posture Amirhossein barati MD

Posture is a "position or attitude of the body, the relative arrangement of body parts for a specific activity, or a characteristic manner of bearing one's body. Ligaments, fasciae, bones, and joints are inert structures that support the body, whereas muscles and their tendinousattachments are the dynamic structures that maintain the body in a posture or move it from one posture to another.

Gravity places stress on the structures responsible for maintaining the body upright in a posture. Normally, the gravitational line goes through the physiological curves of the spinal column and they are balanced. If the weight in one region shifts away from the line of gravity, the remainder of the column compensates to regain equilibrium.

The Equilibrium of Posture For a weight-bearing joint to be stable, or in equilibrium, the gravity line of the mass must fall exactly through the axis of rotation, or there must be a force to counteract the force of gravity. In the body, the counterforce is provided by either muscle or inert structures. Upright posture usually involves a slight anterior/posterior swaying of the body of about 4 centimeters.

In the standing posture, the following occur:

Ankle.The gravity line is anterior to the joint so it tends to rotate the tibia forward about the ankle. Stability is provided by the plantarflexormuscles, primarily the soleusmuscle.

Knee.The normal gravity line is anterior to the joint, which lends to keep the knee in extension. Stabililyis provided by the anterior cruciateligament, posterior capsule (locking mechanism of the knee), and tension in the muscles posterior to the knee (the gastrocnemiusand hamstring muscles). The soleusprovides active stability by pulling posteriorlyon the tibia. With the knees fully extended, no muscle support is required at that joint to maintain an upright posture, but if the knees flex slightly, the gravity line shifts posterior to the joint, and the quadriceps femorismuscle must contract to prevent the knee from buckling.

Hip.The gravity line varies with the swaying of the body. When it passes through the hip joint, there is equilibrium, and no external support is necessary. When the gravitational line shifts posterior to the joint, some posterior rotation of the pelvis occurs, which is controlled by tension in the hip flexor muscles (primarily the iliopsoas). In relaxed standing, the iliofemoralligament provides passive stability to the joint, and no muscle tension is necessary. When the gravitational line shifts anteriorly, stability is provided by active support of the hip extensor muscles.

Trunk.Normally, the gravity line goes through the bodies of the lumbar and cervical vertebrae, and the curves are balanced. Some activity in the muscles of the trunk and pelvis helps maintain the balance. As the trunk shifts, contralateralmuscles contract and function as guy wires. Extreme or sustained deviations are supported by inert structures.

Head.The center of gravity of the head falls anterior to the atlanto-occipital joints. The posterior cervical muscles contract to keep the head balanced. In postures in which the head is forward, greater demand is placed on these muscles. At the extreme of flexion, tension in the ligamentumnuchaeprevents further motion.

Postural Dysfunction Postural dysfunction differs from the postural pain syndrome in that adaptive shortening of soft tissues and muscle weakness are involved. The cause may be prolonged poor postural habits, or it may be a result of contractures and adhesions formed during the healing of tissues after trauma or surgery. Stress to the shortened structures causes pain.

Postural Dysfunction In addition, strength and flexibility imbalances may predispose the area to injury or overuse syndromes that a normal musculoskeletal system could sustain.

Postural Habits Good postural habits in the adult are necessary to avoid postural pain syndromes and postural dysfunctions. Also, careful follow-up in terms of flexibility and posture training exercises is important after trauma or surgery to prevent dysfunctions from contractures and adhesions. In the child, good postural habits are important to avoid abnormal stresses on growing bones and adaptive changes in muscle and soft tissue.

Pelvic and Lumbar Region Lordotic Posture This posture is characterized by an increase in the lumbosacralangle (the angle that the superior border of the first sacral vertebral body makes with the horizontal, which optimally is 30 degrees), an increase in the lumbar lordosis, and an increase in the anterior pelvic tilt and hip flexion. IS This is often seen with an increased thoracic kyphosisand forward head and is called a kypholordoticposture.

Potential Sources of Pain Stress to the anterior longitudinal ligament. Narrowing of the posterior disk space and narrowing of the intervertebralforamen. This may compress the duraand blood vessels of the related nerve root or the nerve root itself, especially if there are degenerative changes in the vertebra or disk.

Potential Sources of Pain Approximation of the articularfacets. The facets may become weight bearing, which may cause synovialirritation and joint inflammation.

Lordoticposture characterized by an increase in the lumbosacralangle, an increased lumbar lordosis, an increased anterior tilting of the pelvis, and hip flexion.

Potential Muscle Impairments Decreased flexibility in the hip flexor muscles (iliopsoas, tensor fasciae latae, rectusfemoris) and lumbar extensor muscles (erector spinae) Stretched and weak abdominal muscles (rectusabdominis, internal and external obliques, and transversusabdominis)

Potential Muscle Impairments Common Causes Sustained faulty posture, pregnancy, obesity, and weak abdominal muscles are common causes.

Causes may be attitudinal (the person feels comfortable when slouching), from fatigue (seen when required to stand for extended periods), or from muscle weakness (the weakness may be the cause or the effect of the posture). A poorly designed exercise program, one that emphasizes thoracic flexion without balancing strength with other appropriate exercises and postural training, may perpetuate these impairments.

Relaxed or Slouched Posture This posture is also called swayback. The amount of pelvic tilting is variable, but usually there is a shifting of the entire pelvic segment anteriorly, resulting in hip extension, and shifting of the thoracic segment posteriorly, resulting in flexion of the thorax on the upper lumbar spine. This results in an increased lordosisin the lower lumbar region, an increased kyphosisin the thoracic region, and usually a forward head.

The position of the mid-and upper lumbar spine depends on the amount of displacement of the thorax. When standing for prolonged periods, the person usually assumes an asymmetric stance in which most of the weight is borne on one lower extremity with pelvic drop (lateral tilt) and hip abduction on the unweightedside. This will affect frontal plane symmetry.

Relaxed or slouched posture characterized by an excessive shifting of the pelvic segment anteriorly, resulting in hip extension, and shifting of the thoracic segment posteriorly, resulting in flexion of the thorax on the upper lumbar spine. A compensatory increased thoracic kyphosisand forward-head placement are also seen.

Flat Low-Back Posture This posture is characterized by a decreased lumbosacralangle, a decreased lumbar lordosis, hip extension, and a posterior tilting of the pelvis.

Flat Low-Back Posture Potential Sources of Pain -Lack of the normal physiologic lumbar curve, which reduces the shock-absorbing effect of the lumbar region and predisposes the person to injury. Stress to the posterior longitudinal ligament Increase of the posterior disk space, which allows the nucleus pulposusto imbibe extra fluid and, under certain circumstances, may protrude posteriorlywhen the person attempts extension.

Flat Low-Back Posture Flat low back posture characterized by a decreased lumbosacralangle, a decreased lumbar lordosis, and a posterior tilting of the pelvis.

Thoracic Region

Round Back or Increased Kyphosis This posture is characterized by an increased thoracic curve, protracted scapulae (round shoulders), and usually an accompanying forward head.

Round Back or Increased Kyphosis Potential Sources of Pain Stress to the posterior longitudinal ligament Fatigue of the thoracic erector spinaeand scapular retractor muscles Thoracic outlet syndrome Cervical posture syndromes

Round Back or Increased Kyphosis Potential Muscle Impairments Decreased flexibility in the muscles of the anterior thorax (intercostalmuscles), muscles of the upper extremity originating on the thorax (pectoralis major and minor, latissmus dorsi, and serratus anterior), muscles of the cervical spine and head attached to the scapula (levators capulae and upper trapezius), and muscles of the cervical region Stretched and weak thoracic erector spinaeand scapular retractor muscles (rhomboids and middle trapezius)