Radiographic and clinical evaluation of cage subsidence after stand-alone lateral interbody fusion

Clinical article

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Indirect decompression of the neural structures through interbody distraction and fusion in the lumbar spine is feasible, but cage subsidence may limit maintenance of the initial decompression. The influence of interbody cage size on subsidence and symptoms in minimally invasive lateral interbody fusion is heretofore unreported. The authors report the rate of cage subsidence after lateral interbody fusion, examine the clinical effects, and present a subsidence classification scale.


The study was performed as an institutional review board–approved prospective, nonrandomized, comparative, single-center radiographic and clinical evaluation. Stand-alone short-segment (1- or 2-level) lateral lumbar interbody fusion was investigated with 12 months of postoperative follow-up. Two groups were compared. Forty-six patients underwent treatment at 61 lumbar levels with standard interbody cages (18 mm anterior/posterior dimension), and 28 patients underwent treatment at 37 lumbar levels with wide cages (22 mm). Standing lateral radiographs were used to measure segmental lumbar lordosis, disc height, and rate of subsidence. Subsidence was classified using the following scale: Grade 0, 0%–24% loss of postoperative disc height; Grade I, 25%–49%; Grade II, 50%–74%; and Grade III, 75%–100%. Fusion status was assessed on CT scanning, and pain and disability were assessed using the visual analog scale and Oswestry Disability Index. Complications and reoperations were recorded.


Pain and disability improved similarly in both groups. While significant gains in segmental lumbar lordosis and disc height were observed overall, the standard group experienced less improvement due to the higher rate of interbody graft subsidence. A difference in the rate of subsidence between the groups was evident at 6 weeks (p = 0.027), 3 months (p = 0.042), and 12 months (p = 0.047). At 12 months, 70% in the standard group and 89% in the wide group had Grade 0 or I subsidence, and 30% in the standard group and 11% in wide group had Grade II or III subsidence. Subsidence was detected early (6 weeks), at which point it was correlated with transient clinical worsening, although progression of subsidence was not observed after the 6-week time point. Moreover, subsidence occurred predominantly (68%) in the inferior endplate. Fusion rate was not affected by cage dimension (p > 0.999) or by incidence of subsidence (p = 0.383).


Wider cages avoid subsidence and better restore segmental lordosis in stand-alone lateral interbody fusion. Cage subsidence is identified early in follow-up and can be accessed using the proposed classification scale.

Abbreviations used in this paper:BMI = body mass index; ODI = Oswestry Disability Index; VAS = visual analog scale; XLIF = extreme lateral interbody fusion.

Article Information

Address correspondence to: Luis Marchi, M.Sc., Vergueiro Street, 1421, Suite 305, São Paulo 04101-000, Brazil. email:

Please include this information when citing this paper: published online May 10, 2013; DOI: 10.3171/2013.4.SPINE12319.

© AANS, except where prohibited by US copyright law.



  • View in gallery

    Intervertebral cages compared in the current study. Left: Standard cage with an anteroposterior width of 18 mm (arrow). Right: Wide cage with an anteroposterior width of 22 mm (arrow).

  • View in gallery

    Subsidence grading. Radiographs showing examples of the different subsidence grades (0–III).

  • View in gallery

    Graph showing the time course of subsidence. Incidence of subsidence by grade (0–III) is shown at each follow-up point. No statistically significant difference was found among the assessments (chi-square test [6 df] = 4.887; p = 0.558).

  • View in gallery

    Graph showing the incidence of subsidence per cage group. The subsidence rate shown is relative to the 12-month radiological assessment. Group rates are statistically different (chi-square test [3 df] = 7.971; p = 0.047).

  • View in gallery

    Case example of fusion after Grade III subsidence. Twelve-month radiographs (A and C) and CT images (B and D) showing fusion obtained after placement of a standard cage despite high-grade subsidence occurrence.


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