Analysis of mechanical variables in Hoffa fracture - A comparison of four methods by finite elements

Abstract

Background: Correct management of Hoffa fractures is a challenge in the clinical context. Open reduction along with internal fixation should be the therapy of choice. Mechanical trials with the main internal fixation systems conducted by individualized finite element (FEM) models, to date, have been neglected. The aim of this study was to biomechanically analyze four fixation methods for the treatment of Type II Hoffa fracture (OTA Classification: 33B3.2∗ lateral) using FEM.

Methods: Four internal fixators were developed to treat Type II Hoffa fracture using finite elements: 4.5 mm cortical screws and 7 mm cannulated screw in anterior-to-posterior and posterior-to-anterior directions (4.5AP, 4.5 PA, 7AP and 7 PA). Under the same conditions, fractural deviation in the vertical, maximum and minimum principal and Von Mises directions in the syntheses used were evaluated.

Results: The vertical displacements evaluated were 0.7 mm, 0.5 mm, 0.8 mm and 0.3 mm; the values of maximum were 6.14 Mpa, 6.15 hPa, 6.0 Mpa and 6.2 Mpa, the values obtained from minimum data were 6.26 Mpa, -6.45 Mpa, -7.3 MPa and -6.8 Mpa and the maximum values of Von Mises peak stress were 185.0 Mpa, 194.1 Mpa, 143.6 Mpa and 741.4 Mpa, for the fixation models 4.5AP, 4.5 PA, 7AP and 7 PA, respectively.

Conclusion: The 7 mm-cannulated screw fixation system yielded the best mechanical results evaluated by FEM in the treatment of Type II Hoffa fracture, causing a decrease in vertical displacement when used in retrograde and in Von Mises peak stress in anterograde.

Keywords: Biomechanics; Finite element analysis; Hoffa fracture; Internal fixation; Screw.

Fig. 1

(A) Construction of Type II Hoffa fracture Model (OTA Classification: 33B3.2∗ lateral), (B) 4.5 mm cortical screw and (C) 7 mm cannulated screw.

Fig. 2

Vertical dislocations of the fracture with the different fixation models. (A) 4.5 mm anterior-to-posterior cortical screw (4.5 AP), (B) 4.5 mm posterior-to-anterior cortical screw (4.5 PA), (C) 7 mm anterior-to-posterior cannulated screw (7AP) and (D) 7 mm posterior-to-anterior cannulated screw (7 PA). The results were 0.7 mm, 0.5 mm, 0.8 mm and 0.3 mm, respectively.

Fig. 3

Peak Von Misses of the different fixation models. (A) 4.5 mm anterior-to-posterior cortical screw (4.5 AP), (B) 4.5 mm posterior-to-anterior cortical screw (4.5 PA), (C) 7 mm anterior-to-posterior cannulated screw (7AP) and (D) 7 mm posterior-to-anterior cannulated screw (7 PA). The results were 185.0Mpa, 194.1Mpa, 143.6 MPa e 741.4Mpa, respectively.

Fig. 4

Qualitative analysis of the relationship between the synthesis material and the bone structure. (A) intimate/grasped relationship between the 7 mm screw and the bone structure. (B) need for a smooth tunnel in the interfragmentary compression technique with the 4.5 mm cortical screw does not allow the same degree of relationship, observed in the 7 mm screw, between the synthesis and the bone structure.