A Hybrid Surgical Approach to Late Posterolateral Instability Following Total Knee Arthroplasty: A Case Report of Posterolateral Corner Reconstruction with Component Retention.

Introduction: Post-operative instability is a challenging complication following total knee arthroplasty (TKA), with most literature addressing coronal or sagittal laxity. Rotational instability, particularly involving the posterolateral corner (PLC), is rare and frequently overlooked. Conventional revision strategies often involve increasing constraint or complete component revision, which may not be appropriate in cases with well-aligned and well-fixed implants. Case Report: A 60-year-old female presented 1-year post-primary TKA with symptomatic instability, manifesting as difficulty stair climbing and diminished confidence in the operated limb. Clinical evaluation revealed varus thrust, a positive dial test at 30°, and posterolateral laxity. Radiographic and computed tomography assessment confirmed well-positioned, stable components with no evidence of infection. Intraoperative findings demonstrated significant rotational instability of the rotating platform polyethylene insert without mechanical failure. A hybrid surgical solution was utilized: retention of the well-fixed components, upsizing of the polyethylene insert, and anatomic PLC reconstruction using a semitendinosus autograft. Postoperatively, the patient achieved marked improvement in functional stability and mobility, resuming independent activities. At 8-month follow-up, validated outcome scores demonstrated substantial enhancement, with no recurrent instability or complications. Conclusion: This case report illustrates a novel hybrid stabilization technique for late PLC-derived rotational instability after TKA. Combining polyethylene insert upsizing with anatomic PLC reconstruction effectively restored knee stability while preserving well-fixed components, presenting a viable joint-preserving alternative to conventional revision arthroplasty in selected patients.