A retrospective study on application of a classification criterion based on relative intervertebral tension in spinal fusion surgery for lumbar degenerative diseases

BMC Surgery · 6 authors, 1 centre

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POPULATION83 patients (45 men, 38 women; mean age 61.5±9.4 years) with lumbar degenerative disease undergoing transforaminal lumbar interbody fusion (TLIF) from January 2018 to July 2019

INTERVENTIONClassification of fusion segments into Group A (Grade I RIT), Group B (Grade II RIT), or Group C (Grade III RIT) based on intraoperative relative intervertebral tension grading

COMPARISONComparison among Group A (n=11 segments), Group B (n=54 segments), and Group C (n=86 segments) for radiographic outcomes, fusion rates, and cage-related complications

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TL;DR

This retrospective study introduces a novel classification system called relative intervertebral tension (RIT) to guide fusion cage size selection during lumbar interbody fusion surgery. Among 83 patients (151 fusion segments), the RIT grading system achieved high fusion rates (96.3–100%) with no significant differences in cage-related complications across grades. The RIT classification provides an objective, intraoperative tool that may reduce reliance on surgeon experience alone and simplify surgical decision-making.

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**Background:** Lumbar interbody fusion (LIF) is widely used for degenerative lumbar diseases, but selection of fusion cage size remains subjective, relying on surgeon experience and preoperative imaging. There is no standardized objective criterion. The authors propose the novel concept of relative intervertebral tension (RIT)—defined as the resistance encountered when a distractor rotates in the intervertebral space—and its grading standards to guide cage size selection without mandatory posterior axial compression.

**Methods:** This retrospective study included 83 eligible patients (45 men, 38 women; mean age 61.5±9.4 years) who underwent TLIF from January 2018 to July 2019. A total of 151 fusion segments were classified intraoperatively into three groups: Group A (Grade I RIT, n=11)—distractor rotates ≤5° and RIT resists pulling force; Group B (Grade II RIT, n=54)—distractor rotates >5° but <90° and RIT resists pulling force; Group C (Grade III RIT, n=86)—distractor can rotate 360° and RIT cannot resist pulling force. For Grade I, the intervertebral space was moderately distracted before cage insertion without compression. For Grade II, cage insertion without compression. For Grade III, cage insertion with intervertebral compression, or a larger cage was selected until Grade I/II criteria were met. Radiographic parameters (ISA, ISH, IFH), fusion rates (Bridwell criteria), and cage-related complications (migration, subsidence) were compared. Mean follow-up was 19.1±3.8 months.

**Key Results:** VAS scores improved from 7.91±0.64 preoperatively to 1.39±0.51 at final follow-up (P<0.05); ODI improved from 54.29±6.18 to 12.05±1.86 (P<0.05). ISA at final follow-up was smallest in Group A (7.94±3.55°) and largest in Group C (10.29±3.41°) (P<0.05). Group B had the largest ISH (12.74±0.88 mm) and IFH (18.09±1.13 mm) at final follow-up (P<0.05), while Group A had the smallest ISH (9.92±0.85 mm) and IFH (15.19±1.06 mm) (P<0.05). Group C values were intermediate (ISH 10.93±0.91 mm, IFH 16.41±1.01 mm). Fusion rates were 100% (Group A), 96.3% (Group B), and 98.8% (Group C) at final follow-up, with no significant difference (P>0.05). Cage migration occurred in 0 (Group A), 1 (1.85%, Group B), and 1 (1.16%, Group C) cases; both required revision surgery. Cage subsidence occurred in 3 (27.27%, Group A), 11 (20.37%, Group B), and 19 (22.09%, Group C) cases, all asymptomatic. No significant differences in complication rates were found (P>0.05). All 8 mm cages (n=14) were used in Group A (100%), while 12 mm cages were most common in Group B (68.52%) and 10 mm cages in Group C (38.37%).

**Clinical Implications:** The RIT classification provides an objective, intraoperative tool for selecting fusion cage size, potentially reducing reliance on subjective surgeon experience. Grade II RIT appears optimal for maintaining intervertebral space and foramen height. Grade III RIT requires posterior axial compression to prevent cage displacement. Grade I RIT, associated with severe disc height loss, carries higher subsidence risk though not statistically significant in this study. The system may simplify surgical decision-making and reduce cage-related complications, though larger prospective studies are needed to validate these findings.

PICO

PPOPULATION

83 patients (45 men, 38 women; mean age 61.5±9.4 years) with lumbar degenerative disease undergoing transforaminal lumbar interbody fusion (TLIF) from January 2018 to July 2019

IINTERVENTION

Classification of fusion segments into Group A (Grade I RIT), Group B (Grade II RIT), or Group C (Grade III RIT) based on intraoperative relative intervertebral tension grading

OOUTCOME

Intervertebral space angle (ISA), intervertebral space height (ISH), intervertebral foramen height (IFH), fusion rates, cage migration, cage subsidence

STUDY TYPE

cohort

SPECIALTY

orthopedic surgery

SUMMARISED BY

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FIDELITY CHECK

100% · A

ORIGINAL PAPER

PMC10064713

A retrospective study on application of a classification criterion based on relative intervertebral tension in spinal fusion surgery for lumbar degenerative diseases

BMC Surgery

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ABSTRACT

Abstract Background As an important part of spinal fusion procedure, the selection of fusion cage size is closely related to the curative effect of the surgery. It mainly depends on the clinical experience of surgeons, and there is still a lack of objective standards. The purpose of this study is to propose the concept of relative intervertebral tension (RIT) for the first time and its grading standards to improve the surgical procedures of lumbar interbody fusion. Methods This retrospective study was conducted from January 2018 to July 2019. A total of 83 eligible patients including 45 men and 38 women with lumbar degenerative disease underwent transforaminal lumbar interbody fusion (TLIF) were included in this study. A total of 151 fusion segments were divided into group A, group B and group C according to the grading standards of RIT. In addition, parameters of intervertebral space angle (ISA), intervertebral space height (ISH), intervertebral space foramen (IFH), fusion rates, cage-related complications and cage heights were also compared among the three groups. Results The ISA in group A was the smallest among three groups in contrast with group C with largest ISA at the final follow-up( P < 0.05). The group A presented the smallest ISH and IFH values( P < 0.05), compared with group B with the largest ISH and IFH values( P < 0.05). These two parameters in the group C were in-between. The fusion rates of group A, group B and group C were 100%, 96.3% and 98.8% at the final follow-up, respectively. No statistical difference in fusion rates and cage-related complications occurred among the three groups( P > 0.05), and a certain correlation between ISH and RIT was also observed. Conclusions The concept of RIT and the application of its clinical grading standards could simplify the surgical procedures of spinal fusion and reduce cage-related complications. Keywords: Lumbar interbody fusion, Relative intervertebral tension, Fusion rate, Cage migration, Cage subsidence

CITATION EXPORT

Yang Hou, Hongyang Shi, Tianyi Zhao et al.. A retrospective study on application of a classification criterion based on relative intervertebral tension in spinal fusion surgery for lumbar degenerative diseases. BMC Surgery. (2023). https://doi.org/10.1186/s12893-023-01968-x

AUTHORS

6 · 1 CENTRES

Yang Hou, Hongyang Shi, Tianyi Zhao, Haoyang Shi, Jiangang Shi, Guodong Shi

1Department of Orthopaedic Surgery, Changzheng Hospital, Second Military Medical University, No. 415 Fengyang Rd, Shanghai, 200003 China