J Korean Neurosurg Soc.  2023 Nov;66(6):703-715. 10.3340/jkns.2023.0071.

Factors Affecting Cage Obliquity and the Relationship between Cage Obliquity and Radiological Outcomes in Oblique Lateral Interbody Fusion at the L4-L5 Level

• Jang C
• Hwang S
• Jin TK
• Shin HJ
• Cho BK

• KMID: 2547464
• DOI: http://doi.org/10.3340/jkns.2023.0071

Abstract

Objective
: This retrospective study investigated the factors that affect cage obliquity angle despite orthogonal maneuvers performed during oblique lateral interbody fusion (OLIF) and assessed the relationship between cage obliquity angle and radiological outcomes post-surgery.
Methods
: Twenty-nine males who underwent L4-L5 OLIF for lumbar degenerative disease between 2019 and 2021 with a followup duration greater than 12 months were analyzed. Radiological parameters were measured including psoas muscle volume, total psoas area index (total psoas muscle area [cm²]/height squared [m2]), distance from the iliac artery to the origin of the psoas muscle (DIAPM), angle between the origin of the psoas muscle and the center of the vertebral disc (APCVD), iliac crest height, disc height, lumbar flexibility (lumbar flexion angle minus extension angle), cage location ratio, cage-induced segmental lumbar lordosis (LL) (postoperative index level segmental LL minus used cage angle), foraminal height changes, fusion grade.
Results
: DIAPM, APCVD, iliac crest height, postoperative index level segmental LL, and cage-induced segmental LL were significantly correlated with OLIF cage obliquity angle. However, other radiological parameters did not correlate with cage obliquity. Based on multiple regression analysis, the predictive equation for the OLIF cage obliquity angle was 13.062–0.318×DIAPM+0.325×A PCVD+0.174×iliac crest height. The greater the cage obliquity, the smaller the segmental LL compared to the cage angle used.
Conclusion
: At the L4-L5 level, OLIF cage obliquity was affected by DIAPM, APCVD, and iliac crest height, and as the cage obliquity angle increases, LL agnle achievable by the used cage could not be obtained.

Keyword

Spinal fusion; Lumbosacral region; Iliac artery; Psoas muscles; Spine

Figure

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  Fig. 1. Flow chart of the selection of patients. TLIF : transforaminal lumbar interbody fusion.

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  Fig. 2. Images illustrating the iliac crest height (A and B); lumbar flexibility (C), which is the difference between flexion and extension Cobb angles; the distance from the iliac artery to the origin of the psoas muscle (DIAPM; D); the angle between the origin of the psoas muscle and the center of the vertebral disc (APCVD; D); cage obliquity (E), which is measured based on a line perpendicular to the line from the spinous process to the center of the intervertebral disc and a line formed by the cage metallic marker; foraminal height (F) measured in sagittal view from the pedicle interior margin of the gastric vertebral body to the upper margin of the pedicle of the lower vertebral body; cage location ratio (G) calculated by the center of the cage compared to the upper endplate of the caudal vertebral body (“2”/”1”) [21].

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  Fig. 3. Three factors that affect cage obliquity angle : iliac crest height, APCVD, and DIAPM. The linear regression graphs for these three factors are shown in (A-C), respectively. APCVD : angle between the origin of the psoas muscle and the center of the vertebral disc, DIAPM : distance from the iliac artery to the origin of the psoas muscle.

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  Fig. 4. Linear regression shows the relationship between cage obliquity angle and postoperative 1-year index level segmental lumbar lordotic angle (A) and cage-induced segmental lumbar lordotic angle, which is the difference between the index level segmental lumbar lordotic angle and the cage angle used (B). LL : lumbar lordosis.

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  Fig. 5. Receiver-operating characteristic (ROC) curve of the APCVD. The area under the ROC (AUC) curve for a cage obliquity angle greater than 15° after oblique lateral interbody fusion (OLIF) is 0.757. When the cutoff value of the APCVD is calculated as 21.58°, the sensitivity, and specificity are 73.3% and 71.4%, respectively. APCVD : angle between the origin of the psoas muscle and the center of the vertebral disc.

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  Fig. 6. Classification according to the locations of the left psoas muscle and the major artery as a result of the study and the distribution of patients in this paper according to this classification. Adopted from Wang et al. [23].

Reference

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