Tibial implant migration of cemented and cementless total and unicompartmental knee arthroplasties in patients with low and normal bone mineral density: a 5-year RSA cohort study of 397 cases

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BACKGROUND AND PURPOSE: Periprosthetic bone may influence the longevity of joint implants. We aimed to investigate the association between bone mineral density (BMD) and tibial implant migration of cemented and cementless knee arthroplasty as a surrogate marker of aseptic loosening. METHODS: In a prospective cohort study, patients were operated on between 2014 and 2018 with a unicompartmental knee arthroplasty (UKA) or a total knee arthroplasty (TKA). Preoperative BMD was measured using dual-energy X-ray absorptiometry of the lumbar spine and hips. Patients were categorized into low or normal T-score groups (threshold: T-score ≤ -1.0). Postoperative tibial implant migration was assessed using radiostereometry at baseline and 1-, 2-, and 5-year follow-ups. The primary outcome was 1-year maximum total point motion (MTPM) differences between T-score groups. Secondary outcomes evaluated the association between continuous migration (MTPM > 0.2 mm between 1 and 2 years) and T-score. RESULTS: 397 patients were included, where 210 patients received a cementless implant (TKA = 78, UKA = 132) and 187 received a cemented implant (TKA = 83, UKA =104). Estimated 1-year mean MTPM differences between the low and normal T-score groups were 0.15 mm (CI -0.25 to 0.55) for cementless TKA, 0.12 mm (CI -0.25 to 0.49) for cemented TKA, -0.21 mm (CI -0.51 to 0.10) for cementless UKA, and -0.15 mm (CI -0.34 to 0.04) for cemented UKA. A 1-unit increase in T-score showed comparable odds of continuous migration within both cemented (OR 0.94, CI 0.68-1.30) and cementless (OR 0.79, CI 0.56-1.12) tibial implants. CONCLUSION: Tibial implant migration was not significantly different between patients with low and normal BMD as defined by T-score groups. These findings should be interpreted cautiously due to small group sizes and wide confidence intervals, highlighting the need for further studies to clarify the role of BMD in implant migration.

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