Integrated Model Of Stability

There is often great confusion around the concepts of core and spinal stability. A simple but excellent model is the integrated model of stability described by physical therapist Diane Lee and clinical anatomist Andry Vleeming. Although initially developed to describe stability in the pelvis it is relevant for any mobile joint and certainly in the spine. They originally describe three factors that when operating together result in optimal stability in a joint:

1. Form closure

2. Force closure

3. Motor control

Form Closure describes the passive integrity of the joint system. “Form” refers to how the parts (joint surfaces) fit together. Ligament stiffness, disc health, joint alignment all contribute to this integrity.

Force Closure refers to active muscular component. Inherent muscle stiffness and appropriate muscle contraction applies tension to the joints in the spine like the guy wires of a tent. Tension creates joint compression maintaining integrity of the joint. Tension and compression in the spine must obey the “goldilocks effect”. Too little compression results in instability and too much compression results overloading the spinal structures; it needs to be just right.

Motor Control is achieved through coordination of the nervous system and muscle feedback to create appropriate amounts of tension. Tension needs to be applied through activating the right muscles at the right times. Unlike the tent pole, the spine has moving parts and changing demands requires near constant changes in muscle activation. Although mechanically the spine may act like a complex tent pole, muscle control is more like an orchestra. All the instruments have to work harmoniously to achieve the desired music. If one or more instruments are out of tune, or come in at the wrong time we don’t get the desired symphony, but noise. If the muscles don’t act harmoniously, then the forces exerted on the spine may not protect it when needed, or worse apply uncoordinated forces which may cause it to buckle under load.

These three systems must work together to achieve the conditions for optimal stability. They work in a continuum so if one system becomes compromised, the other systems can compensate. However certain methods of compensation are clearly less than desirable than others.

If the muscle activity or control are compromised and muscles are not activating when they should, or with inappropriate forces, then injury may occur causing damage to passive joint structures. Research has shown us that these deficits in muscle activation and control can also be caused by previous injury. Therefore motor control and muscle activation deficits can be both a cause and effect of pain. Over time, these deficits are compensated for by the damage and anatomical change to the passive structures. Degenerative changes in discs and joints typically results in instability, but the damage over time like drying out of discs and formation of bone spurs eventually increased joint stability. This stability typically comes only after years of pain and disability.

In the opposite situation where passive structures are compromised, muscle activity and good motor control able to compensate with far more favorable outcomes. For example, if there is disc degeneration and decreased disc height, then ligaments can no longer exert the same stiffness across the vertebrae and prevent undue movement. (You’d rather not rely on ligaments to do this anyways – but that’s another article.)The resulting instability can be countered by appropriately increasing the muscular tension across the involved joints. The only disadvantage with this strategy is that unlike anatomical decay, it is not automatic and requires exercise and practice. In people with previous injury, proper motor control often needs to be re-learned and repeated to become habit.

This integrative model is a very useful way to visualize how stability is achieved. Having good motor control, training multiple muscles and ensuring proper joint mobility and alignment are all important elements in maintaining and restoring spinal stability.

Mark J. Pitcher DC, Msc

chiropractor, exercise physiologist

If you have additional questions about core or spinal stability, or wish to make an appointment with Dr. Pitcher to address stability issues, please feel free to contact us at the clinic 970-479-6262, or by email at drpitcher@vailhealth.com