The effect of the orientation of the noncircular radial head on elbow kinematics.
OBJECTIVE
The objective of this study was to identify the effect of radial head shape and orientation on elbow kinematics in the otherwise intact elbow.


METHODS
Biomechanical study, analyzing simulated active motion of cadaveric arms.


BACKGROUND
A discrepancy exists between the noncircular anatomy of the radial head and radial head prostheses. The effect of radial head shape is unknown.


METHODS
Kinematic effects of radial head shape were tested in six fresh-frozen upper extremities. A custom-made native radial head prosthesis was used to simulate altered shape conditions, by rotating the radial head 90 degrees. Three-dimensional spatial orientation of the ulna was recorded, during simulated active motion. A three factor ANOVA was used to compare (a) nominal and 90 degrees oriented conditions, (b) throughout the flexion arc (c) in three forearm positions (P < 0.05). Post-hoc Tukey tests were done to assess significance.


RESULTS
No significant effect of altering radial head shape was found on total ulnohumeral laxity and angulation during gravity valgus stress. We did find a significant effect on total ulnar axial rotation and rotation during gravity valgus stress.


CONCLUSIONS
The outer shape of the radial head seems to change rotation of the ulna during flexion-extension in an otherwise intact elbow.


CONCLUSIONS
The shape of the radial head effects intact elbow kinematics. Clinical importance of this finding is clear. If a sub-optimally placed radial head prosthesis were to be used in an otherwise intact elbow, the elbow could be at risk for early ulnohumeral arthritis.
van Riet
R P
RP
Mayo Clinic Rochestor, Orthopedic Biomechanics Laboratory, 200 First Street, S.W., Rochester, MN 55902, USA.
Van Glabbeek
F
F
Baumfeld
J A
JA
Neale
P G
PG
Morrey
B F
BF
O'Driscoll
S W
SW
An
K-N
KN
D001696:Biomechanical Phenomena / Q000379:methods; D002102:Cadaver; D004551:Elbow Joint / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D009068:Movement / Q000502:physiology*; D011884:Radius / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation