Four-dimensional computed tomography-derived radiolunate arthrokinematics with a case study in four-corner arthrodesis

The radiocarpal joint, which includes articulations between the radius and the proximal carpal row, transmits force through the central column of the wrist. Chronic disruptions to radiocarpal biomechanics are associated with the development of scapholunate advanced collapse (SLAC) pattern OA. While the radiolunate joint is thought to be typically spared in SLAC progression, degenerative changes can present on the proximal lunate. An investigation of radiolunate arthrokinematics may improve understanding of posttraumatic and postsurgical outcomes, including salvage procedures for SLAC wrist such as scaphoid excision with four-corner arthrodesis (SEFCA). Four-dimensional CT, which captures CT volumes over time or motion, has enhanced our ability to quantify arthrokinematics during functional tasks. We hypothesize that 4DCT-derived radiolunate arthrokinematics during flexion-extension and radioulnar deviation will differ between healthy, uninjured wrists and a wrist three years post-SEFCA. Data were collected from the uninjured wrists of ten participants enrolled in a prospective study of unilateral wrist injury and one participant following SEFCA (n=11, 36% female). The SEFCA arthrodesis was fixed using Kirschner wires prepositioned in the head of the capitate and subsequently advanced into the lunate. Included participants were aged between 18 and 60 years; exclusion criteria included history of injury, surgery, or congenital variant in the contralateral wrist; rheumatologic disease; or connective tissue disease. Static-neutral and dynamic CT data were collected using a dual-source scanner (SOMATOM Flash, Siemens, DE) and commercially-available cardiac sequential scan protocol. 4DCT data were collected over a 1.5-second period as signaled by an ECG simulator. CT volumes were collected at a temporal resolution of 66 ms as participants moved at a cadence of 70 beats per minute (voxel size: 0.234mm × 0.234mm × 0.600mm). Nearest mesh-vertex distances between vertices on the radius and lunate within distance (2.5 mm) and surface-normal angular (60°) thresholds were calculated to define interosseous proximity distributions. Median interosseous proximities at each time point were calculated. Ten participants were aged mean (SD) 30.3 (6.8) years at the time of imaging; the SEFCA participant was 52 years of age and three years postoperative. Median radiolunate interosseous proximities are presented during flexion-extension and radioulnar deviation (Fig. 1). 4DCT has advanced our understanding of wrist arthrokinematics during functional tasks. The current study reveals that radiolunate interosseous proximities in healthy, uninjured wrists remain relatively constant over wrist flexion-extension and radioulnar deviation, with greatest proximities occurring near the extrema of motion. In the SEFCA participant, interosseous proximities were closest in flexion and ulnar deviation; this may be associated with high articular contact pressures in these positions. Interosseous proximities reveal how restricting midcarpal motion in SEFCA impacts adjacent articulations during wrist motion. This study represents a novel use of 4DCT to assess post-arthrodesis outcomes.