Search

Total wrist arthroplasty (TWA) designs suffer from relatively high complication rates when compared to other arthroplasties. Understanding the contact pattern of hip and knee replacement has improved their design and function; however, the in vivo contact pattern of TWA has not yet been examined and is thus the aim of this study. We hypothesized that the center of contact (CoC) is located at the geometric centers of the carpal component and radial component in the neutral posture and that the CoC moves along the principal arcs of curvature throughout primary anatomical motions. Wrist motion and implant kinematics of six patients with the Freedom® total wrist implant were studied during various tasks using biplanar videoradiography. The location of the CoC of the components was investigated by calculating distance fields between the articular surfaces. We found the CoC at the neutral posture was not at the geometric centers but was located 3.5 mm radially on the carpal component and 1.2 mm ulnarly on the radial component. From extension to flexion, the CoC moved 10.8 mm from dorsal to volar side on the carpal component (p 0.0001) and 7.2 mm from volar to dorsal on the radial component (p = 0.0009). From radial to ulnar deviation, the CoC moved 12.4 mm from radial to ulnar on the carpal component (p 0.0001), and 5.6 mm from ulnar to radial on the radial component (p = 0.009). The findings of this study may eventually improve TWA success by advancing future designs through a more accurate understating of their kinematic performance in vivo.

In small joints, where cartilage is difficult to image and quantify directly, three-dimensional joint space measures can be used to gain insight into potential joint pathomechanics. Since the female sex and older age are risk factors for carpometacarpal (CMC) joint osteoarthritis (OA), the purpose of this in vivo computed tomography (CT) study was to determine if there are any differences with sex, age, and early OA in the CMC joint space. The thumbs of 66 healthy subjects and 81 patients with early stage CMC OA were scanned in four range-of-motion, three functional-task, and one neutral positions. Subchondral bone-to-bone distances across the trapezial and metacarpal articular surfaces were computed for all the positions. The joint space area, defined as the articular surface that is less than 1.5 mm from the mating bone, was used to assess joint space. A larger joint space area typically corresponds to closer articular surfaces, and therefore a narrower joint space. We found that the joint space areas were not significantly different between healthy young men and women. Trends indicated that patients with early stage OA have larger CMC joint space areas than healthy subjects of the same age group and that older healthy women have larger joint space areas than younger healthy women. This study suggests that aging in women may lead to joint space narrowing patterns that precede early OA, which is a compelling new insight into the pathological processes that make CMC OA endemic to women.