The Relationship between Structure of the Wrist and Function in a Japanese and Caucasian Population.

Background: Factors such as age and joint structure affect normal wrist motion. The midcarpal joint participates in flexion/extension, radial-ulnar/deviation (RUD), and since lunate/wrist type-2 is likely more stable than a lunate/wrist type-1, we suggest that midcarpal joint structure will affect wrist motion. Our purpose was to compare wrist motion in Caucasian and Japanese populations and to associate motion with midcarpal joint morphology. We hypothesised that radiographic structure would correlate with wrist motion. Methods: A total of 164 patients with normal wrist radiographs were included. Clinical measurements included wrist extension, flexion and RUD. Radiographic measurements included the radiocarpal joint: ulnar variance, radial height, radial inclination, volar inclination and carpal joint measurements: lunate type, capitate circumference and each of its joints contact measured and calculated as a proportion of capitate circumference. Results: The groups differed in wrist motion and in multiple radiographic measurements. When the two populations were analysed together, there were no significant associations between midcarpal joint type and wrist motion. The radiocarpal joint: ulnar variance was correlated with extension and radial deviation. Radial height was directly related to flexion, and both radial height and radial inclination were directly correlated with ulnar deviation. The intracarpal measurements: The main measurement affecting motion was the contact between the capitate and the scaphoid (as a proportion of capitate circumference) with lesser correlations of the contact of the capitate with the trapezoid and hamate. The most significant measurement associated with a lunate type-2 was scaphoid contact with the capitate p = 0.01. Logistic regression demonstrated that the measurements most associated with wrist motion were scaphoid contact with the capitate/capitate circumference and hamate contact with the capitate/capitate. Conclusions: This study supports discrepancies in wrist motion amongst different racial cohorts, and a relationship between bone/joint structure in the wrist and wrist motion. This can help treat wrist pathology. Level of Evidence: Level III (Diagnostic).