Ulnar Variance | Negative, Positive & Normal Values

Ulnar variance, also called the radioulnar index, is a measurement of the relative lengths of the radius and ulna determined on a dorsopalmar radiograph of the wrist. It plays an important role in wrist biomechanics and can have clinical significance in diagnosing and treating certain wrist conditions.

A neutral rotation view is necessary because pronation and supination movements of the forearm alter the relative length of the ulna, causing erroneous measurements in other joint positions.

Ulnar Variance Measure

Various methods for determining ulnar variance have been described and evaluated.

Gelberman method

The Gelberman method is easy to perform. Gelberman defines ulnar variance as the distance between two lines perpendicular to the long axis of the radius:

• On the radial side, a line perpendicular to the radial axis is drawn through the ulnar margin of the radius. It should pass through the midpoint between the dorsal and palmar edges of the ulnar radial margin. 
• On the ulnar side, a line perpendicular to the radial long axis is drawn tangent to the distal articular surface of the ulna. 

See Also: Wrist Pain Causes

Magnetic Resonance Imaging (MRI)

MRI can also be used to measure ulnar variance by comparing the lengths of the ulna and radius on cross-sectional images. It may be particularly useful when evaluating soft tissue abnormalities in addition to bone length.

Computed Tomography (CT) Scan

CT scans can provide accurate measurements of ulnar variance by reconstructing three-dimensional images of the wrist bones. CT scans may be used when a more detailed evaluation of the bones is required, such as in complex fractures or cases requiring surgical planning.

See Also: Wrist Anatomy

Normal Ulnar Variance

An abnormal length of the ulna is associated with different pathologies of the wrist (Kienbock disease, negative ulnar variance; ulno-lunate Impaction syndrome and triangular fibrocartilage tears, positive ulnar variance). Furthermore, considering the ulnar variance is helpful in assessing the degree of posttraumatic instability of the distal radioulnar joint following distal radius fractures.

Positive ulnar variance surgery include ulnar shortening osteotomy, while negative ulnar variance surgery include radial shortening osteotomy.

Carpal Height

Some types of wrist pathology are associated with decreased height of the proximal row of carpal bones. The following indices can be used to quantify this change:

Youm Ratio:

• The ratio is found by dividing carpal height measured in line with the third metacarpal axis by the length of the third metacarpal.
• Normal value= 0.54 ± 0.03

Natrass Ratio:

• To calculate this ratio, the carpal height (a) is divided by the capitate length (b).
• The axis of the third metacarpal shaft is defined first, and the carpal height is measured in line with that axis as the distance from the base of the third metacarpal to the distal radial articular surface.
• Capitate length is defined as the greatest distance between its distal and proximal articular surfaces.
• Normal value: a/b= 1.57 ± 0.05

References

• Gelberman RH, Salamon PB, Jurist JM, Posch JL. Ulnar variance in Kienböck’s disease. J Bone Joint Surg Am. 1975 Jul;57(5):674-6. PMID: 1150712.
• Baratz ME, Larsen CF. Wrist and hand measurements and classification schemes. In: Gilula LA, Yuming Y. Imaging of the Hand and Wrist Philadelphia: Saunders; 1996: 225-259.
• Schmidt DR. Prommersberger IQ. Karpale Morphometrie und Funktion. In: Bildgebende Diagnostik der Hand 2nd ed. Stutt Eart: Thieme; 2004: 122-130
• Steyers CM. Blair WF. Measuring ulnar variance: a comparison of techniques.J Hand Surg Am 1989;14(4):607-612
• Youm Y, McMurthy RY, Flatt AE, Gillespie TE. Kinematics of the wrist L An experimental study of radial-ulnar deviation and flexion-extension. J Bone Joint Surg Am 1978;60(4):423-431
• Natrass GR. King Gj, McMurtry RY, Brant RF. An alternative method for determination of the carpal height ratio. J Bone joint Surg Am 1994;76(1):88-94