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Three simple rules for locking may be derived

from these examples.

1.    Locking is always relative: Segments to be locked are themselves physiologically posi-tioned. For instance, in the first option of the example above, the segments to be locked caudal to the treated segment are placed in dorsal flexion and lateral flexion to the right. That position involves slight left rotation, and therefore is physiological for the segments themselves. So for the normal, unrestricted spine, the position easily attained. But rotation to the right is constrained, which effects the desired locking. Locking is always relative to a particular finał movement, in this case rotation to the right, from a position attained by normal physiological movement.

2.    Locking always involves inflection (changes of flexion): Changes of flexion, either in the sagittal or the frontal planes, or sometimes in both planes, effect locking. In the first option of the example above, the flexion change is from left to right lateral flexion. In the second option, the change is from dorsal to ventral flexion. Inflection is depicted schematically in Fig. 10.

Fig. 10. Schematic representation of inflections used in locking. Curves shown are for illustration only, and indicate flexion deviations from the neutral position of the spine shown in Figures 1 and 2.

Frontal	( ^R	( ^R	L ')	O	Left <-* Right
piane	V N		r'	* t
	O	L )	C_^R	\ R >»_
Sagittal	fv	O	D )		Dorsal «-*■ Ventral
piane	\		G	/
	^D J	D i		\ V	____treated segments
		_ »»			-locked segments

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