Abstract
Introduction
Operative inclination (OI) is defined as the angle between the acetabular axis and the sagittal plane. With the patient in the true lateral decubitus position, this corresponds to the angle formed between the handle of the acetabular component inserter and the theatre floor intra-operatively.
Patients/Materials & Methods
The primary study aim was to determine which method of acetabular component insertion most accurately allows the surgeon to obtain a target OI of 35o.
270 consecutive patients undergoing cementless THA were randomised to one of three possible methods for acetabular component implantation:
1. Freehand,
2. 35o mechanical alignment guide (MAG), or
3. Digital inclinometer assisted
Two surgeons participated. Target OI was 35o in all cases. OI was measured using a digital inclinometer. For the freehand and MAG cases, the surgeon was blinded to inclinometer readings intra-operatively.
Results
Freehand: OI 25.2 – 43.2o. Mean deviation from target 2.92o.
35o MAG: OI 29.3 – 39.3o. Mean deviation from target 1.83o.
Inclinometer assisted: OI 27.5 – 37.5o. Mean deviation from target 1.28o.
Overall, when comparing mean deviation from target OI, a statistically significant difference between both the Freehand/Inclinometer group and Freehand/MAG group was demonstrated (p<0.001). A statistically significant difference between the Inclinometer/MAG groups was also demonstrated (p<0.023).
Discussion
Both the 35o MAG and digital inclinometer assisted methods provided a considerably narrower OI range when compared to the freehand method. Though the range was similar for both the 35o MAG and digital inclinometer assisted methods, the SD was smaller in the inclinometer assisted group.
Conclusion
The novel method of using a digital inclinometer to control operative inclination appears to be more accurate than both the freehand and mechanical alignment guide methods and may help further optimise acetabular component orientation.
