The aim of this study was to investigate the length changes of carpal ligaments when loaded in full extension in vivo. We obtained computed tomography scans of the right wrists in three positions for six volunteers: neutral; 75° extension; and 75° extension with a further 10° of radial deviation. Nine ligaments were measured and analysed with computer modelling. The results showed that the radioscaphocapitate, long radiolunate, and ulnolunate ligaments lengthened the most at full wrist extension, suggesting that they were under greatest load. The radioscapholunate, ulnocapitate, and ulnotriquetral ligaments lengthened further with the addition of wrist radial deviation. At full extension, the dorsal intercarpal ligament inserting on the scaphoid was lengthened. The dorsal radiocarpal and dorsal intercarpal ligaments inserting on the trapezoid were shortened, suggesting reduced loading. In conclusion, a number of volar carpal ligaments lengthened significantly in full wrist extension and the ulnar carpal ligaments were further lengthened at wrist radial deviation.