Cage subsidence in lateral interbody fusion with transpsoas approach: intraoperative endplate injury or late-onset settling

Introduction: Few studies have investigated the influence of cage subsidence patterns (intraoperative endplate injury or late-onset cage settling) on bony fusion and clinical outcomes in lateral interbody fusion (LIF). This retrospective study was performed to compare the fusion rate and clinical outcomes of cage subsidence patterns in LIF at one year after surgery.Methods: Participants included 93 patients (aged 69.0±0.8 years; 184 segments) who underwent LIF with bilateral pedicle screw fixation. All segments were evaluated by computed tomography and classified into three groups: Segment E (intraoperative endplate injury, identified immediately postoperatively); Segment S (late-onset settling, identified at 3 months or later); or Segment N (no subsidence). We compared patient characteristics, surgical parameters and fusion status at 1 year for the three subsidence groups. Patients were classified into four groups: Group E (at least one Segment E), Group S (at least one Segment S), Group ES (both Segments E and S), or Group N (Segment N alone). Visual analog scales (VASs) and the Japanese Orthopedic Association Back Pain Evaluation Questionnaire (JOABPEQ) were compared for the four patient groups.Results: 184 segments were classified: 31 as Segment E (16.8%), 21 as Segment S (11.4%), and 132 as Segment N (71.7%). Segment E demonstrated significantly lower bone mineral density (-1.7 SD of T-score, p=0.003). Segment S demonstrated a significantly higher rate of polyetheretherketone (PEEK) cages (100%, p=0.03) and a significantly lower fusion rate (23.8%, p=0.01). There were no significant differences in VAS or in any of the JOABPEQ domains among the four patient groups.Conclusions: Intraoperative endplate injury was significantly related to bone quality, and late-onset settling was related to PEEK cages. Late-onset settling demonstrated a worse fusion rate. However, there were no significant differences in clinical outcomes among the subsidence patterns.