Alignment in total knee arthroplasty. Correlated biomechanical and clinical observations.

The initial experience with the Freeman-Swanson (ICLH) total knee arthroplasty (1971-1975) led to changes of tibial component size, alignment, instruments, and surgical technique in 1975. Certain patients in this initial series, however, have shown excellent long-term (5 1/2-9 years) results. In patients with overall alignment between 1 degrees and 13 degrees valgus, the success rate was 89%. In patients with knees aligned between neutral and 8 degrees varus, the success rate was only 14%. This startling difference in long-term results was investigated by using eccentric loading tests to simulate varus and valgus malalignment. Knee arthroplasties failed in eccentric loading at very low loads. Failure by lift-off of the unloaded side occurred at 9%-18% and failure of bone due to compression on the loaded side occurred at 34%-51% of the load at failure under ideal uniform loading conditions. Thus, both the long-term clinical study and the laboratory analysis demonstrate the importance of proper overall alignment in total knee arthroplasty.