Evaluation of a novel method to calculate cementless femoral stem level on craniocaudal projection radiographs.

Objective: To assess the accuracy of a proportion-corrected radiographic cementless femoral stem level calculation in a cadaver model.

Study Design: Cadaveric study.

Sample Population: Twelve cadaveric canine femurs.

Methods: Cementless femoral stems were implanted in 12 cadaver femurs at three stem levels. Craniocaudal projection radiographs of the implanted femurs were obtained at 0°, 10°, 20°, 30°, and 45° angulations in the sagittal plane (relative to the radiographic plate) and at 0°, 15°, and 30° internal and external axial rotation. A proportional calculation including actual stem length, radiographically measured stem length, and radiographically measured stem level relative to the greater trochanter (uncorrected stem level) was solved to yield a corrected stem level. The errors of the stem level measurements were compared.

Results: With 0° or 15° of internal rotation, the true stem level differed by more than 0.5 mm from corrected stem level in 2 of 30 tested femoral positions. It differed from the uncorrected stem level in 10 of 30 positions. With 15° and 30° external rotation or 30° internal rotation, the corrected stem level was not more accurate than the uncorrected stem level for any femoral position.

Conclusion: Use of a proportion correction minimized variability in the stem-level measurements due to sagittal angulation (up to 30°) of the femur at 0° or 15° of internal rotation.

Clinical Significance: A proportion correction can improve the accuracy of femoral stem-level assessment on craniocaudal projection radiographs, which may aid in the detection of subsidence after cementless total hip replacement.