Standardized loads acting in knee implants

Bergmann G, Bender A, Graichen F, Dymke J, Rohlmann A, Trepczynski A, Heller MO, Kutzner I · PLoS One

Peak contact forces reached 3,372 to 4,218 N across every activity except jogging, where they reached 5,165 N. The largest torque about the implant stem occurred during walking, at 10.5 Nm, higher than during jogging. Transverse forces and moments varied widely between individuals, especially in non-cyclic activities. Most of the measured high load levels exceed those specified in the ISO 14243 wear test standard, which the authors argue should be revised.

Population

Eight people with instrumented knee implants that measure contact forces and moments inside the joint and transmit them by radio

Intervention

Walking, stair climbing and six further everyday activities, averaged into standardised load profiles

Limitations

Eight people, all with a knee replacement rather than a native knee, so the absolute forces describe an implanted joint and transfer to a healthy one only as an approximation. Averaged load profiles smooth over the between-subject variation the paper itself flags as large. It measures load, not consequence.