Prosthetic radial head components and proximal radial morphology: a mismatch.

A morphometric study of the proximal radius was performed with magnetic resonance imaging scans to measure the anatomic dimensions of the radial head and neck. These dimensions were then compared with the manufacturer's size specifications of commercially available titanium prosthetic radial head components to determine whether these designs adequately match the morphologic characteristics of the proximal radius. A cadaveric correlation was performed to validate the accuracy and reliability of measurements obtained from the magnetic resonance scans. The narrow intramedullary dimensions of the radial neck negated fitting of even the smallest available metallic prosthetic component stem in 18 (39%) of 46 scans reviewed (confidence interval 26% to 53%). Of the 31 male patients who underwent scanning, 4 (13%) would not be able to be fitted with a prosthetic component according to the manufacturer's technique guide (confidence interval 0% to 29%). Of the 15 female patients who underwent scanning, 14 (93%) would not able to be fitted with a prosthetic stem (confidence interval 70% to 99%). In those patients in whom the radial neck could accommodate a prosthetic stem (n = 26), there was ineffective restoration of proximal radial head length in all cases (100%, confidence interval 87% to 100%). The average shortening was 4 mm of proximal radial length (range 1 to 7 mm). Our findings reveal that the commercially available metallic radial head design may overestimate the dimensions of the radial neck. Inadequate sizing of radial head prostheses may lead to an inadvertent change in proximal radial length, with potentially adverse effects on elbow, forearm, and wrist mechanics. Newer designs taking into account these anatomic dimensions may lead to an improvement in function after reconstruction.