Proximal Interphalangeal Joint Silicone Arthroplasty - Comparison of Swanson and NeuFlex® Implants using a New Evaluation Score

Proximal interphalangeal joint arthroplasty with a silicone implant has proven to be successful in cases of degenerative, post-traumatic or rheumatic arthritis. The recent changing of the implant's design by introducing a 30-degree preflexion has replaced the common Swanson implant in some centres. Nevertheless, directly comparing follow-up studies between the two implant forms are still lacking as well as the use of a standard evaluation score for proximal interphalangeal joint arthroplasties. Between 1990 and 2007 a series of 67 proximal interphalangeal joint arthroplasties with a silicone device has been carried out in 54 patients. Among these a retrospective clinical and radiological investigation could be performed on 43 patients with 53 joints at 6-144, in the mean 34 months, after operation. 39 cases of degenerative, 12 cases of post-traumatic, I case of rheumatic arthritis and 1 post-traumatic arthrodesis were treated with 20 Swanson implants and 33 NeuFlex (R) implants. In 41 joints a mediolateral approach taking care of the extensor tendon's integrity was used, in 12 joints the extensor tendon was dissected longitudinally using a dorsal approach. At the time of investigation 5 implants had already been removed due to infection, implant fracture and painful extensive osteophytes. Comparing the remaining prostheses, 18 Swanson implants and 30 NeuFlex (R) implants, the latter showed a better average total range of motion, improving from 42.5 degrees preoperatively to 56 degrees postoperatively, in contrast to the Swanson implants with a deterioration from 50.8 degrees preoperatively to 47.2 degrees postoperatively. However, they were inferior to the classic Swanson implant as the joint's circumference was more enlarged by 1.8 mm in the mean and a geater finger length shortning of average 2.5 mm as well as a higher rate of stress pain and instability (15%) were evident. While the NeuFlex (R) implants led to a better subjective satisfaction, the Swanson implants gained better objective results using a new evaluation score (11% very good, 50% good, 28% satisfactory, 11% bad) than the NeuFlex (R) implants (50% good, 40% satisfactory, 10% bad). Remarkably the NeuFlex (R) devices showed an extremely high rate of early implant fractures after 8-31 months, in the mean 18 months, postoperatively, which was not seen with any of the Swanson implants - in spite of an average duration of 59.4 months.