Adjacent level intradiscal pressure and segmental kinematics following a cervical total disc arthroplasty: an in vitro human cadaveric model.

STUDY DESIGN: In vitro investigation of cervical adjacent level intradiscal pressures (IDPs) following a total disc replacement arthroplasty.

OBJECTIVES: The current in vitro study was undertaken to compare adjacent level IDPs and operative level kinematics following a cervical arthroplasty versus an arthrodesis procedure.

SUMMARY OF BACKGROUND DATA: Clinical data indicate the incidence of symptomatic transition syndrome to be as high as 3% annually following a cervical interbody arthrodesis. Recent developments in the motion preservation technology should, in theory, minimize transition syndrome at the adjacent levels.

METHODS: A total of 10 human cadaveric cervical spines were used in this investigation. Following intact analysis, all specimens were sequentially reconstructed at C5-C6 with 1) total disc replacement (TDR), 2) allograft dowel, and 3) allograft dowel + anterior cervical plate. Testing was performed in displacement control under axial rotation, flexion/extension, and lateral bending loading modes. IDPs were recorded at C4-C5 and C6-C7 whereas peak range of motion (ROM) and NZ were monitored at C5-C6 level.

RESULTS: Similar IDPs were recorded between the intact condition and a TDR reconstruction at both adjacent levels under all loading modes (P > 0.05). However, the C4-C5 IDP values produced under flexion/extension testing for both arthrodesis treatments were significantly higher than the means obtained for the intact and disc replacement groups (P < 0.05). Similar intergroup differences were observed at the C6-C7 level; however, statistical significance was achieved during all three loading methods (P < 0.05). C5-C6 ROM analysis indicated a significantly lower ROM for both arthrodesis constructs compared with intact and TDR groups during flexion/extension testing (P < 0.05). No differences were recorded between the intact and the total disc replacement group under any loading conditions (P > 0.05).

CONCLUSION: This is a first study to document that a cervical disc replacement arthroplasty procedure maintains adjacent level IDPs and reconstruction level kinematics near the preoperative values. Consequently, total disc replacement may provide an alternative to conventional surgical management of cervical discogenic pathology decreasing the incidence of symptomatic transition syndrome.