A Simple Approach to Assessment of a Total Knee Replacement's Rotationary Profile Using Computed Tomography

Abstract

Malrotation is a cause of persistent pain and poor functioning postoperatively in those who undergo a total knee replacement (TKR). The accurate measurement of malrotation is not routinely available in most hospital settings due to an absence of three-dimensional computed tomography (CT) software. An accessible, uncomplicated technique to demonstrate TKR prosthesis malrotation would be of benefit to orthopaedic surgeons worldwide. A patient was reviewed with persistent postoperative pain, having undergone a right TKR 3 years previously for progressive osteoarthritis. Postoperative prosthetic infection, instability, loosening, and fracture were ruled out as causes for the persistent pain. A two-dimensional CT scan was obtained of the patient's affected right knee. Adhesive pieces of paper (Post-it notes) were used to highlight the posterior tibial prosthesis axis, the tibial tuberosity axis, the posterior condylar axis of the femoral prosthesis and the femoral surgical transepicondylar axis, as per the technique described by Berger et al. A protractor was used to assess the degree of malrotation of the tibial and femoral prostheses. Allowing for human error and that of parallax, an immediate assessment was made of the patient's prosthesis using a readily available imaging modality, and malrotation was quickly identified using accessible, affordable everyday stationary equipment.