I'm checking into the various types of wrist replacements out there. I've heard there's a new C-shaped one. How does that work?
You are right. There is a new artifical joint replacement for the wrist called the distal radioulnar joint or DRUJ. More specifically, we're talking about the place where the radius (forearm bone on the thumb side of the wrist) connects to the ulna (forearm bone on the little finger side).
Wrist joint replacements used before this one have failed too many times -- the previous prosthesis (replacement device) loosened, broke, backed out, or had to be removed because the patient was still in so much pain. What's so special about this new implant?
The new C-type prosthesis is a simple rod made of chromium cobalt that is inserted down the length of the ulnar bone. It is attached to the radius with a shorter cross piece also made of chromium cobalt. The shorter radial component has a circle-shaped head with a plastic lining on the inside of the round end. That ring is placed inside a hole cut into the radius just above the wrist.
What makes this device unique is the fact that it has only two parts. Other wrist replacements have four pieces. In the new C-type units, both pieces are coated with hydroxypatite, a calcium crystal that helps form bone mineral. When placed inside or next to the bone, this coating gives new bone cells a compatible surface to attach to. In other words, the hydroxypatite surface promotes bone growth filling in and around the prosthesis.
The new prosthesis is also unusual in that it allows the ulnar rod to move up and down inside the bone (piston-like action) while still turning (rotating) around the radius. Rotation is made possible by the ring on the end of the radial component. Each prosthesis can be custom made (sized) for each individual patient.
But the really good news is that early reports are very favorable. Results are good-to-excellent with the majority of patients reporting decreased pain, increased movement, and improved function.
This new C-type distal radioulnar joint replacement isn't the final word on wrist replacements. It is more likely a stepping stone from a device that didn't work to one that will be even more superior to the one just studied.
The availability of improved implants is good news for anyone with a painful, weak, and unstable wrist joint. In time, more patients will be eligible for this type of wrist replacement. Right now, it's fairly limited to those who develop osteoarthritis after trauma or injury to the wrist and to patients who have the tip of the ulna (at the wrist end) removed for any reason.