[Unicondylar knee arthroplasties demonstrate a significantly increased risk of aseptic revisions compared with unconstrained and constrained TKA : Analysis of aseptic revisions after unicondylar and primary total knee arthroplasty of the German Arthroplasty Register].

Objective: Owing to the ageing population the implantation rate of total knee arthroplasty (TKA) continues to rise. Aseptic revisions in primary TKA are one of the main causes of revision. The aim of the following study was to determine the incidence of and reasons for aseptic revision in constrained and unconstrained TKA and in unicondylar knee arthroplasty (UKA).

Methods: The data collection was carried out with the help of the German Arthroplasty Register (EPRD). The reasons for aseptic revision surgery were worked out using this. The incidence and the comparison of aseptic revisions were analysed with the aid of Kaplan-Meier estimates. A multiple Chi-squared test with the Holm method was used to identify group differences in collateral ligament deficiencies.

Results: In total, 300,998 cases of knee arthroplasties were analysed, of which 254,144 (84.4%) were unconstrained TKA, 9993 (3.3%) were constrained TKA and 36,861 (12.3%) were UKA. The rate of aseptic revisions was significantly increased compared with unconstrained and constrained TKA (p < 0.0001). In constrained TKA, a revision rate of 2.0% for aseptic reasons was reported, whereas in unconstrained TKA 1.1% and in UKA 2.7% revision surgeries were identified. After 7 years the rates of aseptic revisions amounted to 3.3% for constrained TKA, 2.8% for unconstrained TKA and 7.8% for UKA. Ligament instability was the most common cause of aseptic revisions and accounted for 13.7% of unconstrained TKA. In constrained TKA ligament instability led to a revision in 2.8% of cases. In UKA, tibial loosening was identified to be the most common cause of revisions at 14.6%, whereas the progression of osteoarthritis was responsible for 7.9% of revisions. Ligament instability was observed in 14.1% of men compared with 15.9% of women in unconstrained TKA and in UKA in 4.6% of cases for both sexes.

Conclusion: In patients with UKA the rates of aseptic revision are significantly higher than in unconstrained and constrained TKA. Ligament instability was the most common cause of aseptic revision in unconstrained TKA. In UKA, tibial loosening was the most common cause of revision surgery, whereas the progression of osteoarthritis was the second most common cause. Comparable levels of ligament instability were observed in both sexes.

Level of evidence:  III, cohort study.