Can ulnar variance be used to detect overstuffing after radial head arthroplasty?

Background: Overstuffing of the radiocapitellar joint during metallic radial head arthroplasty has been reported to cause loss of elbow flexion, capitellar erosion, and early-onset osteoarthritis. Although this is known, there is no agreed-on measurement approach to determine whether overstuffing has occurred. Questions/purposes: We therefore hypothesized that overlengthening the radial head during radial head arthroplasty changes the ulnar variance in the wrist. Methods: Seven cadaveric radii were implanted with radial head prostheses of increasing thickness. Each specimen was implanted successively with increasingly thick radial head prostheses measuring 2, 4, and 6 mm thicker than the native radial head, and radiographs were taken after implantation of each prosthesis. The ulnar variance with each prosthesis was measured using the method of perpendiculars. Results: The ulnar variance of the native and 2-mm (p = 0.04), 4-mm (p = 0.008), and 6-mm (p = 0.008) overly thick radial head prosthesis-implanted states decreased significantly with each incremental increase in prosthetic head thickness. Conclusions: Implantation of thicker radial head prostheses decreased the ulnar variance. Our results indicate ulnar variance could be used to detect overstuffing of radial head prostheses. Clinical Relevance: The simplicity and reliability of ulnar variance make it a potentially useful indicator of overlengthening after radial head arthroplasty.