Spontaneous tibial insert dislodgement in unicompartmental knee prosthesis
Presentation
Sudden severe left knee pain. Previous medial unicompartmental knee prosthesis insertion.
Patient Data
Two linear radio-opaque markers outline the polyethylene insert that normally sits on the tibial component of the unicompartmental (medial) knee prosthesis.
In a previous X-ray exam, the markers were symmetrically positioned between the femoral and tibial components with an associated lucent gap - this is normal.
Case Discussion
Polyethylene spacers or inserts are inserted between the 2 components of a prosthesis for articulation, much like articular cartilage. They are attached to the tibial component in a knee prosthesis and are prone to wear over time and can lead to foreign body reaction (particle disease or aggressive granulomatosis). Rarely they can dislodge.
Polyethylene is radiolucent; thus, radio-opaque markers are inserted by the manufacturer so that the position of the spacer could be monitored.