Panjabi's Part II defines the neutral zone: the high-laxity region of intervertebral motion around neutral posture where the passive column offers minimal resistance. It asks whether this neutral zone, rather than total range of motion, is the better measure of spinal instability. The paper also proposes a redefinition of clinical instability built around the neutral zone concept.
When you assess spinal stability, total range of motion can look normal even when the segment is unstable. This paper's core teaching is that the neutral zone, the slack region around neutral posture, widens with injury long before range of motion changes. It is the earlier and more sensitive signal.
This reframes stability as a three-part system: passive column, active muscles, and neural control. A moderate passive injury can be compensated by muscle strengthening, but a severe injury can push the segment beyond what muscle can rescue.
That mental model drives two practical points. First, it is the biomechanical basis for spinal stabilization and core-strengthening rehabilitation after injury. Second, it explains why a solid fusion sometimes fails to relieve pain: residual micromotion within the neutral zone keeps straining pain-generating tissue.
For the trauma resident, the takeaway is that instability is about excess laxity around neutral, not just how far the segment ultimately moves.
Panjabi's Part II defines the neutral zone: the high-laxity region of intervertebral motion around neutral posture where the passive column offers minimal resistance. It asks whether this neutral zone, rather than total range of motion, is the better measure of spinal instability. The paper also proposes a redefinition of clinical instability built around the neutral zone concept.
When you assess spinal stability, total range of motion can look normal even when the segment is unstable. This paper's core teaching is that the neutral zone, the slack region around neutral posture, widens with injury long before range of motion changes. It is the earlier and more sensitive signal.
This reframes stability as a three-part system: passive column, active muscles, and neural control. A moderate passive injury can be compensated by muscle strengthening, but a severe injury can push the segment beyond what muscle can rescue.
That mental model drives two practical points. First, it is the biomechanical basis for spinal stabilization and core-strengthening rehabilitation after injury. Second, it explains why a solid fusion sometimes fails to relieve pain: residual micromotion within the neutral zone keeps straining pain-generating tissue.
For the trauma resident, the takeaway is that instability is about excess laxity around neutral, not just how far the segment ultimately moves.