A high inclination angle has been linked to an increased dislocation rate, liner fracture, and increased wear. The aim of this study was to compare the operative (OI) with the radiological inclination (RI) angle and determine the influence of patient morphology on pelvic tilt and cup inclination angle. In the first cohort of 100 patients undergoing uncemented primary total hip arthroplasty, the cup was inserted freehand. In the second cohort of 100 patients, the OI was measured with the aid of a digital inclinometer. RI and pelvic tilt in lateral decubitus were measured.Introduction
Methods
A high radiographic inclination angle (RI) contributes
to accelerated wear and has been associated with dislocation after
total hip arthroplasty (THA). With freehand positioning of the acetabular
component there is a lack of accuracy, with a trend towards a high
radiographic inclination angle. The aim of this study was to investigate
whether the use of a digital protractor to measure the operative
inclination angle (OI) could improve the positioning of the acetabular
component in relation to a ‘safe zone’. We measured the radiographic inclination angles of 200 consecutive
uncemented primary THAs. In the first 100 the component was introduced
freehand and in the second 100 a digital protractor was used to
measure the operative inclination angle. The mean difference between the operative and the radiographic
inclination angles
(∆RI–OI) in the second cohort was 12.3° (3.8° to 19.8°). There was
a strong correlation between the circumference of the hip and ∆RI–OI.
The number of RI outliers was significantly reduced in the protractor
group (p = 0.002). Adjusting the OI, using a digital protractor and taking into
account the circumference of the patient’s hip, improves the RI
significantly (p <
0.001) and does not require additional operating
time. Cite this article:
