TKA Instability

Instability is one of the main mechanisms of failure after total knee replacement. Several studies describe a prevalence of this condition of between 10% and 22%, constituting the second or third cause of prosthetic revision. In order to achieve a satisfactory result, it is necessary to make an accurate diagnosis about the etiology that caused instability in order to provide an appropriate solution. Instability may arise after component loosening, trauma, insert wear, ligamentous instability, or surgical errors. The physical examination of a painful knee arthroplasty should be thorough and methodical. In the first place, one should rule out periprosthetic joint infection. Classically, five types of instability are described after total knee arthroplasty: flexion, extension, mid-flexion, hyperextension, and global instability. The vast majority of patients who present instability after total knee arthroplasty will require surgical treatment, so preoperative planning is extremely important. The surgical approach will depend on the condition of the collateral ligaments, the flexion and extension gaps, the position of the joint line, and the alignment of the components. Surgical options vary from polyethylene insert exchange to revision of both components of the total knee prosthesis with varying levels of constriction. As a general rule, it is recommended to use the implant with the least degree of constriction necessary to restore stability to the knee.