Standardized artificially created stable pertrochanteric femur fractures present more homogenous results compared to osteotomies for orthopaedic implant testing

Abstract

Background: With regard to biomechanical testing of orthopaedic implants, there is no consensus on whether artificial creation of standardized bone fractures or their simulation by means of osteotomies result in more realistic outcomes. Therefore, the aim of this study was to artificially create and analyze in an appropriate setting the biomechanical behavior of standardized stable pertrochanteric fractures versus their simulation via osteotomizing.

Methods: Eight pairs of fresh-frozen human cadaveric femora aged 72.7 ± 14.9 years (range 48-89 years) were assigned in paired fashion to two study groups. In Group 1, stable pertrochanteric fractures AO/OTA 31-A1 were artificially created via constant force application on the anterior cortex of the femur through a blunt guillotine blade. The same fracture type was simulated in Group 2 by means of osteotomies. All femora were implanted with a dynamic hip screw and biomechanically tested in 20° adduction under progressively increasing physiologic cyclic axial loading at 2 Hz, starting at 500 N and increasing at a rate of 0.1 N/cycle. Femoral head fragment movements with respect to the shaft were monitored by means of optical motion tracking.

Results: Cycles/failure load at 15° varus deformation, 10 mm leg shortening and 15° femoral head rotation around neck axis were 11324 ± 848/1632.4 ± 584.8 N, 11052 ± 1573/1605.2 ± 657.3 N and 11849 ± 1120/1684.9 ± 612.0 N in Group 1, and 10971 ± 2019/1597.1 ± 701.9 N, 10681 ± 1868/1568.1 ± 686.8 N and 10017 ± 4081/1501.7 ± 908.1 N in Group 2, respectively, with no significant differences between the two groups, p ≥ 0.233.

Conclusion: From a biomechanical perspective, by resulting in more consistent outcomes under dynamic loading, standardized artificial stable pertrochanteric femur fracture creation may be more suitable for orthopaedic implant testing compared to osteotomizing the bone.

Keywords: Fracture biomechanics; Fracture line analysis; Fracture model; Fracture standardization; Osteotomy; Proximal femur fracture; Stable pertrochanteric fracture.

Fig. 1

Setup with a specimen mounted for creation of a stable pertrochanteric fracture by means of a blunt guillotine blade, with vertical arrow indicating the force direction

Fig. 2

Visualization of the created patterns of a pertrochanteric fracture AO/OTA 31-A1 in Group 1

Fig. 3

Test setup with a specimen mounted for biomechanical testing, with vertical arrow indicating the loading direction

Fig. 4

Exemplified images of a fractured (left) and an osteotomized (right) specimen; on the left, fracture angle of 41° degree is displayed as indicated with a goniometer; on the right, osteotomy saw guide placed in an angle of 41° is presented

Fig. 5

a-c Visualization of the mean shape model and both its mean fracture line (thick red) with SD (thin red) and mean osteotomy line (thick blue) with SDs (thin blue) in a anteroposterior, b lateral, and c posteroanterior view

Fig. 6

a-c Visualization of the mean shape model and the fracture lines of all eight fractured specimens (black) together with their mean (thick red) and SD (thin red) lines in a anteroposterior, b lateral, and c posteroanterior view

Fig. 7

Diagram presenting cycles to failure and failure load in the two study groups with fractured and osteotomized specimens according to the clinically relevant criteria 15° varus deformation, 10 mm leg shortening and 15° femoral head rotation around the neck axis

Fig. 8

Exemplified x-rays of specimens from Group 1 (fractured: a, b) and Group 2 (osteotomized: c, d) – both fixed with DHS – at initial (a, c) and final (b, d) stage of testing, with indicated corresponding number of cycles at test begin and cycles to 10 mm leg shortening