| Abstract / Summary | Knee osteoarthritis (OA) is the most common form of arthritis in adults and is a major cause of joint pain, reduced quality of life and disability. The number of patients with severe OA requiring knee arthroplasty (KA) is increasing, driven by population growth and ageing. In 2024, 15,000 primary KAs were inserted in Denmark – the highest number recorded in the Danish Knee Arthroplasty Register. KA is an effective treatment for severe OA, but up to 5% of implants require revision surgery within the first five years. Revisions are more complex, costlier and associated with higher complications and risks for the patients. Therefore, there is a need to improve the longevity of knee implants. The most common causes of revision are aseptic loosening, infection and instability. Currently, knowledge concerning risk factors for aseptic loosening and strategies to improve tibial implant fixation remains limited. Aseptic loosening is strongly associated with early implant migration, which is measured by radiostereometric analysis (RSA). Implant migration is therefore a validated surrogate marker for long-term implant survival.
This PhD investigated the effect of bone mineral density (BMD), fixation method and adjuvant antiresorptive treatments on early tibial implant migration. The aim was to generate new knowledge that may inform more individualised treatment strategies to improve knee implant longevity, improve patient outcomes, reduce revision rates and lower healthcare costs.
Study I investigated the association between preoperative BMD of the lumbar spine and total hip and tibial implant migration. No association was found between BMD and early implant migration or 1-2-year migration for cemented or cementless tibial implants. This contrasts with previous studies reporting an association between the migration of cementless tibial implants and tibial BMD. Clearer guidelines are needed for the use of cementless tibial implants and preoperative dual-energy X-ray absorptiometry (DXA) in diagnosing osteoporosis or low tibial BMD before surgery. It remains unclear whether preoperative DXA can improve implant survival by informing treatment strategies. Further research is needed to investigate the specific effect of BMD on tibial implant migration and to determine whether routine preoperative DXA could guide fixation choice and improve patient outcomes and implant survival.
Study II investigated the influence of fixation method on tibial implant migration, bone turnover markers and the periprosthetic BMD. Cementless tibial implants had higher early migration than cemented implants, but both groups showed stable migration patterns between 1 and 2 years. Periprosthetic BMD was preserved in the cementless group in the early period after surgery, while BMD declined in the cemented tibial group. Bone turnover markers were comparable between groups after surgery.
Study III investigated the effect of local and systemic adjuvant antiresorptive treatment (zoledronate and denosumab) on tibial implant migration. Both local and systemic antiresorptive treatment reduced tibial implant migration. Local intraoperative zoledronate treatment reduced subsidence and preserved the periprosthetic BMD, which is expected to improve implant survival. Additionally, local zoledronate applied to the cut tibial bone during surgery is a quick, low-cost and safe treatment with clinical potential. These results support implementing adjuvant intraoperative local zoledronate with cementless total tibial implants to reduce revision risk, which will potentially have a profound impact on both the patients and society. Further multicentre studies involving larger cohorts and variant implant types are needed to confirm these promising results.
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