Abstract
Introduction: Aseptic loosening is the main cause of revision in hip replacement surgery. Improved cementation techniques have reduced the rate of loosening of the femoral component, leaving the cemented acetabular cup as the major problem, with reported loosening rates as high as 25% at 12 – 15 years. The ideal method of acetabular cementation has not been fully evaluated.
Aim: To determine the ideal thickness of cement mantle to resist torsional forces.
Method: Mahogany blocks with a 54mm hemispherical hole were used to simulate an acetabular socket. Machined aluminium cups were created in 5 sizes (52mm to 44mm) to give a cement mantle that varied in size from 1mm to 5mm. Three 10mm keyholes were drilled in the blocks and appropriate-sized spacers were inserted to ensure the mantle was accurate and even. Silicone grease was used to prevent any micro-interlock between cement and wood. The cups were then cemented into the wooden blocks using vacuum-mixed Palacos R cement and left to cure in air for 7 days at 37 °C. The constructs were tested to failure using a servo-hydraulic testing machine. Each experiment was repeated six times.
Results: The stiffness of the cement mantle varied according to thickness as follows:
| Thickness (mm) | Stiffness (Nm / Degree) |
|---|---|
| 1 | 58 +/− 4 |
| 2 | 37 +/− 1 |
| 3 | 39 +/− 1 |
| 4 | 25 +/− 0.3 |
| 5 | 24 +/− 0.3 |
Discussion: A stiffer cement mantle will transfer more torque to the bone-cement interface, possibly leading to earlier loosening of the prosthesis. This biomechanical analysis suggests that surgeons should aim to achieve a mantle at least 2mm thick. There appears to be little further mechanical advantage gained if the mantle is increased in thickness beyond 4mm.
Theses abstracts were prepared by Mr Peter Kay. Correspondence should be address to him at The Hip Centre, Wrightington Hospital, Appley Bridge, Wigan, Lancashire WN6 9EP.
