Data from a large national registry was used to study patient and prosthesis characteristics of 2,605 total knee arthroplasty revisions for instability. The study showed that instability increased from 6% of all ﬁrst revision procedures in 2003 to 13% in 2019. The risk of having the procedure revised was lower for minimally stabilized prostheses, males and patients aged over 65 years. The risk was higher for females and patients younger than 65 years. Polyethylene inserts were exchanged for 55% of revision procedures, using a thicker insert in 93% of the cases and there was a change in insert conformity in 24% of cruciate-retaining knees. However, the increase in either thickness or conformity had no effect on the rate of further revision.
Following a revision for knee joint instability, 24% had a second revision within 14 years and recurrent instability accounted for 32% of further revisions. The analysis also found a variation in the types of revision procedures, which probably reflects the diversity in the type and extent of the instability. Although a patient-speciﬁc approach to TKA instability is encouraged, these minor revisions were less successful than major total revisions, which were often due to more constrained prostheses.
The need to have revision surgery for instability is increasing, although revising both femoral and tibial components led to a lower number of patients requiring revision, compared to a change in the insert alone. Recurrent instability was common, which was the most frequent cause for a second revision, however using a fully constrained or hinged device lowered the risk of a further revision.