Injury - 2026-04-01 - Journal Article
Effect of humerus rotation on the initial stability of locking plate fixation for proximal humerus fracture: A biomechanics study.
Chuang MY, Hsu LI, Wu CY, Huang CH, Wei SH
Topics
Key Takeaway
Locking plate constructs for proximal humerus fractures undergo permanent deformation beyond 3.2° of humerus rotation, with energy dissipation increasing approximately fourfold at that threshold.
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Summary
This study investigated the effect of torsional loading on locking plate fixation stability in proximal humerus fracture models using repetitive dynamic mechanical testing with digital image correlation (DIC) strain mapping. Six cadaveric or synthetic fracture models were subjected to cyclic torsional loads, with resistance to torque, maximum torque, and energy dissipation recorded. Construct stability was significantly compromised beyond 3.2° of rotation, with a fourfold increase in non-elastic energy dissipation and DIC-confirmed strain concentration at proximal shaft screw holes and the plate waist.
Key Limitation
The extremely small sample size (n=6) and use of fracture models without specification of bone mineral density or fracture pattern variability severely limits the clinical applicability of the 3.2° threshold.
Original Abstract
BACKGROUND
Limb rotations of the upper arms frequently happen during daily activities, and these actions can produce significant torsional forces which aggravate patients' conditions. However, there is limited research concerning the impact of humerus rotation on the initial stability of locking plate fixation after proximal humerus fracture reconstruction. The current study conducted a biomechanics analysis to investigate this important issue.
METHODS
Dynamic mechanical tests with repetitive torsional loads were executed in six fracture-model specimens. The mechanical behaviors of resistance to torque, maximum torque, and energy dissipation were recorded. A new surveillance system of digital image correlation (DIC) technology was used to observe the continuous strains of the fixation system in real time.
RESULTS
Mean resistance to torque was significantly reduced when the rotation exceeded 3.2°. Beyond 3.2° of rotation, the mean energy dissipation increased by approximately fourfold. DIC observations showed large strains concentrated around the screw holes at the proximal shaft and waist of the plate.
CONCLUSIONS
Under our experimental conditions, we observed a marked rise in non-elastic energy dissipation beyond 3.2° of rotation, which indicated the onset of permanent construct deformation in vitro. Surgeons should remind patients that daily upper extremity torques may affect the initial rotational stability of fixation system after surgery.