Corresponding Author

Mohamed K. Elkazaz

Subject Area

Degenerative, Lumbosacral spine, Minimally invasive procedures

Document Type

Original Study


Background Data: The incidence of interbody cage subsidence in OLIF is 8–9.5%. It occurs mainly secondary to osteoporosis or endplate damage during disc space clearance. An anatomical study correlated the surface area contact and position between the cage and the disc space to the incidence of subsidence. Studies have concentrated on the optimal place in the disc space to place the cage to obtain less incidence of subsidence, as it was reported that the central part of the disc space, called the epiphyseal ring, is the toughest part. Subsidence is usually noted in the superior vertebral endplate. Until now, there has been a lack of data regarding the main cause of subsidence.

Study Design: This is a prospective clinical case study.

Objective: This study aims to assess the subsidence rate in patients undergoing SA-OLIF for degenerative lumbar diseases.

Patients and Methods: Patients with ADS following specific inclusion criteria underwent SA-OLIF. The following data were all analyzed and compared statistically: pre- and postoperative clinical data; back and leg pain VAS and ODI; radiological data; spinopelvic parameters, segmental Cobb’s angle and anterior disc height, and intraoperative data; operative time; the amount of blood loss; complications (intraoperative or postoperative); hospital stay.

Results: A total of 28 patients and 30 levels were operated on by SA-OLIF, with a mean age of 50.54 ± 6.05, including 14 males and 14 females. The mean operative time/min, blood loss, and hospital stay/day was 91.29 ± 14.23, 195.54 ± 42.299, and 2.78 ± 0.875, respectively. The mean of back pain VAS, the mean of leg pain VAS, and ODI changed from preoperatively 7.36 ± 0.98, 6.36 ± 0.911, and 53.71 ± 18.9 to 4.07 ± 1.01, 2.07 ± 0.9, and 45.25 ± 18.76 in 1 year, respectively. Fusion rates were assessed at 6 months and 12 months by MSCT. During the 6-month follow-up period, 83.3% (25 levels) of Grade I and II fusion was interpreted as solid fusion and 6.6% as cage subsidence (2 levels), and during the 12-month follow-up, 89.9% (27 levels) as Grade I and II fusion and 6.6% cage subsidence (2 levels).

Conclusion: Subsidence in standalone OLIF highly contributed to endplate injury during the surgery and osteoporosis; consequently, posterior instrumentation is advised in these patients along with OLIF to decrease the subsidence rate.


OLIF, scoliosis, degenerative lumbar diseases, subsidence, Cobb angle, deformity