TLIF with an obliquely placed rectangular cage: Does cage position or level affect lumbar lordosis?

2011

BACKGROUND

Biomechanical studies of transforaminal lumbar interbody fusion (TLIF) cage positioning show greater segmental lordosis with anterior cage placement. Common TLIF techniques include a semilunar shaped cage placed along anterior disc margin, or a rectangular cage placed obliquely across the disc.

PURPOSE

This clinical study correlates rectangular TLIF cage position (anterior 1/3, middle 1/3, posterior 1/3), anatomic TLIF level, and 1 vs. 2-level TLIF with segmental and regional lordosis, outcomes, and complications in patients followed long-term.

STUDY DESIGN

A review of prospectively collected clinical and radiographic data from a surgical database.

PATIENT SAMPLE

A consecutive series of 72 patients underwent posterior instrumented fusion and TLIF for degenerative disease, recurrent disc herniation, or spondylolisthesis at 1 or 2 levels between L2-S1 (107 discs, average 1.5 levels/patient). Age averaged 58 years (28 – 83 years).

OUTCOMES MEASURE

Visual analog pain scores (VAS), Oswestry disability index (ODI), pain medication records. Continuous data were compared with ANOVA or paired t-tests, as appropriate. Anderson-Darling was used to determine normalcy where sample sizes were sufficient. Discrete data were compared using Mann-Whitney or Sign Test, as appropriate. Frequencies were compared using chi-square.

METHODS

All underwent posterior spinal fusion with instrumentation, and TLIF with an obliquely placed rectangular cage at each level fused. There were 34 single and 35 two level TLIF procedures. Radiograph analysis was performed pre-op, 6 weeks, 1 year, and 2 years. TLIF level, disc height, disc angle (segmental lordosis), regional lordosis (T12-S1), and cage position were measured for each disc fused. Anatomic levels (L3-4 vs. L4-5 vs. L5-S1) were compared along with 1 vs. 2-level TLIFs. Clinical outcomes were obtained pre-op, 1 year, 2 years, and yearly thereafter.

RESULTS

At 35 months follow-up (range 24 – 47 months), complications: adjacent degenerative changes-19, adjacent fracture-3, infection-2, temporary foot-drop-2, nonunion-0, revision surgery-4. Pre-op disc height and angle were similar (L4-L5 pre p=0.5, post p=0.1; L5-S1 pre p=0.6, post p=0.9). Post-op discs heights at L5-S1, L4-5 were taller than L3-4 (16.5mm vs. 13.1mm). For single level fusions, change in disc angle was dependent upon cage position (p=0.02), but not level (p=0.5), other factors showing no preference. Regional lordosis was unaffected by cage position, level, or 1 vs. 2 level TLIF (P=0.9). Patients with 2 levels fused improved VAS 5.7 pre to 3.4 at 2 years (p=0.017); ODI improved 51 pre to 28 at 2 years (p<0.001). Single level TLIF similarly improved VAS from 6.5 pre to 3.8 at 2 years (p=0.026), ODI improved from 48 to 27 at 2 years (p<0.001). A significant difference (p<0.001) was observed in the rate of degenerative disk disease for 2 level TLIFs (26/35) vs. single level TLIF (8/32).

CONCLUSIONS

Rectangular cage position within the disc does affects segmental but not regional lordosis or clinical outcome at 3 years follow-up. Regional lordosis is unaffected by TLIF level and 1 vs. 2-level TLIF. Adjacent level degeneration was more common after 2-level TLIF than single TLIF.