Influence of peri-implant bone quality on implant stability.
BACKGROUND
Insufficient primary stability is still reported for proximal humerus fractures in elderly patients. Fixation stability could be improved by aiming locking screws at bone volumes with better properties. The aims of this study were to investigate the bone regions engaged by the locking screws of a Proximal Humeral Nail (MultiLoc PHN), and to evaluate the influence of peri-screw bone quality on bone-nail construct stability.


METHODS
Twelve cadaveric humeri were divided into two groups. The distal locking part of the PHN was fixed to the specimens. The nails were removed and the bones scanned using HR-pQCT. Bone properties were evaluated at the locations where the proximal locking screws would have been positioned after complete instrumentation. A three-part fracture model was used for mechanical testing of the instrumented bones, considering axial displacement and varus deformation as parameters of interest.


RESULTS
The secondary locking screws targeted bone volumes in the posteromedial part of the humerus with statistically significant higher quality, thus reducing varus deformation. Significant correlation was found between axial displacement and bone properties at the primary proximal screws. Significant correlation was found between the varus deformation and apparent BMD at the secondary locking screws.


CONCLUSIONS
The findings of this study confirmed that directing the proximal locking screws at bone regions with better properties can improve fixation stability.
AO Research Institute Davos, Clavadelerstrasse 8, 7270 Davos Platz, Switzerland. damiano.schiuma@aofoundation.org
Damiano
D
Schiuma
Michael
M
Plecko
Martin
M
Kloub
Stephan
S
Rothstock
Markus
M
Windolf
Boyko
B
Gueorguiev
D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density; D001863:Bone Screws; D005260:Female; D050723:Fractures, Bone / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology; D006801:Humans; D006811:Humerus / Q000166:cytology / Q000000981:diagnostic imaging / Q000293:injuries / Q000502:physiology*; D008297:Male; D055595:Mechanical Phenomena; D008875:Middle Aged; D019736:Prostheses and Implants; D014057:Tomography, X-Ray Computed