Intramedullary Nail Fixation with Posterior-to-Anterior Compared to Transverse Distal Screw Placement for Tibiotalocalcaneal Arthrodesis: A Biomechanical Investigation

Abstract

Background:

Biomechanical studies on retrograde intramedullary fixation for tibiotalocalcaneal fusion have been reported, but no studies have investigated dorsiflexion stiffness, load-to-failure, fatigue endurance, and plastic deformation using different distal screw orientations. Also, no studies have examined the effect of bone density on different distal screw orientations while using a fatigue loading mode.

Methods:

Eight matched pairs of cadaver legs were used. In one leg from each pair an intramedullary nail was inserted with lateral-to-medial distal screws and in the other with posterior-to-anterior screws. These samples underwent dorsiflexion fatigue testing with determination of initial and final stiffness, load-to-failure, and degree of plastic deformation at failure. DEXA scanning was done of each cadaver specimen to determine bone mineral density. Statistical analysis was performed using the Student t-test and a Pearson correlation. Significance level was set at p < 0.05.

Results:

The specimens with posterior-to-anterior screws had a significantly higher fatigue endurance load-to-failure (1130.0 ± 362.0 N compared to 801.0 ± 227 N, p = 0.01). They also had significantly higher final stiffness (203.1 ± 23.1 N/mm compared to 146.6 ± 46.2 N/mm, p = 0.05) and lower plastic deformation (2.4 ± 1.5 mm compared to 3.8 ± 2.3 mm, p = 0.04). There was a statistically significant correlation between bone mineral density and the difference in construct deformation with posterior-to-anterior and lateral-to-medial screw orientation (r = 0.76, p = 0.03).

Conclusions:

In this biomechanical investigation of tibiotalocalcaneal arthrodesis with intramedullary nail fixation, posterior-to-anterior distal screw orientation provided more stable fixation than lateral-to-medial screw orientation.