Kinematics of the ulna during pronation and supination in a cadaver study: implications for elbow arthroplasty.
OBJECTIVE
Aim of this study was to exactly describe and quantify kinematics of the ulna during pro- and supination.


METHODS
Biomechanical study in fresh frozen cadavers.


BACKGROUND
A previous MRI study revealed a varus/valgus motion of the ulna averaging 7.1 degrees during pro-/supination. Axial rotation, however, could not be quantified.


METHODS
Sixteen arms were examined in a new apparatus that fixed the humerus on a template and allowed forearm rotation. Motion of a Kirschner wire placed in the ulna was recorded in steps of 30 degrees by two perpendicularly arranged charge coupled device cameras during pro- and supination.


RESULTS
From supination to pronation the ulna showed a semi-lunar evasive motion in the coronal and transverse plane with an initial varus shift, then a dorsal and finally a valgus shift. Motion in the coronal plane averaged 14.14 degrees (SD 4.78). Valgus angles of the ulna in 30 degrees, 60 degrees and 90 degrees pronation were significant (P<0.05) to each other and the neutral position. Varus angles of the ulna in 30 degrees, 60 degrees and 90 degrees supination (P<0.01) were significant to each other and the neutral position.A maximum ulnar axial pronation rotation of 3.2 degrees (SD 2 degrees ) was noted. Axial rotation angles of 90 degrees and 60 degrees of pronation were significant to each other and to the neutral position (P<0.05), respectively.


CONCLUSIONS
To prevent increased stress on the bone-cement interface in elbow arthroplasty, a mean axial rotation of at least 3.2 degrees should be possible.
Kasten
P
P
Department of Orthopaedic Surgery, University of Heidelberg, Heidelberg 69118, Germany.
Krefft
M
M
Hesselbach
J
J
Weinberg
A-M
AM
D019643:Arthroplasty, Replacement; D001696:Biomechanical Phenomena; D001864:Bone Wires; D006801:Humans; D011403:Pronation / Q000502:physiology*; D016683:Supine Position / Q000502:physiology*; D014457:Ulna / Q000502:physiology*