Combining inertial navigation with transacetabular ligament in total hip arthroplasty via direct anterior approach results in excellent accuracy compared to standard manual technique - A retrospective cohort study

Abstract

Background: Correct acetabular component placement plays a critical role in reducing early revisions after dislocations in total hip arthroplasty (THA). Although the transverse acetabular ligament (TAL) guides anteversion, inclination can only be accurately guided by navigation. In order to overcome the initial disadvantages with navigation, an imageless, easy-to-use inertial navigation system has been recently introduced. This study aims to analyze the accuracy of inclination with this navigation system compared to the standard manual technique.

Methods: Two cohorts, manual technique (MT) and navigation (NAV) cohorts, consisted of 83 and 95 patients, respectively, after exclusion criteria were applied. Inclination target was 38° and anteversion was guided by TAL. Demographic data were collected, and anteroposterior (AP) pelvic and cross-table lateral radiographs were obtained 6 weeks post-operatively. Inclination and anteversion were determined on the AP pelvic and cross-table lateral radiograph, respectively.

Results: A mean inclination of 41.8° (±6.8°) and 38.9° (±4.4°) was found in the MT and NAV cohorts, respectively. There was no statistical difference in gender, age, and BMI. If the inclination was set within 10° of the target (i.e., 38°), 88% of the MT cohort and 97% of the NAV cohort were within the target zone. Accuracy decreased to 53% and 83%, respectively, if the target zone range was narrowed down to ± 5°.

Conclusion: Combining inertial imageless navigation for inclination and TAL as a landmark for anteversion is significantly more accurate compared to the manual technique, without having the limitations and disadvantages of current standard navigational techniques.

Keywords: Navigation; Total hip arthroplasty; Transverse acetabular ligament.

Figure 1

Drawing 38° with a goniometer on the drapes on a plane parallel to the operating table.

Figure 2

Set up inertial navigation device (Navbit^®) during registration.

Figure 3

Acetabular cup inclination was determined as the angle (in degrees) between a line drawn along the rim of the cup and the teardrop line on the AP pelvis (A). Acetabular cup anteversion was measured on the cross-table lateral radiograph as the angle (in degrees) between a line drawn along the rim of the cup and a line perpendicular to the horizontal plane (B).

Figure 4

Cup inclination in degrees per case. (A) and (B) represent the MT and NAV cohorts, respectively. Grey line represents the target (38°). The dotted red line is within 10° of target and the dotted green lines represent within 5°.

Figure 5

The inclination error is defined as the difference between the navigation measurement and the measured radiographic inclination in degrees. This is plotted in accordance with BMI. Red dotted line represents a trendline.