92. The anterior intercrest line is a novel accurate surface marking for identifying the L4/5 disc level: a prospective agreement study with fluoroscopy

BACKGROUND CONTEXT

Anterior exposure for lumbar surgery is increasingly used in contemporary spine practice. There have been no previous reports of reliable surface landmarks for determining the optimal incision site for anterior access without fluoroscopy

PURPOSE

To assess the accuracy of the anterior intercrest line for predicting the surface projection of the L4/5 disc level, compared with the fluoroscopically determined level.

STUDY DESIGN/SETTING

A prospective agreement study of consecutive patients undergoing anterior lumbar exposure for either interbody fusion or total disc replacement surgery at L4/5

PATIENT SAMPLE

The study included all patients undergoing primary anterior lumbar disc surgery at our institution from November 2022 to January 2024. Indications for surgery were severe degenerative disc disease, radiculopathy, or Grades 1–2 degenerative or isthmic spondylolisthesis. Exclusion criteria for surgery were disc disease involving ≥ 3 levels, Grades 3–4 spondylolisthesis, significant iliac artery or aortic pathology, morbid obesity (body mass index [BMI] > 35 kg/m2), previous complex/extensive retroperitoneal surgery, or abdominal/pelvic radiotherapy. Exclusion criterion for this study was transitional lumbosacral anatomy. Outcome measures: The primary outcome measure was the distance from the symphysis pubis to the skin markings for the L4/5 level, as determined by the intercrestal line method or fluoroscopic method.

OUTCOME MEASURES

Agreement of anterior inter-crest line for predicting the surface projection of the L4/5 disc level

METHODS

The anterior inter-crest line was denoted by placing a silk tie anteriorly between the bilateral iliac crests palpated in the midaxillary line. The skin was then marked in the abdominal midline along this line. Next, the surface projection of the L4/5 disc was determined using lateral fluoroscopy and marked on the skin in the anterior midline. The distance between the upper palpable margin of the symphysis pubis and each L4/5 skin mark was measured, and the marking modality difference (MMD) was calculated as the difference in distances between the two methods.

RESULTS

A total of 83 patients were assessed for inclusion; two patients were excluded because of transitional anatomy. The mean patient age was 48±13 years (range, 19 to 77 years), and 60% were male (n=49). The MMD between the fluoroscopically determined L4/5 level and the inter-crest line was 0.36±1.19 cm [95% confidence interval (CI), 0.10 to 0.62; range, −2.5 to 5 cm]. The intraclass correlation coefficient between distances determined by the two methods was 0.84 [95% CI, 0.76 to 0.89], demonstrating high agreement between the techniques. Multiple linear regression analyses revealed no significant associations between MMD and age, sex, BMI, or operative position.

CONCLUSIONS

There was high agreement between the anterior inter-crest line method and fluoroscopy for determining the surface projection of the L4/5 disc. The anterior inter-crest line is a simple, clinically accurate, and reliable tool for planning the location of the skin incision for anterior exposure of the L4/5 disc level. Using this line would reduce radiation exposure, overall operative times, and costs.

FDA Device/Drug Status

This abstract does not discuss or include any applicable devices or drugs.