Degenerative lumbar scoliosis treated with TLIF using expandable vs static height cages: Is there a difference?

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TLIF with cage fixation is commonly used to improve anterior column height, local lordosis, segmental stability, enhance fusion potential, and augment posterior spinal fusion(PSF) with instrumentation in degenerative lumbar scoliosis(DLS).  No clinical or radiographic studies have been done comparing static height TLIF cages(SC) to expandable cages(EC) in adult degenerative deformity.

Compare clinical and radiographic differences after TLIF with SC vs EC, controlling for disc height and lordosis in DLS. Study results will assist in defining the relative indications EC vs SC based on pre-op interspace height and angle.

Study Design
Prospective data retrospectively reviewed 

Patient Sample
Consecutive surgical cohort of 43 adults with DLS who underwent posterior PSF with TLIF at 1-3 levels, L2-S1, using either SC (25) or EC (18), with minimum 2 year follow-up. Patients with anterior surgery were excluded.

Outcome measures
AP/Lateral 18x36 radiograph measurements: disc height and segmental lordosis at TLIF levels; lumbar lordosis, sagittal balance.  Fusion at TLIF levels was defined as bridging bone across the interspace at 2 years, without implant loosening. Clinical: Visual Analog pain scores (VAS), Oswestry Disability Index (ODI), and pain medication use. Mann Whitney, Wilcoxon signed rank test, t-test, and multivariate linear regression were used in statistical analysis.

Clinical outcomes recorded pre-op, 1 year, 2 years, and latest follow-up. Radiographs measured pre-op, 1 year, and 2 years.  TLIF discs were measured for height and angle. For comparison SC vs EC, TLIF disc were categorized by pre-op height (Short: 0-8mm, Medium: 9-12mm, Tall: >12mm) and by angle of segmental Lordosis (Low: 0-4°, Medium: 5-11°, High: >12°). Overall lumbar Lordosis (T12-S1) and Sagittal Balance (C7-S1) were also recorded.

Follow-up averaged 47months (26-68months) for 43 patients (SC group: 57 cages in 25 patients; EC group: 37 cages in 18 patients). There was no significant difference SC vs EC for age (68years, range 40-77years), smoking (10%), prior surgery (47%), levels chosen for TLIF, TLIF disc height (7mm), pre-op sagittal imbalance (8cm) and lumbar lordosis (35°). SC had average 3° more pre-op segmental lordosis at TLIF levels than EC; PSF was similar for both groups (average 6.3 levels, range 3-8 levels), and all had Ponte osteotomies. SC group had more 3 level TLIFs (14 vs 4) and 1-level TLIFs (7 vs 3). After surgery, EC produced better 2-year anterior disc height (14.5mm vs 11.1mm), segmental lordosis (13.7° vs 9.7°), lumbar lordosis (52° vs 47°) and sagittal balance (4.0cm vs 6.0cm) than the SC group.  Series complications were similar SC vs EC: Adjacent fracture-9, symptomatic sagittal imbalance-6 (SC-3, EC-3), revision surgery to extend fusion-3.  Clinical improvement was noted in both SC and EC groups at 2 years (p<0.01) for VAS (preop-6.5, 2 year-3.4), ODI (preop-49.3, 2 year- 27.2), and pain medication, without  significant difference SC vs EC. 

At 2 years post instrumented posterior fusion and TLIF for DLS, EC trended toward better disc height, segmental lordosis, lumbar lordosis, and sagittal balance compared to SC, even though the SC group had 3 times as many 3-level TLIF’s as the EC group.  The preliminary and cautious observation that EC may perform better than SC long-term in DLS warrants further study.