The basal thumb joint, the joint at the base of the thumb, allows you to pivot and swivel your thumb at will. However, for people with arthritis affecting that joint, such movements can be very painful, if movement is possible at all. There are surgeries that may help reconstruct the joint, which include removing tissue from the joint or implanting silicone, but just as they have some advantages, they have some disadvantages as well.
In the 1970s, experimentation began with a joint replacement for the basal thumb joint. They were a ball-and-socket prosthesis similar to hip and shoulder implants. As well as having several designs, some were cemented while others were uncemented. And, between the cemented and uncemented, loosening of the implant was the most common complication, particularly among the uncemented implants.
Since the introduction of the ball-and-socket implants, researchers developed a newer model that better replicated the original joint and had a more “saddle-like” appearance. The authors of this article evaluated the effectiveness of the Avanta SR TMC prosthesis, one of these newer implants, looking at the range of motion, strength, and functioning, as well as any complaints of pain and implant loosening.
Thirteen patients had 15 basal thumb implants. Eleven of the 13 had a diagnosis of idiopathic osteoarthritis, “wear-and-tear” arthritis of unknown cause, and two had posttraumatic osteoarthritis. The average follow-up after surgery was 36 months and the average age of the patients was 58 years, ranging from 47 to 68 years. Eight of the implants were placed in the patients’ dominant hand and two of these patients had a second surgery in the other hand six months after the first surgery.
Researchers measured, both before and after surgery, range of thumb motion angle, grip and pinch strength, pain, and function. Pain was assessed with the sequential occupational dexterity assessment (SODA) and Michigan Hand Outcomes Questionnaire (MHQ). With the SODA assessment, the patients rated how much pain they experienced while doing every day tasks, such as opening jars, writing, and using utensils. The MHQ raged how much pain was present while at rest, as well as hand function, work-related activities, aesthetics (how the hand looks), and overall satisfaction. When assessing function in one hand, the researchers asked the patients to perform a 9-hole peg test. X-rays from both before and after surgery were evaluated for the angle of the thumb and spaces in the joint.
After gathering the data, the researchers found, according to the SODA scores, the patients reported a significant decrease in pain, although the MHQ findings were not as significant. There was not much improvement in the affected hand alone, as seen by the 9-hole peg test, meaning the time it took to take the pegs out of the board and put them back was not faster after surgery than it was before. However, when using SODA and MHQ to evaluate hand function, there was a significant improvement in the ability to do daily activities. Although, in general, most patients were satisfied with the outcome, there were no significant changes in their function at work and the aesthetics of the hand.
According to x-ray examination, the researchers found that the angles of the joint were within 10 degrees of the ideal position (90 degrees) and that there had been no shortening in the joints and, in seven cases, there was lengthening of the space. There were no signs of loosening within the implant.
One patient, who had minimal pain after the surgery, fell on the operated hand seven months after. This fall resulted in more pain and limited use of the thumb. She did not seek medical help until nine months after the fall, where x-rays showed that there was an old fracture at the base of the thumb that had not been there before the surgery. Surgery was done to replace the implant, however it became infected and further surgery was needed. The only other reported complication was one other patient who had a nerve injury that occurred during the surgery.
The authors concluded that this particular implant, the Avanta SR TMC, is provided significant improvement both in function when both hands were used and in pain relief, but did not provide a significant change in range of motion or strength when the hand was used alone. The prosthesis was found to be sound at follow-up, with no loosening noted.