Reverse shoulder arthroplasty glenoid fixation: is there a benefit in using four instead of two screws?
BACKGROUND
To allow osseous integration to occur and thus provide long-term stability, initial glenoid baseplate fixation must be sufficiently rigid. A major contributing factor to initial rigid fixation is baseplate screw fixation. Current baseplate designs use a 4-screw fixation construct. However, recent literature suggests adequate fixation can be achieved with fewer than 4 screws. The purpose of the present study was to determine whether a 4-screw construct provides more baseplate stability than a 2-screw construct.


METHODS
A flat-backed glenoid baseplate with 4 screw hole options was implanted into 6 matched pairs of cadaver scapulas using standard surgical technique. Within each pair, 2 screws or 4 screws were implanted in a randomized fashion. A glenosphere was attached allowing cyclic loading in an inferior-to-superior direction and in an anterior-to-posterior direction. Baseplate motion was measured using 4 linear voltage displacement transducers evenly spaced around the glenosphere.


RESULTS
There was no statistical difference in the average peak central displacements between fixation with 2 or 4 screws (P = .338). Statistical increases in average peak central displacement with increasing load (P < .001) and with repetitive loading (P < .002) were found.


CONCLUSIONS
This study demonstrates no statistical difference in baseplate motion between 2-screw and 4-screw constructs. Therefore, using fewer screws could potentially lead to a reduction in operative time, cost, and risk, with no significant negative effect on overall implant baseplate motion.
Department of Orthopedic Surgery, State University of New York Upstate Medical University, Syracuse, NY 13210, USA.
Jaison
J
James
Mari A
MA
Allison
Frederick W
FW
Werner
Devin E
DE
McBride
Niladri N
NN
Basu
Levi G
LG
Sutton
Vipul N
VN
Nanavati
D019643:Arthroplasty, Replacement / Q000295:instrumentation*; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D006801:Humans; D007595:Joint Prosthesis; D011474:Prosthesis Design; D012540:Scapula / Q000601:surgery*; D012785:Shoulder Joint / Q000601:surgery*; D016474:Weight-Bearing
Basic Science Study; Biomechanics; Cadaver Model; Reverse shoulder arthroplasty; glenoid fixation