Abstract
Introduction: Acetabular introducers have an inbuilt inclination of 45 degrees to the shaft. With the patient in the lateral position the operator aims to align the introducer shaft to vertical to implant the acetabulum at 45 degrees. We examined if a bulls-eye spirit level attached to an introducer improved the accuracy of implantation.
Methods: A small circular bulls-eye spirit level was attached to the handle of an acetabular introducer directly over the shaft. A sawbone hemipelvis was fixed to a horizontal, flat surface. A cement substitute was placed in the acetabulum and subjects asked to implant a polyethylene cup into the acetabulum, aiming to obtain an angle of inclination of 45 degrees. Two attempts were made with the spirit level dial masked and two attempts made with it unmasked. The distance of the air bubble from the spirit level’s centre was recorded by a single assessor. The angle of inclination of the acetabular component was then calculated. Subjects included a city hospital’s Orthopaedic consultants and trainees.
Results: Eighteen subjects completed the study, with no significant difference in performance between consultants and trainees. Accuracy of acetabular implantation when using the unmasked spirit-level improved significantly in all grades of surgeon. With the spirit level masked, 11 out of 36 attempts were accurate at 45 degrees, 19 attempts ‘closed’ (< 45degrees) and 6 were ‘open’ (> 45 degrees). With the spirit level visible, all subjects achieved an inclination angle of exactly 45 degrees on both attempts. The mean difference between masked and unmasked implantation angle was 0.94 degrees (95% CI 0.64 to 1.24, p< 0.0001).
Discussion: A simple device attached to the handle of an acetabular introducer can significantly improve the accuracy of implantation of a cemented cup into a saw-bone pelvis in the lateral position. This technique may be easily transferable into an in-vivo study
Correspondence should be addressed to Mr John Hodgkinson, BHS, c/o BOA, The Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London WC2A 3PE.
