Biomechanical comparison of lumbar total disc arthroplasty, discectomy, and fusion: effect on adjacent-level disc pressure and facet joint force.

OBJECT

With the increasing advocacy for total disc replacement (TDR) as a potential alternative to fusion in the management of lumbar degenerative disc disease, intradiscal pressures (IDPs) and facet joint stresses at the adjacent levels of spine have generated considerable interest. The purpose of this study was to compare adjacent-level IDPs and facet joint stresses among TDR, discectomy, and fusion.

METHODS

Ten fresh human cadaveric lumbar specimens (L2-S1) were subjected to an unconstrained load in axial torsion, lateral bending, flexion, and extension by using multidirectional flexibility test. Four surgical treatment modes-control (disc intact), discectomy, TDR, and fusion-were tested in sequential order at L4-5. During testing, the IDPs and facet forces following each treatment were calculated at the adjacent vertebral levels (L3-4 and L5-S1).

RESULTS

Intradiscal pressures and facet force pressures were similar between the intact condition and the TDR reconstruction at the L3-4 and L5-S1 levels under all loading conditions (p > 0.05). Compared with the intact and TDR groups, the discectomy and fusion groups had higher IDPs at the L3-4 and L5-S1 levels under all loading conditions (p < 0.05). No significant difference in the facet force pressure was noted among the intact, discectomy, and TDR groups at the L3-4 and L5-S1 levels under any loading conditions (p > 0.05). However, the facet force pressure produced for fusion was significantly higher than the mean values obtained for the intact, discectomy, and TDR groups at the L3-4 and L5-S1 levels under all loading conditions (p < 0.05).

CONCLUSIONS

Lumbar TDR maintained adjacent-level IDPs and facet force pressures near the values for intact spines, whereas adjacent-level IDPs tended to increase after discectomy or fusion and facet forces tended to increase after fusion.