Controlling the angle between the distal locking screw and tibiotalar joint tangent helps to reduce the occurrence of misalignment of distal tibial fractures treated with intramedullary nail fixation
Authors: He Miao , Liu Jian , Deng Xu , He Miao 
Published: July 2022

Abstract
Background
Studies have shown that on the coronal plane, whether the direction of the distal locking screw is parallel to the tangent line of the tibiotalar joint can be used to determine whether there is varus or valgus deformity after the treatment of distal tibial fractures with intramedullary nail (IMN) fixation. However, there has been no statistical analysis of the included angle on the coronal plane, and there have been no reports on whether there is a relationship between the direction of the distal locking screw on the sagittal plane or the included angle of the tangent line of the tibiotalar joint and the postoperative alignment of distal tibial fractures treated with IMN fixation.

Objective
Our aim was to evaluate the relationship between the angles formed by the distal locking screw and the tibiotalar joint tangent (ADTTs) on the sagittal and coronal planes and postoperative alignment in the treatment of distal tibial fractures with IMN fixation.

Methods
We performed a retrospective analysis of 100 patients with distal tibial fractures treated with IMN fixation using the suprapatellar approach. On the coronal and sagittal planes, the ADTTs were arranged from small to large and divided into 4 groups, namely, groups A, B, C and D. One-way ANOVA was used to compare the lateral distal tibial angle (LDTA) and anterior distal tibial angle (ADTA) among all groups, and the chi-square test was used to compare the incidence of postoperative tibial misalignment among all groups. Univariate analysis was performed using chi-square tests to identify factors that might be associated with dislocation, including fibular open reduction and internal fixation (ORIF), limited open reduction, ADTT, IMN diameter, injury mechanism, open vs. closed fracture, comminution, and fibular fracture level. Then, the statistically significant variables in the univariate analysis were included in a multivariate logistic regression equation to evaluate the independent factors related to misalignment.

Results
On the coronal plane, the ADTTs of groups A, B, C and D were < 0°, 0°-1.3°, 1.3°-2.7° and > 2.7°, respectively. The mean LDTAs of groups B and C (0°-1.3° and 1.3°-2.7°), group A (< 0°) and group D (> 2.7°) were 89.5 ± 1.6°, 92.0 ± 3.2° and 85.8 ± 3.5°, respectively (P < 0.01). Deformity greater than 5° were more likely in groups A and D than groups B and C [14 of 50 (28%) vs. 1 of 50 (2%), P < 0.001]. On the sagittal plane, the ADTTs of groups A, B, C and D were < 8.9°, 8.9°-10.4°, 10.4°-11.7° and > 11.8°, respectively. The average ADTAs of groups B and C (8.9°-10.4° and 10.4°-11.7°), group A (< 8.9°) and group D (> 11.8°) were 80.4 ± 1.3°, 83.1 ± 3.7° and 77.9 ± 2.5°, respectively (P < 0.01). Deformity greater than 5° was more likely in groups A and D than groups B and C [13 of 50 (26%) vs. 0 of 50 (0%), P < 0.001]. An ADTT of 0°-2.7° on the coronal plane and 8.9°-11.7° on the sagittal plane (OR: 0.08, P = 0.02) and limited open reduction (OR: 0.21, P < 0.01) were independent factors that reduced the likelihood of misalignment.

Conclusion
The alignment of distal tibial fractures after surgery is sensitive to the ADTT and use of limited open reduction. Controlling the ADTT between 0° and 2.7° on the coronal plane and between 8.9° and 11.7° on the sagittal plane is helpful to reduce the occurrence of misalignment after the treatment of distal tibial fractures by IMN fixation.