Abstract
Metacarpophalangeal (MCP) arthroplasty usually involves the fitting of a silicone spacer, commonly Swanson prosthesis, but more recently the Sutter prosthesis has been introduced.
Four Sutter MCP prostheses, two each sized 30 and 40, were removed from the right hand of a female patient. The patient aged 61 years ate revision, had longstanding rheumatoid arthritis. Using a single station finger stimulator1 two Sutter size 50 MCP prostheses were tested. This stimulator ran at a speed of 100 cycles per minute. During each of these cycles, which flexed the test prosthesis through a 90° arc of motion, the load across the test prosthesis varied between 10N and 15N after 3000 cycles, the stimulator applied a static ‘pinch’ load and the whole combined load cycle began again. Ringer solution heated at 37°C was used as a lubricant. Clinically, the prostheses had been implanted for 53 months. All four had fractured at the junction of the hinge and distal stem. In the simulator tests the Sutter size 50 prosthesis managed just over 10 million cycles of flexion-extension, including over 3300 ‘pinch’ loads before fracture occurred, at the junction of the distal stem and hinge. The second prosthesis fractured in the same manner after 5.3 million cycles of flexion-extension.
These are the first reported in vitro results of fracture of Sutter prosthesis as well as the first paper to state the site of ex vivo fractures of Sutter prostheses. A computer model described in a recent paper 2 indicated that failure of the Sutter prosthesis should occur at the central hinge region. Clearly the in vitro results and the ex vivo experience disagree with the computer model. McArthur and Milner 3 have shown clinically that the Swanson joint appears to be superior to the Sutter implant, a result confirmed elsewhere4. The finger stimulator has previously caused fracture of Swanson pros-thesis in a time and a manner comparable with surgical experience1. Therefore another correlation with ex vivo results, but testing the Sutter prostheses has further validated the finger simulator.
Abstracts prepared by Dr P E Watkins, Hodgkin Building, Guys Campus, King’s College London.
1 Joyce et al. (2000) J Eng Med214 H5519–526. Google Scholar
2 Williams et al. (2000) J Hand Surg25B212–220. Google Scholar
3 McArthur et al. (1998) J Hand Surg23B574–577. Google Scholar
4 Bass et al. (1996) J Hand Surg21A813–818. Google Scholar
