Preoperative surgical planning in total hip arthroplasty: pitfalls and pearls for femoral offset measurements

BACKGROUND: Preoperative planning for total hip arthroplasty (THA) is essential to achieve a favorable outcome and long-term implant survival. Radiographic planning is still widely used, with intrinsic limitations of the technique. Surgeons often do not have access to proper hip radiographs due to erroneous acquisition or limited motion in the osteoarthritic hip. The femur is often captured externally rotated and the femoral neck appears shortened. Surgeons need to be aware of this pitfall and overcome this bias. To restore the femoral offset (FO) on inaccurate radiographs, the virtual line connecting the intertrochanteric line to the intertrochanteric crest, called the double profile of the greater trochanter (DPGT), could be the length to correct the underestimated FO.METHODS: This retrospective study was performed at the University Hospital of Florence. Overall, 676 consecutive radiographs were analyzed. 119 patients with monolateral coxarthrosis were enrolled. FO on healthy hip was compared with pathological FO, the respective DPGT was added to the formers.RESULTS: The results show that the FO on the osteoarthritic hip is statistically shorter than the FO on the healthy hip along the entire distribution. It can be assumed that there is no difference between the FO of healthy and pathological hips when summed to the respective DPGT (-0.4958; 0.0025 mm, P<0.001).CONCLUSIONS: To date, there are no quantitative measures to assess the degree of femoral external rotation on radiographs. Preliminary results show that the addition of DPGT to FO is a reproducible method that showed consistency in our cohort.