The anterior offset of the standard entry point for tibial intramedullary nails: A transparent 3D-CT image based analysis.

Background: This study examines the relationship between the anterior offset of the tibial intramedullary nail (TIN) entry point and the tibial shaft axis to enhance the fit and alignment of TINs, using transparent 3D-CT in an accurate lateral view to minimize rotational artifacts.

Methods: Data were collected from 100 adult patients undergoing tibial CT scans. Measurements included the anterior offset from the tibial axis to the entry point, tibial tubercle offset, tibial plateau length, posterior slope, tibial length, isthmus diameter, and the isthmus-to-tibial length ratio.

Results: Key findings reveal a median anterior offset of 9.8 mm from the tibial axis to the entry point, with 7 % of cases having an offset of less than 5 mm-potentially insufficient for standard TINs. The tibial tubercle offset was 16.7 mm, and the distance between the entry point and tubercle was 24.5 mm. The median tibial plateau length was 44.8 mm, and the posterior slope was 7.7°. The tibial length measured 330.4 mm, with a median isthmus diameter of 10.4 mm and an isthmus-to-tibial length ratio of 39.7 %. Correlations were found between entry point offset and tibial plateau length, tubercle offset, and age. The entry point was positioned 1.2 mm (median) anteroposteriorly and 6.5 mm mediolaterally from the anterior edge of the tibia.

Conclusion: The median anterior offset from the tibial axis to the starting point was approximately 10 mm, with 7 % of cases having an offset of less than 5 mm, which is too small for most TINs available. Surgeons should be cautious about cases with a small anterior offset to minimize risks during intramedullary nail insertion.