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Ulnar Variance

- Discussion:
    - mean ulnar variance is 0.9 mm (range: 4.2 to 2.3 mm);
    - functional anatomy:
           - 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%;
           - reference:
                  - The distal radioulnar joint. Anatomy, biomechanics, and triangular fibrocartilage complex abnormalities.
    - negative ulnar variance is associated w/ Kienbock's disease
    - positive ulnar variance is associated w/:
           - SLD;
           - ulnar impaction syndrome;
           - tears of triangular fibrocartilage;
           - lunotriquetral ligament tears;
           - previous excision of radial head
           - note that with increasing age, ulnar variance tends to become more positive;
    - positive ulnar varience may develop in child gymnasts, due to "stress related changes" in the distal radial physis;
           - the chronic compressive loads borne by the radius, leads to premature closure of the distal radial physis;

- Measurement:
    - requires zero rotation view: (measured on PA radiograph w/ wrist in neutral supination/pronation);
    - draw transverse line at the level of the lunate fossa, and a second transverse line at the level of the ulnar head;
           - the difference indicates ulnar variance;
    - forearm supination will decrease ulnar variance;
    - forearm pronation will increase ulnar variance;
           - in the report by Tomaino MM, et al, the author notes that static unloaded radiographs may underestimate variance in wrists in which power grip and pronation results in significant proximal migration of the radius;
           - the author investigated the effect of a maximum grip effort in combination with forearm pronation on ulnar variance in 22 patients who presented with ulnar wrist pain;
           - pronated grip x-ray view resulted in statistically significant increases in ulnar variance;
           - the author recommended that preoperative ulnar variance should be measured using both neutral rotation and pronated grip x-rays before selecting treatment for causes of ulnar wrist pain that are affected by radioulnar length so that dynamic increases in ulnar variance are considered;
           - ref: The importance of the pronated grip x-ray view in evaluating ulnar variance 
    - in the report by Jung JM, et al (2001), the authors studied the radiographs of the wrists of 120 healthy volunteers in order to determine the normal range of ulnar variance;
           - pronation posteroanterior, supination AP and neutral PA views were taken of each wrist before and during
                  a maximum grip under identical conditions;
                  - mean normal ulnar variance in neutral rotation was +0.74 ± 1.46 mm, a value which was significantly lower in males than in females;
                  - they found negative variance in 26% of cases;
                  - they measured maximum ulnar variance (UVmax, +1.52 ± 1.56 mm) when gripping in pronation and minimum ulnar variance (UVmin, +0.19 ± 1.43 mm) when relaxed in supination;
                  - they subtracted UVmin from UVmax to calculate a mean maximum dynamic change in ulnar variance of 1.34 ± 0.53 mm.
           - ref: Changes in ulnar variance in relation to forearm rotation and grip

The distal radioulnar joint. Anatomy, biomechanics, and triangular fibrocartilage complex abnormalities.

Ulnar variance determination.

Measuring Ulnar Variance: a comparison of techniques.

Gymnast Wrist: an epidemiologic survey of ulnar variance and stres changes of the radial physis in elite female gymnasts.

Ulnar Variance in Children - standard measurements for evaluation of ulnar shortening in juvenile rheumatoid arthritis.

Kienbock disease and negative ulnar variance.