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

Abstract

Background

There have been no previous reports of reliable surface landmarks for determining the optimal incision site for anterior lumbar spine access without fluoroscopy. We aimed 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.

Methods

Prospective agreement study of consecutive patients without transitional anatomy undergoing anterior exposure for either interbody fusion or total disc replacement surgery at L4/5. The primary outcome measure was the distance from the symphysis pubis to the skin markings for the L4/5 level, as determined by the intercrest line method or fluoroscopic method. The anterior intercrest line was determined by placing a silk tie between the bilateral iliac crests palpated in the mid-axillary line. The skin was marked in the anterior midline along this line. The surface projection of the L4/5 disc was determined using lateral fluoroscopy and marked in the anterior midline. The distance between the upper palpable margin of the symphysis pubis and each L4/5 skin mark was measured. The marking modality difference (MMD) was the difference in distance between the 2 methods.

Results

Of 81 patients (49 males, 32 females) the MMD was 0.36 ± 1.19 cm. The intraclass correlation coefficient between distances determined by the 2 methods was 0.84, demonstrating high agreement between the techniques. Single predictor and multiple linear regression analyses revealed no significant associations between MMD and age, sex, BMI, or operative position.

Conclusion

There was high agreement between the anterior intercrest line method and fluoroscopy for determining the surface projection of the L4/5 disc. The anterior intercrest 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.