Assessment and classification of subsidence after lateral interbody fusion using serial computed tomography

Abstract

<jats:sec> <jats:title>OBJECT</jats:title> <jats:p>Intervertebral cage settling during bone remodeling after lumbar lateral interbody fusion (LIF) is a common occurrence during the normal healing process. Progression of this settling with endplate collapse is defined as subsidence. The purposes of this study were to 1) assess the rate of subsidence after minimally invasive (MIS) LIF by CT, 2) distinguish between early cage subsidence (ECS) and delayed cage subsidence (DCS), 3) propose a descriptive method for classifying the types of subsidence, and 4) discuss techniques for mitigating the risk of subsidence after MIS LIF.</jats:p></jats:sec> <jats:sec> <jats:title>METHODS</jats:title> <jats:p>A total of 128 consecutive patients (with 178 treated levels in total) underwent MIS LIF performed by a single surgeon. The subsidence was deemed to be ECS if it was evident on postoperative Day 2 CT images and was therefore the result of an intraoperative vertebral endplate injury and deemed DCS if it was detected on subsequent CT scans (≥ 6 months postoperatively). Endplate breaches were categorized as caudal (superior endplate) and/or cranial (inferior endplate), and as ipsilateral, contralateral, or bilateral with respect to the side of cage insertion. Subsidence seen in CT images (radiographic subsidence) was measured from the vertebral endplate to the caudal or cranial margin of the cage (in millimeters). Patient-reported outcome measures included visual analog scale, Oswestry Disability Index, and 36-Item Short Form Health Survey physical and mental component summary scores.</jats:p></jats:sec> <jats:sec> <jats:title>RESULTS</jats:title> <jats:p>Four patients had ECS in a total of 4 levels. The radiographic subsidence (DCS) rates were 10% (13 of 128 patients) and 8% (14 of 178 levels), with 3% of patients (4 of 128) exhibiting clinical subsidence. In the DCS levels, 3 types of subsidence were evident on coronal and sagittal CT scans: Type 1, caudal contralateral, in 14% (2 of 14), Type 2, caudal bilateral with anterior cage tilt, in 64% (9 of 14), and Type 3, both endplates bilaterally, in 21% (3 of 14). The mean subsidence in the DCS levels was 3.2 mm. There was no significant difference between the numbers of patients in the subsidence (DCS) and no-subsidence groups who received clinical benefit from the surgical procedure, based on the minimum clinically important difference (p &gt; 0.05). There was a significant difference between the fusion rates at 6 months (p = 0.0195); however, by 12 months, the difference was not significant (p = 0.2049).</jats:p></jats:sec> <jats:sec> <jats:title>CONCLUSIONS</jats:title> <jats:p>The authors distinguished between ECS and DCS. Radiographic subsidence (DCS) was categorized using descriptors for the location and severity of the subsidence. Neither interbody fusion rates nor clinical outcomes were affected by radiographic subsidence. To protect patients from subsidence after MIS LIF, the surgeon needs to take care with the caudal endplate during cage insertion. If a caudal bilateral (Type 2) endplate breach is detected, supplemental posterior fixation to arrest progression and facilitate fusion is recommended.</jats:p></jats:sec>

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

“…These results are consistent with previous literature 10,11) . However, a longer follow-up period and larger number of cases are necessary to clarify the influence of cage subsidence on clinical outcomes.…”

“…Malham et al described two types of cage subsidence in LIF: early cage subsidence and delayed onset subsidence (DCS) 11) . They analyzed the clinical and radiological outcomes of DCS cases and concluded that DCS did not affect interbody fusion rates or clinical outcomes.…”

Optimizing surface characteristics for cell adhesion and proliferation on titanium plasma spray coatings on polyetheretherketone

“…However, bone density varies between patients and because of the significantly higher Young's modulus compared with human cortical bone, metals can be prone to subsidence. To mitigate the risk of cage subsidence, some surgeons may opt for cages with larger footprints or choose to use supplemental fixation [20]. The drawbacks of these supplemental fixation techniques, however, are additional posterior surgery, screw or plate dislodgement, soft tissue injury, higher incidence of adjacent level degenerations, and heterotrophic ossification [21].…”

Anterior and Lateral Lumbar Interbody Fusion With Supplemental Interspinous Process Fixation: Outcomes from a Multicenter, Prospective, Randomized, Controlled Study

“…[1][2][3][4][5][6][7][8][9][10][11][12] However, given the inherent axial and coronal stability of a large anterolateral cage, the structural necessity of invasive/extensive PSF in ALIF/LLIF has come into question, particularly in single-level application. Accordingly, a growing body of literature exploring less invasive and less demanding alternatives for secondary stability in ALIF/LLIF has emerged.…”