Accuracy During Surgery

Computer navigation can be used in Total Hip Arthroplasty (THA) to improve the accuracy of the acetabular cup component orientation ^1-5. The Navbit® Sprint system is a palm-sized navigation device that provides the surgeon with a real-time measure of the orientation of the acetabular cup. The Navbit Sprint is small and accurate, through using an inertial navigation system and patient registration which does not rely on anatomical landmarks.

This article summarises the evaluation of the accuracy of the navigation system and end-to-end process of the Navbit Sprint during surgery with key findings:

• The registration process enabled accurate measurements;

• The total error in the end-to-end process for the Navbit Sprint system is low;

• The Navbit Sprint was found to be accurate and precise.

The Navbit Sprint system is an accurate navigation device that provides the surgeon with intraoperative acetabular cup inclination and anteversion angles during THA.

Strategy for Assessing Accuracy

To provide surgeons with confidence in the accuracy of the Navbit Sprint system, the device was challenged-tested in a variety of ways. The accuracy of the navigation system was assessed using bench testing. The accuracy of the registration process was assessed through testing the end-to-end surgical process, firstly in a simulated surgical setting using cadavers and then in a clinical setting with patients. This article covers Navbit Sprint accuracy in the end-to-end clinical setting.

Accuracy of the End-to-End Surgical Process

In an ongoing study, the Navbit® Sprint System is being used during THA and hip resurfacing surgery, alongside an existing optical navigation method, to measure acetabular cup orientation. For the 102 patients (107 hips) to date, the surgeon used the direct anterior approach for 54 hips (57% female) and the posterolateral approach for 53 hips (22% female). The intraoperative measurements from the devices were compared to the angles calculated from the post-operative CT scans.

The Navbit® Sprint System was accurate and precise. Compared with the CT measurements, 96% of the posterior and 100% of the direct anterior measurements of acetabular cup orientation were within ±10° of the target, shown in Figures 1 and 2. The mean absolute errors for both measurements in both surgical positions are shown in Figure 3, and were well below the target of 10°. The mean and median absolute errors are provided in Table 1.

Figure 3: Absolute Accuracy of Navbit Sprint System

Table 1: Navbit Mean and Median Absolute Error vs CT Scan

Discussion

The Navbit Sprint system uses a novel navigation system and a novel method of registration of the patient. The accuracy of the Navbit Sprint system was measured during surgery alongside an optical navigation device.

The registration process enables accurate measurements

The accuracy of the device and registration process were assessed during surgery with patients. The measurements were accurate and precise. The results indicated that using this device would result in acetabular cup orientations within ±10° of the target, compared with the much less accurate and precise results generally seen in THA surgery. Therefore, the Navbit Sprint device and registration process provide the surgeon with accurate intraoperative measurements.

The total error in the end-to-end process is low

Surgery assessed the entire Navbit Sprint system and process. Surgery includes error from the navigation system and the registration process, as well as variability that would arise from other sources such as patient anatomy and surgical method. With all of these errors included, the Navbit Sprint was able to generate accurate intraoperative measurements.

The Navbit Sprint is accurate and precise

The Navbit Sprint System is accurate and precise with errors consistently below 3°.

Conclusion

The Navbit Sprint System is an accurate navigation device that provides the surgeon with real-time acetabular cup inclination and anteversion angles during THA.

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The accuracy of the Navbit Sprint System was assessed using bench testing, simulated surgeries, and clinical end-to-end surgery.