DELTA VS PLIF FIXATION IN THE TREATMENT OF GRADE II ISTHMIC SPONDYLOLISTHESIS: A BIOMECHANICAL STUDY

Abstract

“Delta fixation” was developed to treat low-grade L5 isthmic spondylolisthesis. It involves placement of pedicle screws into L5 and from S1 through the L5/S1 disc into L5 (Fig.1). A biomechanical comparison to standard Posterior Lumbar Interbody Fusion (PLIF) with two anterior cages and pedicle screws in L5 and S1 was made. Eight fresh frozen human specimens were instrumented with both fixations and tested. Delta fixation was significantly more stable in resisting rotation. It requires less manipulation of the nerve roots and spares the cost of the fusion cages.

Our objective is to compare the stability of Delta versus PLIF fixation in the treatment of low grade isthmic spondylolisthesis

Delta fixation provides superior initial stability, and therefore is an acceptable alternative to PLIF for the treatment of low grade isthmic spondylolisthesis of L5-S1.

Symptomatic low-grade isthmic spondylolisthesis of L5 is often managed with PLIF. This procedure requires extensive manipulation of the cauda equine, posterior resection of the disc and the placement of two inter-body cages as spacers in addition to pedicle screws in L5 and S1.

Delta Fixation has been developed to provide stable fixation with less nerve root manipulation and without the use of inter-body cages. It is therefore a safer alternative method of fixation that spares the additional cost of the fusion cages.

When comparing Delta fixation to PLIF fixation the only statistically significant difference was found in axial rotation. Delta fixation had 2.05 degrees less ROM and 0.90 degrees less NZ compared to PLIF fixation with P values of 0.0052 and 0.0104 respectively. This demonstrates that the delta fixation is more stable than PLIF fixation.

Eight fresh frozen human spines were used. Matched pairs were created and block randomization used to create two groups: PLIF fixation and Delta fixation groups. The specimens were instrumented with a grade II spondylolisthesis of L5-S1, tested, and then re-instrumented with the alternative fixation and tested again. Vertical displacement, axial rotation, flexion– extension and side bending were tested using an MTS machine.

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