and tips

Although MT is found at all levels of the vertebral column it is at its thickest in the cervical and lumbar areas and it is superficial from level L₃ down.

Anatomically, in cadavers, the TAb and IOf muscles have been found to be fused at this palpation point (Marshall and Murphy 2003). The therapist should be aware they are palpating both muscles, however this is deemed clinically acceptable when considering that they are also functionally compatible.

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Can they activate the local muscle stabilizers during the task? Or do they primarily use a global muscle contraction to gain stability.

Can they maintain the contraction? If they can recruit the local stabilizers, do they have good muscle endurance? If not, this may lead to trunk instability linked to muscle weakness or fatigue.

Is there appropriate co-contraction of the local stabilizers? There should be simultaneous contraction of MT and TAb but the degree of contraction of each will be dictated by the task requirements. During a unilateral limb movement the contralateral pair of stabilizers (MT and TAb) should contract more strongly and in a bilateral task there should be symmetry of contraction.

  Clinical hints and tips

During a simple bilateral arm raise through shoulder flexion the COM is displaced forward and therefore stabilizer activity is greatest in the back extensors. During a unilateral leg lift through hip flexion, the COM is initially displaced backwards and therefore the greatest stabilizer activity is recorded in the abdominals to maintain the alignment of the pelvis.

Do they activate the local stabilizers prior to limb movement? This is evidence of an anticipatory contraction. Poor sequencing of muscle recruitment may result in trunk instability and the need for compensatory strategies. However, in electromyographical (EMG) studies the anticipatory response is a fraction of a second and is unlikely to be identifiable in practice. Appreciation of a simultaneous activation is more realistic.

Do they use compensatory strategies? Common examples include breath holding, over use of the global stabilizers, excessive use of the shoulder elevators or hip adductors/flexors. These are strategies used to provide false stability.

Therapist: realign pelvis/lumbar spine

1 If no muscle contraction can be palpated with the patient in their posture of choice (Fig. 25.3) then the therapist should try altering the alignment of the patient’s pelvis/lumbar spine. A neutral alignment of the pelvis and lumbar spine is correlated with the preferential recruitment of the local stabilizer muscles (O’Sullivan et al. 2006).

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2 The therapist should instruct or facilitate the patient towards a more neutral alignment (Fig. 25.4).

3 Reassess as for observation and palpation.

Figure 25.3 Posture of choice (sitting).

Figure 25.4 Neutral pelvis and lumbar spine (sitting).

  Clinical hints and tips

Any soft tissue shortening or pain in the region of the pelvis and lumbar spine will limit the individual’s ability to attain a neutral alignment. Perfect is rarely possible but a movement towards neutral may still be beneficial.

Therapist: assessment of individual muscle components

If the patient is still unable to recruit the appropriate muscles with the pelvis/lumbar spine in a neutral alignment then the therapist should evaluate the patient’s ability to activate the local muscle components individually.

Transversus abdominus (TAb)

a To evaluate TAb, use crook lying (i.e. supine with knees bent up to 90°) (Fig. 25.5). The aim is to encourage an isolated contraction of TAb through the alignment of a neutral pelvis and lumbar spine.

b The instruction to the patient will be dependent on the initial position adopted by the individual. A patient who adopts crook lying with an anteriorly tilted pelvis and extended lumbar spine needs an instruction such as ‘flatten your back’ or ‘push your back down onto the bed’ or ‘pull your belly button in’. Whereas a patient who initially presents in posterior pelvic tilt and lumbar spine flexion will need to raise their back towards neutral.

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c A rolled towel (2 inches thick) placed under the patient’s back, at waist level (Fig. 25.5), allows for a larger movement by which to achieve neutral making the task easier for the patient to comprehend and feel.

d Initially the therapist may ask the patient just to tighten these muscles (an isometric contraction).

e If an isometric contraction can be initiated limb movements may be added in the same position to assess whether the contraction can be maintained during a challenge.

f The therapist should then return to the observation and palpation assessment protocol and re-test.

Figure 25.5 Modified crook lying.

Multifidus (MT)

a To evaluate MT, use sitting. The aim is to focus on a contraction of MT through a neutral alignment of pelvis and lumbar spine.

b From upright sitting the therapist instructs and/or facilitates a release of the lumbar spine into flexion. This allows for a larger movement to achieve neutral and is therefore easier for the patient to comprehend and feel (Fig. 25.6).

c The patient is then guided towards a neutral sitting posture using facilitation. Simultaneously, the patient should attempt to activate the appropriate muscle while being given immediate accurate verbal feedback on the accuracy of recruitment from the therapist.

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d If an isolated contraction of MT is achieved, limb movements may be added in the same position to assess whether the contraction can be challenged.

e The therapist should then return to the observation and palpation assessment protocol and re-test.

Figure 25.6 Preparation: Release of lumbar spine.

  Caution

Remember that the local stabilizers need only work with low force to achieve segmental stability, therefore be careful not to over motivate the patient.

Recording

A simple heading and text description of all the therapist’s findings is acceptable, or notation with a key on a body chart.

Analysis

The findings from an assessment of trunk stability should be considered in relation to other assessment tools (S3.19–34) and especially postural control/balance as the two are highly integrated. Analysis and synthesis of all this information may allow the therapist to predict a possible cause of the trunk instability.

In terms of the above example, the cause of the increased postural sway is likely to be altered sensory feedback (proprioception). This is reinforced when vision is withdrawn and the patient presents with an increase in sway.

Outcome measure