Adjustment of leg length using imageless navigation THA software without a femoral tracker

Adjustment of leg length discrepancy is an important factor influencing the outcome of total hip arthroplasty (THA). However, leg length discrepancy after THA has been reported to be associated with inferior clinical outcome in previous studies. A new version of the imageless navigation software "OrthoPilot THAplus" has been developed to assess the leg length adjustment and offset value. The clear advantage of this system is the elimination of the need for femoral pin insertion, which is associated with potential complications and additional surgical invasion.

In this study, the accuracy of this newly developed system was evaluated in 50 consecutive hips implanted with primary THA. The operative results of these 50 patients were compared with those of another 50 consecutive primary THA patients operated on with the previous navigation system that was not equipped with the leg length adjustment system.

After surgery, the average leg length discrepancy in the THA plus group was 0.9 mm (range -5 to 5 mm), while the corresponding value in the other group with the older software was 2.9 mm (range -13 to 20 mm), showing a significant difference.

The accuracy and reproducibility of new software added to the imageless THA navigation system in achieving equalization of leg length were assessed. Comparison of the surgical results as compared with the control group performed with the conventional navigation system showed the advantage of this system over the previous system.