title: Placement of a palpable marker adjacent to the mid-inguinal point: assessment of a clinical method for detecting the femoral head centre during knee arthroplasty.
abstract: Localization of the centre of the femoral head is vital when using extra-medullary femoral alignment systems in knee arthroplasty. This study investigated the accuracy of a palpable marker placed in the groin for detecting the centre of the femoral head. A table tennis ball, 38 mm in diameter, was taped 2.5 cm perpendicular to the mid-inguinal point in patients having a plain radiograph of the pelvis. The mean horizontal distance between the centre of the table tennis ball and a vertical line passing through the centre of the femoral head was 8.62 mm (range 0-28.6, SD 6.76). In 100% of cases the horizontal distance between the centre of the table tennis ball and a vertical line passing through the centre of the femoral head was less than one diameter of the table tennis ball. Using a theoretical mechanical axis model our clinical method would confer an error equal to or less than 2 degrees from the weight-bearing axis of the knee in up to 98% of cases. In conclusion, our results suggest that the clinical method reported here provides a simple and reliable way of localizing the centre of the femoral head in knee arthroplasty.
authors.affiliation: University of Manchester, Department of Orthopaedics, Manchester Royal Infirmary, UK.
authors.forename: R S
authors.initials: RS
authors.lastname: Samarji
authors.forename: C P
authors.initials: CP
authors.lastname: Charalambous
authors.forename: S
authors.initials: S
authors.lastname: Waldron
authors.forename: J
authors.initials: J
authors.lastname: Noble
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D005270:Femur Head / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D006621:Hip Joint / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000601:surgery*; D006801:Humans; D008297:Male; D008875:Middle Aged; D019047:Phantoms, Imaging; D055618:Radiation Equipment and Supplies; D011859:Radiography; D015203:Reproducibility of Results; D055815:Young Adult