Conus medullaris termination: Assessing safety of spinal anesthesia in the <scp>L2</scp>–<scp>L3</scp> interspace
Bibliographic record
Abstract
BACKGROUND: Classic teaching is that spinal anesthesia is safe at or below the L2-L3 interspace. To evaluate this, we sought to determine the percentage of individuals with a conus medullaris termination (CMT) level at or below the L1-L2 interspace. Further, the relationship of CMT level to age, sex, body mass index (BMI), and spinal pathology was examined, as was the reliability of using Tuffier's line (TL) as an anatomical landmark. METHODS: This retrospective study evaluated magnetic resonance images of 944 adult patients to determine the CMT level. The relationship between age, sex, height, BMI, and spinal pathology and CMT level was explored by logistic regression. The correspondence of the TL line to the L4-L5 interspace and the presence of overlap with the CMT were examined using 720 lumbar x-rays of the same patient cohort. RESULTS: Of 944 patients (mean age, 57.8 years; 49% male), 18.9% had CMT at or below the L1-L2 interspace, and spinal anesthesia at the L2-L3 interspace was found to carry a 0.7% incidence of neuraxial risk. Only the presence of congenital spinal abnormalities was found to be significantly predictive of having a CMT at or below the L1-L2 interspace. TL was found to correspond to the L4-L5 interspace in 99.8% of patients with lumbar x-rays. CONCLUSIONS: Spinal anesthesia at the L2-L3 interspace, using TL as an anatomical landmark, is safe in >99% of patients. However, caution must be exercised in all patients as demographic variables were found to be limited in predicting a low CMT level. EDITORIAL COMMENT: Unlike previous smaller studies, this retrospective study included MRI data from a total of 944 patients. The present study confirms that spinal anesthesia at the L2-L3 interspace or below can be considered safe. The findings indicate that Tuffier's line can be used as a reliable anatomical landmark.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.004 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".