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Updated: Aug 5, 2026
Three-dimensional Navigation-guided, Prone, Single-position, Lateral Lumbar Interbody Fusion Technique
Published on: July 15, 2021
"The protective buffer": Adequate L4-S1 lordosis restoration reduces the symptomatic conversion of radiographic ASD
Chen Wang1, Zhifeng Dong2, Jing Jia1
1Gansu Provincial Hospital, The 1st Clinical Medicine College, Gansu University of Chinese Medicine, Lanzhou, 730000, Gansu Province, China.
Background:
Inadequate restoration of L4-S1 segmental lordosis (SL) is a recognized contributor to adjacent segment disease (ASD). However, evidence regarding its impact on long-term revision rates remains conflicting, primarily due to short follow-up periods that fail to capture the critical transition from radiographic degeneration to symptomatic disease.
Purpose:
To evaluate the 5-year impact of L4-S1 SL restoration on revision rates and to introduce the concept of "Symptomatic Conversion Rate" to quantify the clinical progression of ASD.
Study Design:
A multicenter, retrospective cohort study.
Patient Sample:
A total of 232 patients who underwent L4-S1 transforaminal lumbar interbody fusion (TLIF) with a minimum 5-year follow-up were included. The cohort was stratified into Adequate and Inadequate Restoration groups based on postoperative L4-S1 SL.
Outcome Measures:
The primary endpoint was the 5-year revision surgery rate. Secondary endpoints included radiographic parameters (pelvic tilt [PT], pelvic incidence-lumbar lordosis [PI-LL] mismatch), implant failure rates, and patient-reported outcome measures (Oswestry Disability Index [ODI], Visual Analog Scale [VAS]). The "Symptomatic Conversion Rate" (the percentage of patients with radiographic ASD progressing to symptomatic ASD) was also assessed.
Methods:
Clinical and radiographic data collected at a minimum of 5 years postoperatively were retrospectively analyzed. The cohorts were compared to assess the influence of L4-S1 SL restoration on long-term survivorship, functional recovery, and ASD progression.
Results:
Baseline demographics and PI were comparable between groups (P > 0.05). At the 5-year follow-up, the Inadequate Group exhibited significant pelvic retroversion (PT increased to 21.82° vs. 17.26° in the Adequate Group, P < 0.001). Although radiographic ASD was prevalent in both cohorts (58.1% vs. 38.1%), the Symptomatic Conversion Rate was markedly higher in the Inadequate Group (73.3% vs. 28.1%, P < 0.001). Consequently, the 5-year revision rate was significantly greater in the Inadequate Group (26.4% vs. 2.4%, P < 0.001). The Inadequate Group also demonstrated inferior ODI scores (28.5 vs. 14.2, P < 0.001) and an increased incidence of screw loosening.
Conclusions:
Inadequate L4-S1 SL restoration is an independent risk factor for long-term revision surgery and implant failure following TLIF. Precise restoration provides a crucial "biomechanical buffer," preventing compensatory pelvic retroversion and significantly reducing the conversion of radiographic ASD into symptomatic disease. Achieving this protective buffer should be a primary surgical objective to maximize long-term construct survivorship.
