When Polyethylene Exchange Is Appropriate for Prosthetic Knee Instability.

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering

Background:

• Prosthetic knee instability is a frequent complication following total knee arthroplasty (TKA), leading to patient dissatisfaction and device failure.
• Management strategies for TKA instability depend on accurate classification of the instability pattern, as some cases require revision surgery while others may be amenable to polyethylene exchange (PE) alone.

Purpose of the Study:

• To retrospectively review and classify a series of patients who underwent isolated polyethylene exchange (PE) for managing prosthetic knee instability after TKA.
• To evaluate the efficacy of PE-only management for TKA instability using the OrthoCarolina Prosthetic Knee Instability Classification System.

Main Methods:

• A retrospective chart review of 1606 revision TKA cases identified 4% that underwent isolated PE for prosthetic knee instability.
• Patients were classified using the OrthoCarolina Prosthetic Knee Instability Classification System.
• The study included 41 patients with an average follow-up of 43 months.

Main Results:

• Among patients treated with PE only for appropriate indications (coronal instability with competent ligaments or global instability), 63% reported knee stability, while 37% remained unstable.
• Pain improvement was reported by 59% of patients, but 41% were dissatisfied with pain relief post-revision.

Conclusions:

• The outcomes of PE-only treatment for TKA instability, even when indicated, are unpredictable, with approximately 50% of patients achieving both stability and adequate pain relief.
• This low-morbidity option does not guarantee favorable results, underscoring the significant challenge in managing prosthetic knee instability.
• Prevention of prosthetic knee instability during primary TKA surgery is crucial.