The function of the thoracic wall is to not only protect the contents of the thoracic cavity but also provide the mechanical function of breathing. (K.L. Moore & A.F. Dalley 4th edition, pp62)
During respiration, the upper and lower ribs produce different movements. In the upper three ribs, the axis of movement is coronal between the costovertebral and costotransverse joints, giving it a pump handle movement. The axis of movement in the lower ribs is in the sagittal plane thus making a bucket handle movement, and ribs in between merely blend in with both of these motions.

Other functions are shock absorption, support for the trunk, attachment for muscles and ligaments, and protection for thoracic organs, spinal cord and spinal nerves. Although there is movement in the thoracic skeleton, the overall structure is relatively rigid to aid its protective role.

The thorax consists of 12 thoracic vertebrae and their intervertebral disks, 12 pairs of ribs and the sternum. (Locomotor Systerm 1992, by Kahle, Leonhardt & Platzer, pp70)

Ribs 1-7 are called true ribs because they join directly to the sternum. The lower five ribs are called false ribs as they join to the sternum via the costal cartilage. Ribs 11-12 can be distinguished as floating ribs. The ribs restrict sidebending, but an element of rotation complements the movement.

The 12 vertebrae in the thoracic spine vary in size, from the upper vertebrae being relatively smaller than the lower vertebrae. A T1 vertebra slightly resembles a cervical vertebra, and a T12 vertebra resembles a lumbar vertebra. Specialised costal facets on the thoracic vertebrae specify where and how ribs attach. The thoracic cage has a kyphosis shape because the vertebral bodies are wedge shaped and the intervertebral (IV) discs are smaller than in the cervical and lumbar spine. The disc: vertebra ratio is 1:5. There is a greater range of movement in flexion than in any other range of movement. This is due to the tip of each spinous process (SP) being at the level of the vertebral body just inferior to it, thus constricting range in extension.

This restrictive movement helps protect the thoracic organs and superior abdominal cavities by providing rigidity to the structure. The kyphosis shape to the thorax also contributes to its protective function by acting as a shock absorber.

The diaphragm is the main muscle of inspiration in the respiration mechanism. Its attachment to the thoracic skeleton is to the xisphisternum of the sternum, and inner surfaces of lower six ribs and costal cartilages.

During inspiration, the diaphragm contracts and descends, and other muscles contract, thus expanding the thorax to allow the lungs to fill with air. Expiration requires the reverse of this process, so the thoracic volume decreases by relaxation of muscles of inspiration and gravity. In deep breathing, accessory muscles of expiration also contract to help force air out of the lungs more efficiently.
There are two types of muscles in respiration. Primary muscles are used all the time and for quiet breathing. Diaphragm (main muscle of inspiration), levatores costarum, intercostals externi, scalenus anterior, scalenus medius and scalenus posterior are all primary muscles.

The accessory muscles come into use for when extra effort is required, such as during exercise. These include iliocostalis cervicis, sternocleidomastoid, pectoralis major, pectoralis minor, latissimus dorsi, serratus anterior, serratus posterior superior and quadratus lumborum.

It would not be surprising for these muscles to be hypertonic in the patient in the question. An osteopath may want to increase range of movements in the restricted areas. This could be achieved by articulation of the joints to help relieve tight ligaments and muscles with techniques such as rotation and sidebending of the thoracic vertebrae. Direct work on the muscles such as cross-fibre soft tissue massage will not only decrease the tension in the muscles, but can help improve posture. This can have a considerable effect on the patient’s general sense on well-being on a psychological level.

Posted by Mr. Trishul Vadi (Principal Osteopath in West Wickham, Beckenham, Bromley & South East London) on Monday, October 11th, 2010