Abstract
Mobile bearing total knee prostheses have a potential for bearing dislocation or spinout. Surgeons must understand the etiology and management of this unusual complication. Prior reports have identified bearing dislocations as an important complication surgical technique and surgeon experience being important associated factors. We have observed an unusual case of dislocation of a posterior-stabilized rotating-platform total knee arthroplasty, which had both a cam-post mechanism and a rotating platform. The patient, a 79-year-old woman with knee osteoarthritis and lumbar canal stenosis underwent primary total knee arthroplasty using a mobile bearing prosthesis. Six weeks after the operation, she sustained a complete dislocation of the PFCΣ RP-F prosthesis. We tried closed reduction without anesthesia. The causes of posterior dislocation are multifactorial. Potential contributory factors may include component malposition, extensor mechanism and patella dysfunction, prosthesis design and an increased flexion gap. Posterior translation of the tibia “drives” the rotation while the knee is in flexion. Muscle weakness of the quadriceps was present, as a result of lumbar canal stenosis. After surgery (laminectomy), the quadriceps deficiency was ameliorated. Surgical error in soft tissue balancing is the cause in the majority of cases with failure to achieve correct balance, particularly the flexion gap.
