TMC implant shows good results, problematic radiographic findings

Researchers suggest long-term follow-up to determine potential subsidence rate.

Researchers studying the Orthosphere, a spherical ceramic device designed for trapeziometacarpal arthroplasty, have expressed concerns over subsidence and trapezium fractures.

However, patients implanted with the device as part of a clinical study reported satisfaction and had good function, according to Jay Pomerance, MD, an orthopedic hand surgeon in practice in Arlington Heights, Ill..

Pomerance presented the results of the retrospective study at the Joint Annual American Society for Surgery of the Hand/American Society for Hand Therapists Meeting in San Antonio. He had conducted the study with co-author Brian D. Adams, MD, of Iowa City, Iowa.

Ultimately, the researchers found that clinical outcomes and radiographic findings did not agree. “The Orthosphere (Wright Medical Inc.) is attractive because of its simplicity, small size, good motion, avoidance of cement, preservation of surrounding joints, minimal dissection, rapid recovery, short immobilization and implant wear,” Pomerance said. “The early results were promising. ... The radiographic results were concerning,” he noted.

Surgeons performed 50 trapeziometacarpal (TMC) arthroplasties in 49 patients between 1997 and 2003. Average follow-up was 3.3 years, ranging from one to seven years. Patients averaged 59 years old at the time of surgery and half were employed.

The criteria for patient participation included stage 2 or 3 osteoarthritis by the Eaton classification, pain, no previous surgery and minimal osteopenia.

The researchers assessed patient satisfaction (pain and function), range of motion and pinch strength. They used radiographic evaluations to detect preoperative arthritis, implant and metacarpal subluxation, implant subsidence, fractures and adjacent skeletal reactions, Pomerance said.

Pain relief, strength and function

Thirty-two of the 35 patients who completed the study were very satisfied or satisfied with pain relief and improved function. Only two patients reported having more pain after surgery and two patients had persistent unexplained pain.

Patient strength generally remained unchanged, with grip strength averaging nine pounds. Pinch strength was lower in the affected thumb compared with the unaffected thumb. But all patients achieved opposition to the tip of the small finger with two-thirds having the ability to reach the small finger PIP crease.

Subsidence and fractures

The researchers reported no early perioperative complications, such as fractures, infection or dislocations. However, 47 patients showed radiographic evidence of implant subsidence after two years’ follow-up. Subsidence appeared in either the metacarpal or trapezium and tended to advance in the first two years after surgery before stabilizing in some patients.

Sclerotic lines around the implant formed early, but correlated with less subsidence. Osteopenia coincided with greater subsidence. Trapezium fractures appeared in 15 thumbs and complete trapezium resorption appeared in one. Trapeziometacarpal impingement stemming from subsidence appeared in two thumbs.

“Patient satisfaction did not correlate with radiographic findings, including subsidence and trapezium fractures,” Pomerance said. “The inability of the bone to tolerate stress, especially at the trapezium, creates a high risk of failure. ... We recommend caution when considering the implant,” he added.

The authors noted in their study abstract that “Spherical, ceramic implant TMC arthroplasty was found to have a substantial incidence of subsidence and eventual trapezium fracture. ... Clinical outcome did not correlate with adverse radiographic findings, suggesting that changes are slowly progressive and tolerated.”

For more information:
Adams B, Pomerance J. Outcome of spherical ceramic TMC arthroplasty. PAS02. Presented at the Joint Annual ASSH/ASHT Meeting. Sept. 22-24, 2005. San Antonio.