Outline View

Chain of Events

Normal Structure & Movement

  • The sacroiliac joint is the core structure of the musculoskeletal system.
  • Positioned at the center of movement, shock absorption, and load transfer between the upper and lower body, the sacroiliac joint functions as a regulator of pelvic and trunk muscles and directly influences posture and spinal segmental stability.
  • Instead of functioning as a wedge, the sacrum functions as a cone with the articular surfaces curling around the edges.
  • Shock absorption and rebound constitute the two primary innate movements of the body, of which nutation and counternutation are the major subset, directly involving the core.
  • All muscles that attach to the sacrum or innominates directly act, through various attachments and vectors, to move the sacroiliac joints; this movement is coordinated throughout the musculoskeletal system.
  • The muscles can be divided into either nutators or counternutators.
  • The interplay between these two patterns governs all normal and dysfunctional musculoskeletal movement.
  • Connective tissue (including ligaments) and muscles suspend all bones of the body in a tensegrity network such that pressure at any point, through either pulling or pushing, is immediately transferred throughout the structure.
  • The sacrum is pulled around the non-weight-bearing axial sacroiliac joints in a pivoting motion, within the context of nutation and counternutation.
  • This configuration allows the large anterior/posterior motions of gait to transfer to flexion/extension in the innominates, with components of lateral flexion and rotation, then translate to the sacrum, curl around the sacral edges, and pull the sacrum into nutation and counternutation, which travels up the spine, where nutation/counternutation are recognized by its components of flexion/extension, lateral flexion, and rotation.
  • Simultaneously, energy is transferred from the spine to the legs, providing a synchronized muscular force, assisted by gravity, which facilitates energy transfer and maximizes performance.

The Sacroiliac Nutation Lesion

  • A normal sacrum is suspended by ligaments.
  • Excess nutation inducing force sprains the ligaments.
  • The sacrum is forced beyond its normal range of nutation.
  • Ligaments tear, the joint separates, & fluid enters joint space.
  • Spinal Instability.
  • The sacrum drops and wedges between the ilia, resulting in aberrant motion.
  • Sacral movement changes from smooth gliding to a wobbling pattern with compressive, rotary, and shearing forces.
  • Instead of healing, the body adapts.
  • The normal mechanism of force transference becomes compromised.
  • As a tensegrity structure, in which ligaments and muscles share responsibility for maintaining joint tension, the muscles must take on a greater role when the ligament is insufficient.
  • The structural framework shifts to distribute gravitational and muscular forces in a manner that avoids overloading the injured ligament.
  • Ligamento-muscular compensation patterns include activation of counternutation muscles and inhibition of nutation muscles on the lesioned side with reciprocating muscular reactions on the contralateral side.
  • A large mass of ligaments causes considerable muscular reaction, even at low levels of stress.
  • Muscular coordination is compromised for joint stability.
  • Smooth power transmission will be disrupted, resulting in decreased power, endurance, and coordination.
  • Imbalance occurs between the tight counternutation muscles and inhibited nutation muscles on the injured side, which is magnified by the imbalance between the injured side and the non-injured, or less-injured side.
  • Because most of the muscles from the head to the knees attach to either the sacrum or innominates, they become directly involved, and the effect is transferred throughout the kinematic chain.
  • Movement patterns are changed.
  • Chronicity develops through positive feedback loops.
  • Eventually, poor balance and postural control may develop into abnormal posture, altered gait, and disturbed joint motion patterns throughout the structure.
  • The pelvis will torque, the spine will twist, the extremities will rotate, and joints will move in recognizable asymmetrical patterns.
  • Muscles distant to the pelvis can become involved, affecting distant joints.
  • Degenerative osteoarthritic changes follow, beginning with surface roughening, developing into a central ridge and groove, and resulting in erosion, plaque formation, fibrotic changes, loose connective tissue strands, amorphous debris and, possibly, fusion.
  • Due to poor blood supply, ligaments heal poorly, if at all, so the joint may remain hypermobile and degenerate indefinitely.
  • The patient suffers more from the compensation pattern than the original injury.
  • Pain and weakness may occur in any tight or inhibited muscle, dependent on use.
  • Treatment involves stabilizing the sacroiliac joint, then decompressing the compensating structural alterations, and returning the spinal curves toward normal.
  • Structural alterations may occur.
  • Overcompensation Patterns include:
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