The remnant axial cortical length of the proximal femur in pertrochanteric fractures: a three-dimensional computed tomography study and its clinical implications

Abstract

Background: Cortical buttress are important factors for postoperative stable reconstruction of per/inter-trochanteric fractures. The study aimed to measure the remnant axial cortical length (RACL) of the proximal circumference of the femur, and to determine which part of the RACL can be used reliably to postoperatively sustain the head-neck fragment as a cortical support pattern.

Methods: Eighty patients with trochanteric hip fractures admitted from January 2015 to January 2016 were included in a retrospective study. Their pre-operative computed tomography (CT) images were used to form 3D-CT reconstructions via Mimics software. After simulated rotation and movement for fracture reduction, the RACL, its three component parts-namely, the remnant anterior cortex (RAC), remnant lateral cortex (RLC), and remnant posterior cortex (RPC) -the γ angle between the anterior and posterior cortex, and the Hsu's lateral wall thickness (LWT) were evaluated.

Results: Patients with an A1 fracture (21/80) had a longer RACL (88.8 ± 15.8 mm) than those with an A2 fracture (60.0 ± 11.9 mm; P < 0.01). The RAC, RLC, and RPC of the RACL in A1 fractures were also significantly longer than those in A2 fractures (P < 0.001). However, the most significant difference among the three components of the RACL was in the RPC, which was 27.3 ± 7.8 mm in A1 fractures and 9.2 ± 6.6 mm in A2 fractures. In addition, the coefficient of variation of the RAC was only 20.0%, while that of the RPC was 75.5%. The average γ angle in A1 fractures was 16.2 ± 13.1°, which was significantly smaller than that in A2 fractures, which was 40.3 ± 14.5° (P < 0.001). There was a significant statistical difference in the LWT between A1 and A2 fractures (P < 0.001). There were significant differences in the RACL, RAC, RLC, RPC, γ angle, and LWT among the five subtypes (P < 0.001).

Conclusions: The RAC is relatively stable in pertrochanteric fractures. Fracture reduction through a RAC buttress may help to enhance the postoperative stable reconstruction of per/inter-trochanteric fractures and make possible good mechanical support for fracture healing.

Keywords: Circumferential proximal cortex; Fracture reduction; Pertrochanteric fracture; Remnant anterior cortex.

Fig. 1

Illustration of 3D model of a pertrochanteric fracture after reconstruction. Each segment was reduced to normal anatomical positions; A anterior, B lateral, and C posterior views. d1: RAC, d0: RLC, and d2: RPC. Red: femoral head and neck, blue: femoral shaft, and green: posterior fragment. RAC: remnant anterior cortex, RLC: remnant lateral cortex, RPC: remnant posterior cortex

Fig. 2

Illustration showing coronal (A) and axial (B) CT images of a patient with AO/OTA 31 A2 fracture. The central axis of the femoral head and neck was set as the x-axis, the central axis of the femoral shaft was set as the y-axis, the z-axis was perpendicular to the x-axis and y-axis, and the common plane of the x-axis and y-axis was set as the coronal plane. The axial CT plane was angled 130° upward to the femoral head and neck. The RACL of the proximal femur was measured as the length of the remnant lateral cortex on the central axis of the head and neck (blue line). Line 1 (L1) was a line tangential to the lateral wall of the proximal femoral fracture. Point (a) was the intersection of the x-axis and the lateral edge of the cortex, point (b) was a remnant anterior cortical extremity, and point (c) was a remnant posterior cortical extremity. Line 2 (L2) was a straight line passing through points (b) and (c). The γ angle was the angle between L1 and L2. The RACL was further divided into the RAC (d1), the RLC (d0), and the RPC (d2). Red: femoral head and neck, blue: femoral shaft, and green: posterior fragment. AO/OTA, AO Foundation and Orthopaedic Trauma Association, RAC: remnant anterior cortex, RACL: remnant axial cortical length, RLC: remnant lateral cortex, RPC: remnant posterior cortex

Fig. 3

Representative CT images showing the RAC (d1), RLC (d0) and RPC (d2) of the RACL in patients with an A1 fracture (A) and in patients with an A2 fracture (B). The RAC, RPC, and RPC (red line) in A1 fractures were significantly longer than those in A2 fractures. Patients with A2 fractures involved the posterior wall fragment. RAC: remnant anterior cortex, RACL: remnant axial cortical length, RLC: remnant lateral cortex, RPC: remnant posterior cortex

Fig. 4

Correlation analyses between the RAC/RPC and the γ angle in trochanteric fractures. Linear regression analyses showed that there was no correlation between the RAC and the γ angle (A), and that there was a linear negative correlation between the γ angle and the RPC (B). RAC: remnant anterior cortex, RPC: remnant posterior cortex