Panjabi reviewed the evidence that the neutral zone, the low‑resistance motion near neutral posture, reflects spinal stability, and proposed how it relates to clinical instability.
Narrative review of cadaver experiments, live‑animal studies and mathematical models of spinal motion.
Methods
Scope
Neutral zone as a measure of spinal stability
Instability hypothesis
Topics
Injury
Disc degeneration
Muscle force
Instrumented fixation
Neutral zone vs range of motion
Key Points
Across cadaver, animal and modeling studies, the neutral zone tracked other measures of instability and usually changed more than range of motion did.
In porcine cervical extension‑compression trauma, the axial rotation neutral zone rose far more than range of motion, which increased by 240%.
After cadaveric thoracolumbar burst fractures, every neutral zone increase was significant, including 49% in flexion and 80% in lateral bending, and no elastic zone increase was.
A C5‑C6 external fixator in cadaveric cervical spines reduced range of motion by only 38% on average, a smaller fall than in the neutral zone.
A simulated muscle force on the spinous process of an injured spine brought the neutral zone back near intact values, while range of motion stayed the same.
In one cadaveric lumbar study the flexion‑extension neutral zone rose with disc degeneration while range of motion did not change, a link Panjabi calls suggestive rather than conclusive.
Board pearl
The neutral zone is the motion near neutral posture where the passive spine gives little resistance. It widens with injury and narrows with muscle force or instrumented fixation.
Authors' conclusion
The spinal stabilizing system adjusts so that the neutral zone remains within certain physiological thresholds to avoid clinical instability.
Panjabi reviewed the evidence that the neutral zone, the low‑resistance motion near neutral posture, reflects spinal stability, and proposed how it relates to clinical instability.
Narrative review of cadaver experiments, live‑animal studies and mathematical models of spinal motion.
Methods
Scope
Neutral zone as a measure of spinal stability
Instability hypothesis
Topics
Injury
Disc degeneration
Muscle force
Instrumented fixation
Neutral zone vs range of motion
Key Points
Across cadaver, animal and modeling studies, the neutral zone tracked other measures of instability and usually changed more than range of motion did.
In porcine cervical extension‑compression trauma, the axial rotation neutral zone rose far more than range of motion, which increased by 240%.
After cadaveric thoracolumbar burst fractures, every neutral zone increase was significant, including 49% in flexion and 80% in lateral bending, and no elastic zone increase was.
A C5‑C6 external fixator in cadaveric cervical spines reduced range of motion by only 38% on average, a smaller fall than in the neutral zone.
A simulated muscle force on the spinous process of an injured spine brought the neutral zone back near intact values, while range of motion stayed the same.
In one cadaveric lumbar study the flexion‑extension neutral zone rose with disc degeneration while range of motion did not change, a link Panjabi calls suggestive rather than conclusive.
Board pearl
The neutral zone is the motion near neutral posture where the passive spine gives little resistance. It widens with injury and narrows with muscle force or instrumented fixation.
Authors' conclusion
The spinal stabilizing system adjusts so that the neutral zone remains within certain physiological thresholds to avoid clinical instability.