1. Patterns of Failure in the Distal Radius Following Treatment for AO 23-A3.2 Fractures Using Two-Column Volar Plates
Deana Mercer, MD; Christina Salas, PhD; Justin Brantley, BS; Evan Baldwin, MD

2. Disclosure
None

3. Purpose
To investigate damage during cyclic testing in a model of extra-articular distal radius fracture with dorsal comminution treated using two-column volar plating.

4. Background
The distal radius is the most common fracture site in the upper extremity.
Dorsally displaced, unstable fractures are commonly treated with locked plate fixation using a volar approach.
Hypothesis: Damage analysis of matched, paired specimens with simulated fracture treated with volar plating may provide information on whether implant geometry or screw trajectory may affect fracture stability

5. Methods Ten matched pairs of fresh-frozen, cadaveric distal radii
DEXA scans were obtained on all specimens
Osteotomy simulating an AO type 23-A3.2 fracture was created
Group I : Geminus® (Skeletal Dynamics) – dual head design for independent two-tier scaffolding
Mean age at time of death = 39yrs
Group II : Acu-Loc® 2 Proximal VDR (Acumed) – single head design for enhanced ulnar buttressing
Group I
Group II

6. Methods Mechanical testing Cyclic axial loadingP A
Mechanical testing
Cyclic axial loading
Sinusoidally compressed N; rate of 1Hz for 5,000 cycles
Bone/implant damage was calculated from reduced Modulus of Elasticity, E= PL/Ad
Damage = 1-[E_final/E_initial]; E_initial calculated at cyclic 5; E_final calculated at every 500th cycle
Damage is defined as the period between a state of material perfection and the onset of crack initiation. Indirectly quantified by monitoring reduction in stiffness under applied loading.

7. Methods Mechanical testing Statistical Analysis
Constructs not failed during cyclic loading were subject to a ramped load to failure at 1 mm/s.
Statistical Analysis
Paired t-test used to compare stiffness and ultimate load at failure (p≤0.05)
Regression analysis used to identify relationships between bone density and ultimate load

8. Results: Cyclic Testing
Group II specimens experienced significantly more damage under cyclic loading. (p=0.02)
Group I: (+/-0.10)
Group II: (+/-0.11)

9. Results: Ramped Load to Failure
Stiffness
Group I: (+/-160.3) N/mm
Group II: (+/-150.3) N/mm
p=0.02
Ultimate load
Group I: 1280 (+/-292) N
Group II: 854 (+/-611) N
p=0.04
No correlation between total areal bone density and ultimate load for Group I or Group II (R2=0.10 and R2 = 0.32, respectively)

10. Results: Modes of Failure
Complete distal fragment collapse leading to plate bending
Group I: 5 of 10
Group II: 2 of 10
Fracture of the lunate fossa
Group I: 5 of 10
Group II: 8 of 10

11. Conclusion
Damage may offer indication of implant’s ability to support physiologic loading during the early post-operative period
Mechanical test results show Group II specimens experienced greater damage accumulation during cyclic testing and lower stiffness/ultimate load when loaded to failure
Patient-specific finite element models will be used to investigate stress/strain in constructs to determine how differences in implant geometry and screw trajectory correlate with findings

12. Thank you.