Anatomical Wrist Patterns on Plain Radiographs

Abstract

Objective/Hypothesis: It is recognized that in many joints, structure dictates function and later pathology. Interpreting the structure is complicated by the existence of multiple joints as well as variability in bone shapes and anatomical patterns in the wrist. Previous studies have evaluated lunate and capitate shape in an attempt to understand functional anatomical patterns. The purpose of this study was to describe anatomical shapes and wrist patterns in normal wrist radiographs using bone shape and measurements of joint contact and position. We hypothesized that we will find significant relationships between measurements enabling us to identify one or more patterns of wrist anatomy. Materials and Methods: Seventy plain posteroanterior and lateral wrist radiographs were evaluated. These radiographs were part of a previously established normal database, had all been read by a radiologist as normal, and had undergone further examination by 2 hand surgeons for quality. Measurements included lunate and capitate shape, ulnar variance, radial inclination and height, volar tilt, distance and angle between 2 lines of reference and percentage of the lunate and capitate radial to these lines as well as the percentage of capitate circumference on PA radiographs that articulate with the lunate, scaphoid, and trapezoid. Results: We found a significant association between lunate and capitate shape using a dichotomal classification system for both lunate and capitate types ( P = .003). Type 1 wrists had a lunate with no contact on the PA radiograph with the hamate bone (as described) and a spherical distal capitate. Type 2 wrists had a lunate with a facet for the hamate bone and a flat distal capitate. When using this distinction between type 1 and 2 wrists, we found that type 1 wrists were associated with a greater amount of contact between the scaphoid and capitate ( P = .04) and a smaller amount of contact area with the hamate bone ( P = .05). There was an inverse relationship between measured contact between the capitate and lunate and the amount of contact between the capitate and hamate ( P = .004). Conclusions: We were able to identify significant relationships within the joints of the wrist, especially in midcarpal joint. Further study needs to be done to better describe the 2 types of wrist patterns more precisely, to describe other joints/parameters in the wrist and their association with these anatomical variants, and then to understand their influence on wrist biomechanics and pathology.