Towards better understanding of small joint arthroplasty in the hand. Silicone implants, osseointegrated implants and functional outcome

Today the most widely used implants for small joint arthroplasty in the hand are flexible silicone implants, introduced by Swanson in the 1960 s. They are encapsulated by connective tissue, which allows pistoning movements in the bone marrow canal This type of implant, mostly used in rheumatic patients, gives high patient satisfaction, relief of pain, correction of deformity and a changed arc of motion towards a more functional position. With time, recurrence of deformity and bony changes occur. Newer implant designs based on the same concept have been introduced, e.g. Avanta (former Sutter). Osseointegration as a method to fixate titanium to bone was introduced by Brånemark in the 1970 s and has been used in dental implant surgery with excellent long-term results. A constrained implant for metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints in the hand was developed based on the osseointegration concept, with titanium fixtures for anchorage to bone connected by a flexible silicone spacer.Aims of these studies were to: 1) compare clinical results after MCP joint arthroplasty with Swanson implants and Avanta implants and 2) evaluate results after MCP and PIP joint implants, based on the concept of osseointegration and 3) evaluate the success of the fixation. Methods used were a 1) prospective, randomised study comparing Swanson and Avanta implants and 2) retrospective follow-up of MCP and PIP joints based on osseointegration. Clinical and radiographical evaluations were made of all patients. The fixation was evaluated separately in a radiographical study, using a descriptive scoring.Results show that Swanson and Avanta implants give high patient satisfaction, correction of deformity and change of arc of motion. Avanta implants provided 7 degrees more improvement in range of motion than Swanson implants. No improvement was seen in grip strength or hand function. 20% of Avanta implants and 13 % of Swanson implants fractured, with a higher risk for implant fracture in men.The results with osseointegrated MCP and PIP implants showed high patient satisfaction, correction of deformity, improved range of motion and a significant improvement in hand function. There was a high fracture frequency of the silicone spacers (25% and 18%, respectively). In the larger material looking at fixation 450 of 478 fixtures were assessed as osseointegrated. A higher risk of loosening was seen when anchorage was seen only to spongious bone as compared to cortical bone.Conclusions: The outcome with Swanson and Avanta implants was similar and the fracture frequency with increased risk in men indicates that limited indications for surgery in men or restricted loading might improve results. Implants based on osseointegration gave good clinical results with improved hand function, but due to the high fracture frequency the silicone spacer was abandoned. Osseointegration as method for fixation is predictable and reliable and works well in one stage surgery also in patients with rheumatoid arthritis