Revision total knee arthroplasty for instability – outcome for different types of instability and implants

Abstract Background Given the mixed outcome after revision TKA for instability in the literature and the relative high recurrence of instability we were interested in the outcome of a cohort of patients operated for various types of clinical instability and with different type of implants. Methods Seventy-seven patients with unstable TKA were completely revised (19 hinged and 58 condylar implants). We classified the patients in three instability groups based on the literature: 1. Anterior-posterior flexion instability (N=29); 2. Medial-lateral flexion instability (N=16) and 3. Multiplane instability (N=32). Patients were evaluated up to 24 months postoperative, concerning KSS, ROM, VAS pain and VAS satisfaction. Results For the total group all outcome scores improved but substantial residual pain (VAS=41) was reported. For type of instability, the clinical outcome was similar for all groups. For type of implant, the hinged group had lower postoperative outcome scores, but similar satisfaction scores compared to those in the condylar group. There was a considerable number of insert changes and secondary patellar resurfacing in the condylar group compared to no reoperations in the hinged group. Recurrent instability was not seen in the anterior-posterior flexion instability group and in patients who received a condylar constraint type implant. Conclusions We recommend three options in revision total knee arthroplasty for instability: 1. hinged implants in cases with severe ligament instability in multiple planes or bone loss, 2.condylar implants with a posterior-stabilized insert in cases with isolated posterior cruciate ligament insufficiency, and 3. condylar implants with condylar constraints in all other cases.