Stability of scaphotrapeziotrapezoid novel arthrodesis apparatus

BACKGROUND: Traditional scaphotrapeziotrapezoid limited intercarpal arthrodesis contains Kirschner wire, U-shaped nail, AO/ASIF steel plate and so on. Long-term plaster external fixation was needed following surgery. USA-designed arthrodesis apparatus is mainly suitable for European and people from USA, but not fit for Asian. OBJECTIVE: To simulate scaphotrapeziotrapezoid limited intercarpal arthrodesis, and to test the stability of the novel arthrodesis apparatus developed by the group according to anatomic form of dorsal joint fovea of Chinese scaphotrapeziotrapezoid. DESIGN, TIME AND SETTING: The observational study was performed at the Laboratory of Biomechanics of the Department of Orthopaedics, Nahtong University from April 2006 to March 2007. MATERIALS: A total of 40 fresh forearm samples of corpses that were not subjected to antiseptic treatment were used for this study. Radiograph verified that these samples did not develop wrist joint affection or abnormal alinement. METHODS: The cadaver models were imitated limited intercarpal instability before scaphotrapeziotrapezoid arthrodesis used circular plate. Then, simulated flexion 50 degree , extenion 35 degree , ulnar deviation 30 degree , radial deviation 10 degree ultimate activities (50000). CT scan and 3-D reconstruction should be taken before and after motion. MAIN OUTCOME MEASURES: The index of the radial-scapho angle (RSA), radial-scapho distance (RSD), scapho length (SL), trapezium-trapezoid inclination (TTI), trapezium-trapezoid width (TTW) were measured. RESULTS: Prior to motion RSA, RSD, SL, TTW and TTI were (38.725 plus or minus 2.230) degree , (18.988 plus or minus 1.216) mm, (1.686 plus or minus 0.191) cm, (27.360 plus or minus 1.571) mm and (114.975 plus or minus 2.293) degree . Following motion RSA, RSD, SL, TTW and TTI were (38.800 plus or minus 2.388) degree , (19.215 plus or minus 1.443) mm, (1.683 plus or minus 0.209) cm, (27.718 plus or minus 1.910) mm, (115.300 plus or minus 3.023) degree . No significant difference in above-described indexes was determined before and after motion (P>0.05). CONCLUSION: The novel STT limited intercarpal arthrodesis apparatus shows confidential stability. Thus, wrist joint can do exercises in an early stage at the range of 35 degree dorsal extension, 50 degree palmar flexion, 10 degree radial deviation and 30 degree ulnar deviation.