A study to determine the variability of PIP joint Size measurements was performed among 24 normal adults. Joint size measurements were shown to be reproducible to within 2 mm, irrespective of the times at which they are taken. Size of the joint, age, sex, and menses had no significant effect upon the magnitude in which the PIP joints varied. A diurnal and a cyclic pattern was observed among all PIP joint sizes.Measurement of joint swelling is one of numerous methods employed by investigators as an index of disease activity and drug efficacy in rheumatoid arthritis. The use of standard jewelers' rings, to measure the circumference of the proximal interphalangeal (PIP) joints, was introduced in 1951 (1). A gauge which tightens around the joint has also been used in PIP joint measurements (2). A method, in which swelling of the entire hand is measured by the volume of water it displaces, was introduced in 1956 (3). The variation of this method in normal subjects has since been studied (4).A new device to measure PIP joint circumferences has been shown to be useful for readily measuring PIP joint sizes (5).The instrument, the Arthrocircameter,* utilizes a flexible polyethylene strap which forms a loop to place around the joint. The loop tightens about the joint by a spring contained within the instrument. The joint's circumference is then read from a dial ranging from 40 to 100 mm, in 1 mm increments. The accuracy of the Arthrocircameter was determined by a previous study in which nine observers each measured seven cylinders of known circumferences ranging from 46 to 87 mm (6). The standard deviation of their errors was 0.3 mm, indicating that less than 5% of their errors exceeded 1 mm. These same observers were also shown to be able to reproduce their own measurements of a normal subject's PIP joint with a precision of approximately 2 mm.The purpose of the present study was to determine the variability of PIP joint size measurements, as taken by the Arthrocircameter, in normal subjects. Age, sex, menses, time of day, and weekly intervals were studied for the effects they have upon PIP joint sizes.
MATERIALS AND METHODSThe subjects selected for this study were 24 normal adults, 12 men and 12 women. One subject was left-handed, and one was ambidextrous. To determine the effect of age, the study population contained two age g r o u p~2 3 to 37 years of age and 39 to 57 years of age. These groups were balanced with equal numbers of men and women in each age group.
Arthritis and