219. Transforaminal lumbar interbody fusion may prevent early postoperative pedicle screw loosening

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 (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 fusion rates compared to PLF using pedicle screws alone in the treatment of single level lumbar degenerative conditions. STUDY DESIGN/SETTING 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 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 (VAS) for low back pain and leg pain and Oswestry Disability Index (ODI). METHODS Postoperative thin-cut CTs were examined for pedicle screw loosening and fusion status. One-way analysis of variance (ANOVA) 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 A total of 83 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%). 7.23% of Group A patients demonstrated loosening of one or more screws compared to 18.3% of Group B (Chi-Square value 4.98; p=0.0256). Six-month fusion rates were 36.1% in Group A vs 44.3% in Group B. 12-month fusion rates increased to 58.6% in Group A vs 73.1% in Group B. among Group A patients not yet fused at 6 months, screw loosening was associated with a 0% rate of fusion at 12 months vs 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=0.0336). 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 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. Increased age is an independent risk factor for early screw loosening. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.