What is postural alignment?

Postural alignment refers to the relationship between body segments and in basic terms refers to the structure of the musculoskeletal system, bones, joints and muscles. The alignment of the musculoskeletal system, within normal limits, is important in terms of minimizing stresses on soft tissue, minimizing muscle effort and providing sensory information to the centres involved in motor control (the control of movement). Hence, the musculoskeletal alignment plays a significant role in facilitating efficient movement during functional activities (Lennon 2003; Mayston 2000a,b; Carr and Shepherd 2003).

The importance of sensory feedback to successful motor control is well established (Kandel et al. 2000), with all decisions made by the nervous system being based upon the sensory feed forward/feedback it receives. A successful outcome is therefore reliant upon receiving sufficient accurate sensory information, a large amount of which comes from the somatosensory receptors (S3.23) embedded in the musculoskeletal system. In the main, this information relates to proprioception (S3.23), joint and muscle position and movement sense. Therefore it is the alignment of the musculoskeletal system which informs the nervous system of its present state for the planning of movement and also its ongoing state during movement when outcome can be monitored.

The alignment of body segments is therefore critical in both posture (arrested movement) and movement itself. The relationship between posture and movement can be viewed as integral in terms of body segment alignment with similar patterns or strategies observed in both. To appreciate any deviations from a normal range, the therapist requires knowledge of the normal parameters of posture and movement patterns and the range of normal presentations.

Why do I need to assess postural alignment?

A deviation from the most efficient alignment of the musculoskeletal system can occur as a direct effect of various neurological impairments, e.g. as a result of hypertonia, hypotonia (S3.21); pain (S3.29); weakness (S3.30) or altered sensation (S3.23). The malalignment of one body segment may also produce further deviations from normal range in other segments. For example, hypotonia involving the shoulder complex will directly result in reduced stability at the glenohumeral joint and possibly a subluxation. However, the changes in biomechanics will also immediately influence the alignment of both the upper limbs and the trunk as the patient finds strategies to compensate and remain balanced. The extra effort required to move and the stresses on soft tissue may later produce pain which will further limit the biomechanics of the movement. Over time, soft tissue adaptation occurs and the new compensatory strategies become learned via the physiological processes of neuroplasticity (Ungerleider et al. 2002; Marrone 2007).

Following a change in the musculoskeletal alignment of a body, there is a corresponding change in the somatosensory feedback to the nervous system. In the case of patients with a neurological deficit, they may be further disadvantaged by having a direct lesion involving the sensory system which may limit the amount and accuracy of the feedback. Potentially this could lead to an inaccurate motor plan being implemented and ultimately an inefficient, unsuccessful movement.