• Viknesh Kamalanathan, Kieffer Will K M WKM, Mark Zhu, Joseph F Baker, and Peter A Robertson.
• Department of Orthopaedic Surgery, Auckland City Hospital, Auckland, New Zealand.
• Spine. 2020 Sep 1; 45 (17): 1178-1184.

Study DesignRetrospective cohort.ObjectiveWe aimed to assess the changes in adjacent segmental lordosis (SL) across the intervertebral disc space following single level posterior lumbar interbody fusion (PLIF).Summary Of Background DataAdjacent segment degeneration is well documented following fusion surgery as are the spinopelvic parameters. What isn't known is the effect of fusion surgery on the adjacent SL of the lumbar spine following PLIF.MethodsPreoperative and 1-year postoperative erect lateral radiographs were analyzed for lordotic angulation of all lumbar segments and pelvic incidence (PI) in patients undergoing L4/5 or L5/S1 PLIF.ResultsFourty seven PLIFs achieved a mean of 7° increase in SL at L4/5 (P < 0.05) and 11° at L5/S1 (P < 0.05). In L5/S1 PLIF the lordosis gain was associated with lordosis reduction at adjacent segments 3° at L4/5 (P < 0.05); 1° at L3/4 (P < 0.05), 0° at L2/3(NS); 0° at L1/2(NS), and modest gain in overall lordosis (3°). At L4/5 PLIF the global lordosis increased by 5°, but less so at the adjacent discs (L5/S1 = 1°; L3/4 ≤ 1°; L2/3 ≤ -1°, and; L1/2 = <-1°). 19% of cases had a PI-LL > 10° preoperatively, reducing to 4° postoperatively.ConclusionSL increased significantly at the PLIF level. At L5/S1 minimal overall lordosis change occurred however there was reduction in lordosis at adjacent levels representing reduced adjacent segment "compensation." Conversely L4/5 PLIF showed minimal change at adjacent levels but greater overall lordosis increase. Lumbar lordosis (LL) assessment requires monosegmental assessment as well as overall measure of the LL. PLIF surgery changes both LL and SL at adjacent levels.Level Of Evidence3.

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