Effects of different posterior occipitocervical angles on the range of motion and intradiscal pressure of subaxial cervical spine in occipitocervical fusion

English Keywords:Occipitocervical fusion  Posterior occipitocervical angle  Range of motion  Intradiscal pressure

English Abstract:

  【Abstract】 Objectives: To analyze the range of motion(ROM) and intradiscal pressure(IDP) of lower cervical spine in occipitocervical fixation with different posterior occipitocervical angles(POCA), and explore the selection strategy of POCA in occipitocervical fusion(OCF) surgery. Methods: 8 fresh frozen human occipitocervical cadaveric specimens(C0-T1, cephalic end included the bony structure of the skull base below the occipital tuberosity) were selected, including 4 males and 4 females, aged 25-45 years, and bone abnormalities and destruction were excluded with X-ray fluoroscopy. The speciemens were removed of muscles and fat tissues and preserved with ligaments, joint capsules and intervertebral discs as the normal group. Specimens were loaded with 2N·m in a servo-hydraulic materials testing system for measuring the ROM and IDP of C3/4, C4/5, C5/6 and C6/7 in the directions of flexion, extension, left torsion and left lateral bending with the help of optoelectronic motion analysis system and miniature pressure transducers. Then, the specimens were subjected to occipitocervical fixation with different POCAs as 5 experimental groups, which were: neutral position group(POCA=111°), neutral position-standard deviation(SD) group(POCA=101°), neutral position+SD group (POCA=121°), neutral position-2SD group(POCA=91°), and neutral position+2SD group(POCA=131°). The fixed segments were C0, C2 and C3. All experimental groups used the displacement control protocol to perform experiment, and the ROM and IDP of C3/4, C4/5, C5/6 and C6/7 in four directions were measured. Results: After occipitocervical fixation, ROM in the four directions of C0-C3 was significantly reduced compared with the normal group(P<0.001). Of the four directions, the change of POCA had regular impacts on ROM and IDP of the 4 segments in flexion and extension: in flexion, with the increase of POCA, ROM and IDP of each segment showed a decreasing trend; In extension, with the increase of POCA, ROM of each segment showed an increasing trend, while IDP showed a decreasing trend. When POCA was in the neutral position, ROM in flexion or extension of each segment was significantly greater than that of normal group, yet there was no extremely increased ROM in flexion as POCA was too little or in extension as POCA was too large, and there was no significant difference of IDP compared with that of the normal group(P>0.05). The change of POCA had no regular effect on ROM and IDP of 4 segments in left torsion and left lateral bending, although ROM increased significantly compared with that of the normal group. Conclusions: In OCF surgery, fixing POCA in a neutral position, the ROM and IDP of subaxial cervical spine are approximately normal.