Thumb Mp Fusion

MP arthritis of the thumb is a potentially debilitating disorder whose treatment is relative successful for the surgeon who thoroughly evaluates the entire thumb axis, because involvement of other joints will dictate the most appropriate treatment.

Fusion is generally successful, and very little variability in results exists between methods. This treatment option is also supported by most of the existing literature on this topic [5,7,12,14]. Osteotomy type, whether flat or chevron, makes no the tension-band group were also shown to be lower than the Kirschner-wire group (5% versus 15%). In essence, Kirschner-wire MP arthrodesis was successful 85% of the time, whereas the tension-band procedure had a success rate of 95%. The major drawback to tension-band arthrodesis is that this procedure can be technically challenging and time-consuming.

Arthrodesis of the MP joint using a cannulated screw and threaded washer has been reported [5] as an easier way to provide compression at the osteotomy site and improve union rates. In this procedure, performed under regional anesthesia, the extensor mechanism and the joint capsule are divided at the interval between the EPB and the EPL tendons. A chevron osteotomy is then performed, followed by bone segment approximation. The thumb is placed at key pinch configuration with 10° to 15° of flexion, neutral rotation, and radial/ulnar deviation [5]. A 1.1-mm threaded guide pin is passed from the dorsal aspect of the metacarpal through the metacarpal head, and into the medullary canal of the phalanx. Once this is complete, a threaded washer is placed

Arthrodesis
Fig. 7. Anteroposterior (AP) radiograph showing MP fusion using a cannulated screw and washer. (From Schmidt CC, Zimmer SM, Boles SD. Arthrodesis of the thumb metacarpophalangeal joint using a cannulated screw and threaded washer. J Hand Surg [Am] 2004; 29(6):1048; with permission.)

significant difference in overall fusion rate. Compression across the osteotomy site has been shown to promote better fusion. In the past, tension banding was the best way to provide compression across the osteotomy site. The drawback to this procedure was is that it is technically challenging and time-consuming. Technological advancement in fixation hardware has brought on several new types of cannulated headless screws that allow for easy and fast compression. These screws provide all of the benefits of tension banding in a fraction of the time. Results of these compression screws are very similar to tension banding, and this is the authors' preferred method of fixation.

Arthroplasty remains a viable option in patients who have significant CMC or IP joint involvement. Patients who find the most benefit from this procedure are those who have significant CMC involvement, such that opposition of the thumb is very painful. In these patients, the extra motion over the MP joint relieves pressure at the CMC, and therefore reduces pain on active use of the hand.

Overall, the authors recommend fusion as a first option for the rheumatoid or osteoarthritic patient who has monoarticular involvement of the MP joint of the thumb, because this procedure is relatively simple, provides good pain relief, and does not significantly limit range of motion of the thumb axis. In patients who have extensive involvement of the CMC or the IP joint, the authors recommend arthroplasty as an effective way to remove strain at these joints, prevent further injury, and relieve pain. When it comes to choosing between Silastic or metal-polyethylene implants, the authors do not have much experience with the metal-polyethylene prostheses, and the data are still scarce in demonstrating any improvement over the Swanson prosthesis. Although it has been shown to have a high fracture rate, the Swanson Silastic arthroplasty has been used for a much longer period of time, and has had clinical studies demonstrating 90% improvement in function. It has been the authors' experience that these fractures do not translate into clinical failures, and as a result, we therefore recommend the Swanson arthroplasty as the implant of choice when considering arthroplasty of the MP joint of the thumb.

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