Total knee dislocation due to rotatory malalignment of tibial component: a case report.

Dislocation of a total condylar knee replacement occurred because of rotatory malposition of the tibial component. The dislocation was evaluated by open operation and in the laboratory. It can be prevented by: directing the tibial component at the tibial tubercle; not using the posterior edge of the tibia to align the tibial component; recognizing the "contradictory rotation" of the tibia. At operation the tibia externally rotates with flexion and lateral patellar dislocation for exposure. However, the screw-home mechanism in normal gait causes the tibia to internally rotate with flexion. This difference of rotation increases the likelihood of dislocation. Other problems caused by rotatory malposition of the tibial component are: patellar subluxation in a hinged knee prostheses; patellar malalignment, patellar pain and possible prosthetic patellar loosening; abnormal eccentric loading of the tibial component and subsequent tibial-component loosening in all knee prostheses.