Intramedullary cortical bone strut improves the cyclic stability of osteoporotic proximal humeral fractures.
BACKGROUND
Proximal humeral fractures treated with locking plate can fail due to varus collapse, especially in osteoporotic bone with medial cortex comminution. The use of an intramedullary strut together with locking plate fixation may strengthen fixation and provide additional medial support to prevent the varus malalignment. This study biomechanically investigates the influence of an intramedullary cortical bone strut on the cyclic stability of proximal humeral fractures stabilized by locking plate fixation in a cadaver model.


METHODS
Ten cadaveric humeri were divided into two groups statistically matched for bone density. Each specimen was osteotomized with 10 mm gap at the surgical neck. The non-augmented group stabilized with locking plate alone; in the augmented group, a locking plate was used combined with an intramedullary cortical bone strut. The strut was retrograded into the subchondral bone, and three humeral head screws were inserted into the strut to form a plate-screw-strut mechanism. The cyclic axial load was performed to 450 N for 6000 cycles and then loaded to failure. Construct stiffness, cyclic loading behavior and failure strength were analyzed to identify differences between groups.


RESULTS
The augmented constructs were significantly stiffer than the non-augmented constructs during cycling. On average, the maximum displacements at 6000 cycles for non-augmented and augmented groups were 3.10 ± 0.75 mm and 1.7 ± 0.65 mm (p = 0.01), respectively. The mean peak-to-peak (inter cycle) displacement at 6000 cycles was about 2 times lower for the augmented group (1.36 ± 0.68 mm vs. 2.86 ± 0.51 mm). All specimens showed varus collapse combined with loss of screw fixation of the humeral head. The failure load of the augmented group was increased by 2.0 (SD = 0.41) times compared with the non-augmented group (p < 0.001).


CONCLUSIONS
The stability and strength of the locking plate augmented with an intramedullary strut were significantly increased. For bone with poor quality, the subsidence of the locked screws led larger displacement, decreased the stability of the constructs, however, the plate-screw-strut mechanism provided more rigidity to stabilize the fixation. This study emphasized the importance of intramedullary support for the proximal humeral fractures fixed with a locked plate under cyclic loading, especially in bone with poor quality. This work is based on the results of cadaver model, further in vivo analysis is necessary to determine if the clinical results can be extrapolated from this data.
['Hsiao|Chih-Kun|CK|', 'Tsai|Yi-Jung|YJ|', 'Yen|Cheng-Yo|CY|', 'Lee|Cheng-Hung|CH|', 'Yang|Teng-Yao|TY|', 'Tu|Yuan-Kun|YK|']
D000368:Aged D000369:Aged, 80 and over D001696:Biomechanical Phenomena D015519:Bone Density D001860:Bone Plates D001863:Bone Screws D002102:Cadaver D000071538:Cortical Bone D005260:Female D005594:Fracture Fixation, Intramedullary D018460:Fractures, Comminuted D006801:Humans D058430:Humeral Head D008297:Male D058866:Osteoporotic Fractures D012784:Shoulder Fractures D014057:Tomography, X-Ray Computed D016474:Weight-Bearing
Humeral fractures Locking plate Intramedullary strut Stiffness Cyclic loading Osteoporosis