Introduction: The level of femoral neck resection is important during THR. Intraoperative landmarks include the greater trochanteric tip, lesser trochanter and femoral head height. However, intraoperative identification can be difficult. It is possible to use callipers from the apex of the femoral head in the long axis of the femur but this produces geometrical error resulting in under resection.

We describe a simple method that resects the posterior femoral head to allow uniplanar measurement with a ruler.

Inclusion Criteria: Uncemented THR performed by the senior authors (MSB & LV).

Methods: Neck resection level was calculated from templated preoperative AP radiographs as the distance from the femoral head apex.

After head dislocation via a posterior approach, the head is resected with an oscillating saw parallel to posterior neck in the coronal plane

A ruler is placed on the cut surface with a clip attached at the templated resection level and the level marked.

Standard operative technique to insert prosthesis ensuring stability and leg length equalisation.

Pre and postoperative AP radiography were compared to calculate accuracy.

Results: 22 Uncemented THR’s, M:F = 10:12, Mean age = 54.5yrs (range 43–83yrs), Range of variation in resection level = −3 to +8mm, Mean (95%CI) of variation in resection level = +3.61mm (±0.26mm)

Assuming 20% radiographic magnification = +2.95mm (±0.20mm)

Discussion: Our results are comparable to other methods described in the literature and illustrate that this simple technique can accurately translate the templated neck resection level using standard Arthoplasty tray equipment.

Litigation for leg length discrepancy is becoming more prevalent in UK practice and with differing radiograph magnification levels careful planning and sound surgical technique is essential.

Digitised calibrated radiographs and templates are becoming standard practice and this simple technique will continue to ensure accurate leg length equalisation