Comparing rates of early pedicle screw loosening in posterolateral lumbar fusion with and without transforaminal lumbar interbody fusion.

BACKGROUND CONTEXT

Addition of interbody fusion via a transforaminal approach (TLIF) has become a popular surgical option for treatment of degenerative lumbar conditions. Although technically more complicated than posterolateral fusion surgery (PLF), it has been suggested that TLIF provides superior immediate stability and protects against early pedicle screw loosening. This theory has never been formally examined in a clinical study.

PURPOSE

To determine the impact of TLIF on early pedicle screw loosening and radiographic fusion rates compared with PLF using pedicle screws alone in the treatment of single level lumbar degenerative conditions.

STUDY DESIGN

Retrospective computed tomography (CT) based review.

PATIENT SAMPLE

One hundred ninety-three patients underwent TLIF+PLF with local autograft bone or PLF alone with local autograft bone.

OUTCOME MEASURES

Radiographic fusion rates and screw loosening were measured at 6 and 12 months using strict CT criteria. Patient self-reported outcome measures included Visual Analog Scale for low back pain and leg pain and Oswestry Disability Index.

METHODS

Postoperative thin-cut CTs were examined for pedicle screw loosening and radiographic fusion status. Early screw loosening rates were determined using 6-month postoperative CT, whereas radiographic fusion rates were determined using 12-month postoperative CT. One-way analysis of variance was used to determine significant differences in mean outcome scores and other continuous measures between groups at baseline and follow-up. Chi-square test of independence or Fisher's exact test was used to compare proportions between groups on categorical measures.

RESULTS

Eighty-three patients underwent TLIF+PLF (Group A) and 115 patients underwent PLF alone (Group B). At 6-month follow-up, loosening was observed in 49 of 792 total screws (6.19%). Of Group A, 7.23% of patients demonstrated loosening of one or more screws compared with 18.3% of Group B (Chi-Square value 4.98; p=.0256). Six-month radiographic fusion rates were 36.1% in Group A versus 44.3% in Group B. Twelve-month radiographic fusion rates increased to 58.6% in Group A versus 73.1% in Group B. Among Group A patients not yet fused at 6 months, screw loosening was associated with a 0% rate of radiographic fusion at 12 months versus 41.2% without screw loosening. Rates for Group B were 6.25% and 70.3%, respectively. Patient age was a significant independent predictor of loosening (p=.0336).

CONCLUSIONS

TLIF appears to have a protective effect, reducing rates of early screw loosening by approximately 60% versus PLF. However, this effect appears independent of actual overall radiographic fusion rates which may be approximately 20% lower with TLIF at 12 months. TLIF may have advantages in patients where early loosening is a particular concern, for example, in the setting of increased patient age.