A CLINICAL METHOD FOR LOCATING THE FEMORAL HEAD CENTRE DURING TOTAL KNEE ARTHROPLASTY

Abstract

Purpose: Localisation of the femoral head is essential during total knee arthroplasty for assessing the overall alignment of the leg. The purpose of this study is to describe and report the accuracy a clinical method of estimating the centre of the femoral head.

Method: A line is drawn joining the anterior superior iliac spine and the pubic tubercle on the patient lying supine on the operating table. The point where femoral artery crosses this line is estimated. The Femoral head centre is marked 1.5 cm lateral to this point. This point was marked with an ECG electrode which has a radiopaque and prominent centre that is easily felt through the drapes. A radiograph was then made with the tube at 1 metre from the plate and centred over the hip marker.

The error in the hip marker placement is measured as the transverse mm (corrected for magnification) of the marker from the centre of the head, which is located on the radiograph using a template of concentric. The potential angle of error in coronal alignment of the associated knee replacement is calculated trigonometrically from femoral and tibial lengths.

Patients: The study group was comprised of 73 consecutive patients (100 knees) who underwent primary Total knee replacement. There were 36 males and 37 females.

Results: The average error was 8 mm (Range 0–30 mm). It was lateral to the femoral head in 47 patients and medial in 53 patients. The error was significantly greater in female patients (7mm:10mm, p < .05). The calculated potential error in coronal alignment was < 20 in 84% of patients and < 30 in 99% of the knees.

Conclusion: This is a clinically useful method of locating the centre of the femoral head for surgeons who find + 3 degrees of error in coronal alignment acceptable. For those striving for greater accuracy a preoperative hip marked radiograph may be more helpful.