Introduction Correct postoperative leg alignment and stability of total knee prothesis over the full range of movement is one critical factor for successful TKA. This can only be achieved by correct implantation of prothesis and soft tissue handling. Still arthrotomy, surgical approach and handling of patella are discussed controversially.

Materials and Methods In a cadaver specimen study we evaluated the influence of everted or subluxated patella on limb axis during balancing of the knee in three different standard surgical approaches. For each approach we operated five knees. Leg alignment was visualised by Ci CT-free DePuy/BrainLAB navigation system. First, physiological leg alignment was measured. Then the different approaches were performed and a.p. leg axis was first measured and compared as well with everted as with subluxed patella in extension and second in 90 degrees flexion.

Results Eversion of patella leads to an alteration in leg axis compared to subluxed patella of 0.58 degrees (SD: 0.03, range: 0.54–0.6) limb axis in valgus direction in full extension. In 90 degrees flexion we found a mean deviation of leg axis of 0.48 degrees (SD: 0.11, range: 0.38–0.6) with everted patella compared to subluxed patella.

Discussion The surgeon has to be aware of this falsifying influence of everted patella to the a.p. limb axis.