Purpose: Simple generalized thresholds for assessing functional impairment in clinical testing are limited, as they fail to consider patient-specific properties such as age, body height, and body mass index. A previously developed machine learning-based model for personalized testing using the five-repetition sit-to-stand (5R-STS) test, that estimates personalized upper limits of normal (ULN) to identify objective functional impairment (OFI) was externally validated to evaluate its performance and generalizability across cohorts. Methods: Only healthy individuals were included in the study. After the machine learning-based model was applied to this external dataset, expected and observed 5R-STS test times were compared using standardized performance assessment metrics including root mean square error (RMSE), mean absolute error (MAE), and R ² values. Additionally, a Bland–Altman analysis was performed to assess agreement between observed and expected values. Validation of the expected ULN involved comparing the proportion of individuals exceeding their personalized thresholds with the corresponding proportion based on the generalized threshold. Subgroup analyses by test setting and country of residence were additionally performed, along with a graphical assessment of model performance. Results: Application of the model to 171 healthy individuals resulted in an RMSE of 2.33 (95% CI: 1.93 to 2.73) seconds, MAE of 1.70 (95% CI: 1.47 to 1.94) seconds, and R ² of 0.064 (95% CI: -0.25 to 0.15). The Bland–Altman analysis demonstrated a mean bias of -1.1 s. Based on the personalized ULNs, OFI was classified in 17.5% of individuals, compared to 6.4% when using the generalized threshold of 10.4 s. These analyses indicated limited external generalization, with acceptable approximation for some faster and mid-range test times but systematic underestimation of slower test times. Multivariable regression analyses showed that remote testing was independently associated with greater prediction bias and higher odds of personalized ULN exceedance compared with supervised testing (adjusted mean difference: − 0.90 s; adjusted OR: 10.7). Exploratory country-of-residence analyses showed differences across the three largest national subgroups. 130 (76.1%) rated ease of use as excellent, and 145 (84.9%) rated clarity of instructions as excellent. 143 participants (83.6%) indicated that they prefer the 5R-STS over a battery of questionnaires. Conclusions: In the context of personalized testing, moving toward individually focused precision assessment of patients requires rigorous external validation to ensure the robustness of such applied computational methods. In this external validation, the model demonstrated limited generalization including a systematic underestimation of slower test times and insufficient personalized ULN calibration. These findings indicate that external validity of models derived from single-center data can be limited, underscoring the importance of comprehensive external validation and, potentially, multicenter retraining before clinical implementation.

Instability of the craniocervical junction is a potentially life-threatening condition requiring surgical stabilization. Traditional occipital plate fixation carries risks of construct loosening and intracranial complications due to variable skull thickness, particularly after posterior fossa decompression where plate fixation is challenging. Occipital condyle screws (OCS) provide direct fixation into the occipital condyles (OCs). However, comprehensive outcome data remains sparse. This systematic review and meta-analysis evaluated anatomical parameters, technical aspects, and surgical outcomes of OCS fixation in craniocervical stabilization. Following PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) guidelines, PubMed/MEDLINE, Embase, and Scopus were searched for studies reporting techniques and outcomes of occipitocervical fixation using OCS. Two reviewers independently extracted data, and study quality was assessed using the Newcastle-Ottawa Scale, when possible. Random-effects meta-analysis was performed. The primary endpoint was to characterize the technical aspects of craniocervical fixation using OCS and to ascertain its overall feasibility, defined by morphometric suitability, technical success rates, and complication rates. Thirty studies met inclusion: 12 cadaveric (618 specimens), 10 imaging (1,604 participants), and 8 surgical (284 patients). Morphometry consistently showed larger OC in male populations. Bicortical screw placement achieved 100% technical success. Standard 3.5-mm screws (18–24 mm) were commonly used. Recommended trajectories varied (sagittal with 18°–28° angulation; axial with 22°–37° angulation). No major symptomatic vascular or permanent neurological complications occurred. Meta-analytic data revealed significant differences in morphometric measurements of the OC and differences in the OCS length and angulation parameters. OCS fixation appears to be an anatomically feasible and technically promising fixation strategy in selected patients when anatomy and technique are carefully evaluated. Population-specific morphometric variability mandates individualized preoperative assessment. Future comparative studies should define long-term outcomes, fusion rates, and optimize region-specific surgical parameters.

Simulation-based training is a key component of modern neurosurgical education, providing a repeatable environment for procedural practice. External ventricular drain (EVD) placement is a common emergency procedure performed in the early stages of neurosurgical training. This study presents the design, fabrication, and evaluation of a modular phantom targeting a specific brain subregion, intended to replicate the mechanical and procedural aspects of EVD insertion with improved material efficiency and reusability compared to existing full-brain approaches. A human cranium model was generated from medical imaging data and 3D-printed in two configurations. Both housed a replaceable polyvinyl alcohol (PVA) hydrogel brain sample containing a ventricular cavity. Mechanical tests compared three hydrogel variants for stability and haptic fidelity during controlled catheter advancement. A user study with seven experienced neurosurgeons provided a preliminary qualitative assessment of realism, ergonomics, and simulation fidelity through questionnaires and semi-structured interviews. Modified hydrogel designs with enlarged or reinforced ventricles demonstrated greater mechanical stability and higher insertion resistance (∼0.6 N) compared to the standard configuration (∼0.4 N), with force-displacement profiles suggesting more consistent haptic feedback during ventricular entry. Surgeons rated cranial realism highly (visual M = 4.43, tactile M = 4.00), though brain visual realism scored lower (M = 2.71), likely reflecting the absence of meninges and cortical surface detail. The proposed phantom represents an early-stage platform for EVD simulation, offering reproducibility, low cost, and modularity supporting repeated use and anatomical customization. Further validation with larger and more diverse cohorts is needed to substantiate its educational value.