**3. PRI tests to evaluate tri-planar musculoskeletal relationship and function**

**2.7. Biomechanical dysfunction begins in the sagittal plane**

148 Innovations in Spinal Deformities and Postural Disorders

plane neutrality as weight shifts from one side to the other.

The sagittal alignment of the pelvis and ribcage affects muscle length and strength throughout the body. With any activity, the positional relationships of the structures and of the muscles that attach to them change. However, when the body is at rest, the ribcage and pelvis should be in a relative sagittal neutral position with muscle groups at their resting length. In an alternating reciprocal activity such as gait, there should be a moment of relative sagittal

**Figure 11.** (A) Muscles of the left anterior interior chain and right brachial chain. Copyright—3D4 medical modified with

permission by the Postural Restoration Institute®. (B) A classic example of a Left AIC, right BC pattern.

When this relative state of neutrality is no longer possible due to overactive right-dominant patterning, the left AIC, right BC pattern takes precedence. The left hemipelvis chronically positioned in swing phase of gait is anteriorly rotated. The spine balances this forward momentum with backward tilting as tonic, shortened paraspinal muscles take on the responsibility of keeping the spine erect. The left psoas and iliacus muscles adaptively shorten as the left transverse abdominis and internal oblique muscles are stretched between their insertions on the anterior lower ribs and the now more distal iliac crest. The left anterior ribcage flares, further weakening the overstretched left lateral abdominal muscles. With diminished opposition to left diaphragm recoil, because of lengthened abdominals and a loss of ZOA, the fibers of the left diaphragm orient more vertically, and the diaphragm assumes a greater role as a back extensor muscle than as a respiratory muscle. Its directional pull on the spine is forward Taking into account the universal predisposition for human left AIC, right BC patterning, PRI tests accurately assess structural relationships such as sagittal plane position of the hemipelvis and ribcage and rotational orientation of the lumbar, thoracic, and cervical spines. Other palpatory tests reveal the patients' ability or inability to expand both apical lungs fields and both posterior mediastinal spaces. Initial testing exposes underlying patterning based on the left AIC, right BC model. Therefore, patients who exhibit typical findings for these patterns are not in a neutral state. It has to be understood that results from any further testing of range of motion, or strength, including core strength, would be based on their compensatory strategies. Deviation from predictable configuration implicates pathological compensation.

Neutral posture is defined by an alignment of body segments involving minimal amount of stress and strain and which is conducive to maximal efficiency in use of the body. It also optimizes diaphragmatic respiration. The neutral position of a muscle is equivalent to physiological rest [19]. This equates with musculoskeletal relative balance in a body, which is physiologically and functionally asymmetric. It is, therefore, imperative to first restore this neutrality. Once accomplished, further testing will give accurate information about weaknesses or restrictions in joints limiting appropriate frontal plane and transverse plane balance and function. Only with the restoration of musculoskeletal neutrality can appropriate, compensatory-free strengthening be initiated.

Over 25 PRI tests are available for initial assessment and to guide exercise progression as the patient progresses toward functional strength, respiratory competence, and upright alternating reciprocal activity. During treatment, the PRI tests are often applied before and after therapeutic exercise to determine its effectiveness, to reveal weakness or improvements in strength, and to further guide appropriate exercise progression. Three basic tests are described below.
