Sagittal alignment assessment after short-segment lumbar fusion for degenerative disc disease.

PURPOSE: To investigate whether differences in spinopelvic parameters, and especially spinopelvic alignment, could be associated with adjacent segment disease (ASD) or pseudarthrosis after short-segment lumbar fusion.

METHODS: Retrospective study of patients offered mono- or bisegmental transforaminal lumbar interbody fusion (TLIF) with polyetheretherketone (PEEK) or titanium cages, due to degenerative disease. Of 419 patients, 32 (7.6%) presented pseudarthrosis (nonunion group), 29 (6.9%) developed symptomatic ASD (ASD group), and 358 patients (85.5%) showed evidence of uncomplicated fusion (control group). Standard spinopelvic parameters were measured in all patients before and after surgery. The differences of the values within the parameters (Δ values) were also calculated. A comparative analysis within and among groups was performed. Patients were also analyzed by cage characteristics (large vs small, titanium vs PEEK).

RESULTS: All studied parameters changed significantly after surgery both in the control and ASD group, while in the nonunion group, only LL and PI-LL changed significantly (PI-LL increased from 10 ± 11° to 14 ± 10°, p = 0.008). Patients in the nonunion group presented greater SS before and after surgery, greater PI-LL after surgery, and higher PI, while ASD patients presented greater absolute mean ΔPT value. Age, size, and type of cage were not related to fusion, nonunion, or ASD.

CONCLUSIONS: Greater SS, greater PI, and a PI-LL mismatch greater than 10° are associated with failed bony fusion, while ASD is related to a greater difference between the pre-operative and post-operative values of PT. Neither the type nor the size of cage seem to have a significant impact on either solid bony fusion, nonunion, or ASD rates. Thus, we recommend on the study of patients' sagittal alignment in the pre-operative setting even when treating patients with short-segment lumbar interbody fusion.