Impressive Long-term Outcomes in Revision TKA with Constrained Prostheses

Time is an enemy of all orthopaedic implants, just as it is the bane of native joints. It is therefore helpful to accurately measure how long and well specific implant types last. That is what Kim et al. have done with their 19-year follow up of 90 patients (107 knees) who underwent total knee arthroplasty (TKA) with a constrained condylar knee prosthesis. Their findings appear in the April 15, 2020 issue of The Journal of Bone & Joint Surgery.

Knee arthroplasty surgeons often choose constrained prostheses to improve joint stability in patients with ligament dysfunction, and the typically longer stems of these implants can also compensate for poor bone stock. Kim et al. evaluated the same patient population (mean age of 65 years; mean BMI of 26.9 kg/m²) that they reported on in an earlier study, finding the following outcomes after a mean follow-up of 19 years:

• 96% survival in terms of mechanical failure
• 91% survival in terms of reoperation for any reason
• Patient-reported outcome scores that remained significantly improved from pre-revision values
• Only 1 knee with osteolysis around a component

Among the few knees that required re-revision, 5 such operations were performed due to aseptic loosening and 4 due to infection. The authors note that these very good long-term results are similar to those in previous studies of revision TKAs using various implant types. Kim et al. attribute these findings to several possible factors:

• Low prevalence of comorbidities, including obesity, among the patients
• Excellent surgical technique, including good cementing and correct flexion and extension gaps
• Use of compression-molded polyethylene