# Long-term migration of monoblock vs modular design in uncemented total knee arthroplasty: a secondary report of a randomized trial using radiostereometric analysis

## TL;DR

This study compares the long-term performance of two types of knee implants and finds that one design reduces early movement but not long-term migration.

## Contribution

The study provides 7-year RSA data showing monoblock design reduces early micromotion compared to modular design in TKA.

## Key findings

- Monoblock implants showed significantly lower mean MTPM (0.78 mm) compared to modular (1.17 mm) after 7 years.
- Early migration was lower in monoblock, but continuous migration after 12 months was similar between groups.
- Results confirm previous findings about the benefits of monoblock design in reducing early implant movement.

## Abstract

Backside wear of the polyethylene insert in total knee arthroplasty (TKA) has been described to produce clinically significant levels of polyethylene debris, which can lead to aseptic loosening and osteolysis. Monoblock design eliminates backside wear of the polyethylene and therefore could improve long-term fixation. This randomized clinical trial (RCT) using radiostereometric analysis (RSA) compares micromotion of monoblock and modular polyethylene inserts with 7 years’ follow-up.

65 patients (mean age 61 years) were randomized to receive either monoblock (n = 32) or modular (n = 33) uncemented trabecular metal tibial components. 35 patients (monoblock = 18, and modular = 17) completed 7 years’ follow-up. The primary endpoint of the study was maximum total point motion (MTPM). Implant translation and rotation are reported as secondary endpoints.

After 84 months, the modular group had a statistically significant higher mean MTPM of 1.17 (95% confidence interval [CI] 0.90–1.41) mm compared with the monoblock group of 0.78 (CI 0.55–0.88) mm (P = 0.02). However, there was no difference in continuous migration (from 12–84 months), which was 0.13 mm in the monoblock group and 0.16 mm in the modular group.

There was significantly lower early migration in the monoblock group compared with the modular group but no difference in continuous migration after 12 months, which confirms the finding of previous publications.