gms | German Medical Science

Objectives: Helical plates used for proximal humeral shaft fracture fixation avoid the radial nerve distally as compared to straight plates. Several clnical reports exist in the literature, however, there is no consensus regarding their optimal design as there are reports ranging from 45° to 90° helical plate designs. The aim of the study was to investigate in a human cadaveric model the biomechanical competence of straight lateral plates versus 45°-helical plates used for fixation of proximal comminuted humeral shaft fractures.

Methods: Eight pairs of humeral cadaveric humeri underwent CT scaning for BMD evaluation and were instrumented using either a long straight PHILOS plate (Group1) or a 45°-helical plate (Group2) for treatment of an unstable proximal humeral shaft fracture simulated by means of a 3cm osteotomy gap. All specimens were tested under quasi-static loading in axial compression, internal and external rotation, and bending in 4 directions. Subse-quently, progressively increasing cyclic loading in internal rotation until failure was applied and interfragmentary movements were monitored by motion tracking.

Results and conclusion: Trabecular volumetric BMD was 131.7 ± 32.1 mgHA/cm³ in Group 1, and 120.9 ± 28.6 mgHA/cm³ in Group 2, with no significant differences between the groups (p>=0.333).

During non-destructive testing axial displacement (mm) in Group 1 was 3.13±0.31 and 2.60±0.42 in Group2, p=0.02. Flexion/extension deformation (°) in Group1 and 2 was 0.56±0.42 and 0.43±0.23, p=0.55. Varus/valgus deformation (°) was 6.39±0.44 in Group1 and 5.13±0.87 in Group2, p=0.02. Shear (mm) and torsional (°) displacement under torsional load were 5.36±0.76 and 17.75±1.06 in Group1, and 5.36±0.76 and 5.03±0.46 in Group2, p>=0.09. During cyclic testing shear and torsional displacements showed no significant differences between the groups, p>=0.12 and p>=0.24. Cycles to catastrophic failure were 10,000±1,401 in Group1 and 9,082±1,933 in Group2, p=0.71.

From a biomechanical perspective, 45°-helical plating is associated with lower axial and varus/valgus displacement during axial loading and demonstrated comparable resistance to failure as well as torsional and shear displacement during cyclic testing in internal torsion. Therefore, 45°-helical plates can be considered as valid alternative to straight plates in the treatment of proximal humeral shaft fractures.