Objectives Coronoid fractures account for 2 to 15% of the cases with elbow dislocations and
usually occur as part of complex injuries. Comminuted fractures and non-unions necessitate
coronoid fixation, reconstruction or replacement. The aim of this biomechanical study
was to compare the stability of coronoid replacement using an individualized 3D printed
prosthesis with a curved cemented intramedullary stem to both radial head grafted
reconstruction and coronoid fixation with 2 screws. It was hypothesized that the prosthetic
replacement will provide superior stability over the grafted reconstruction and screw
fixation.
Methods Following CT scanning, 18 human cadaveric proximal ulnas were osteotomized at 40%
of the coronoid height and randomized to 3 groups (n = 6). The specimens in Group
1 were treated with a 3D printed stainless steel coronoid prosthesis with curved cemented
intramedullary stem, individually designed based on the contralateral coronoid scan.
The ulnas in Group 2 were reconstructed with an ipsilateral radial head autograft
fixed with two anteroposterior screws, whereas the osteotomized coronoids in Group
3 were fixed in situ with two anteroposterior screws [Fig. 1 ].
Fig. 1. Specimens in the 3 study groups prepared for biomechanical testing by means of prosthetic
treatment (Group 1, left), radial head autograft reconstruction (Group 2, middle),
and coronoid screw fixation (Group 3, right).
All specimens were biomechanically tested under ramped quasi-static axial loading
to failure at a rate of 10 mm/min. Construct stiffness and failure load were calculated.
Statistical analysis was performed using One-Way ANOVA with Bonferroni Post Hoc tests
at a level of significance 0.05.
Results and Conclusion Prosthetic treatment (Group 1) resulted in significantly higher stiffness (1166.8
± 316.6 N/mm) and failure load (1044.2 ± 301.9 N) compared to radial head autograft
reconstruction (Group 2: 440.8 ± 99.1 N/mm; 441.5 ± 125.6 N; p ≤ 0.002) and coronoid
screw fixation (Group 3: 267.9 ± 147.9 N/mm; 304.4 ± 171.1 N; p < 0.001), respectively.
Stiffness and failure load did not reveal any significant differences between Group
2 and Group 3 (p ≥ 0.846). In cases of coronoid deficiency, replacement of the coronoid
process using a patient specific 3D printed prosthesis with a curved cemented intramedullary
stem seems to be an effective method to restore the buttress function of the coronoid
under axial loading, providing superior stability over both radial head graft reconstruction
and coronoid screw fixation, while achieving anatomical articular congruity. The stability
provided by this prosthesis type with curved cemented intramedullary stem could allow
for early patient mobilization. The implant may prove to be beneficial for patients
with irreparable comminuted coronoid fractures, radial angulation or non-unions.
Stichwörter Elbow, Coronoid Process, 3D Printed Individualized Prosthesis, Intramedullary Stem,
Biomechanical Testing
