The findings of this systematic review are constrained by the same methodological limitations that characterize the underlying literature. All included studies were retro- spective, with inherent sele

The gap

Consensus across the literature

Supporting evidence — 3 representative gaps

• Management of pediatric brain arteriovenous malformation: a systematic review of retrospective studies (2026) · doi

  The findings of this systematic review are constrained by the same methodological limitations that characterize the underlying literature. All included studies were retro- spective, with inherent selection bias and confounding by indication. Outcome definitions—particularly oblitera- tion—were inconsistent (DSA-confirmed cure vs. MRI- based assessments), and follow-up ascertainment varied across cohorts, limiting comparability and precluding robust pooled estimates. Notably, no minimum follow-up duration was pre-specified for inclusion because the crite- rion required only that at least one post-management out- come be reported. This permissive threshold introduces substantial heterogeneity in follow-up duration (ranging from 3 months to a median of 19.1 years across cohorts) and limits the comparability of recurrence and oblitera- tion estimates across studies. Angioarchitectural report- ing beyond SM grade was incomplete and nonuniform, with nidus size reported as diameter or volume using het- erogeneous thresholds. Finally, reporting of functional outcomes and complications was variably structured and often not standardized across modalities. These limita- tions substantiate the rationale for a descriptive synthesis and reinforce that inference should remain modality- and cohort-contextual rather than comparative. 1 3Neurosurgical Review (2026) 49:424  424 Page 14 of 15

  Keywords: across follow review oblitera tion cohorts comparability estimates duration reported systematic constrained methodological limitations characterize
• Transradial versus transfemoral access for diagnostic cerebral angiography: a systematic review and meta-analysis of randomized and prospective studies with grade assessment (2026) · doi

  A major methodological innovation of the present meta‑ analysis is the deliberate restriction of eligible studies to randomized controlled trials and prospective observa‑ tional cohorts, with systematic exclusion of retrospective datasets commonly included in prior pooled analyses. This choice of study design is justified on multiple bases. Retrospective studies are inherently susceptible to selec‑ tion bias as operators performing TRA might select anatomically favourable patients with favourable vessel conditions, hence underestimating complications. More‑ over, retrospective studies are unable to control for tem‑ poral trends in operator experience, institution‑specific protocols, and the concomitant evolution of equipment, all of which confound outcome attribution. Furthermore, the inclusion of studies from multiple international cen‑ ters improves the external validity and generalizability of the pooled findings across diverse neurointerventional settings. Prospective studies ensure comparable baselines, specified outcome definitions, and standardized follow‑ up, thereby reducing the selection bias. The inclusion of RCTs and prospective observational studies allowed subgroup analysis to evaluate the source of heterogene‑ ity, which would have been obscured in a single‑design meta‑analysis. Lastly, the use of a random‑effects model throughout, validated sensitivity analyses, GRADE‑based certainty assessment, and Newcastle‑Ottawa Scale evalu‑ ation of cohort quality further strengthened confidence in the robustness of the pooled estimates. This design choice differentiates the present analysis from prior pooled studies and strengthens confidence in the comparative estimates. However, this study had multiple limitations. First, the total number of events recorded for outcomes such as neurological complications and access‑site complications was relatively low, reducing the statistical power and wid‑ ening the confidence intervals. Second, high heterogene‑ ity was observed for time to ambulation (I2 = 99%) and access‑site complications (I2 = 81%), reflecting variations in operator experience, learning curve phases, and insti‑ tutional protocols. Lastly, patient‑reported outcomes, including satisfaction, pain scores, and quality of life, were not uniformly reported and could not be analyzed despite their clinical importance. Publication bias could Khan et al. Egyptian Journal of Neurosurgery (2026) 41:99 not be formally assessed because only a few studies were available per outcome.

  Keywords: pooled complications prospective retrospective design multiple bias outcome confidence present meta prior analyses choice favourable
• Ceramic-on-ceramic versus polyethylene-based bearings in total hip arthroplasty: a meta-analysis (2026) · doi

  This meta-analysis has several limitations that warrant con- sideration. First, although the overall pooled sample across studies was substantial, individual comparisons varied widely in sample size, with some analyses driven by small single-center cohorts and others by large registry datasets. Second, the included studies encompassed a mix of ran- domized trials and observational designs, the latter carrying inherent risks of selection bias, residual confounding, and uncontrolled variability in patient factors and surgical tech- nique. Third, heterogeneity existed in implant designs, fem- oral head sizes, liner geometries, and bearing generations, all of which may influence wear behavior, noise phenom- ena, and complication rates, thereby limiting direct com- parability. In particular, differences in study populations, registry-based data, baseline infection risk, and periopera- tive factors may have influenced the observed PJI difference in the CoC versus MoHXLPE comparison. Additionally, follow-up durations differed between studies, from short- to long-term assessments, making temporal alignment of out- comes challenging. Reporting of key variables, including preoperative functional scores, BMI, and radiographic end- points, was not reported in all studies, reducing the ability to perform deeper subgroup or sensitivity analyses. Finally, outcome definitions such as noise phenomena, osteolysis, 1 3European Journal of Orthopaedic Surgery & Traumatology (2026) 36:239  239 Page 16 of 18 and instability were not standardized across studies, which may contribute to measurement variability. Additionally, the included studies did not consistently report whether noise led to dissatisfaction, activity limitation, or revision, limiting pooled assessment of the clinical consequences of squeaking. Moreover, because several pooled estimates incorporated observational or registry-derived data, the results should be interpreted as comparative associations rather than definitive causal effects of bearing material. These limitations underscore the need for future large-scale, prospective randomized studies with standardized protocols, harmonized outcome definitions, and consistent reporting of implant designs to more accurately delineate the compara- tive performance of THA bearing surfaces.

  Keywords: pooled registry designs bearing noise several limitations sample across analyses large included observational variability factors