Potential errors in axial alignment using intramedullary instrumentation for total knee arthroplasty.

Accurate restoration of normal limb alignment is crucial for the long-term survivorship of total knee arthroplasty (TKA). A mathematical model was used to evaluate the maximum error in varus and valgus alignment that could occur when cutting the tibia or femur during TKA using intramedullary (IM) guides of varying length and diameter. Minor deviations in the insertion point of IM instrumentation during TKA can result in malalignment of several degrees. This error can be minimized by careful attention to the entry point of the IM instrumentation or by increasing the IM rod diameter and length used during primary TKA.