Effect of activity level after a posterior-stabilized TKA on the relative bone mineral density measured on standard radiographs in periprosthetic tibial bone

Abstract

Background: The aim of this study was to evaluate the effect of activity level after a posterior-stabilized total knee arthroplasty (TKA) on the relative bone mineral density (rBMD) measured on standard radiographs in periprosthetic tibial bone. Methods: A retrospective review identified 110 patients (110 knees，20 men/90 women) who underwent PS TKA with 5 years follow-up. Patients activity level was evaluated by University of California Los Angeles (UCLA) activity score, and the rBMD in periprosthetic tibial bone was measured on anteroposterior X-ray images. Clinical assessments included Western Ontario and McMaster Universities (WOMAC), Knee Society score (KSS) and visual analogue scale (VAS). Nonlinear regression analysis was used to assess the impact of activity levels on periprosthesis bone density.Results: During 5-year follow-up period, the bone density in the medial, lateral and distal areas decreased compared with that before surgery (p<0.0001). There was a U-shaped distribution between UCLA activity rating and rBMD loss, with the lowest rBMD loss when the UCLA activity score was between 6-8 at 1 and 3 years. The curve fitting of UCLA activity level and rBMD% showed there was a parabolic relationship between UCLA activity level and rBMD% at 1 and 3 years after surgery (P<0.001, P=0.001), while there was no significant relationship between UCLA activity level and rBMD% at 5 years after surgery (P=0.436).Conclusions: We found that physical activity had a significant effect on radiographic measurements of BMD at 1 and 3 years but not at 5 years. Moderate activity may be associated with less proximal tibial BMD loss after TKA, therefore it may be the most appropriate activity intensity for patients with TKA.