Stress Radiograph Confirmation of Translational Instability After Cruciate-Retaining Total Knee Arthroplasty

INTRODUCTION: Late rupture of the posterior cruciate ligament (PCL) in cruciate-retaining total knee arthroplasty (TKA) can lead to increased AP instability. This results in increased stress on the medial hamstrings resulting in hamstring-based pain. We looked to identify patients with late PCL failure using a lateral stress radiograph. METHODS: A prospective cohort analysis was completed at a single institution. Eligible patients were divided into two groups based on the amount of anterior knee pain. Pain was defined as a visual analog scale of greater than or equal to 3. Each group completed a visual analog scale, Knee Injury and Osteoarthritis Outcome Score Junior, Patient-Reported Outcome Measurement Information System score and underwent a lateral posterior stress/nonstress radiograph. Amount of posterior translation and posterior tibial slope was measured. RESULTS: Patients who had painful TKAs at the follow-up had lower Knee Injury and Osteoarthritis Outcome Score Junior (45.86 ± 13.52 versus 78.00 ± 13.26 P < 0.001). Those patients were also found to have significantly higher posterior tibial translation with stress radiograph (6.89 ± 1.874 versus 3.91 ± 2.15 mm P < 0.001) and significantly increased tibial slope (6.51 ± 2.37° versus 3.98 ± 1.79°, P = 0.004). Seven of the 14 patients in the pain group underwent revision surgery, with 6 patients found to have incompetent PCLs. DISCUSSION: Patients with increased AP translation and increased posterior tibial slope after cruciate-retaining TKA are likely to have worse pain and outcome measures.