The effects of varus tibial alignment on proximal tibial surface strain in total knee arthroplasty - The posteromedial hot spot

The aim of this study was to determine the effect of varus tibial alignment on proximal tibial strain in total knee arthroplasty. Fourteen paired fresh-frozen cadaver tibiae had photoelastic coating applied. The right tibiae were cut in neutral alignment, and the left tibiae were cut in 5degrees of varus. Components were cemented and loaded with 3 x body weight, varying medial to lateral load. Surface microstrain was measured. There was a statistically increased hot spot of highly concentrated strain in the posteromedial quadrant of the proximal tibia in varus-cut bones (P<.05). In neutral alignment, the strain was nearly equal medial and lateral. The increased strain observed helps elucidate the mechanism of increased failure rates of a total knee arthroplasty inserted in varus alignment. Neutral alignment may have a protective effect.