Introduction: The goal of the study was to determine the precision of a three-dimensional pre-operative planning tool using a specific software (HIP-PLAN^®) and an anatomic cementless neck-modular stem.

Method: 223 patients who underwent a primary total hip replacement had a CT Scan before and after surgery. A pre-operative three-dimensional planning based on the CT-scan was performed. A cementless cup and a neck-modular stem were used. A computational matching of the pre-operative and the post-operative CT-scans was performed in order to compare the values of the planned anteversions and the planned displacement of the hip rotation center to the post-operative values.

Results: The implanted component was the same as the one planned in 89% for the cup and 94% for the stem. For the mean femoral anteversion, there was no significant difference between the planned value (26.1° +/−11.8) and the post-operative value (26.9° +/−14.1). There was a poor correlation between the planned values and the actual ones for the acetabular cup anteversion (coefficient 0.17). The hip rotation center was restored with a precision of 0.73 mm +/3.5 horizontally and 1.2 mm +/−2 laterally. Limb length was restored with a precision of 0.3 mm +/−3.3 and the femoral off-set with a precision of 0.8 mm +/−3.1. There was no significant modification of the femoral off-set (0.07 p=0.7) which was restored or slightly increased in 93% of cases. Almost all the surgical difficulties were predicted

Conclusion: HIP-PLAN^® software is a reliable three-dimensional pre-operative planning tool which allows acurate prediction of components and hip anatomy.