Surgical strategy used in multilevel cervical disc replacement and cervical hybrid surgery: Four case reports

Figure 10 The mechanism underlying the condition occurring in case 4. A: The impact force generated by tapping processes allowed the C5 vertebra as well as the upper tab at C5/6 to move backward; B: While the posterior border of the ball continued to contact the posterior border of the socket at C5/6, the backward movement of the upper tab at C5/6 was restricted due to the design of the prosthesis. Therefore, a shearing force was generated between the C5 vertebral body and the upper tab at C5/6. Affected by this shearing force, the upper tab at C5/6 finally migrated forward; C and D: If we inserted the prosthesis using a top-down sequence, the anterior border of the socket on the lower tab at C4/5 would barely contact the ball on the upper tab at C4/5. Therefore, no shearing force would be generated between the lower tab at C4/5 and the C5 vertebral body, and the prosthesis would not migrate.