Background Most of data obtained from musculoskeletal ultrasonography (MUS) is expressed in terms of subjective interpretations of images. Evolutive comparisons into same patients or assessment of existence of mild synovitis in subjects without symptoms but in risk to develop arthritis are difficult to achieve due to a lack of more objective measures. Age, sex, or constitutional features can modify morphological parameters of joints, so an index capable to be independent to this factors and easily reproducible is needed.
Objectives To test an capsular height index in terms of reproducibility and independence from constitutional factors, age and sex.
Methods One hundred and fifty adult subjects without any known rheumatologic disease were recruited to perform an MUS of the second metacarpophalangeal joint of both hands. Data about age, sex, weight and height were collected. All MUS assessment were performed using a GE Logic 9 machine with a 13MHz linear probe. Probe was placed in the longitudinal axis, parallel to the second finger axis on the dorsal aspect of the joint. Joint capsular height index (JOCHI) was measured using a vertical line between the highest point of the joint capsule and the point where the cartilage is implanted and divided by the longest diameter of the capsule as a measured between the points where it establish visual continuity with the cortical bone. Correlation tests of JOCHI and its separated components were tested against age, sex, height and weight. Also a Kendall´s Tau test was performed to determine reproducibility.
Results Concordance between measures realized in different times was high (Kendall’s Tau 0,781 p < 0,001). Longitudinal capsule diameter was significantly correlated with patients height (Pearson’s 0,681 p > 0,05), Capsule Height was significantly correlated with subject height (Pearson’s 0,609 p > 0,05) and weight (Pearson’s 0,633 p > 0,05). The average capsule height and longest diameter did not showed statistically significant differences between subjects of different sex or age (quintile distribution). JOCHI showed a Pearson´s coefficient of 0.320 (p>0.05) with height, 0.201 (p>0.05) with age and 0.287 (p>0.05) with weight of subjects. JOCHI was similar among subjects of different sex and there was no differences into the measure of JOCHI in subjects of distinct age quintiles. There were not significative differences between height and diameter of the joint and age, weight or height of subjects (all magnitudes were distributed in quintiles). Average JOCHI in the dominant hand was 0.416 SD 0.073 and 0.384 SD 0.062 in the non dominant hand (p<0.048, Fisher´s exact test).
Conclusions JOCHI has demonstrated by means of our results that has a low intra-observation variability and is independent of main morphometric characteristics as well of age and sex. JOCHI seems a useful tool into the assessment of: (1) Patients with inflammatory diseases with potential joint compromise but without joint symptoms, (2) Patients in clinical remission status who are closed followed up to determine a flare, and (3) subjects which are under suspicious to be affected by a inflammatory rheumatic disease but no joint compromise is clinically evident. The evolutive changes in JOCHI in same subjects and margins normality should be focus of future research.
Disclosure of Interest None Declared