BACKGROUND CONTEXT:
Transforaminal lumbar interbody fusion (TLIF) or anterior lumbar interbody fusion with percutaneous pedicle screws (ALIFPS) offer significantly higher radiographic fusion rates than other fusion techniques for L5-S1 isthmic spondylolisthesis (IS). As it stands, there is a relative paucity of comparative data of the two techniques.

PURPOSE:
To define the clinical, radiographic, and financial differences between TLIF and ALIFPS for L5-S1 IS.

DESIGN/SETTING:
A retrospective cohort study conducted at a single tertiary care center.

PATIENT SAMPLE:
Sixty-six patients who underwent either TLIF or ALIPFS for L5-S1 IS at a single tertiary care center between 2009 and 2014.

OUTCOME MEASURES:
Quality of life outcome scores including the EuroQol-5 Dimensions (EQ-5D), Pain Disability Questionnaire (PDQ), and Patient Health Questionnaire-9 (PHQ-9). Sagittal balance parameters including: pelvic incidence, pelvic tilt, sacral slope, segmental lordosis, total lordosis, degree of slip, disc height, and L1-axis S1 distance (LASD). Cost measures included in-hospital charges, hospital length of stay (LOS), and post-admission costs accrued over 1 year.

METHODS:
Quality of life (QoL) outcome scores, radiographic data, and financial data were collected with a minimum of 1-year follow-up. Clinical results were investigated using the PDQ, PHQ-9, and EQ-5D. Radiographic measurements included lumbar lordosis, segmental lordosis, pelvic tilt, pelvic incidence, height of disc, L-1 axis S-1 distance, and the degree of slip. Cost data were generated based on patient-level resource utilization. Comparative data were presented as median with interquartile range (IQR). Continuous variables were compared using either independent Student t tests assuming unequal variance or Mann-Whitney U tests for parametric and nonparametric variables, respectively. The minimally clinical important difference (MCID) used for each questionnaire was as follows: PDQ (26), PHQ-9 (5), and EQ-5D (0.4).

RESULTS:
A total of 66 patients met inclusion criteria. In the ALIFPS cohort, PDQ scores improved from 69 [47, 82] to 26 [18.2, 79.7], p=.02. In the TLIF cohort, PDQ scores improved from 73 [46, 85] to 48.5 [23, 67.5], p=.01. Both groups also showed a significant improvement in EQ-5D scores at 1 year, but the ALIFPS group showed a significantly greater improvement in EQ-5D scores at 1 year (0.1 [0,0.2] vs. 0.2 [0.1, 0.4], p=.02). Furthermore, only the ALIFPS cohort showed a significant improvement in segmental lordosis. The ALIFPS cohort showed a significantly greater improvement in disc height than did TLIF (3.5 [2, 5.5] vs. 6.7 [4.1, 10], p=.01). No significant differences were found in the direct costs of both procedures.

CONCLUSIONS:
Our findings suggest that anterior lumbar interbody fusion with percutaneous pedicle screws can achieve better clinical outcomes compared with TLIF for the treatment of IS. We believe the superior radiographic outcomes achieved through ALIFPS, namely a greater restoration of segmental lordosis and disc height, may have contributed to the improved clinical outcomes presented in the current study.