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

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>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.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>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.</jats:p></jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>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 &gt; 0.999) or by incidence of subsidence (p = 0.383).</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>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.</jats:p></jats:sec>

Cage subsidence in lateral interbody fusion with transpsoas approach: intraoperative endplate injury or late-onset settling

“…We could not analyze the effect of cage width on endplate injury, as only 18-mm cages were available in our country; this might account for results that differed from those in previous literature 1,2) . In conclusion, intraoperative endplate injury was significantly related to bone quality, and late-onset settling was related to cage type (PEEK cage).…”

“…Several factors are reported to cause cage subsidence in intervertebral fusions including LIF: reduced bone quality 12,13) , older age 13) , multilevel procedures 1,14) , narrow cage 1,2) , and use of rhBMP-2 15) . However, the abovementioned reports mixed two types of cage subsidence (intraoperative injury and postoperative spontaneous settling).…”

“…Several reports have described postoperative cage subsidence in LIF series, with an incidence of 0.3%-22% [1][2][3] . Many reports have mixed two types of cage subsidence, one results from intraoperative endplate injury and the other (late-onset settling) occurs gradually over the postoperative course.…”

Is the Lateral Transpsoas Approach Feasible for the Treatment of Adult Degenerative Scoliosis?

“…Fifth, our study was neither a large case series nor a comparative study, and some analyses were not possible (for example, analysis of the subset of patients with subsidence); nevertheless, our study is the largest case series of stand-alone treatment of degenerative scoliosis at the time of this report. Sixth, subsidence was evaluated only up to 3 months and some authors claim that later evaluation may give different results; however, our subsidence evaluation was based on a study [22] suggesting that 3-month subsidence has no significant progression with lateral placed cages. Finally, we did not report side effects related to the psoas entry and the lumbar plexus in detail because at the time of data collection we did not have a standardized method to record this variable such as that published by Le et al [21]; nevertheless, we observed no permanent deficit 6 months after surgery.…”

“…Sagittal alignment was measured by means of global lordosis and sacral slope. Subsidence was classified as described previously [22,23] in radiographs in the AP and lateral views and CT scans, based on the amount of cage subsidence into the vertebral endplates: absent or low-grade = 0% to 49%; and high-grade = 50% to 100% collapse of the level. Fusion status was determined oriented as described previously [6,14,15] in plain neutral and flexion-extension radiographs and eventually CT scans in cases with no clear conclusion on the radiographs.…”