This Article Full Text Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal My Folders Download to citation manager Google Scholar Articles by Wroblewski, B. M. Articles by Fleming, P. A. PubMed PubMed Citation Articles by Wroblewski, B. M. Articles by Fleming, P. A.

The principle of low frictional torque in the Charnley total hip replacement

¹ The John Charnley Research Institute, Wrightington Hospital, Hall Lane, Appley Bridge, Wigan, WN6 0TS, UK.

Correspondence should be sent to Mr P. D. Siney; e-mail: paulsiney{at}hotmail.com

The design of the Charnley total hip replacement follows the principle of low frictional torque. It is based on the largest possible difference between the radius of the femoral head and that of the outer aspect of the acetabular component. The aim is to protect the bone-cement interface by movement taking place at the smaller radius, the articulation. This is achieved in clinical practice by a 22.225 mm diameter head articulating with a 40 mm or 43 mm diameter acetabular component of ultra-high molecular weight polyethylene.

We compared the incidence of aseptic loosening of acetabular components with an outer diameter of 40 mm and 43 mm at comparable depths of penetration with a mean follow-up of 17 years (1 to 40).

In cases with no measurable wear none of the acetabular components were loose. With increasing acetabular penetration there was an increased incidence of aseptic loosening which reflected the difference in the external radii, with 1.5% at 1 mm, 8.8% at 2 mm, 9.7% at 3 mm and 9.6% at 4 mm of penetration in favour of the larger 43 mm acetabular component.

Our findings support the Charnley principle of low frictional torque. The level of the benefit is in keeping with the predicted values.