Biomechnical stability of proximal humeral fracture fixated by a locking plate plus different fibular allografts

Abstract

Objective To investigate the ability of locking plate construct plus fibular autograft that varies in way of augmentation to withstand varus stresses in a model of proximal humeral fracture. Methods Wedge osteotomy was conducted in the humeral surgical necks of 12 shoulders from 6 cadaveric specimens to create models of proximal humeral fracture. There were 3 males and 3 females; their average age at death was 83 years (from 75 to 87 years). The 12 left and right cadaveric humeri were randomly divided into equal groups A and B (n=6) for autogenous iliac bone graft. All the fibular autografts were harvested without distinction from the thinnest and even part of the fibular shaft. A fibular autograft of 8 cm was placed vertically in group A while a fibular autograft of 6 cm was placed slantly in group B. After the fractures were fixated with the proximal humerus internal fixation locking system (PHILOS), varus stress was repeatedly applied to the proximal humerus until the internal fixation failed in the fracture model. The 2 groups were compared in terms of number of compression, number of compression leading to 1 mm deformation, and average shape variable after each press. Results Cut-out of the lateral cortex of the humeral head by the humeral screw and plate loosening to different extents were observed in both groups. The number of compression leading to internal fixation failure was 31,338±5,994 for group A and 30,608±8,015 for group B; the number of compression leading to 1 mm deformation was 2,808±1,501 for group A and 3,153±2,024 for group B; the average shape variable after each press was 0.52±0.39 μm/time for group A and 0.53±0.47 μm/time for group B. All the above comparisons between the 2 groups showed no significant differences (P>0.05). Conclusion As locking plate construct plus slant fibular autograft augmentation provides no more strength to withstand repetitive varus stresses than locking plate construct plus vertical fibular autograft augmentation, it is not necessary to adopt the former way of augmentation in clinic practice for proximal humeral fracture. Key words: Shoulder joint; Bone plates; Transplantation, heterotopic; Biomechanics; Proximal humeral fracture