Study Design.

A multicenter case-control study.

Objective.

The aim of this study was to investigate the independent predictors of osseous union after posterior lumbar interbody fusion (PLIF).

Summary of Background Data.

PLIF is usually performed to treat lumbar degenerative diseases in elderly patients. Some patients exhibit intervertebral pseudoarthrosis.

Methods.

We analyzed 66 elderly patients with osteoporosis who underwent PLIF from 2011 to 2014 (all women, mean age 71 years, follow-up period≥ 6 months). Patients were randomly allocated to receive either treatment with weekly teriparatide, starting at 1 week postoperatively, or no teriparatide. Preoperative lumbar spine radiographs were obtained, and the amount of anterior slippage was measured. Osseous union was assessed by computed tomography at 6 months postoperatively.

Results.

Thirty-three patients (50%) showed complete osseous union, while 33 did not. Teriparatide was administered in 20 (61%) patients of the union group and in 9 (27%) patients of the nonunion group (P< 0.01). The preoperative anterior slippage of the cranial vertebra next to fusion segment< 2 mm was observed in 16 (49%) and 4 (12%) patients in the union and nonunion groups, respectively (P< 0.01). Multivariate regression analysis showed that teriparatide administration (odds ratio, 4.75; 95% confidence interval: 1.51–14.90; P< 0.01) and preoperative anterior slippage of the cranial vertebra next to fusion segment< 2 mm (odds ratio, 5.90; 95% confidence interval: 1.53–22.70; P< 0.01) were independently associated with osseous union within 6 months after PLIF. At 6 months postoperatively, the mean femoral neck bone mineral density significantly increased by 1.1% in the union group and decreased by 1.3% in the nonunion group (P< 0.05).

Conclusion.

Weekly teriparatide administration and preoperative anterior slippage of the cranial vertebra next to fusion segment< 2 mm were independent predictors of osseous union within 6 months after PLIF. Our findings suggest that biological and mechanical factors may influence the improvement of spinal fusion.

Level of Evidence: 4

Posterior lumbar interbody fusion (PLIF) or posterolateral fusion is widely used to treat lumbar degenerative diseases in elderly patients and to manage dynamic instability. 1, 2 However, some patients exhibit complications related to poor bone quality such as pseudoarthrosis and instrumentation failure postoperatively. 3, 4 Delayed union or pseudoarthrosis after PLIF is associated with poor improvements in health-related quality of life (QOL). 5 Therefore, the achievement of fusion after PLIF is essential to obtain better QOL outcomes.