Poor bone quality need not be a barrier for total knee arthroplasty (TKA) in patients with rheumatoid arthritis (RA), say surgeons.
"Our data suggest a TKA system that uses an osseointegration technique for fixation offers good clinical function and pain relief for patients with RA," comment Leo Whiteside (Missouri Bone and Joint Center, St. Louis, USA) and co-authors.
The two common forms of TKA are fixed either by in-growth to dense, porous bone, or by cement attachment. Porous in-growth fixation is generally used in young, heavy patients with hard bone while the cement technique is more often used in elderly patients, especially those with RA.
However, recent studies have suggested that porous in-growth fixation might also be suitable for older RA patients with some slight modification to the implant materials used.
Giving joint implants a porous coating has greatly improved outcomes both of hip replacement and in patients with RA, Whiteside and colleagues note in the journal Clinical Orthopaedics and Related Research.
For the current trial, Whiteside et al tested the benefits of a sintered bead, porous-coated implant used to replace 64 knees in 47 patients with RA. They used standard implants except in patients with major bone defects. In these patients, they added long diaphyseal stems to the implants to help stabilize them.
After a follow-up period of approximately 10 years, the authors report that 98.4% of the implants were still viable with no failures because of loosening, which is the usual cause of failure in patients with RA.
Radiography confirmed that the implants were remarkably stable, with no evidence of migration or widening radiolucent lines.
In addition to their stability and viability, the implants were associated with significant and sustained improvements in patient-reported pain and function scores.
The authors conclude that the sintered-bead porous-coated implant is viable in the long term. They add that even arthritic bone stock "appears capable of supporting press-fit implants, even when it is deficient and requires supplementary fixation of the implants."