Hinged external fixator placement at the elbow: navigated versus conventional technique

During the application of a hinged external elbow fixator, exact placement of the central pin remains difficult. Proper placement often necessitates multiple drilling attempts and fluoroscopic localization, which can be time consuming. We hypothesized that use of computerized navigation would enable a more precise placement of the central axis pin and would reduce the total number of drilling attempts.

Twelve elbow models incorporating soft tissue coverage were used in this study. First, the optimal placement trajectory (OPJ) of the axis pin was defined in the anterior-posterior (AP) and lateral planes of the elbow. Six elbows were used with the navigation system and the axis pin was inserted in combination with a conventional fluoroscopy system under constant two-dimensional guidance from the virtual images. The pins for the remaining six elbow specimens were implanted conventionally under fluoroscopic guidance. The distances and angular deviations from the OPJ position were measured, and the results for the conventional placement and computer navigation groups were compared. To determine the definitive axis pin placement, a CT scan of each elbow with 1-mm slice thickness was used and the results were measured based on the defined optimal pin placement. AP plane angulations and lateral plane distances were calculated in relation to the optimal insertion trajectory for each specimen. Finally, we counted the overall number of drilling attempts needed to find the optimal position for the axis pin.

For the AP angulations, of the six elbows implanted using the conventional technique, half (n=3) had deviations of ≥20° from the optimal axis. In contrast, in the navigated group, all cases (n=6) were within 20° of the optimal axis in the AP plane. The mean AP angulation deviation in the conventional group was 20.5°, compared to 15° in the navigation group (p=0.077). For the lateral distances, the mean distance from the drilling point to the point of optimal placement was 3.83 mm in the conventional group, versus 1.83 mm in the navigation group (p=0.042). For all navigated cases, only one drilling attempt was necessary to achieve the desired position of the axial pin.

Compared with the conventional method of axis pin placement for an elbow fixator, two-dimensional navigation allows a reduction in the number of drilling attempts required. Furthermore, the accuracy in terms of AP angulation and lateral distance from a defined optimal placement is better when compared to that obtained with the conventional technique.