INTRODUCTION
Unilateral biportal endoscopy (UBE) has developed from a minimally invasive decompression technique into a broader spinal surgical platform. It is now applied in lumbar degenerative disease, fusion surgery, thoracic pathology, intradural lesions, tumor-related procedures, and revision or salvage settings. This expansion is supported by several technical advantages of the biportal approach, including separation of the viewing and working portals, flexible triangulation, continuous irrigation-assisted visualization, and the use of conventional spinal instruments through a minimally invasive corridor [1-3].
As UBE indications have widened, technical innovation requires more structured evaluation. Procedural feasibility alone does not establish clinical value. The safety and relevance of a new technique may depend on corridor design, preservation of stabilizing structures, irrigation and pressure control, neural protection, dural management, pleural safety, and procedure-specific anatomical constraints [2-6]. These considerations are particularly important when UBE is extended beyond standard lumbar decompression into thoracic, intradural, tumor-related, fusion, or salvage procedures, where the margin for technical error may be narrower.
The Journal of Minimally Invasive Spine Surgery and Technique (JMISST) published a concentrated group of UBE-focused Technical Notes in 2025, Volume 10. These articles described lumbar fusion construct modification [7], ergonomic corridor redesign [8], anatomical standardization [9], extended contralateral decompression [10], hybrid endoscopic workflow design [11], thoracic discectomy [12], thoracic interbody cage insertion [13], lumbar intradural lesion management [14], multiregional lesion or tumor excision [15], and endoscopic salvage of cement leakage after instrumentation [16]. This single journal-year corpus provides a focused opportunity to examine how contemporary UBE innovation is described, categorized, and translated into surgeon-oriented technical guidance.
Technical Notes often represent an early stage of procedural development before comparative studies, multicenter validation, or long-term outcome data become available. Their value depends not only on procedural novelty, but also on how clearly they report operative rationale, anatomical indications, technical steps, safety considerations, imaging confirmation, outcomes, complications, and practical relevance. However, UBE Technical Notes have rarely been examined using a structured article-level framework.
Accordingly, this study aimed to perform a structured content analysis of UBE-focused Technical Notes published in JMISST during 2025, Volume 10. We characterized the included articles according to anatomical domain, procedural tier, technical focus, reporting characteristics, safety emphasis, and practical surgical relevance.
MATERIALS AND METHODS
1. Study Design
This study was a structured content analysis of UBE-focused Technical Notes published in JMISST during 2025, Volume 10. The analysis focused on anatomical domain, procedural complexity, technical strategy, safety-related content, reporting characteristics, and practical surgical relevance.
2. Source Identification and Eligibility
All regular and supplementary issues of JMISST Volume 10 were screened through the official journal archive. Screening was performed independently by 2 reviewers. Titles, journal-assigned article types, and abstracts were assessed first, followed by full-text review of potentially eligible articles. Disagreements were resolved by consensus.
Articles were included if they were published in JMISST during 2025, formally classified as Technical Notes, involved UBE in a human spinal procedure or anatomy-based technical application, and provided sufficient technical detail for structured extraction.
Articles were excluded if they were not Technical Notes, did not involve UBE, represented noneligible publication types, or lacked adequate technical description. Eligibility was determined by journal-assigned article type rather than title wording alone.
3. Data Extraction
A predefined extraction matrix was developed before full-text review. Extracted variables included article design, anatomical region, indication, principal technical focus, portal configuration, scope angle, localization method, operative strategy, stability- or construct-related considerations, irrigation and outflow strategy, hemostasis, visualization maintenance, neural, dural, pleural, or pressure-related precautions, complication reporting, postoperative imaging, follow-up or outcome reporting, supplementary video availability, practical surgical relevance, key operative pearl, dominant risk mechanism, and preventive technical consideration.
4. Procedural Classification
Each Technical Note was assigned to 1 of 3 predefined procedural tiers according to anatomical constraint, technical objective, and operative complexity.
Tier 1, lumbar refinement and fusion innovation, included ergonomic corridor modification, anatomical standardization, extended or multilevel decompression, hybrid endoscopic workflows, and lumbar fusion construct innovation.
Tier 2, thoracic expansion, included thoracic discectomy, thoracic interbody cage insertion, and related reconstructive applications.
Tier 3, advanced-complexity applications, included intradural procedures, tumor or lesion excision, and revision or salvage procedures related to prior instrumentation or technically constrained pathology.
When more than one category was possible, classification was based on the principal technical focus of the article.
5. Article-Level Reporting Score
An article-level reporting score was used to compare reporting completeness across the corpus. This score was a descriptive measure of technical transparency, not a validated risk-of-bias or methodological-quality tool. The 5 domains were selected because they reflect key elements needed for surgeon-oriented interpretation of technical innovation.
One point was assigned for each of the following items: postoperative imaging confirmation, follow-up or outcome reporting, explicit complication reporting, substantive safety discussion, and supplementary video availability. Each article received a score from 0 to 5, with higher scores indicating more complete reporting of clinically relevant and safety-related technical information.
The procedural-tier classification and article-level reporting score are summarized in Figure 1.
6. Analytical Approach
The article was the unit of analysis. Variables were summarized descriptively using counts and proportions. Reporting scores were summarized overall and by procedural tier.
Because this study analyzed a complete journal-year corpus of Technical Notes rather than patient-level clinical datasets, meta-analysis was not performed. Descriptive analysis was combined with interpretive synthesis to identify recurrent patterns in lumbar workflow refinement, fusion and reconstruction-related innovation, and physiologic or safety control in thoracic and advanced-complexity UBE applications.
RESULTS
1. Study Corpus and Publication Distribution
Screening of all regular and supplementary issues of JMISST Volume 10 identified 10 UBE-focused articles that met the eligibility criteria (Figure 2). All included articles were formally classified by the journal as Technical Notes, although title wording varied and included terms such as “technical report,” “case report,” or “review” [7-16]. The included articles were published in Volume 10, Supplement 1 (n=5), Volume 10, Supplement 2 (n=4), and Volume 10, No. 2 (n=1).
2. Anatomical Domains and Procedural Tiers
The included Technical Notes were heterogeneous in anatomical scope and content design. Most were single-case or small-case Technical Notes. The corpus also included one retrospective technical series of 31 patients [15] and one anatomy-oriented technical note based on more than 1,000 operated lumbar levels [9].
Using the predefined classification, 5 articles (50.0%) were assigned to Tier 1, representing lumbar refinement and fusion innovation; 2 articles (20.0%) to Tier 2, representing thoracic expansion; and 3 articles (30.0%) to Tier 3, representing advanced-complexity applications. Thus, although lumbar-focused innovation was the largest category, half of the corpus addressed thoracic, intradural, lesion/tumor, or revision/salvage applications.
Tier 1 included lumbar fusion construct modification [7], ergonomic corridor redesign [8], anatomical standardization [9], extended contralateral 2-level decompression [10], and hybrid endoscopic workflow design [11]. Tier 2 included upper thoracic discectomy [12] and thoracic interbody cage insertion for proximal junctional failure [13]. Tier 3 included lumbar intradural lesion excision [14], multiregional lesion/tumor excision [15], and endoscopic salvage of cement leakage after cement-augmented pedicle screw fixation [16] (Table 1).
3. Reporting Characteristics
Postoperative imaging confirmation was reported in 8 of 10 Technical Notes (80.0%), using magnetic resonance imaging, computed tomography, plain radiography, or combined imaging according to procedural objective. Imaging confirmation was not reported in the ergonomic right-sided lumbar note [8] or the anatomy-focused technical note [9].
Follow-up or outcome reporting was present in 9 of 10 articles (90.0%), although reporting depth and duration varied. Longer follow-up was reported in the thoracic discectomy note, with 27- and 17-month outcomes without recurrence or reherniation [12], and in the hybrid workflow note, with sustained improvement at 6 months and 1 year [11]. The anatomy-oriented technical note was the only article without patient-level follow-up [9].
Explicit complication reporting was identified in 7 of 10 articles (70.0%), whereas substantive safety discussion was present in all articles (100%). Supplementary video availability was documented in 4 of 10 articles (40.0%) (Table 2). The median article-level reporting score was 4 (range, 1–5). The highest median score was observed in Tier 2 thoracic expansion articles (median, 5), followed by Tier 1 lumbar refinement/fusion innovation and Tier 3 advanced-complexity applications, both with median scores of 4 (Table 2).
4. Safety and Complication-Reporting Patterns
Safety-related content was consistently present across all procedural tiers, but the format and depth of complication reporting varied (Tables 2 and 3). Some articles explicitly reported the presence or absence of complications, whereas others embedded safety considerations within operative technique, preventive strategy, or technical pearls.
In Tier 2 thoracic applications, safety emphasis centered on spinal cord vulnerability, pleural awareness, fluoroscopic localization, and irrigation-pressure control. The T1–2 discectomy note reported no major or minor perioperative complications and emphasized cord-level risk, continuous saline outflow, and the steep learning curve of thoracic UBE [12]. The thoracic cage insertion note reported no specific complications at 6 months and discussed costovertebral corridor anatomy, pleural protection, pressure control, and maintenance of outflow [13].
In Tier 3 advanced-complexity applications, safety discussion was particularly prominent. The lumbar intradural lesion note addressed hydrostatic pressure control, nerve-root behavior as an intraoperative indicator of pressure balance, dural closure, and cerebrospinal fluid leakage prevention [14]. The multiregional lesion/tumor series provided a structured complication-avoidance framework addressing cerebrospinal fluid leakage, postoperative hematoma, spinal hypertension, irrigation-pressure management, and criteria for conversion or termination during intradural work [15]. The cement-leakage salvage note emphasized diagnostic uncertainty, full-root exploration, careful cement removal, and avoidance of iatrogenic isthmic injury [16].
In Tier 1 lumbar refinement and fusion innovation, safety reporting was mainly preventive and technique-oriented. Reported themes included portal planning, dural-tear prevention, preservation of pars and facet boundaries, low radiofrequency settings near neural structures, controlled adhesiolysis, conversion readiness, and careful cage insertion in constrained or poor bone-quality settings [7-11].
5. Practical Technical Themes
Three practical technical themes emerged from the structured analysis. First, lumbar refinement articles emphasized stability-conscious decompression and access design. These included preservation-oriented portal planning, avoidance of unnecessary facet or pars violation, contralateral sublaminar access, and workflow modifications intended to improve anatomical control [8-10]. Practical technical insights and stability-related implications of the lumbar UBE Technical Notes are summarized in Table 4.
Second, fusion and reconstruction articles emphasized construct-oriented innovation. The dual hybrid cage note described combined polyetheretherketone (PEEK) and expandable cage placement to increase fusion surface area, restore disc height, and improve segmental alignment within the UBE platform [7]. The thoracic cage insertion note extended reconstructive UBE principles to a thoracic revision setting using a costovertebral corridor and hybrid endoscopic-open strategy [13].
Third, thoracic and advanced-complexity applications emphasized physiologic and environmental control in constrained operative fields. Relevant strategies included pressure-aware irrigation, pleural protection, dural closure, full-root exploration, conversion readiness, and staged technical adoption rather than direct extrapolation from standard lumbar decompression [12-16].
DISCUSSION
This structured content analysis of UBE-focused Technical Notes published in JMISST during 2025 identified 3 principal findings. First, contemporary UBE innovation extended beyond conventional lumbar decompression into lumbar refinement and fusion innovation, thoracic expansion, and advanced-complexity applications. Second, the included Technical Notes consistently provided surgeon-oriented technical guidance and safety discussion. Third, reporting maturity varied across articles, particularly regarding complication reporting, follow-up depth, and supplementary operative visualization [7-16]. These findings suggest that current UBE development is defined not only by expansion of indications, but also by increasing attention to corridor design, preservation of stabilizing structures, construct planning, and physiologic control in constrained operative fields.
The lumbar UBE subgroup was heterogeneous and included fusion construct modification, ergonomic portal redesign, anatomical standardization, extended contralateral decompression, and hybrid endoscopic workflow design [7-11]. This pattern suggests that lumbar UBE innovation is increasingly focused on refinement of surgical execution rather than simple expansion of procedural indications. This distinction is clinically important because the benefits of UBE depend not only on the minimally invasive access route, but also on technical precision, anatomical orientation, surgeon experience, and complication-prevention strategy [1-3,17,18].
A prominent theme in the lumbar subgroup was stability-conscious decompression and access planning. The extended contralateral approach emphasized preservation of the pars interarticularis while permitting decompression of the same nerve root across 2 levels through a single corridor [10]. The anatomy-focused Technical Note translated endoscopic lumbar anatomy into practical landmarks that may reduce orientation error and unnecessary facet or pars violation [9]. Similarly, the right-sided ergonomic approach proposed a more direct ipsilateral working strategy for selected right-sided pathology [8]. Together, these reports indicate that lumbar UBE refinement is moving toward preservation-oriented surgery, in which decompression is balanced against protection of posterior stabilizing structures. These practical and stability-related implications are summarized in Table 4.
Fusion-related construct innovation represented another important direction of development. The dual hybrid cage Technical Note proposed combining a contralateral PEEK cage with an ipsilateral expandable cage to increase the functional interbody support surface, restore disc height, and improve segmental alignment within the UBE platform [7]. This approach reflects a shift from corridor feasibility toward construct engineering under endoscopic conditions. Existing literature on UBE-transforaminal lumbar interbody fusion suggests that endoscopic fusion may provide favorable perioperative characteristics in selected patients; however, long-term mechanical durability, subsidence resistance, fusion reliability, and comparative superiority remain incompletely established [4,19-21]. Therefore, the dual hybrid cage strategy should be viewed as a technically meaningful innovation that requires further biomechanical and prospective clinical validation.
The thoracic Technical Notes formed a distinct procedural tier and highlighted the importance of anatomical constraint and physiologic tolerance in cord-level endoscopic surgery [12,13]. In the T1–2 discectomy note, the main challenges included level localization under restricted fluoroscopic conditions, continuous outflow maintenance, and cautious instrument handling within a narrow thoracic corridor [12]. In the T10–11 cage insertion note, thoracic reconstruction required costovertebral corridor access, selective osseous resection, pleural awareness, and controlled irrigation during hybrid endoscopic-open revision surgery [13]. These reports show that thoracic UBE should not be interpreted as a direct extension of lumbar decompression. Instead, thoracic applications introduce a different risk environment, where spinal cord vulnerability, pleural proximity, fluoroscopic limitations, and restricted corridor geometry become central technical constraints. This emphasis on outflow maintenance and pressure-aware irrigation is supported by recent work on real-time water-pressure monitoring in UBE, which highlights the safety importance of controlled water dynamics, particularly at cervical and thoracic levels [22].
Advanced-complexity applications, including intradural surgery, multiregional lesion/tumor excision, and cement-leakage salvage, further emphasized the transition from access innovation to risk-management innovation [14-16]. The lumbar intradural lesion note described gravity irrigation, pressure-aware workflow, intraoperative nerve-root behavior as a pressure indicator, clip-assisted dural closure, and postoperative confirmation of facet preservation [14]. The multiregional lesion/tumor series provided a broader complication-avoidance framework addressing cerebrospinal fluid leakage, postoperative hematoma, spinal hypertension, irrigation-pressure management, and criteria for conversion or termination during intradural work [15]. The cement-leakage salvage note illustrated the role of UBE as a diagnostic and therapeutic revision platform, allowing full-root exploration and targeted cement removal while attempting to preserve stabilizing structures [16]. These safety-relevant mechanisms are summarized in Table 3.
A key contribution of this study is the article-level assessment of reporting completeness. Postoperative imaging confirmation was reported in 80.0% of Technical Notes, follow-up or outcome reporting in 90.0%, explicit complication reporting in 70.0%, substantive safety discussion in 100%, and supplementary video availability in 40.0% [7-16]. The median article-level reporting score was 4, with the highest median score observed in thoracic expansion notes. These results indicate that the 2025 JMISST UBE Technical Note corpus was not only procedurally diverse, but also heterogeneous in reporting maturity. Some articles provided structured follow-up and complication reporting, whereas others offered rich technical guidance with less standardized clinical documentation.
This observation directly addresses the relationship between technical innovation and safety reporting. The present analysis suggests that UBE innovation may advance faster than standardized reporting of complications, follow-up, and operative visualization. This does not reduce the value of Technical Notes. Rather, it clarifies their role within the literature. Technical Notes often communicate transferable operative knowledge before comparative trials, prospective registries, or long-term outcome studies become available. Their impact therefore depends on the clarity with which they describe indication, operative rationale, technical steps, safety mechanisms, postoperative verification, and complications. This interpretation is consistent with the SUPER (Surgical techniqUe rePorting chEcklist and standaRds) reporting guideline, which emphasizes detailed, transparent, and reproducible reporting of surgical techniques [23]. The value of the present analysis lies in applying a structured article-level framework to examine procedural innovation, safety reporting, and transferable technical guidance across the corpus.
The findings also have practical implications for training and clinical adoption. Prior literature has shown that the benefits of UBE are influenced by surgeon experience and that complications such as dural tear, incomplete decompression, neural injury, and epidural hematoma may be more frequent during the early learning phase [1,3,17,24-26]. This issue becomes especially important when interpreting thoracic, intradural, tumor-related, and salvage procedures. Feasibility in expert hands does not automatically establish general reproducibility. Several advanced Technical Notes in this corpus explicitly emphasized pressure control, conversion readiness, cautious case selection, or staged experience before attempting technically demanding procedures [12-15]. Therefore, procedural expansion should be accompanied by structured training, careful patient selection, standardized complication reporting, and prospective validation.
This study has limitations. First, it was restricted to a single journal and a single publication year, and therefore may not represent the full global UBE technical literature. Second, although all included articles were formally classified as Technical Notes, they varied in design, including single-case reports, small-case Technical Notes, a retrospective technical series, and an anatomy-oriented experiential synthesis [9,15]. Third, eligibility was based on the journal-assigned article type. Therefore, UBE-related technical content published under other categories, such as Case Reports, Video Articles, Original Articles, or Reviews, was not included, and some technical innovations may have been excluded if they appeared outside the formal Technical Note category. Fourth, the unit of analysis was the article rather than the patient, so pooled clinical outcomes or comparative effect estimates could not be generated. Fifth, some stability-related and practical interpretations were derived from operative descriptions and technical rationale rather than independent biomechanical testing or long-term comparative follow-up. Finally, the article-level reporting score was a descriptive measure of reporting completeness, not a validated risk-of-bias or methodological-quality tool.
Despite these limitations, the study provides a structured framework for understanding how UBE innovation is being developed and communicated within a focused journal-year corpus. By organizing the 2025 JMISST Technical Notes according to anatomical domain, procedural tier, safety emphasis, and reporting completeness, this analysis identifies both areas of technical progress and areas requiring stronger reporting standardization. Future studies should extend this approach across multiple journals and years, incorporate prospective registries stratified by procedural complexity, and evaluate whether emerging fusion, thoracic, intradural, and salvage applications achieve durable clinical and biomechanical validation. Such work will be necessary to translate technical feasibility into reproducible and broadly generalizable clinical practice.
CONCLUSION
This structured content analysis of UBE-focused Technical Notes published in JMISST during 2025 showed that UBE innovation extended beyond conventional lumbar decompression into lumbar refinement and fusion innovation, thoracic expansion, and advanced-complexity applications.
Across the corpus, technical development was characterized by increasing attention to preservation-oriented decompression, construct-related planning, and physiologic safety in constrained operative environments. However, follow-up, complication reporting, and supplementary operative visualization remained variable. These findings support the value of structured reporting and further clinical validation as UBE continues to expand into fusion, thoracic, intradural, lesion/tumor, and revision or salvage applications.
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