Assessment and classification of subsidence after XXXX using serial computed tomography.

@entity1 @entity717 @entity11375 @entity130
UNASSIGNED: OBJECT Intervertebral cage settling during bone remodeling after lumbar @entity11375 ( @entity11375 ) 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) @entity11375 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 @entity11375 . METHODS A total of 128 consecutive @entity1 (with 178 treated levels in total) underwent MIS @entity11375 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 @entity130 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). @entity1 -reported outcome measures included visual analog scale, @entity717 Index, and 36-Item Short Form Health Survey physical and mental component summary scores. RESULTS Four @entity1 had ECS in a total of 4 levels. The radiographic subsidence (DCS) rates were 10% (13 of 128 @entity1 ) and 8% (14 of 178 levels), with 3% of @entity1 (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 @entity1 in the subsidence (DCS) and no-subsidence groups who received clinical benefit from the surgical procedure, based on the minimum clinically important difference (p > 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). CONCLUSIONS 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 @entity1 from subsidence after MIS @entity11375 , 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.
