OBJECTIVETo measure the pressure changes inside the cervical nucleus pulposus in fresh human cervical specimen by imitating different rotary manipulations.

METHODSThe load of 100 N was applied for 5 second on the six fresh male cervical samples by using material test system, which imitated the human head weigh and the strength of cervical extensor muscle. After that, traction, rotation and pulling on the samples were performed in different sequence under the force of 150, 200, 300 N respectively. Three states were included in adding the load state A: samples were loaded with traction and then rotation to the biggest angle, pulling backward for 15 degrees; state B: samples were loaded with rotary stress to the biggest angle and then loaded with traction, pulling backward for 15 degrees; state C: samples were loaded simultaneously with traction and rotary stress to the biggest angle, pulling backward for 15 degrees. The internal pressure of cervical nucleus pulposus at segment of C(3,4), C(4,5), C(5,6), and C7 was measurred by micro-pressure sensors for state A, B, C and for the imitation of head weight and the strength of cervical extensor muscle.

RESULTSThe pressure inside the cervical nucleus pulposus at segments C(5,6), C(6,7) was higher than that at segments C(3,4) and C(4,5) (P < 0.05) by loading stress with 100 N for 5 seconds. The internal pressure of the nucleus pulposus decreased with the increase of traction (P < 0.05), and increased when traction and rotary force were loaded. State A, the value of increased pressure within the nucleus pulposus became smaller and smaller while increasing of the traction force loaded (P < 0.05). State B, the increase of internal pressure in nucleus pulposus became obvious as loading pressure increased (P < 0.05). State C, the internal pressure in nucleus pulposus was not increased obviously (P > 0.05). There was a transitional pressure raise inside all cervical nucleus pulposus when pulling added after different sepuence traction and rotary strength was applied, however, the internal pressure of state A was significantly higher than that of state B or C (P < 0.05). There was also a transitional pressure raise inside all cervical nucleus pulposus when pulling added in different strength (P < 0.05),the internal pressure by pulling with 150 N was obviously higher than that with 200 N and 300 N (P < 0.05).

CONCLUSIONThe order of rotation first and traction second should be avoided when practice of rotary manupuplation in case protrusion of the nucleus pulposus. Meanwhile, proper traction should be applied along with rotary manipulation in order to increase its safety.