Ulnar Variance

Ulnar Variance:
- in general the most radial part of ulna and the most ulnar side of the radius are at level
- w/ neutral variance, 80% of load is born by radius and 20% by ulna;
- 2.5 mm increase in ulnar varience will increase load borne by ulno-carpal joint from 18% to 42%;
- a 2.5 mm decrease in the ulno-carpal variance will decrease the load borne by the ulno-carpal joint to 4.3%;

- draw transverse line along lunate fossa (ulnarmost part of distal radial surface)
and another at level of ulnar head (radial most part of distal ulnar surface) = the difference is Ulnar Variance
- this requires Zero rotation view (PA view with shoulder 90 deg abducted, elbow 90 deg flexed and forearm neutral
= forearm supination decreases ulnar variance, and pronation decreases ulnar variance
- mean ulnar variance is 0.9mm (range 4.2-2.3mm) [wheelessonline.com]

-ive Ulnar variance: Kienbock's disease
+ive UV: SLD (Scapholunate instability) >4mm scapholunate space = Terry Thomas Sign, Ulnar impaction syndrome, tears of triangular fibrocartilage, lunotriquetral ligament tears, previous excision of radial head, increasing age

*case report of the rare lunate fracture with +ive UV with Kienbock's disease
(link)
*images from standford.edu