Knee Arthroplasty Instability Study

Total knee replacement (TKR) instability is a poorly defined entity. The diagnosis is based on symptoms and clinical tests of knee laxity. A subjective feeling of instability, such as giving away is not always present in the unstable knee; however, the patient will rather have non-specific symptoms like pain and swelling. On the other hand, symptoms of instability may be present without excessive laxity. The evaluation of abnormal laxity is also uncertain due to individual variations of normal laxity and the subjectivity of manual laxity testing. Different instrumented methods have been developed in order to reduce subjective bias. Stress radiography is one such test which has been utilised to objectively measure medial and lateral joint opening during varus/valgus stress and anteroposterior translation when subjected to sagittal stress. The limits of acceptable laxity measured by stress radiography is however not established. The aim of this study is to determine thresholds of acceptable laxity as measured by stress radiography.

Inclusion Criteria:Patients with cruciate retaining (CR) TKR with ≥12 months follow upExclusion Criteria:TKR implants with higher constrained articulations (posterior stabilized (PS), condylar constrained (CC) and hinged implants)Suspected infectionRange of motion (ROM) limitations that infers with protocol of stress testing; combined flexion contracture >30 degrees and flexion deficit < 80 degreesSuspected instability in contralateral knees