IN-VIVO MEASUREMENT OF DRUJ TRANSLATION

Distal radio-ulnar joint (DRUJ) instability is increasingly recognised and can lead to disabling symptoms. Clinical assessment can detect gross instability but is much less reliable for subtle instability. The normal range of DRUJ dorso-palmar translation is not known. Previous biomechanical research has studied DRUJ kinematics using cadaveric models. We aim to develop a simple, reliable and reproducible tool to measure DRUJ stability and thereby assess the normal range of DRUJ dorso-palmar translation in-vivo. A test rig was designed and 20 volunteers recruited. The rig held the subject’s elbows at 90° flexion with the distal ulnar secured and the forearm in neutral rotation. Dorso-palmar shear force was applied to the distal radius and displacement measured 3 times on each wrist alternately by the same operator. Volunteers with previous wrist injuries were excluded. Ten male and 10 female volunteers were recruited. Mean male age 39.1 years (range 22–74). Mean female age 35.8 years (range 25–57). Mean male translation 5.4mm (range 3–9, SD 1.1). Mean female translation 5.5mm (range 4–7, SD 0.9). Mean right sided translation 5.3mm (range 3–8, SD 1.0). Mean left sided translation 5.6mm (range 3–9, SD 1.0). Total mean translation 5.5mm (SD 1.0). Same-sided mean measurements for two subjects taken days apart varied by only 1mm. Intraclass correlation coefficient was 0.93. The rig is reliable, reproducible and appears to be a valid test of DRUJ translation. The mean DRUJ translation in neutral is 5.5mm. Contralateral sides and between sexes were comparable. We anticipate that the rig will be a research tool to guide clinical practice in DRUJ instability.